The 4th Topics of Particle, Astro and Cosmo Frontiers (TOPAC 2026) 第4届粒子物理、天体物理和宇宙学前沿国际学术研讨会

16 Apr 2026, 08:00 → 21 Apr 2026, 17:00 Asia/Shanghai

第4届粒子物理、天体物理和宇宙学前沿国际学术研讨会
将于 2026 年 4 月 17 日至 4 月 21 日在成都电子科大举办
English Version Follows

前所未有的高能对撞数据、更高精度的粒子物理测量以及不断升级的暗物质、宇宙学与天文观测，正推动粒子物理、天文与宇宙学进入深度交叉融合的新阶段，持续催生检验标准模型与探索新物理的前沿课题。中微子振荡与暗物质等超出标准模型的关键现象，与天文和宇宙学密切相关；引力波与超高能中微子观测则开启了多信使天文学的新窗口，为理解早期宇宙的极端物理过程提供了全新探针。

本次会议为期四天，将搭建相关领域专家学者的高水平交流平台，围绕味物理、中微子、暗物质、天体粒子物理、宇宙学与引力波观测等主题，系统梳理国内外最新理论与实验进展，深入讨论未来可能的发展方向，推动我国在粒子-天体-宇宙学交叉前沿领域的持续发展。

同时，我们还计划引入：（i）强耦合新物理专题特别分会；（ii）强耦合新物理国际合作网络发起会，以推动强耦合新物理与QCD及强相互作用相变等领域的交叉合作，形成长期、稳定的国际协作机制。本次会议除口头报告外，还将提供海报展示的机会，欢迎大家提交口头报告和海报摘要，并积极参会。

TOPAC 系列
第一届会议于 2023 年在上海交通大学李政道研究所举办；
第二届会议于 2024 年在东南大学举办；
第三届TOPAC 会议于 2025 年在中山大学举办；
本届会议由电子科大（成都清水河校区）举办。

一．会议时间：
2026年 4月 16 日下午：报到
2026 年 4 月17 日至 4 月 20 日：线下报告
2026 年 4 月 21 日：离会

二．会议注册：
网上注册截止日期：2026 年 4 月 9 日
会议网址：https://indico-tdli.sjtu.edu.cn/event/4560/

三．会议注册费（现场缴费）：
教师、博士后：1800元
学生：1300元
会议期间餐饮住宿及交通费用自理。

四．组委会名单（按姓名序排列）
安海鹏（清华大学）
边立功（重庆大学）
葛韶锋（上海交通大学李政道研究所）
龚云贵（宁波大学）
何小刚（上海交通大学李政道研究所）
Roman Pasechnnik（隆德大学）
Francesco Sannino（丹麦高等研究中心，量子物理研究中心）
舒菁（北京大学）
王志伟（电子科技大学，大会主席）
张永超（东南大学）

五．会议国际学术顾问委员会（按姓名序排列）
Bai, Yang (白杨) — University of Wisconsin–Madison, USA
Cacciapaglia, Giacomo — Sorbonne Université, Paris, France
Cao, Junjie (曹俊杰) — Zhengzhou University, Zhengzhou, China
Deandrea, Aldo — Université Claude Bernard Lyon 1, Lyon, France
Fukushima, Kenji — The University of Tokyo, Tokyo, Japan
Huang, Mei (黄梅) — University of Chinese Academy of Sciences (UCAS), Beijing, China
Kouvaris, Chris — National Technical University of Athens, Athens, Greece
Liu, Jianglai (刘江来) — Tsung-Dao Lee Institute (TDLI), Shanghai, China
Panero, Marco — University of Turin, Turin, Italy
Strumia, Alessandro — University of Pisa, Pisa, Italy
Volkas, Raymond R.  — University of Melbourne, Melbourne, Australia
Wang, Wei (王伟) — Shanghai Jiao Tong University, Shanghai, China
Wu, Xinggang (吴兴刚)— Chongqing University, Chongqing, China
Yang, Jin-Min (杨金民) — Henan Normal University, Xinxiang, China
Yu, Hai-Bo (郁海波) — University of California, Riverside, USA
Zhou, Ning (周宁) — Tsung-Dao Lee Institute (TDLI), Shanghai, China

六．会务秘书—江璐
    电话：+86 15021500353
    邮件：Ljiang@uestc.edu.cn

 

The 4th Topics of Particle, Astro and Cosmo Frontiers (TOPAC 2026)

Will be held at the University of Electronic Science and Technology of China (UESTC), Chengdu, from April 17 to April 21, 2026.

Unprecedented high-energy collider data, increasingly precise particle-physics measurements, and rapidly advancing observations in astronomy, cosmology, and gravitational waves are ushering in a new era of deep synergy among particle physics, astrophysics, and cosmology, continuously generating frontier topics for testing the Standard Model and exploring new physics. Neutrino oscillations and dark matter particles, as key beyond-Standard-Model phenomena, are closely connected to astrophysics and cosmology; meanwhile, observations of gravitational waves and ultra-high-energy neutrinos are opening a window to multi-messenger astronomy, providing entirely new probes of extreme physical processes in the early Universe. 

This four-day meeting will provide a platform for experts to exchange ideas across multiple themes, including flavor physics, neutrinos, dark matter, astrophysics, cosmology, and gravitational waves, to systematically review the latest theoretical and experimental progress worldwide, discuss possible future directions, and promote sustained development of this interdisciplinary frontier in China. 

In addition, we plan to introduce (i) a dedicated special session on strongly coupled new physics, and (ii) an “Initiation Meeting” to launch an international collaboration network on strongly coupled new physics, aiming to foster cross-disciplinary collaboration with QCD and strong-interaction phase transitions and to establish a long-term, stable international collaboration mechanism. Besides oral presentations, the conference will also provide opportunities for poster sessions. We warmly welcome submissions of abstracts for oral and poster presentations and encourage active participation.

TOPAC History

• The 1st TOPAC was held in 2023 at the Tsung-Dao Lee Institute, Shanghai Jiao Tong University.
• The 2nd TOPAC was held in 2024 at Southeast University.
• The 3rd TOPAC was held in 2024 at Sun Yat-sen University.

TOPAC 2026 will be hosted by UESTC (Qingshuihe Campus), Chengdu, China.

1. Conference Dates

• April 16, 2026 (afternoon): Registration and check-in
• April 17–20, 2026: On-site talks
• April 21, 2026: Departure

2. Registration

• Online registration deadline: April 9th, 2026
• Conference website: https://indico-tdli.sjtu.edu.cn/event/4560/

3. Registration Fees (Payable on site)

• Faculty& Postdoctoral Researchers: 1800 RMB
• Students: 1300 RMB
• Participants are responsible for their own meals, accommodation, and transportation during the conference.

4. Organizing Committee (in alphabetical order by pinyin)

• Haipeng An (Tsinghua University)
• Ligong Bian (Chongqing University)
• Shaofeng Ge (Tsung-Dao Lee Institute, Shanghai Jiao Tong University)
• Yungui Gong (Ningbo University)
• Xiaogang He (Tsung-Dao Lee Institute, Shanghai Jiao Tong University)
• Roman Pasechnik (Lund University)
• Francesco Sannino (Quantum Field Theory Center, Danish Institute for Advanced Study)
• Jing Shu (Peking University)
• Zhi-Wei Wang (Chair, University of Electronic Science and Technology of China)
• Yongchao Zhang (Southeast University)

5. International Academic Advisory Committee (in alphabetical order by pinyin) 

Bai, Yang (白杨) — University of Wisconsin–Madison, USA
Cacciapaglia, Giacomo — Sorbonne Université, Paris, France
Cao, Junjie (曹俊杰) — Zhengzhou University, Zhengzhou, China
Deandrea, Aldo — Université Claude Bernard Lyon 1, Lyon, France
Fukushima, Kenji — The University of Tokyo, Tokyo, Japan
Huang, Mei (黄梅) — University of Chinese Academy of Sciences (UCAS), Beijing, China
Kouvaris, Chris — National Technical University of Athens, Athens, Greece
Liu, Jianglai (刘江来) — Tsung-Dao Lee Institute (TDLI), Shanghai, China
Panero, Marco — University of Turin, Turin, Italy
Strumia, Alessandro — University of Pisa, Pisa, Italy
Volkas, Raymond R.  — University of Melbourne, Melbourne, Australia
Wang, Wei (王伟) — Shanghai Jiao Tong University, Shanghai, China
Wu, Xinggang (吴兴刚)— Chongqing University, Chongqing, China
Yang, Jin-Min (杨金民) — Henan Normal University, Xinxiang, China
Yu, Hai-Bo (郁海波) — University of California, Riverside, USA
Zhou, Ning (周宁) — Tsung-Dao Lee Institute (TDLI), Shanghai, China

6. Conference Secretary—Lu Jiang

• Phone: +86 150-2150-0353
• Email: Ljiang@uestc.edu.cn

 

 

TOPAC会议通知.pdf

Friday, 17 April

08:30 → 08:40 Opening

Opening Session by the University President. Awarding Ceremony for Honary Professor Raymond Volkas. Opening Speech by Dean of School of Physics & chair Zhi-Wei Wang.

08:40 → 10:40 Plenary Theory 1: Flavor and CP Violation (Room 567, Chair Zhi-Wei Wang)

08:40 VISHnu

I will describe the VISHnu model, which is a DFSZ axion-majoron model variant with the following features: (a) No cosmological domain wall problem, thus permitting a post-inflationary axion. (b) Identification of the Peccei-Quinn breaking scale with the type-I seesaw scale, thus explaining the tiny neutrino masses. (c) Baryogenesis via leptogenesis. (d) Successful inflation driven by a non-minimal coupling of the Peccei-Quinn scalar to the Ricci scalar. And, of course, (e) a solution to the strong CP problem.

Speaker: Raymond Volkas (The University of Melbourne)

Volkas-TOPAC-2026.pdf

09:10 How Viable is Electroweak Baryogenesis?

Speaker: Prof. Michael Ramsey-Musolf

MJRM TOPAC 26.pdf

09:40 Flavor Physics in the Precision Era: Rare Decays, Lepton Universality, and New-Physics Targets

With the steady running of the LHCb and Belle II experiments, as well as the precision achieved from Lattice QCD for non-perturbative hadronic parameters, we are entering the era of precision flavor physics. In this talk, I will introduce the role played by flavor physics in precisely testing the Standard Model and indirectly probing physics beyond it. Then, I will give some examples to illustrate how precision flavor physics helps us to achieve this goal. I will also discuss the lepton universality and its violation indicated by the R(D) and R(D*) anomalies, the b->s nu nu decays and their implications for the dark sector, as well as some deviations observed in non-leptonic B decays.

Speaker: Xin-Qiang Li (Central China Normal Univerisy)

10:10 Baryonic CP Violation in Theory

The first observation of CP violation in baryon decays in last year is a historic milestone for particle physics. This talk summarizes theoretical progress in the field, highlighting the accurate predictions preceding the discovery and discussing subsequent developments.

Speaker: Fu-Sheng Yu (Lanzhou University)

BaryonCPV-FSY.pdf

10:40 → 11:00 Coffee Break

11:00 → 12:30 Plenary Experiment 1: Collider (Room 567, Chair Man-Qi Ruan)

11:00 Vector Boson Scattering and Electroweak Symmetry Breaking: Status and Outlook

Speaker: Haijun Yang (Shanghai Jiao Tong University (CN))

TOPAC2026-VBS-HaijunYang.pdf

11:30 Search for the QCD critical point and Strange-Dibaryon at RHIC-STAR （QCD相变临界点与奇异双重子态的实验寻找）

Speaker: Xiaofeng Luo (Central China Normal University)

12:00 ATLAS Updates on Higgs-Top Yukawa Coupling and Probing CP Violation

Measurements of the Higgs boson production in association with top quarks provide a direct probe of the Higgs-top Yukawa coupling, a key parameter in the Standard Model. This talk presents the latest ATLAS results on ttH and tH production using the full Run 2 dataset of 140 fb⁻¹ at √s = 13 TeV, with a focus on the multi-lepton final state. The measured ttH signal strength is σ_ttH/σ_SM = 0.63⁺⁰·²⁰₋₀·¹⁹, corresponding to an observed significance of 3.3σ. Furthermore, the CP structure of the top-Higgs Yukawa coupling is probed through a combined analysis of ttH and tH events. Values of the CP mixing angle |α| > 62° are excluded at 68% confidence level, setting important limits on possible CP-odd contributions to the Higgs-top interaction, which is closely connected to the CP violation required to explain the baryon asymmetry of the universe.

Speaker: Kun Liu (TDLI / SJTU)

ATLAS_HiggsTop.pdf

13:30 → 15:20 Plenary Theory-Experiment Interplay 2: Precision Searches (Room 567, Chair Shao-Feng Ge)

13:30 Determining the Nature of Dark Matter with Astronomical Observations: Dwarf Galaxies and Small-Scale Structure

Despite decades of intensive direct detection searches across different dark matter candidates, no conclusive particle signal has been identified. This motivates complementary constraints on dark matter properties model independently from astronomical observations. In this talk, we focus on wave-like ultralight dark matter (ULDM) and its dynamical impact on dwarf galaxies. We will show that some observations favor a wave like dark matter and how the wave dark matter can remain consistent with existing limits.

Speaker: 效军 毕 (中科院高能所)

bixj-TOPAC.pdf

14:00 Search for Ultralight Dark Matter and Gravitational Wave in the Geomagnetic Field

Speaker: Lei Wu (Nanjing Normal Univeristy)

14:30 High sensitivity magnetometry with ferromagnetic spins and its applications in fundamental physics

Due to their high spin density and low spin projection noise, ferromagnetic systems are expected to be powerful tools for high-precision metrology. This presentation will discuss our recent investigations into physics beyond the Standard Model, utilizing ferromagnetic spins as a platform."

Speaker: Wei Ji (Peking University)

14:55 Di-Higgs Recent Highlights and Summary

The talk will present the latest highlights and summary of di-Higgs studies from ATLAS and CMS experiments at the LHC.

Speaker: Yanlin(彦麟) Liu(刘)

TOPAC2026-HH-Yanlin_Liu.pdf

15:20 → 15:40 Coffee Break

15:40 → 17:30 Plenary Theory 3 (GUT Special Session): Unification (Room 567, Chair Xin-Qiang Li)

15:40 Asymptotic Grand Unified models

We present the idea of asymptotic grand unification, where the gauge couplings run to a unique fixed point in the ultraviolet, thanks to the presence of a compact extra dimension and to a specific choice group structure and multiplet content. We introduce a minimal model based on a SU(5) gauge theory but also discuss SO(10) and other generalisations, giving also few results on the expected phenomenology.

Speaker: Aldo Deandrea (University Lyon 1)

16:10 Consistent high temperature symmetry non-restoration in 3+1 dimensions

The phenomenon of symmetry non-restoration goes back to Weinberg around
50 years ago: some systems may exhibit spontaneous symmetry breaking at
large temperature. Only recently however this same behavour has been found
in UV complete models, being previous examples only effective theories with
a UV cutoff. I will describe such a UV complete model both at large and
finite number of colours.

Speaker: Borut Bajc

chengdu26.pdf

16:40 Asymptotic grand unification in SO(10)

Asymptotic unification, distinct from the conventional concept of unification, suggests that couplings unify at a non-trivial ultraviolet (UV) fixed point. Theory with an interacting UV fixed point is normally referred to as asymptotic safety to address the famous UV Landau pole problem. Alternative to a usual grand unified theory (GUT), an asymptotic GUT gradually unifies gauge couplings in the deep UV limit. Using an economical and realistic particle content setup, we demonstrate that asymptotic grand unification can be achieved in SO(10) with one extra dimension. One intermediate scale, the Pati-Salam symmetry breaking scale, is included below the compactification scale. The top, bottom and tau masses are split, and the smallness of the neutrino mass is explained via inverse seesaw. Due to the absence of large-dimensional Higgs representations, gauge couplings exhibit asymptotic safety and are thus asymptotically unified, regardless of their initial values. In contrast, Yukawa couplings can achieve asymptotic freedom if the negative gauge contributions dominate over the positive Yukawa terms.

Speaker: Ye-Ling Zhou (HIAS-UCAS)

YLZ_TOPAC2604.pdf

17:05 Modulus stabilization of modular flavor models in Jordan frame supergravity

We propose to discuss the modular flavor model and the stabilization of single modulus field in the Jordan frame supergravity with non-minimal scalar-curvature coupling of the form $\Phi(\tau,\bar{\tau})R$. Modular invariance and positivity of the scale factor constrain stringently the form of the frame function, consequently the Kahler potential. We discuss some general properties of scalar potentials after the scale transformation from the Jordan frame to the Einstein frame. We find that the shape of the resulting scalar potential in the Einstein frame is quite different from that of ordinary single modulus stabilization mechanism. The scalar potential could be stationary at the $i\infty$ fixed point, leading to a runaway type vacuum. We also discuss numerically the modulus stabilization for some simplified scenarios.

Speaker: Fei Wang (Zhengzhou University)

17:30 → 17:40 Coffee Break

17:40 → 18:45 Astroparticle Highlight: Low-Energy Probes (Room 567, Chair Yong-Chao Zhang)

17:40 Radiative corrections to inverse beta decay and neutron decay at low energies

We compute electromagnetic radiative corrections in the inverse beta decay at reactor antineutrino energies within the heavy baryon chiral perturbation theory, provide the most accurate cross-section predictions for this process, and present a complete error budget. For the first time, we consistently include quantum electrodynamics, chromodynamics, and electroweak contributions and present the positron energy spectrum accounting for radiative corrections. Our calculation also improves on previous evaluations by incorporating permille-level contributions. The results can be readily applied to normalize the reactor antineutrino flux, improve on the reconstruction of the antineutrino energy, make precise measurements of neutrino oscillation parameters at JUNO, and search for new physics at nuclear power plants. Additionally, we quantify the relation between the experimental value of the nucleon axial-vector charge and its evaluations within the lattice quantum chromodynamics.

Speaker: Sasha Tomalak (Institute of Theoretical Physics, Chinese Academy of Sciences)

Chengdu_April_Sasha_Tomalak_2026.pdf

18:05 Probing oscillation between visible photon and dark photon by optical time-domain reflectometry

Dark photons, which can kinetically mix with ordinary photons, represent
the simplest extension to the standard model. Detecting their
oscillations with visible photons could provide crucial insights into
the nature of dark matter and fundamental interactions beyond the standard model. We propose a novel laboratory-based approach to detect dark photon oscillations using a laser in an Optical Time-domai Reflectometry (OTDR) setup. The laser light propagating through the optical fiber undergoes oscillations with the dark photon, leading to measurable changes in the power flow. These oscillations can be precisely measured, leveraging its high sensitivity and efficiency in detecting small variations in the optical signal. This approach could provide a new avenue for probing dark photon oscillations in the laboratory and greatly improve the current experimental sensitivity to dark photon in a wide mass range.

Speaker: Wenyu Wang (Beijing University of Technology)

darku1-osc-wenyu .pptx

18:30 Multi-messenger probes of ultralight dark matter

Speaker: Bohua Li (Guangxi University)

17:40 → 18:45 Formal Theory (Room 352, Chair Teng Fei)

17:40 Constructing Massive Vector Amplitudes from Consistency Conditions

Based on the general principles of Lorentz symmetry and unitarity, we introduce two consistency conditions -- on-shell gauge symmetry and strong massive-massless continuation -- in constructing amplitudes of massive gauge theory with elementary particles. In particular we argue that on-shell gauge symmetry can be understood as a consequence of Lorentz symmetry, unitarity and massive-massless continuation. Based on these two conditions, combined with the little group transformation and consistent factorization, we construct 3-point and 4-point vector-boson/scalar amplitudes that correspond to renormalizable interactions, then analyze the underlying theories and models. Given the particle masses, almost all possible vertices, including those involving Goldstone modes, are uniquely fixed. The only exceptions are triple and quartic scalar self-couplings. In addition, all particle masses must have the same physical origin. If the number of vector bosons is smaller than 3, the underlying theories for the amplitudes are either massive gauge theories with spontaneous symmetry breaking (S.S.B.) or Stueckelberg theory. The necessary condition for the latter is that the scalars have equal masses. We also discuss different models depending on the number of scalars involved. If the number of vector bosons is larger than 3, the underlying theory must be Yang-Mills theory with S.S.B. In both Abelian and non-Abelian cases, the specific shape of the Higgs potential cannot be determined, which explains the fact that scalar self-couplings are undetermined, and the relations between the masses are generally nonlinear.

Speaker: Prof. Junmou Chen (Jinan University)

18:05 Hypergeometric function representation of Feynman integral

Embed in Grassmannians, we can obtain the analytical hypergeometric function representation of multi-loop Feynman integrals with masses. We can make the classification among those hypergeometric function solutions by geometric configurations, and generalize Gauss relations among the hypergeometric functions to complete analytic continuation of the solutions. This method can be applicable to the high-order corrections of physical quantities.

Speaker: Prof. Hai-Bin Zhang (Hebei University)

Hypergeometric function representation of Feynman integral.pdf

18:30 Black hole induced false vacuum decay in a heat bath in (1+1) dimensions

The possibility that a black hole catalyzes vacuum decay is an interesting and important topic both phenomenologically and theoretically. One of the issues is the choice of the vacuum state. To address it, we consider a (1+1)-dimensional toy model of a scalar field with inverted Liouville potential in an external background of a dilaton black hole. We study the decay of a general out-of-equilibrium state describing the evaporating black hole immersed in the thermal bath with a different temperature. We analytically derive the exponential suppression factor of the tunneling rate and show how they interpolate between the results of the previous study on those for the Hartle-Hawking vacuum and Unruh vacuum. We also find the non-thermal sphaleron configuration analytically when there is no dilaton barrier and construct the semiclassical solution describing tunneling onto this sphaleron. Our study would be the first step to examine the vacuum decay around a black hole in our cosmic history.

Speaker: Bowen Hu (中国科学院大学杭州高等研究院)

26TOPAC_BH induced FOPT.pptx

17:40 → 18:40 Parallel Astroparticle: Dark Probes (Room 368, Chair Xiang Xiao)

17:40 Probing Neutrino-philic Scalars in Muon and Double Beta Decay

Self-interacting neutrinos are well-motivated particles in order to solve problems such as Hubble tension in cosmology. Neutrino-philic scalars, such as flavons and Majorons, can be solutions to BSM puzzles, such as lepton number and lepton flavour violations. New muon decay channels (e.g. µ → eϕ, µ → eϕϕ) will be introduced by neurtino-scalar couplings and µ → eνν will have additional contribution from scalar one-loop effect. Scalar-facilitated neutrino self-interaction can also contribute to two-neutrino double beta decay, the shape of the two-electron spectrum in double beta decay experiments can therefore be modified. The interference between SM and scalar facilitated diagrams will enhance the sensitivity to new physics when the final state particles are the same as SM process. These new channels and enhancements will lead to a wider neurtino-scalar coupling parameter space that can be tested in future experiments.

Speaker: Zhong Zhang (Southeast University)

TOPAC_ZZ.pdf

17:55 Parton Evolution Effects in Cosmic-Ray Boosted Dark Matter

In this talk, I discuss parton evolution effects in the framework of cosmic-ray boosted dark matter. When dark matter particles are accelerated by high-energy cosmic rays, the large hierarchy between the scattering scale and the dark-sector masses can induce a dark parton shower. At high-threshold detectors, a similar hierarchy in the DM–electron scattering process leads to collinear splittings that can be described by introducing a dark matter parton distribution function (DM PDF). I will show that both types of parton evolution lead to a suppression of the electron recoil rate at neutrino detectors.

Speaker: Dr Cong(聪) Zhang(张) (中国科学院理论物理研究所)

CongZhang_CRDM_showering_DMPDF.pdf

18:10 Probing 5.5 MeV solar axion at the PandaX experiment

We focus on the detection of 5.5 MeV solar axions from the pp-chain via electron-positron pair production at the PandaX experiment. Previous work established the relation between axion and photon cross sections for massless axions. We verify this relation numerically in the massless limit. Then we compute the cross section for finite axion mass (< 1 MeV) and derive the corresponding mass correction. Our results show that the cross section increases with axion mass, modifying the original relation.

Additionally, we point out that the cross section scales as $Z^2$, giving high-$Z$ targets like xenon a significant advantage. By combining this $Z$-enhancement with finite-mass corrections, this work provides a more complete theoretical basis for solar axion searches in high-$Z$ detectors such as PandaX. Furthermore, we estimate the sensitivity for PandaX-4T and show that future PandaX-nT can achieve a sensitivity comparable to Borexino.

Speaker: Ruofei Feng (Southeast University)

17:40 → 18:45 Parallel Cosmology: Early Universe (Room 302, Chair Yong Tang)

17:40 Chiral gravitational wave background from axion-like fields

Axions and axion-like particles can be probed through gravitational waves indirectly, often referred to as “audible axions”. The usual concept of audible axion relies on the coupling between the axions and the gauge fields. Here we consider an axion-like mechanism with coupling to the Nieh–Yan term. This interaction leads to the direct and efficient production of gravitational waves during the radiation-dominated era, originating from the tachyonic instability of the gravitational perturbations with the Nieh–Yan term. We calculate the energy spectral density of the chiral gravitational wave background and the comoving energy density of axion-like fields. Based on the numerical results, we explore the parameter space of axion masses and decay constants for detectable gravitational wave signals, either in pulsar timing arrays or space-based gravitational wave detections.

Speaker: Yun-Long Zhang (NAOC)

260407ZhangYLchiral.pdf

18:05 Impact of Cosmological Phase Transitions on FIMP Dark Matter

For feebly interacting massive dark matter particle (FIMP) dark matter, variations in particle mass during cosmological phase transitions can affect the dark matter production mechanism. Meanwhile, reheating, entropy injection, and phase coexistence during phase transitions, especially supercooled phase transitions, also influence the evolution of dark matter abundance to varying degrees. This talk will review their overall impacts on the relic density for different FIMP DM scenarios.

Speaker: 阳 张 (河南师范大学)

张阳20260417成都.pdf

18:30 Gravitational Wave Signature of Aspherical Bubbles Driven by Thermal Fluctuation

Cosmological first-order phase transitions are a well-motivated source of stochastic gravitational waves (GWs), but most predictions are made based on the highly idealized model of perfectly spherical vacuum bubbles, neglecting thermal fluctuations. In this work we use $(3+1)$-dimensional lattice simulations of a scalar model with thermal initial conditions to quantify how thermal fluctuations distort bubble profiles and modify the resulting GW spectrum. We find that thermal fluctuations can strongly break spherical symmetry at early times, allowing even an isolated bubble to emit GWs. In multi-bubble simulations, thermal fluctuations systematically reshape the spectrum, suppressing the infrared part while enhancing and broadening the high-$k$ tail. We further provide an analytical estimate for the ultraviolet regime of the GW spectrum, which is in good agreement with our lattice results and suggests that this regime is dominated by thermal fluctuations. These effects could leave observable imprints in future GW searches.

Speaker: Mr Yang Xiao (Henan Normal University)

19:30 → 20:20 Special Evening Plenary Session 1: Frontier Probes (Room 567, Chair Huai-Ke Guo)

19:30 Gauge-Independent Gravitational Waves from Supercooled Phase Transitions in a Minimal Dark U(1) Sector

First-order phase transitions in hidden gauge sectors can generate stochastic gravitational wave backgrounds and provide a powerful new probe of dark sector physics. In this talk, I will present a gauge-independent analysis of gravitational waves from a minimal dark U(1) sector containing a dark Higgs and a dark photon, with the option of an additional vectorlike dark fermion as a viable dark matter candidate. By combining the Nielsen identity with a controlled derivative expansion and power-counting framework, one can construct a gauge-independent effective action in both the high-temperature and supercooled low-temperature regimes, thereby obtaining robust predictions for bubble nucleation and the resulting gravitational wave signals. I will discuss how the microscopic model parameters map onto detector-facing observables ranges relevant to pulsar timing arrays and future space-based interferometers. The results show that supercooled phase transitions generally lead to stronger and more readily detectable signals than parametrically high-temperature transitions, while also highlighting the complementarity between gravitational wave observations and dark matter phenomenology in this minimal dark-sector setup. Our results provide the most reliable and concrete predictions to date for a minimal gauged dark sector.

Speaker: Wan-Zhe Feng (Tianjin University)

19:55 An unexpected possible extraction of \alpha_s using EEC in the post-confinement region

We present precision predictions for the quantum scaling of the post-confinement plateau of the energy-energy correlator (EEC). The analysis follows the light-ray operator product expansion (OPE) description of the near-side EEC, in which the plateau is controlled by the leading $J=5$ channel and its timelike anomalous dimension. We assess the impact of the plateau prediction on possible $\alpha_s$ extraction and find that the present experimental setup already supports a meaningful sensitivity study.

Speaker: Xiaohui Liu (Beijing Normal University)

talk-chengdu.pdf

20:25 → 22:00 Poster Session

20:40 Probing Dark Matter Spike with Gravitational Waves from Early EMRIs in the Milky Way Center

Cold dark matter may form dense structures around supermassive black holes (SMBHs), significantly influencing their local environments. These dense regions are ideal sites for the formation of extreme mass-ratio inspirals (EMRIs), in which stellar-mass compact objects gradually spiral into SMBH, emitting gravitational waves (GWs). Space-based gravitational-wave (GW) observatories, such as LISA and Taiji, will be sensitive to these signals, including early-stage EMRIs (E-EMRIs) that persist in the low-frequency band for extended periods. Here we investigate the impact of dark matter-induced dynamical friction on E-EMRIs in the Milky Way Center, model its effect on the trajectory, and calculate the resulting GW spectrum.

Speaker: chen feng (中国科学院大学)

Saturday, 18 April

08:30 → 10:30 Plenary Experiment 2: Astroparticle (Room 567, Chair Xiao-Gang He)

08:30 Cosmic Rays, SNRs and μ-Quasars in LHAASO's View

Speaker: zhen cao (中国科学院高能物理研究所)

09:00 PandaX: Status and Prospects

Speaker: Jianglai Liu (Shanghai Jiao Tong University)

09:30 First Oscillation Results and Future Prospects of JUNO

Speaker: Yufeng Li (Institute of High Energy Physics)

10:00 Status of the Hai-Ling Project

Speaker: Prof. Donglian Xu (T D Lee Institute)

10:30 → 10:50 Coffee-Break

10:50 → 12:20 Plenary Theory 4: QFT Frontiers and Strong Dynamics (Room 567, Chair Bo Feng)

10:50 Origin of Mass and Scattering Amplitudes: from Higgs to Pauli, Kaluza-Klein, and Chern-Simons

Speaker: Hong-Jian He (TDLI & SJTU)

11:20 Spacetime Symmetry dictates EFT Operators: from SMEFT to Dark Matter and Nuclear EFTs

Speaker: Jiang-Hao Yu

11:50 Glueball Dark Matter under Precision Control: Relic Abundance, Portals, and Direct Detection

Confining dark sectors offer a minimal and predictive route to composite dark matter (DM). I connect nonperturbative glueball physics to cosmological evolution and to laboratory searches. Using lattice-calibrated thermodynamics, we revisit the relic abundance of stable scalar glueballs and show that strong-coupling effects can shift standard abundance estimates by up to an order of magnitude, yielding a robust mapping between the confinement scale and the observed DM density (including its dependence on the dark-to-visible temperature ratio). We then show how heavy-fermion portals can naturally suppress electromagnetic couplings of composite states, opening broad viable parameter space for heavy glueball/axion-like DM. Finally, I present new results for C-odd vector glueball (''oddball'') DM coupled to photons via light electrically charged vector-like fermions portal, namely, its coherent nuclear scattering dominated by two off-shell photons. Matching an EFT to nonperturbative glueball form factors predicts a steep scaling, $\sigma_{\rm SI}\propto \Lambda_D^{2.15} m_\psi^{-8}$, so current and next-generation xenon detectors probe a distinctive light-portal window with $\Lambda_D \sim$ sub-GeV - few GeV and $m_\psi \sim$ few - tens of GeV, compatible with collider and precision constraints.

Speaker: Roman Pasechnik (Lund University)

12:20 → 12:25 Group Photo

13:30 → 15:00 Plenary Theory-Experiment Interplay 5: Cross Frontiers (Room 567, Chair Tian-Jun Li)

13:30 Axion Theory and Phenomenology

Speaker: Jia Liu (Peking University)

14:00 Measurements and implications of Galactic cosmic ray spectra

Precise measurements of energy spectra of cosmic rays are crucial to understanding the physics of cosmic rays. New progresses of measurements of the Galactic cosmic ray spectra by DAMPE and LHAASO will be introduced. The physical implications of these new measurements will be discussed.

Speaker: Qiang Yuan (Purple Mountain Observatory)

14:30 Learning from all Particles/Hits: AI usage at Collider/Cosmic-Ray Frontier

Speaker: Manqi RUAN (Institute of High Energy Physics, Beijing, China)

Learning From all Particles-TOPAZ-v2.pdf

13:30 → 15:00 Strongly Coupled BSM Network Initiation Meeting (by invitation only, Room 302, Chair Zhi-Wei Wang)

15:00 → 15:20 Coffee Break

15:20 → 16:30 Panel Discussion (Room 567, Panelist: Zhen Cao, Bo Feng, Hong-Jian He, Jiang-Lai Liu, Francesco Sannino, Raymond Volkas, Yi-Fang Wang, Host: Zhi-Wei Wang)

17:00 → 19:30 Conference Dinner

Sunday, 19 April

08:15 → 09:45 Plenary Theory 6: Fundamental Probes （Room 567, Chair Zong-Guo Si）

08:15 Self-Interacting Dark Matter and Dark Sectors: Small-Scale Structure as a Precision Probe

Speaker: Haibo Yu (University of California, Riverside)

2026TOPACHAIBOYUpdf.pdf

08:45 Electroweak Box Diagrams from Lattice QCD: γW and γZ Corrections for Precision Tests of the Standard Model

Speaker: Xu Feng

09:15 High-Frequency Gravitational Waves in Planetary Magnetospheres: New Detection Opportunities and Constraints

Speaker: Tao Liu (HKUST)

2026_04_HFGWs_TOPAC2026.pdf

09:45 → 10:00 Coffee Break

10:00 → 11:30 Plenary Theory 7: New QFT Methods (Room 567, Chair Hong-Jian He)

10:00 Integration & Reduction

In various physical situations, we need to do various integration. In this talk I will present recent developments how to do these integrations efficiently.

Speaker: Bo Feng (South China Normal University (SCNU))

10:30 Truth and Beauty: Quantum Entanglement Theory and Its Generic Searches at the Colliders

The quantum entangled state, which does not violate the Bell non-locality, can violate the Bell non-locality due to the super-activation. Thus, the quantum entanglement is indeed one of the most important properties of quantum mechanics, i.e., Truth of Nature. We shall propose the quantum entanglement theory from mathematical point of view, i.e., Beauty of Theory. For pure states, considering a general quantum system with N particles, we show that the quantum space (the total spin polarization parameter space) is complex projective space, and the classical space (the spin polarization parameter space for classical theory) is the cartesian product of the complex projective spaces. Thus, the classical space is the (generalized) Sagre variety in the quantum space, and the quantum entanglement space is the difference of these two spaces. For mixed states, the sufficient and necessary conditions for quantum entanglement can be given as a set of algebraic equations, which are simple and can be solved easily for physical systems. In addition, we propose a generic method to calculate the quantum range and classical range for the expectation value of any physics observable at the collider, and thus we can probe the quantum entanglement spaces which the previous ways cannot. However, there is a circular argument issue. Furthermore, we will briefly explain how to probe the quantum entanglement consistently in high energy physics by determining the spin analyzing powers and excluding the local hidden variable theory, i.e., evade the circular argument issue and solve the no-go theorem problem.

Speaker: Tianjun Li (Henan Normal University)

11:00 Frontier of multi-loop multi-leg Feynman integrals

With the development on differential equations and computational algebraic geometry methods, the era of analytic computation of multi-loop multi-leg Feynman integrals is coming. We analytically computed all 2loop 6point and 3loop 5point planar massless Feynman integrals. This is a mile stone of analytic feynman integral computation. Furthermore, based on analytic Feynman integrals, we present a new bootstrap method to obtained 2-loop 6-point amplitudes in QCD.

Speaker: Yang Zhang (University of Science and Technology of China)

11:30 → 12:25 Plenary Theory 8: Strongly Coupled Theory Special Session (Room 567, Chair Xiao-Feng Luo)

11:30 Emergent Hadron Mass in QCD: From the Gluon Mass to Observables

Visible matter is characterised by a single mass scale; namely, the proton mass. The proton’s existence and structure are supposed to be described by quantum chromodynamics (QCD), the strong interaction part of the Standard Model; yet, absent Higgs boson couplings, chromodynamics is scale-invariant. Thus, if the Standard Model is truly a part of the theory of Nature, then the proton mass is an emergent feature of QCD; and emergent hadron mass (EHM) must provide the basic link between theory and observation. This presentation will sketch recent progress in elucidating the character of EHM. Special emphasis will given to the three pillars of EHM namely, the momentum-dependent gluon mass, QCD's process-independent effective charge, and the running quark mass; their role in stabilising strong interaction theory; and their measurable expressions in a diverse array of observables.

Speaker: Craig Roberts

2604_ TOPAC4_RobertsCD.pptx

12:00 Functional qcd meets cosmology

Speaker: Fei Gao

13:30 → 14:55 Plenary Theory 9: Dark Signals (Room 567, Chair Hai-Bo Yu)

13:30 Constraining Higgs potential with multi-Higgs production

Speaker: 宗国 司 (山东大学物理学院)

14:00 Looking for lights from the darkness: Signals from MeV-scale solar axion-like particles

We investigate the photons from the decay of axion-like particles, produced in the solar activity. The nontrivial geometry indicates a wide angular distribution of these photons, which can even come from directions which deviate significantly from the direction of the sun. We consider some detection setups including space and terrestrial experiments in the pole region. There is a critical height for the terrestrial searches, below which there is no flux at all for some regions of the parameter space. One can explore the coupling of axion-like particle to photons up to $10^{-13}$ GeV$^{-1}$, if the flux of MeV-scale photons can reach the order of $10^{-15}$ erg cm$^{-2}$ s$^{-1}$ in future experiments.

Speaker: Yongchao Zhang (Southeast University)

solar_axion_TOPAC2026.pptx

14:30 dark matter signals at gravitational wave detectors

Speaker: Fa Peng Huang (Sun Yat-sen University)

Fapeng_dm_v2.pdf

14:55 → 16:10 Plenary Theory 10: BSM Constraints (Room 567, Chair Xu Feng)

14:55 Positivity Bounds in SMEFT

Speaker: Shuang-Yong Zhou (University of Science and Technology of China)

15:20 Morphology of the Galactic Center Gamma-Ray Excess

The Galactic Center Gamma-Ray Excess (GCE) remains one of the most intriguing puzzles in astrophysics, with leading interpretations including dark matter annihilation and an unresolved population of millisecond pulsars. In this talk, I present two complementary studies on the GCE morphology. First, I show that the GCE morphology is robust against variations in point source and galactic disk masking, consistently favoring either a nearly spherical profile or a peanut-shaped profile, depends on the background diffuse emission models. Second, motivated by recent Galactic surveys including Gaia, I extend the analysis to generic triaxial and tilted dark matter halos, finding that while the GCE spectrum and inner cuspiness are robust against halo triaxiality and tilt, its morphology can discriminate between different triaxial halo configurations and is more compatible with a dark matter origin than a stellar one.

Speaker: Yiming Zhong

15:45 Probing Ultralight Dark Matter with Laser Interferometers in Space

Speaker: Yong Tang (University of Chinese Academy of Sciences)

成都_Yong_Tang.pdf

16:10 → 16:30 Poster Awards and Coffee Break

16:30 → 18:40 BSM Highlight (Room 567, Chair Cheng-Cheng Han)

16:30 When inverse seesaw meets inverse electroweak phase transition: a novel path to leptogenesis

Speaker: Prof. Ke-Pan Xie (Beihang University)

Chengdu.pdf

16:55 Probing Dark Shower Models at Colliders using Long-Lived Particle Searches

TBD

Speaker: Wei Liu (Nanjing University of Science and Technology)

talk-LLP-ds.pdf

17:20 Long-lived Particle searches

In this work we study the prospect of detecting light scalars at the FASER. We develop the general formalism for the scalar production and decay from mesons at LHC, given modified couplings of the scalars to the SM particles, as well as summarizing the relevant GeV-scale experiment constraints. We then analyze the reaches of light scalars in the large $\tan\beta$ region of the Type-I 2HDM, in which a light scalar with relatively long life time could be accommodated. We also have studies in the framework of NMSSM.

Speaker: Wei Su (SYSU)

TOPAC2026-WEISU.pdf

17:45 The Fate of Chiral gauge theory

The infrared structure of gauge theories with chiral fermions remains largely unexplored. In this work we investigate the Bars--Yankielowicz class using the functional renormalisation group, building on recent developments in gauge--fermion systems that provide clear criteria for confinement and dynamical symmetry breaking.
We show that two distinct phases arise: one exhibiting both confinement and symmetry breaking at small numbers of colours, and another characterised by confinement without symmetry breaking in the large-colour limit. The latter realises a novel regime, opening the possibility of exotic spectra and phenomena that can now be studied within a systematic framework.

Speaker: Haolin Li (Sun Yat-Sen University)

TOPAC2026_Haolin.pdf

18:05 Two Higgs doublet models with a new U(1) gauge symmetry

In this talk, we discuss two Higgs doublet models in which a new U(1) gauge symmetry is introduced. We investigate if these models are allowed by current phenomenological data without introducing a scalar field except for two Higgs doublet ones. We find they are excluded by constraints from scalar boson decays associated with new gauge boson Z'. Then a dark vector-like fermion is introduced to modify branching ratio of Z' and we searched for allowed parameter region taking all the phenomenological constraints into account. Finally we show allowed region that can avoid all the constraints.

Speaker: Takaaki Nomura (Sichuan University)

Nomura0419.pdf

18:25 The Supersymmetric Pati–Salam Model Consisting of Only Small Representations: Theory and Phenomenology

In this talk, we will present a supersymmetric Pati-Salam model with only small representations as a potential candidate for physics beyond the Standard Model. The model features a Higgs sector with bifundamental fields $H_R+\bar H_R=(4,1,2)+(\bar 4,1,2)$, $H_L+\bar H_L=(4,2,1)+(\bar 4,2,1)$ as well as a pair of bi-doublet fields $h_a=(1,2,2)$ where $ a=1,2$, with three families of fermions accommodated in $ (4,2,1)+(\bar 4,1,2)$ as usual. The matter spectrum is augmented with three copies of neutral singlets that mix with ordinary neutrinos to realize the seesaw mechanism. The model introduces supersymmetric R-symmetry and a global discrete $\mathbb{Z}_n$ symmetry ($n > 2$) that prevents disastrous superpotential couplings, while its spontaneous breaking implies the existence of domain walls. We will discuss theoretical and phenomenological aspects of this model, including potential UV completion from string theory, its near-conformal RG running of gauge couplings, domain walls, proton decays, inflationary scenario, and gravitational waves as a potential probe of this model.

Speaker: Ruiwen Ouyang (HIAS, UCAS)

16:30 → 18:35 Collider Physics (Room 352, Chair Yan-Lin Liu)

16:30 PKMu缪子散射探测及新物理探索

本报告将介绍了基于缪子散射的科学研究项目PKMu (Probing and Knocking with Muons)及其近期进展, 该项目旨在利用缪子探索超越标准模型的潜在物理现象. 在缪子散射探测暗物质研究中, 项目利用阻性板气体室等高精度缪子径迹探测器, 建立宇宙射线缪子散射实验平台, 开展了为期63天直接探测实验, 通过详细的宇宙射线散射模拟与实测对比, 揭示了宇宙射线多组分对散射信号的贡献, 对缪子和低速暗物质的散射截面给出实测限制; 在缪子散射对暗玻色子与带电轻子味破坏的研究中, 结合高原子序数靶材和缪子-电子散射的实验设计, 模拟结果展现出在亚GeV质量区间及独立参数空间探索中的独特优势. 此外, 对缪子-电子散射中的量子纠缠与Bell不等式进行了模拟分析, 模拟结果显示在GeV能区具备良好的观测条件. 未来, 也将在国内国际缪子源上进行更深入的缪子散射研究. 总体而言, PKMu研究项目不仅提出了新一系列缪子散射实验构想, 还结合模拟与实验验证提供了系统的可行性分析, 为暗物质搜寻、暗玻色子探索及量子力学基础问题研究开辟了新的途径.

参考文献：
arXiv:2507.23458 (已经被PRL正式接收）
科学通报 71卷, 4期: 894 - 903 (2026)
J. Appl. Phys. 139, 014903 (2026)
Phys. Rev. D 110, 016017 (2024)
Mod. Phys. Lett. A 2530008 (2025)
J. Phys. G: Nucl. Part. Phys. 52 075002 (2025)
Phys. Rev. D 111, 116018 (2025);

Speaker: Qite Li (Peking University)

16:55 Light and Heavy Scalar Resonances in the NMSSM with Correct Dark Matter Relic Abundance

Recent CMS analyses report an excess in the diphoton-plus-b ̄b channel, indicative of a heavy resonance around 650GeV decaying into a Standard Model (SM)-like Higgs boson and a lighter scalar near 95GeV. The case for a 95GeV state is further supported by diphoton excesses observed by both CMS and ATLAS, as well as a b ̄b excess previously observed at the Large Electron-Position collider. This study presents a unified interpretation of these anomalies within the framework of the General Next-to-Minimal Supersymmetric Standard Model that naturally accommodates a light singlet-dominated CP-even scalar boson hs near 95 GeV and a heavier doublet-like scalar boson AH near 650 GeV. Through a comprehensive scan of the parameter space, we demonstrate that the model can explain these excesses at 2 σ level while satisfying constraints from the dark matter relic density, direct detection experiments, the properties of the 125GeV Higgs boson, B-physics observables, and searches for electroweakinos at the Large Hadron Collider (LHC). The interpretation features a Bino-dominated lightest neutralino as the dark matter candidate, whose relic abundance is achieved primarily via As funnel annihilation or coannihilation with S ̃-like χ ̃02s into hsAH final states. Our findings provide clear predictions for testing this scenario at the high-luminosity LHC and future colliders.

Speaker: Jingwei Lian (Henan Institute of Science and Technology)

成都2026-连经伟.pdf

17:20 Complementary Probes of Neutrino Mass Ordering at Colliders

The ordering of neutrino masses remains an open question in particle physics. While upcoming oscillation experiments aim to resolve this using low-energy probes, complementary approaches are needed to test neutrino mass generation more broadly. In this talk, I will show how high-energy collider experiments can provide such a probe within the minimal Type-I seesaw framework. Focusing on a scenario with two nearly degenerate heavy neutral leptons (HNLs), I will explain how the structure of light–heavy neutrino mixing is constrained by the observed neutrino masses, leading to flavor specific signatures for normal and inverted mass orderings. I will demonstrate that future high-luminosity Z-pole colliders, such as CEPC and FCC-ee, can probe these flavor patterns for very small mixing strengths and, in favorable cases, distinguish between the two orderings. This highlights collider searches for HNLs as a complementary tool to neutrino oscillation experiments in addressing the neutrino mass ordering problem.

Speaker: Supriya Senapati (Nanjing University of Science and Technology)

Supriya_Senapati_TOPAC26.pdf

17:35 Primordial black hole formation and multimessenger signals in a complex singlet extension of the standard model

Speaker: Chikako Idegawa (Sun Yat-sen University)

ChikakoIdegawa_TOPAC2026.pdf

16:30 → 18:40 Parallel Cosmology & Astrophysics: Cosmic Signals (Room 302, Chair Zhao-Feng Kang)

16:30 Leptophilic Scalar Dark Matter: Evading direct detection and prospective neutron star heating

Leptophilic dark matter offers a well-motivated framework in which conventional nuclear-recoil limits can be strongly suppressed, while viable parameter space remains testable through astrophysical observations. In this talk, I will present a study of scalar leptophilic dark matter in a gauged $\mathrm{U(1)}_{L_\mu-L_\tau}$ extension of the Standard Model, including secluded and pseudo-Nambu–Goldstone boson benchmark realizations. After imposing relic-density, direct- and indirect-detection, and neutrino-trident constraints, viable sub-TeV to TeV parameter regions remain. I will emphasize that neutron star heating provides a powerful complementary probe of these models: even when terrestrial direct-detection signals are suppressed, dark matter capture in neutron stars can still yield observable heating signatures. This complementarity makes old neutron stars a promising probe of thermal dark matter scenarios that evade strong constraints from conventional direct-detection searches.

Speaker: Chengfeng Cai (Sun Yat-sen University)

16:55 Soliton mergers and radio transients — A new window on dark photon dark matter

Ultralight dark photons can form stable, compact clumps that possess macroscopic coherence, called solitons. When two such solitons collide and merge, the merged object can suddenly convert its stored dark-sector energy into ordinary radio photons through a process called parametric resonance. The merger rate scales steeply with local soliton number density (merger rate ∝ density²), so regions near supermassive black holes — where dark matter can form dense, spiky profiles — are especially important for producing detectable bursts.

We use the lack of such narrow, powerful radio transients in existing surveys to set concrete limits. For dark photon masses that correspond to radio frequencies (~10⁻⁶–10⁻⁴ eV), current nondetections imply that at most a few percent of dark matter can reside in these solitons. Alternatively, if a large fraction of dark matter were in solitons, the coupling that converts dark photons to ordinary photons must be extremely small. These bounds come from comparing predicted burst rates and energies with radio telescope exposure and nonobservation.

Speaker: Hong-Yi Zhang

17:10 Probing the wave nature of light new physics

Many well-motivated UV theories contain bonsonic light degrees of freedom, which can exhibit various wave-like behaviors at low energy. This leads to many new ideas and novel observables in recent years to probe new physics in astrophysical and laboratory setups alike. In this talk, I will briefly review a few examples in leveraging the wave-like features to test axions and ultralight dark matter. These include the axion-induced supernova remnant radio echo, the soliton-imprinted galaxy rotation curves, axion-induced neutron star X-ray signals. I will end with a new axion-photon resonant conversion mechanism induced by spatially varying magnetic field background and show its phenomenological consequences to the LSTW experiments and solar axion searches.

Speaker: Chen Sun (ICTP, Trieste)

talk_short_ChenSUN.pdf

17:25 Confinement and Chiral Phase Transitions: The Role of Polyakov Loop Kinetics Terms

We studied a crucial but often oversimplified ingredient in predicting gravitational-wave signals from QCD-type phase transitions: the kinetic term of the Polyakov loop. For the first time, we derive this term from first principles in finite-temperature pure SU(3) Yang-Mills theory, incorporating a field-dependent renormalization factor—a calculation we also extend to theories with more colors. Employing this derived kinetic term alongside three commonly-used effective potentials (the Haar-measure, polynomial, and quasi-particle models), we demonstrate that it substantially modifies the predicted GW energy spectrum from confinement transitions by 1-2 orders of magnitude. Based on this, we provide the first complete analysis of the chiral transition within the Polyakov–Nambu–Jona-Lasinio (PNJL) framework, described by the quark condensate. Our results reveal a clear dichotomy: while the Polyakov-loop kinetic term critically shapes GWs from confinement transitions, it has a negligible impact on the dynamics of the chiral transition, which is dominated by fermion condensation effects.

Speaker: Dr Jiang Zhu (TDLi institution)

ZJ_TOPAC2026.pdf

17:40 Domain Walls in Extended Higgs Sectors: Electric Charge Violation and Electroweak Symmetry Restoration

Extended Higgs sectors such as the 2HDM and N2HDM provide new discrete symmetries, which, upon spontaneous symmetry breaking, can lead to the formation of topological defects called domain walls. In this talk, I discuss some consequences of these domain walls on the early universe, such as electroweak symmetry restoration necessary for Electroweak baryogenesis via domain walls, as well as the possibility of having electric charge breaking domain walls in the 2HDM, which lead to exotic effects such as the transformation of electrons into sterile neutrinos. This provides a new mechanism for the production of sterile neutrinos as dark matter.

Speaker: Mohamed Younes Sassi (Tsung-Dao Lee Institute, Shanghai Jiao Tong University)

topacconferencemohamedfinal.pdf

17:55 Model Parameter Reconstruction of Electroweak Phase Transition with TianQin and LISA: Insights from the Dimension-Six Model

We investigate the capability of TianQin and LISA to reconstruct the model parameters in
the Lagrangian of new physics scenarios that can generate an electroweak SFOPT. Taking the dimension-six Higgs operator extension of the Standard Model as a representative scenario for a broad class of new physics models, we establish the mapping between the model parameter Λ and the observable spectral features of the stochastic gravitational wave background. We begin by generating simulated data incorporating Time Delay Interferometry channel noise, astrophysical foregrounds, and signals from the dimensional-six model. The data are then compressed and optimized, followed by geometric parameter inference using both Fisher matrix analysis and Bayesian nested sampling with PolyChord, which efficiently handles high-dimensional, multimodal posterior distributions. Finally, machine learning techniques are employed to achieve precise reconstruction of the model parameter Λ. For benchmark points producing strong signals, parameter reconstruction with both TianQin and LISA yields relative uncertainties of approximately 20–30% in the signal amplitude and sub-percent precision in the model parameter Λ. TianQin’s sensitivity is limited to stronger signals within its optimal frequency band, whereas LISA can reconstruct parameters across a broader range of signal strengths. Our results demonstrate that reconstruction precision depends on signal strength, astrophysical foregrounds, and instrumental noise characteristics.

Speaker: Aidi Yang

chengdu-reconstruction.pptx

18:10 Gravitational waves and primordial black holes produced by dark meta stable vacuum decay

Inspired by string theory and cosmological constant problem, it is plausible that the Universe’s vacuum structure is characterized by a landscape of metastable vacua. If the dark vacuum is metastable, bubbles of lower-energy phases can nucleate at an approximately constant rate. Because the Hubble expansion rate is monotonically non-increasing with cosmic time, such nucleation can eventually lead to percolation and completion of a dark-sector phase transition. In this work, we investigate the phenomenological consequences of this transition, focusing on the resulting stochastic gravitational-wave background and the potential formation of primordial black holes.

Speaker: Tingyu Li (Tsinghua University)

TOPAC_TingyuLi.pdf

18:25 Ultra-Low Nucleation Phase Transitions: Super-Hubble Bubbles and Non-Standard Dynamics

Supercooled phase transitions have attracted significant interest as potential sources of strong, low-frequency gravitational wave signals detectable by Pulsar Timing Arrays (PTAs). A nucleation temperature $T_n$ is often used to characterize the onset of the transition, defined by a threshold on the nucleation rate. However, in the regime of ultra-low nucleation rates, $T_n$ may not exist, but this does not necessarily imply that the transition cannot complete. We show that even when nucleation remains suppressed and bubble separations exceed the Hubble scale, early-time bubbles can grow and eventually collide at late times, leading to completion. This presentation focuses on the completion condition and the associated dynamics in the regime of ultra-low nucleation rates.

Speaker: Haibin Chen

16:30 → 18:35 Parallel Dark Matter & Neutrinos (Room 368, chair Pei-Zhi Du)

16:30 Probing Majorana Neutrinos and Dark Matter at MeV-scale with PandaX

Liquid xenon experiments have advanced dark matter direct detection. While traditionally focused on keV-scale signals, the MeV region also offers rich information for studying neutrinos and dark matter. The PandaX-4T experiment at the China Jinping Underground laboratory uses 3.7 tons of natural xenon. We have developed a dedicated data analysis framework extending its energy range to the MeV scale, systematically characterized the detector response and background model, and searched for neutrinoless double beta decay, axion-like particles/dark photons, and more. This talk will highlight these achievements.

Speaker: Xiang Xiao (Sun Yat-sen University)

16:55 Discrete flavour and CP symmetries in light of JUNO and neutrino global fit

Working within the reference three-neutrino mixing framework, we confront the lepton mixing predictions derived using non-Abelian discrete flavour and CP symmetries with the first JUNO data on the solar neutrino mixing parameters $\sin^2\theta_{12}$
and with the results of the latest global neutrino data analysis. We focus on symmetry breaking patterns for which the lepton PMNS mixing matrix depends only on one or two free real parameters. Performing a comprehensive statistical analysis in each of the considered cases, we report the best fit values, the $3\sigma$ C.L. allowed ranges and the $\chi^2$-distributions of the lepton mixing observables - the three mixing angles and the three CP-violation phases. We find that the JUNO measurements can disfavour or rule out a number of the mixing patterns associated with specific types of breaking of the discrete flavour and CP symmetries.
The synergy of JUNO, DUNE and T2HK data can provide an exhaustive test of the considered approach to lepton mixing based on non-Abelian discrete lepton flavour symmetries combined with the CP symmetry.

Speaker: Cai-Chang Li (西北大学)

17:20 Neutrino fog at CJPL

The neutrino floor, a theoretical sensitivity limit for dark matter direct detections, is being redefined as the boundary of a dynamic ``neutrino fog", where neutrino signals become inevitable, obscuring DM detection due to the statistical and systematic uncertainties. This study provides the first site-specific analysis of the neutrino floor at China Jinping Underground Laboratory (CJPL), leveraging its unique geographic and environmental characteristics. We quantify how CJPL's suppressed atmospheric neutrino flux (around 30% lower than Laboratori Nazionali del Gran Sasso ) reshapes the neutrino floor, thereby enabling improved sensitivity to high-mass WIMPs (mass $>10 \rm GeV$). Using a gradient-based framework, we derive CJPL's neutrino floor and estimate the detection prospects for the PandaX-xT experiment. Our results demonstrate that a 500 tonne-year exposure with PandaX-xT could touch the floor, probing spin independent cross-section down to $\sigma_{n}\sim 3\times 10^{-49} \rm cm^2$ at a DM mass of 70 GeV/$c^2$.

Speaker: Xuewen Liu (Yantai University)

17:45 Latest results from the LUX-ZEPLIN (LZ) dark matter experiment

LUX-ZEPLIN (LZ) is a dark matter direct detection experiment, operating deep underground at the Sanford Underground Research Facility (SURF), USA. Utilizing a 7-tonne dual-phase xenon time projection chamber in conjunction with a robust veto system, LZ aims to primarily detect Weakly Interacting Massive Particles (WIMPs), one of the most promising dark matter candidates. Currently, LZ provides the most stringent constraints on WIMPs heavier than 5 GeV/c2. In this talk, I will review the current status of LZ and highlight our recent efforts in search for WIMPs, alongside explorations of other beyond the Standard Model phenomena.

Speaker: YONGHENG XU

18:05 RELICS: A liquid xenon time projection chamber for reactor CEvNS

Exhibiting the largest cross-section of all interaction channels for MeV neutrinos, coherent elastic neutrino-nucleus scattering (CEvNS) offers a compelling pathway for the remote monitoring of nuclear reactors. Liquid xenon time projection chambers (LXeTPCs) have emerged as an ideal technology for CEvNS detection, primarily due to their low backgrounds and energy thresholds. The RELICS (REactor neutrino LIquid xenon Coherent Scattering) experiment leverages this technology to target reactor CEvNS. RELICS is designed to perform precise measurements of the CEvNS cross-section, thereby advancing our understanding of fundamental neutrino properties and facilitating the search for physics beyond the Standard Model. This talk will introduce the status of the RELICS experiment and discuss its physics potential.

Speaker: Jun Wang (Westlake University)

18:20 Probing Collapsed Dark Matter Halos with Fast Radio Bursts

The observations of ultra-dense substructures in strong lensing systems challenge the standard
cosmology model at small scales. Self-interacting dark matter (SIDM), as one of the alternatives
to the cold collisionless dark matter (CDM) of the standard cosmology model, provides a natural
mechanism for forming such structures via gravothermal core-collapsing. We show that strong grav-
itational lensing of fast radio bursts (FRBs) provides a new way to effectively probe these structures
and to understand dark matter self-interactions. Core-collapsed SIDM halos exhibit steeper central
density profiles than CDM halos, enhancing the lensing cross section and producing longer time
delays between FRB images. We model the SIDM core-collapsed halo with a power-law profile
whose center is cored, and compute lensing properties for subhalo and host halo lensing, including
maximal impact parameters and time-delay distributions. Future observatories, such as BURSTT,
SKA2-Low, and SKA2-Mid, could detect 105–106 FRBs over a decade, yielding statistically sig-
nificant time-delay distributions that can probe core-collapse parameters of SIDM halos including
self-interaction cross section strengths to σ/m ≲ min{18 cm2/g, 40λsub cm2/g}.

Speaker: 雨轩 何 (City University of Hong Kong)

19:30 → 20:20 Special Evening Plenary Session 2 (Room 567, Chair Si-Chun Sun)

19:30 Quantum Sensing Frontiers for Dark Matter and New Physics

Speaker: Christina Gao

TOPAC26_Gao.pdf

19:55 Large Neutrino "Collider"

We propose using current and future large-volume neutrino telescopes as "Large Neutrino Colliders" (L$\nu$Cs) to explore TeV-scale physics beyond the Standard Model. Cosmic neutrinos with energies above 100 PeV colliding with nucleons in the detector reach center-of-mass energies beyond the 14 TeV limit of the Large Hadron Collider (LHC). Using recently predicted and measured high-energy and ultra-high-energy neutrino fluxes from IceCube and KM3NeT, we estimate mass-scale sensitivities for representative new physics scenarios at 1-30 km$^3$ L$\nu$Cs. Our results demonstrate that L$\nu$Cs provide a novel avenue to probe multi-TeV particles with sensitivities comparable to, or even surpassing, those of the LHC.

Speaker: 可平(Keping) 谢(Xie) (李政道研究所)

LnuC_TOPAC2025.pdf

20:20 → 20:35 Desert Break

20:35 → 21:20 Special Evening Plenary Session 3 (Room 567, Chair Ke-Pan Xie)

20:35 Supercooled Phase Transitions with Radiative Symmetry Breaking (online)

First-order phase transitions produce gravitational waves and primordial black holes. They always occur in field theories where symmetries are radiatively broken and masses are correspondingly generated. These theories predict a period of supercooling: phase transitions become effective at temperatures much smaller than the symmetry-breaking scale. I will discuss a model-independent approach to study phase transitions in this scenario, which can be adopted if supercooling is strong enough. Perturbative methods can be used to determine the effective action and such model-independent approach allows us to obtain ready-to-use formulas that can be applied to any specific model of this sort.

Speaker: Prof. Alberto Salvio (University of Rome and INFN Tor Vergata)

21:05 Cosmic birefringence and p-form fields

A tantalizing hint of beyond Standard Model (SM) physics lies in the polarization structure of the CMB. Joint analysis of WMAP, Planck, and ACT data suggests that the linear polarization plane of CMB photons has, since the surface of last scattering, rotated by an angle β ~ 0.3 degrees at over 4.5 σ significance. This is a parity violating phenomenon that can't be described using SM degrees of freedom. An axion-like coupling to the Chern-Simons term predicts a nonzero β, but it is not the only explanation. In this talk, we will overview the essential physics of cosmic birefringence and the role an axion may play. Then, we will explore two alternatives, namely, the possible explanation of cosmic birefringence coming from 2-form dark matter or 3-form dark energy.

Speaker: Tucker Manton (HIAS UCAS)

TManton_TOPAC2026.pdf

Monday, 20 April

08:15 → 09:45 Plenary Theory 11: Flavor/Neutrinos (Room 567, Chair Raymond Volkas)

08:15 Spontaneous Leptogenesis in Type I Seesaw

Type-I seesaw models with a spontaneously broken B−L symmetry provide a natural framework for spontaneous leptogenesis driven by a Majoron. The kinetic background of the Majoron acts as a CP-violating source, generating a lepton asymmetry both through the decay of right-handed neutrinos and through equilibration via inverse-decay processes. We construct the Boltzmann equations in a fully consistent manner, incorporating both effects, to enable a quantitative analysis. When the neutrino Yukawa coupling is large enough to maintain B−L violating interactions in thermal equilibrium, the resulting asymmetry closely tracks its equilibrium value. In contrast, when this condition is not satisfied, a nontrivial interplay emerges between decay and inverse-decay dynamics, determined by the Yukawa coupling strength and the initial abundance of right-handed neutrinos.

Speaker: EUNG JIN Chun (Korea Institute for Advanced Study)

260420 Chengdu KLeptognesis.pdf

08:45 Neutrinoless Double Beta Decay in the Multi‑Isotope Era: From Discovery to Mechanism

Speaker: Frank Deppisch (University College London)

deppisch-topac26.pdf

09:15 Semileptonic decay of heavy flavor meson

The study of semileptonic decay plays an important role in extracting the CKM matrix element, where the relevant form factor encodes the nontrivial strong interaction dynamics. We will overview the current achievements on the semileptonic decay, especially from the viewpoint from the relativistic quark model. The observables such as branching fraction, forward-backward asymmetry and polarization will be predicted, confronting with the experimental measurement.

Speaker: Xian-Wei Kang (Beijing Normal University)

09:45 → 10:00 Coffee Break

10:00 → 10:50 Plenary Theory 12: Novel Probes and EFT (Room 567, Chair Wen-Yuan Ai)

10:00 Hunting Dark Matter with Gravitational Wave detectors

This talk will focus on how gravitational-wave experiments can help probe dark matter candidates. The first part will demonstrate how data from the LIGO-Virgo-KAGRA Collaboration can be leveraged to distinguish between annihilating weakly interacting massive particles and a population of millisecond pulsars as the source of the long-standing GeV gamma-ray excess at the Galactic Center. I will then show how these same detectors enable the direct detection of ultralight dark matter candidates, including dark photons, axions, and dilatons.

Speaker: Yue Zhao (HKUST)

10:25 Weak Gravity Conjecture in the sky: gravitational waves from preheating in Einstein-Maxwell-Scalar EFT

The effective field theory (EFT) concept provides a necessary tool for obtaining general predictions of low-energy theory valid below its unitarity-breaking scale (cutoff scale). Early Universe inflation and subsequent reheating could be a unique setup for testing potentially observable effects coming from the derivative expansion of the corresponding EFT around the flat space vacuum. In this work, we consider an EFT describing perturbative reheating dominated by the decay of inflaton to photons caused by the dimension-5 operator. We compute the graviton production during reheating and high frequency gravitational wave signal due to the bremsstrahlung effect in the presence of R F F operator. It may lead to the dominant contribution at high momenta if the EFT cutoff is lower than the Planck mass. Assuming the general consequences of the unitarity and causality constraints, which imply that all EFT operators should be present, and be suppressed by the scales following from the dimension analysis, we obtain the observational constraints (CMB bound for the dark radiation) on the mass of the inflaton and UV cutoff of gravity. We find that for the typical parameters of large field inflation models, the gravitational cutoff scale cannot be lower than 10^15 GeV.

Speaker: Anna Tokareva (Hangzhou Institute for Advanced Study)

TOPAC.pdf

10:50 → 12:30 Plenary Theory-Cosmology 13: Particle Cosmology (Room 567, Chair Yi-Fu Cai)

10:50 Cosmological Collider Signals from Right-Handed Neutrino Loops

Cosmological Collider Signals from Right-Handed Neutrino Loops

Speaker: Chengcheng Han (Sun Yat-sen university)

RightHandedNeutrino.pdf

11:15 Supernova cooling from neutrino-devouring dark matter

Supernova cooling provides a powerful probe of physics beyond the Standard Model (SM), in particular for new, light states interacting feebly with SM particles. Unlike previous supernova studies focusing on annihilation or bremsstrahlung, we identify neutrino-initiated conversion as a dominant and previously unexplored production channel for fermionic dark matter (DM) via the neutrino-devouring process inside a core-collapse supernova, which contributes to the excessive cooling of the supernova. By incorporating state-of-the-art supernova simulation data and the full time evolution information, we derive stringent and robust limits on DM interactions.

Speaker: Ningqiang Song (Institute of Theoretical Physics, Chinese Academy of Sciences)

TOPAC2026-Song.pdf

11:40 Self-similar inverse cascade from higher-form symmetry

In the conventional turbulence studies, it has been revealed that inverse cascades driven by conserved quantities integrated over the entire space, such as helicity in three spatial dimensions
On the other hand, in terms of the higher-from symmetry, we are getting to know that there are also conserved charges are defined by integration over subspaces.
In this talk, I will demonstrate a new mechanism where higher-form symmetries naturally induce a self-similar inverse cascade. Taking axion electrodynamics with non-linear topological interaction as a paradigmatic example, it is shown that the conserved charge associated with its 1-form symmetry drives the system toward large-scale coherent structures through a universal scaling behavior characterized by analytically determined scaling exponents.
Our findings suggest that higher-form symmetries can provide a fundamental organizing principle for understanding non-equilibrium phenomena and the emergence of coherent structures in turbulent systems.

Speaker: Kohei Kamada (HIAS UCAS)

KK_0420_TOPAC.pdf

12:05 On-shell Approaches for Gravitational Wave Physics: waveform and beyond

The detection of gravitational waves has created a pressing need for high-precision theoretical models for binary systems. In this talk, I will review recent progress in the analytic computation of physical observables for binary black hole and neutron star systems using modern on-shell methods. I will focus on how the on-shell methods, which focus directly on gauge-invariant observables, offer significant simplifications over traditional formalisms. Furthermore, they provide new insights into the structure of classical general relativity. As an illustration, I will present a newly identified violation of the peeling behavior in the asymptotic metric.

Speaker: Fei Teng (Fudan University)

amplitudesMeetGW.pdf

13:30 → 14:40 Parallel Formal Theory 2: Formal Cosmology (Room 352, Chair Teng Ma)

13:30 Shockwaves and Time Delays in Einstein-Maxwell Effective Field Theory

We derive the shockwave metric in four-dimensional Einstein--Maxwell effective field theory (EFT) by performing an ultra-relativistic boost of the charged black hole solution accompanied by a rescaling of its mass and charge, including leading order EFT corrections. In contrast to the neutral (Schwarzschild) case, where higher derivative operators leave the shockwave geometry unchanged, we show that electrically charged shockwaves receive non-trivial EFT corrections. We then compute the time delay experienced by a probe photon traversing the resulting charged shockwave. We find that two EFT contributions, the correction to the shockwave geometry and the backreaction induced by the probe photon, are both essential for obtaining a physical time delay that is invariant under field redefinitions of the metric.

Speaker: Dr Minyuan Jiang (Nanjing Normal University)

causality Chengdu2026.pdf

13:55 Two-Step Cosmological Selection: Electroweak Scale and Its Unifying Legacy

The hierarchy problem between the electroweak (EW) scale and the Planck scale remains a central puzzle in modern physics. A promising approach is the cosmological selection via volume-weighted dynamics in a multiverse landscape, where the EW scale is dynamically selected as the configuration that maximizes the vacuum energy. We propose a two-step cosmological selection (TCS) mechanism. By minimally extending the Standard Model with a complex scalar singlet $\chi$ and $U(1)$ symmetry, the origin of the EW scale is explained elegantly by the TCS mechanism. The mechanism also has the potential to account for the neutrino masses generation. Once the $U(1)$ symmetry is broken explicitly by the soft breaking terms, the framework predicts a viable dark matter candidate. Its abundance can be produced via ultra-relativistic freeze-out during reheating and correlates directly with the reheating temperature.

Speaker: jinlei yang (Hebei University)

14:20 Frictional effect and scaling properties in domain wall networks

Domain walls arise in various physical contexts, such as early universe phase transitions. Their interaction with the surrounding plasma determines their motion and the scaling behavior of the networks. We study the friction exerted by a thermal plasma on domain walls in the thin-wall regime using the ballistic approximation. The resulting friction, dependent on wall velocity and temperature, is incorporated into the wall’s equations of motion to analyze its effect on network evolution. As an application, we explore implications for dark matter models and the associated gravitational wave signals.

Speaker: Yi-Song Lu

13:30 → 14:45 Parallel Theory-BSM: BSM Probes (Room 368, Chair Ke-Ping Xie)

13:30 Composite Asymmetric Dark Matter from Primordial Black Holes

We investigate a cogenesis scenario for composite asymmetric dark matter framework: a dark sector has a similar strong dynamics to quantum chromodynamics in the standard model, and the dark-sector counterpart of baryons is the dark matter candidate. The Hawking evaporation of primordial black holes plays the role of a source of heavy scalar particles whose CP-violating decay into quarks and dark quarks provides particle--anti-particle asymmetries in baryons and dark matter, respectively. Primordial black holes should evaporate after the electroweak phase transition and before the big-bang nucleosynthesis for explaining the baryon asymmetry of the Universe and for consistent cosmology. We find that this scenario explains the observed values for both baryon and dark matter energy densities when the heavy scalar particles have a mass of 10^6-10^9 GeV and the primordial black holes have masses of 10^7-10^9 g.

Speaker: Yoshiki Uchida (South China Normal University)

20260420_TOPAC2026.pdf

13:45 Direct Detection of Composite Asymmetric Dark Matter

We investigate the direct detection constraint on the composite asymmetric dark matter (ADM), where the confining gauge dynamics realized in the dark sector. The dark baryonic matter is the dark matter candidate, in particular it is similar to our baryons when we assume the SU(3) dark QCD in the dark sector. In addition, the dark sector is connected to the standard model sector through the dark photon portal to alleviate several cosmological problems, and we can probe the dark sector through the same dark photon. As for the direct detection, through the dark photon, the dark baryons can scatter off our baryons and leptons. When the dark baryons are charged under the U(1)_D (called dark proton), ordinary matter couples to the dark matter through the current interaction. Meanwhile, when the dark baryons are neutral under the U(1)_D (called dark neutron), ordinary matter couples to the dark matter through dipole interaction. In this talk, I will discuss the current constraints on and the future sensitivities to the composite ADM from the direct detection experiments.

Speaker: Takumi Kuwahara (Peking U)

TOPAC2026_Kuwahara.pdf

14:00 Scattering of non-relativistic finite-size particles and puffy dark matter direct detection

In this work we consider the scattering between non-relativistic particles with different finite sizes. We first calculate their interaction potential and apply the partial wave method to obtain their scattering cross section. Our findings show that the particle size can significantly affect the scattering between non-relativistic particles. Then we apply such a study to direct detection of puffy dark matter. We find that the finite size of the target nucleus may introduce non-perturbative effects that differ from the scenario of point-like dark matter. For large-size dark matter particles, this non-perturbative regime in the dark matter–nucleus scattering cross section effectively disappears; while for small values of the size-to-range ratio in the scattering process, a significant non-perturbative regime can maintain. Finally, for the direct detection of nugget-type puffy dark matter with a small number of constituent particles, we find that the stability conditions for the formation of bound-state dark matter can provide constraints on the dark matter–nucleus scattering cross section.

Speaker: 许 武龙

Wu-Long Xu TOPAC 2026.pdf

14:15 Prospects of Light Scalar and U(1)_{B-L} gauge boson at FASER(2)

We did a full simulation of sensitivity reach of $U(1)_{B-L}$ gauge boson with the contribution of a light scalar. We consider a minimal extension of the standard model with a $U(1)_{B-L}$ gauge group.

Speaker: Zihao Guo (School of physics, Southeast University)

Zihao_Guo_1430.pdf

14:30 Cosmological Collider Searches beyond the Hubble Scale with Planck Data

Searches for primordial non-Gaussianity (NG) has the potential to not only reveal the physics of cosmic inflation, but also the structure of fundamental interactions at the highest energies. The cosmological collider (CC) physics program exemplifies this possibility and demonstrates how searches for oscillatory NG can lead to mass-spin spectroscopy of extremely heavy states. Adopting an effective field theory approach, we find the class of Feynman diagrams that can give the largest NG mediated by a heavy scalar particle with mass $M\sim H$, the inflationary Hubble scale. We compute the full shape of the NG and perform the first search for this shape using Planck data, finding no evidence for NG. This search loses its sensitivity as $M\gg H$ since quantum vacuum fluctuations cannot efficiently produce such heavier particles. We then focus on a mechanism where a chemical potential excites on-shell scalar particles with mass $M\gg H$. Computing the full shapes, we perform the first CC search for particles parametrically heavier than $H$ using Planck data. For a range of chemical potential $\omega$ and $M$ satisfying $\omega-M \simeq 3H$, we find a global $1.7\sigma$ evidence for non-zero NG, after taking into account the look-elsewhere effect.

Speaker: Yisong Zhang (Tsinghua University)

slides_TOPAC2026_v2.pdf

13:30 → 14:40 Parallel Theory-Cosmology 2: Dark Cosmology (Room 302, Chair Sheng-Feng Yan)

13:30 How large are curvature perturbations from slow first-order phase transitions?

When strongly supercooled cosmological first-order phase transitions (FOPTs) are sufficiently slow, super-horizon inhomogeneities can be generated. We compute these super-horizon curvature perturbations by employing a gauge-invariant, multi-fluid formalism. By resolving the gauge ambiguities inherent in conventional separate-universe simulations, we demonstrate that Primordial Black Holes are unlikely to be produced by these super-horizon inhomogeneities. We also derive a fitting formula for the resulting curvature perturbations and discuss potential observational constraints on FOPTs imposed by limits on primordial curvature perturbations and associated scalar-induced gravitational waves.

Speaker: 驰 田 (安徽大学)

田驰.pptx

13:55 Exploring Inelastic Self-Interacting Dark Matter with Linear Cosmology

Inelastic self-interacting dark matter (iSIDM) provides a well-motivated extension of the cold dark matter paradigm, featuring multiple internal states connected by inelastic conversion processes. In this presentation, I will present a linear-cosmology framework for iSIDM, starting from a model-independent microphysical parameterization of the inelastic cross section and deriving the corresponding background and perturbation equations in an effective Boltzmann-code description. I will then discuss the resulting cosmological evolution, including the homogeneous chemical evolution and thermal history of the dark sector, demonstrating how these dynamics imprint characteristic signatures on the growth of density perturbations and the linear matter power spectrum. Finally, I will illustrate how the linear-theory predictions of iSIDM can be connected to existing data by translating the modified transfer function into two commonly used phenomenological constraints—those derived from the Lyman-α forest and high-redshift UV luminosity functions—thereby obtaining a preliminary mapping of the viable parameter space.

Speaker: 欣辰 段 (中国科学院紫金山天文台)

Topac_4th.pdf

14:10 Strongly Coupled Dark Sectors from the Dark Matter–Baryon Coincidence

There are many reasons to believe in the existence of a strongly coupled dark sector. One of them is the observed similarity between the energy densities of dark matter and baryons, known as the dark matter–baryon coincidence problem. In this talk, I will explain why this comparability points toward an asymmetric strongly coupled dark sector at the QCD scale. I will further discuss model-building attempts to fully resolve the coincidence problem, highlighting the key features of the corresponding strongly coupled dark sectors, including their spectra and phenomenology.

Speaker: Yi Chung (IBS, CTPU-PTC)

TOPAC_Yi_Chung.pdf

14:25 Equivalence Principle Violation from Dark Matter Coherent Scattering

We discuss how coherent scattering of dark matter with macroscopic targets can generate observable forces and lead to signals of equivalence principle violation. For dark matter masses around the eV scale, coherent enhancement in homogeneous or random materials opens new possibilities for torsion-balance experiments and related searches.

Speaker: Dr Chuan-Yang Xing (China University of Petroleum (East China))

EP in DM@TOPAC2026.pdf

13:30 → 14:45 Theory-Cosmology Highlight 1: Cosmological Signals (Room 567, Chair Ning-Qiang Song)

13:30 A Comprehensive Effective Field Theory Framework for Coherent Elastic Neutrino-Nucleus Scattering

Coherent elastic neutrino-nucleus scattering (CEνNS) is critical for testing the Standard Model electroweak sector, exploring neutrino properties, and searching for new physics (NP), with recent experiments (e.g., COHERENT, CONUS+, PandaX-4T, XENONnT) highlighting the need for a systematic theoretical framework. We have constructed a comprehensive end-to-end effective field theory (EFT) framework for CEνNS, covering the full energy scale hierarchy from the ultraviolet (UV) to the nuclear sector. It includes low-energy EFT (LEFT) operators up to dimension 8 (with QCD renormalization group running), spurion-method matching to the chiral Lagrangian, full power counting analysis for nuclear response functions (accounting for nucleon number enhancement), and matching of relevant LEFT operators to Standard Model EFT operators (with tree-level UV completions). Using CEνNS experimental data, this framework enables combined analysis to constrain EFT operator scales and neutrino non-standard interaction parameters.

Speaker: Gang Li (Sun Yat-sen University)

13:55 Hidden Correlations of Reionization Optical Depth in Cosmology

The reionization optical depth $\tau_{\rm reio}$ has interesting connections to existing cosmological anomalies. As first studied in the context of the Hubble tension in our previous paper, a larger $\tau_{\rm reio}$, which could be achieved by removing the Planck low-$\ell$ polarization data, could boost $H_0$ slightly, resulting in a mild reduction of the tension between the early- and late-universe determinations of $H_0$. It has been shown later that a larger $\tau_{\rm reio}$ could also relieve other anomalies including: the tension between BAO and CMB data, the neutrino mass tension, and the latest DESI plus supernovae data's tension with the standard cosmological constant scenario. In this paper, we systematically analyze the correlations between $\tau_{\rm reio}$ and relevant cosmological parameters in the existing cosmic observation anomalies. In addition to Pearson correlation coefficients extracted directly from the covariance matrix, we also study partial correlation coefficients which measure intrinsic relationships between pairs of parameters removing the influence of other parameters. Introducing these methods of partial correlations to cosmology,
we show that $\tau_{\rm reio}$ has weak intrinsic correlations with the parameters responsible for the tensions and anomalies discussed. The large direct Pearson correlations that allow larger $\tau_{\rm reio}$ inferences to alleviate the cosmological tensions each arise from complicated networks through multiple parameters. As a result, the relationships between $\tau_{\rm reio}$ and each anomaly are not independent of other parameters. We also introduce causal inference methods to cosmological data analyses, computing correlations to clarify the impact of large scale polarization data and the effects of CMB observations from ACT and SPT.

Speaker: Lingfeng Li

Reionization_and_Tensions_TOPAC.pdf

14:20 Non-Abelian Domain walls: oreo and CP violation

The spontaneous breaking of an $A_4$ flavour symmetry can lead to the formation of domain walls. We study this phenomenon in the scenarios of real and complex $A_4$ symmetric scalar theories and discover new kinds of domain walls, which we denote as ``oreo''-type composite domain walls and CP-violating domain walls.

Speaker: Bowen Fu (Northeastern University, Shenyang)

14:45 → 15:00 Coffee Break

15:00 → 15:55 Plenary Theory 14 (Composite Higgs Special Session): Composite Higgs (Room 567, Chair Aldo Deandrea)

15:00 Composite Higgs, ALPs, and partially composite tops

We present a class of models of electro-weak symmetry breaking based on strongly coupled gauge theories. We discuss the requirements imposed by flavor and CP violation on the strong dynamics. All these models give rise to an ALP that is an interesting target for searches at the high luminosity run of LHC. We present its effective lagrangian and some of the current bounds.

Speaker: Gabriele Ferretti (Chalmers University)

Chengdu26.pdf

15:30 Heavy axion in Composite Higgs model

We present a UV-complete extension of the Standard Model based on the gauge group (SU(5)\times SU(3)c^{\prime}\times Sp(2){TC}^{\prime}\times SU(2)L\times U(1)_Y), which breaks in two steps to QCD and a technicolor sector. Three axions cancel the three (\theta)-terms. Small instantons from the confining (SU(3)_c^{\prime}) and (Sp(2){TC}^{\prime}) sectors generate axion potentials, raising their masses to the eV range---well above the QCD axion. The model includes a composite Higgs ((SU(4)/Sp(4))) yielding a 125 GeV Higgs. Anomaly cancellation is verified. This provides a concrete ``hypercolored axion'' realization with multiple heavy axions.

Speaker: Teng Ma

15:55 → 18:30 Plenary Theory 15: Gravitational Waves (Room 567, Chair Ye-Ling Zhou)

15:55 Search Results for Physics Beyond the Standard Model with LIGO-Virgo-KAGRA's O1-O4a Observing Runs

I will discuss the recently released results on searches of physics beyond the standard model with LIGO-Virgo-KAGRA's most recent O1-O4a observing runs, including searches for cosmological first order phase transitions, cosmic strings, domain wall, primordial black holes, induced gravitational waves, and direct searches for dark matter, etc.

Speaker: Huaike Guo (University of Chinese Academy of Sciences)

Huaike_Guo_TOPAC-2026.pdf

16:20 From microphysics to Gravitational Waves for cosmological phase transitions

The possibility that future gravitational-wave detectors could observe the relic background from a cosmological phase transition has triggered intense progress in the theoretical description of these events. A detection of such a signal would probe energy scales far beyond those accessible to particle colliders, providing insight into fundamental questions about the early Universe, including the origin of the baryon asymmetry, the nature of dark matter, and the possible existence of exotic relics such as primordial black holes or cosmic strings.

If the transition is first order, it proceeds through the nucleation and expansion of bubbles of the new phase. The resulting gravitational-wave signal is therefore directly determined by microscopic properties of the transition, including the bubble nucleation rate, fluctuation determinants, and the velocity of the expanding bubble walls. Making reliable predictions therefore requires a precise treatment of thermal field theory, out-of-equilibrium dynamics, and the interaction of the bubble wall with the primordial plasma.

To enable systematic studies of models beyond the Standard Model, connecting microphysics to observable signals must be implemented in reliable and automated computational tools. Recent and forthcoming programs for determining bubble fluctuation determinants and bubble-wall velocities represent important steps in this direction. In this talk, I will review recent advances in modelling phase-transition dynamics, discuss the challenges that remain, and outline how improved automation will sharpen gravitational-wave predictions for upcoming experiments.

Speaker: Philipp Schicho (University of Geneva)

From microphysics to Gravitational Waves for cosmological phase transitions

topac26.pdf

16:50 Intertwining Axion and gravitational waves, generations and detection.

Firstly, we briefly discuss how the hypothetical beyond-the-Standard-Model particle, the axion, can produce gravitational waves through several mechanisms. Then we present some of our recent proposals for detecting axions/gravitational waves, including cryogenic quantum transport technology, traditional spin systems, and specially engineered artificial magnetoelectric materials. We demonstrate that room-sized detectors have promising sensitivity to axions with masses from kHz to GHz, and that a similar device can also be used for high-frequency gravitational wave detection over the same frequency range.

Speaker: Prof. Sichun Sun (Beijing Institute of Technology)

17:15 Isocurvature Induced Gravitational Waves at Pulsar Timing Arrays

The standard cosmological model (ΛCDM model) assumes adiabatic initial conditions for primordial density perturbations. However, many new physics scenarios can deviate from this assumption and predict isocurvature perturbations across a large range of scales. In this talk, I will discuss interesting features of gravitational waves induced by isocurvature perturbations. I will also show that observations from pulsar timing arrays can place stringent limits on isocurvature at around $10^6$/Mpc.

Speaker: Peizhi Du (University of Science and Technology of China)

Iso_induced_GW_TOPAC2026.pdf

17:40 Supercooled Dark-Sector Phase Transitions and the PTA Gravitational-Wave Signal

Speaker: Pedro Schwaller (Mainz University)

TOPAC_2026_Pedro_Schwaller.pdf

18:05 How a gravitational wave background affects particle processes

In one of his final papers, Steven Weinberg, together with Raphael Flauger, asked whether gravitational waves (GWs) can be attenuated through their interactions with matter. They argued that no attenuation occurs, owing to a cancellation between graviton absorption and stimulated emission, as inferred from leading-order soft-graviton arguments.

In this talk, I revisit this reasoning and show that it fails for the converse problem: the influence of a gravitational-wave background on matter. For unstable particles, real graviton emission and absorption appear to enhance decay rates. However, these apparent effects are a mirage, arising from an overreliance on leading-order perturbation theory.

To resolve this issue, we formulate a new version of Weinberg’s soft graviton theorem that properly accounts for the presence of a graviton medium. We find that the mutual transparency of matter and gravitational radiation is preserved in general cases. However, we also identify an extreme regime where a new IR effect might emerge.

Speaker: Wenyuan Ai (Tsung-Dao Lee Institute, Shanghai Jiao Tong University)

TOPAC_WenyuanAi_Aril_2026.pdf

18:30 → 18:35 Closing Remark