Registeration

Opening Speech

Was There an Electroweak Phase Transition

• Michael J. Ramsey-Musolf (TDLi institude)

Determining the thermal history of electroweak symmetry breaking is a forefront challenge for particle physics and cosmology. The occurrence of a first order electroweak phase transition (EWPT) would have profound implications for explaining the origin of the cosmic baryon asymmetry and generation of primordial gravitational radiation. I discuss recent theoretical developments in assessing the possibility of an EWPT in beyond Standard Model theories and highlight the corresponding phenomenological implications.

Status of the CEPC Project

• Haijun Yang (Shanghai Jiao Tong University (CN) and TDLI)

The discovery of the Higgs boson marked the beginning of a new era in HEP. Precision measurement of the Higgs boson properties and exploring new physics beyond the Standard Model using Higgs as a tool become a natural next step beyond the LHC and HL-LHC. Among the proposed Higgs factories worldwide, the Circular Electron Positron Collider (CEPC) with 100km circumference was proposed by the Chinese HEP community in 2012. CEPC is an e+e- Higgs factory to produce Higgs/W/Z bosons and top quarks which aims to measure Higgs, EW, flavor physics and QCD with unprecedented precision and to probe new physics beyond the SM. With the official release of CEPC Accelerator Technical Design Report (TDR) in December, 2023, we are intensively preparing accelerator Engineering Design Report (EDR) and reference detector TDR. The purpose is to submit CEPC proposal to Chinese government for approval and start construction within the “15th five-year plan (2026-2030)”. In this talk, the overview and global aspects of the CEPC project, highlights of CEPC physics, accelerator and detector R&D will be presented.

Nano-hertz gravitational waves and cosmic phase transition

• Jin Min Yang (ITP, CAS, Beijing)

Will talk about cosmic phase transition and nano-hertz gravitational waves is given. Two examples of new physics models are illustrated, which respectively predict a supercool first-order electroweak phase transition and a first-order phase transition in the dark sector at MeV scale. Both models are shown to be able to explain the reported evidences of nano-hertz gravitational waves.

Degeneracy Enhancement of Neutron-Antineutron Oscillation in Neutron Star

• Shao-Feng Ge (TDLI-SJTU)

We explore the fermion oscillation in a degenerate environment. The direct consequence is introducing a Pauli blocking factor 1−fi, where fi is the phase space distribution function, for each intermediate mass eigenstate during propagation. It is then much easier for a state with larger existing fraction or density to oscillate into other states with less degeneracy while the reversed process is not enhanced. This can significantly modify the oscillation behaviors. We apply this degenerate fermion oscillation to a concrete scenario of neutron-antineutron oscillation in neutron star. It turns out antineutrons receive a standing fraction to annihilate with the environmental neutrons. The subsequent neutron star heating can put an extremely stringent bound on the baryon number violating cross mass term between neutron and antineutron.

Detecting Axion-like Particles with Gravitational Waves

• Huan Yang (Tsinghua University)

In this talk I will review the progress of using LIGO events to probe/constrain the parameter space of Axion-like particles (ALPs), which may be generated through the super-radiant process around rotating black holes, and/or coupling with nuclear matter around neutron stars. I will also discuss current efforts trying to understand dynamical effects induced by ALP clouds in a compact object binary system and observational signatures in future GW/EM detections.

Consequencies of phase transitions happened during inflation

• Haipeng An (Tsinghua University)

I will discuss the phenomenological consequencies of phase transitions happened during inflation.

The impact of chiral effects on lepton flavor asymmetry in the early Universe

• Kohei Kamada (HIAS UCAS)

Anomalous transport phenomena, such as the chiral magnetic effect, arise from the chiral anomaly in gauge theories and have recently gained attention in hadron and condensed matter physics. These effects can also lead to intriguing phenomena in the early Universe, where chirality is well-conserved at temperatures above 100 TeV. One example is the chiral plasma instability, in which helical hypermagnetic fields are amplified due to chiral asymmetry, ultimately contributing to baryon asymmetry through the decay of hypermagnetic helicity. In particular, we highlight that a large lepton flavor asymmetry, possibly present before electroweak symmetry breaking and consistent with a vanishing total B-L, generally corresponds to a significant chiral asymmetry. This asymmetry induces the amplification of strong helical magnetic fields, leading to baryon overproduction. Our findings suggest that this mechanism imposes a stricter constraint on lepton flavor asymmetry than those derived from Big Bang Nucleosynthesis (BBN). Similar to how large lepton asymmetry before electroweak symmetry breaking is constrained by the SU(2) chiral anomaly through electroweak sphalerons to prevent baryon overproduction, we conclude that large lepton flavor asymmetry is also constrained by the U(1) hypergauge chiral anomaly.

拍照合影

The exploration into U(1) hidden sectors using gravitational waves

• Wan-Zhe Feng (Tianjin University)

Abstract: A variety of supergravity and string-based models feature hidden sectors with U(1) gauge groups, playing significant roles in particle physics and cosmology. As constraints on dark matter tighten, exploration into these hidden sectors intensifies. These hidden sectors can engage in feeble interactions with the visible sector and vary between feeble and normal strength with each other. In scenarios where all hidden sector particles are produced via the freeze-in mechanism, they do not reach thermal equilibrium with standard model particles in the thermal bath. Consequently, the hidden sector sustains a distinct temperature from the visible universe, posing challenges in calculating the evolution of these particles. We have devised a general method to compute the complete evolution of hidden sector particles in this model class. My discussion will cover the U(1) extension of the standard model, focusing on various dark matter candidates. The detection of gravitational waves offer an alternative way to explore the details of hidden sectors. Gravitational wave originated from a weakly coupled U(1) hidden sector will be discussed.

Towards the precise calculation of acoustic gravitational waves sourced from first-order phase transitions ------ a new hydrodynamic-simulation-based framework

• Xiao Wang (Monash University)

Phase transition gravitational waves could be a novel probe for fundamental physics in the near future. Hence, precise calculation of phase transition gravitational waves is essential for detecting the sign of new physics. I will discuss a framework that could allow us to omit some unnecessary approximations and give a relatively more accurate calculation of gravitational waves generated by the sound wave mechanism. With some benchmark models, I will demonstrate the procedures of this framework and show the corresponding results.

Bubble wall velocity from local equilibrium: A new approach

• Shao-Jiang Wang (Institute of Theoretical Physics, Chinese Academy of Sciences)

Cosmological first-order phase transitions (FOPTs) serve as comprehensive probes into our early Universe with associated generations of stochastic gravitational waves and superhorizon curvature perturbations or even primordial black holes. In characterizing the FOPT, phenomenological parameters like transition temperatures, strength factors, bubble separations, and energy budgets can be reliably extracted from the macroscopic features of the underlying particle physics models except for the terminal velocity of the bubble wall expansion, making it the last key parameter to be determined most difficultly due to the non-equilibrium nature of the microscopic transition model. In this talk, I will introduce a new approach to determine the bubble wall velocity model-independently assuming local equilibrium.

Cosmological implications of radiative electroweak symmetry breaking theories

• Ke-Pan Xie (Beihang University)

Radiative symmetry breaking (classically conformal) theories are plausible solution to the hierarchy problem. Such a paradigm also induces very rich cosmological implications via first-order phase transitions in the early Universe. This talk will discuss those effects.

Wess-Zumino-Witten Interactions of Axions

• Jia Liu (Peking University)

We present a consistent derivation of the complete Wess-Zumino-Witten interactions of axions, including the counter-term necessary to guarantee the gauge invariance of the Standard Model. By treating the derivative of the axion field as a background gauge field and incorporating auxiliary chiral rotation phases, we ensure consistency in the axion-interaction Lagrangian. This approach allows us to derive basis-independent physical interactions of axions with gauge bosons and vector mesons. As an example, we explore the interaction of $a$-$\omega$-$\gamma$ to illustrate the potential for searching for axion-like particles at colliders.

Panel Discussions

• Xiao-Gang He
• Michael J. Ramsey-Musolf (TDLi institude)

晚宴

QCD Phase Structure under a Rotation

• Pengfei Zhuang (Tsinghua University)

The rotation effect on the QCD phase structure is still an open question: Lattice simulations favor confinement but model calculations favor deconfinement. We discuss this problem in the frame of resumed QCD.

Study the QCD Phase diagram with Beam Energy Scan at RHIC

• Xiaofeng Luo (Central China Normal University)

Understanding the properties of quark matter and its phase structure is crucial for advancing our knowledge of the universe's evolution and the composition of visible matter. Over the past two decades, numerous experimental observations have provided evidence for the existence of strongly interacting quark-gluon plasma (sQGP) in relativistic heavy-ion collisions. As a result, exploring the QCD phase structure at high baryon densities—such as mapping the first-order phase transition boundary and locating the QCD critical point—has become a primary objective in heavy-ion collision research. Between 2010 and 2021, the first and second phase of the Beam Energy Scan (BES-I) at RHIC wrere completed, with the STAR experiment collecting data from Au+Au collisions at energies ranging from 200 GeV to 3 GeV (Collider and Fixed-target mode). In this talk, I will present the latest experimental progress in exploring the QCD phase structure at RHIC, with a special emphasis on the search for the QCD critical point. I will also discuss new facilities designed for exploring the high baryon density region and outline future research plans.

Glueballs on the lattice

• Ying Chen (Institute of High Energy Physics, Chinese Academy of Sciences)

This talk will review the current status of the glueball relevant lattice QCD study.

Lattice simulation of SU(2) dark glueball

• Wei Wang

The presence of dark matter, a fundamental cosmic constituent constituting a significant portion of the universe’s mass-energy content, has captivated the scientific community for decades. Recently, there has been a growing fascination with strongly interacting dark matter. We will focus on the intrinsic appeal of SU(2) glueballs as potential dark matter candidates and their implications for particle physics. A detailed exposition of mass, wave function analyses, and interaction potential offers fresh insights into the nature of SU(2) glueballs and their potential role in elucidating the mysteries of dark matter.

Probing dark matter halos with extreme mass ratio inspirals

• Yungui Gong (Huazhong University of Science and Technology)

Using the static and spherically symmetric metric for a black hole immersed in dark matter (DM) halos with Hernquist, Burkert, and Navarro-Frenk-White density distributions, we study the possibility of the detection of DM halos and the distinction between different DM halos with the extreme mass ratio inspiral systems (EMRIs). We also consider gravitational waves from the EMRIs consisting of primordial black holes inspiralling inside neutron stars within the Galaxy to probe the internal structure of neutron stars.

Constraining dark matter properties by astronomical observations

• 效军 毕 (中科院高能所)

Recently observed ultra diffuse dwarf galaxies or dark matter deficit dwarf galaxies may have important implications on the properties of dark matter particles. In the talk I will give explanations of the observations based on numerical simulation. It shows that the standard cold dark matter seems difficult to give a satisfied explanation to data.

Can Supercooled Phase Transitions Explain the Gravitational Wave Background Observed by Pulsar Timing Arrays?

• Chih-Ting Lu (Nanjing Normal University)

Several pulsar timing array collaborations recently reported evidence of a stochastic gravitational wave background (SGWB) at nHz frequencies. While the SGWB could originate from the merger of supermassive black holes, it could be a signature of new physics near the 100 MeV scale. Supercooled first-order phase transitions (FOPTs) that end at the 100 MeV scale are intriguing explanations, because they could connect the nHz signal to new physics at the electroweak scale or beyond. Here, however, we provide a clear demonstration that it is not simple to create a nHz signal from a supercooled phase transition, due to two crucial issues that could rule out many proposed supercooled explanations and should be checked. As an example, we use a model based on nonlinearly realized electroweak symmetry that has been cited as evidence for a supercooled explanation. First, we show that a FOPT cannot complete for the required transition temperature of around 100 MeV. Such supercooling implies a period of vacuum domination that hinders bubble percolation and transition completion. Second, we show that even if completion is not required or if this constraint is evaded, the Universe typically reheats to the scale of any physics driving the FOPT. The hierarchy between the transition and reheating temperature makes it challenging to compute the spectrum of the SGWB.

Intertwining Axion and gravitational waves, generations and detection.

• Sichun Sun (Beijing Institute of Technology)

Firstly, we discuss how the beyond the Standard Model hypothetical particle, the axion, can produce gravitational waves through several different mechanisms either in the astrophysical setting or the early universe. Then we present our recent new detection proposals for axions/gravitational waves using cryogenic quantum transport technology. The electric signal is enhanced by the high-quality factor of a resonant LC circuit and then amplified and detected by the cryogenic measurement technique. We demonstrate that this setup has promising sensitivity for axions with mass from kHz to GHz, and a similar device can also be used for high-frequency gravitational wave detection with the same frequency range.

Dark matter formed through a cosmological first-order phase transition and its associated gravitational wave signals

• Fa Peng Huang (Sun Yat-sen University)

We systematically discuss the new dark matter formation mechanism from a cosmological first-order phase transition and its associated gravitational wave signals.

暗色区相变动力学

• kang zhaofeng (华中科技大学(HUST))

暗色区是新物理模型构造中常见的一个对象，其早期的相变可能是一级相变，从而产生随机引力波信号。但研究的非微扰性是一个困难，本报告将简要介绍其相关方面及其进展。

Collective excitations from boosted dark matter

• 斌 祝

Plasmon, a collective mode of electronic excitation in solid-state detectors, provides a novel way to detect light dark matter (DM). In this work, we present the conditions of DM to produce plasmon resonance, requiring relativistic velocities for light DM, and generalize the collective excitation framework to account for relativistic DM. As a demonstration, we consider the cosmic ray boosted DM (CRDM) and find that the plasmon resonance can be significantly enhanced in the scenario with a light mediator. Utilizing the first data from SENSEI experiment with the skipper-CCDs at SNOLAB, we obtain a new strong limit on the sub-MeV DM-electron scattering cross section.

Excustion with Informal Dinner at City Center

Sphaleron in the Higgs Triplet Model

• Shun Zhou (IHEP)

We study the vacuum structure of the gauge and Higgs fields and calculate the saddle-point sphaleron configuration in the Higgs Triplet Model (HTM). The coupled nonlinear equations of motion of the sphaleron are solved using the spectral method. We find the inclusion of the triplet scalar could in principle significantly change the sphaleron energy compared with the Standard Model (SM).

Pulsar Polarization Arrays

• Jing Ren (Institute of High Energy Physics)

As one of the major dark matter candidates, the ultralight Axion-Like Dark Matter (ALDM) exhibits a pronounced wave nature on astronomical scales and offers a promising solution to small-scale structure issues within local galaxies. While the linearly polarized pulsar light travels through the ALDM galactic halo, its position angle (PA) can be subject to an oscillation induced by the ALDM Chern-Simons coupling with electromagnetic field. The Pulsar Polarization Array (PPA) is thus especially suited for the detection of the ultralight ALDM, by correlating polarization data across the arrayed pulsars. We conduct the first-ever PPA analysis to detect the ultralight ALDM, using the polarization data of 22 millisecond pulsars from the third data release of Parkes Pulsar Timing Array. To accomplish this task, we develop a Bayesian framework dedicated to analyzing the time series of PA residuals of these pulsars. We find that the PPA provides the most stringent constraints on the ALDM Chern-Simons coupling so far for the relevant mass range. We also demonstrate the crucial role of cross-correlation analysis in recognizing the nature of the derived limits.

Cosmic gauge strings and superstrings in the Early Universe

• Ye-Ling Zhou (HIAS-UCAS)

Cosmic string is a well-known topological defect widely predicted in field theories. It is regarded as one of the main sources of gravitational wave (GW) background that might be observed in the coming future. Most relevant studies have focused on cosmic strings in gauge field theory, which we call cosmic gauge strings. On the other hand, superstring theories also predict this defect, and it is called cosmic superstring. More than what we know about cosmic gauge strings, cosmic superstrings provide different types of cosmic strings and predict different inter-commutating probabilities among them, making the phenomenological consequences distinguishable from gauge strings. In this talk, I will compare the evolution between cosmic gauge strings and superstrings. The consequent GW signals and experimental hints will also be discussed.

SRF Cavity Searches for DP

• JING SHU (PKU)

Dark photons have emerged as promising candidates for dark matter, and their search is a toppriority in particle physics, astrophysics, and cosmology. We report the first use of a tunable niobiumsuperconducting radio-frequency cavity for a scan search of dark photon dark matter with innovativedata analysis techniques. We mechanically adjusted the resonant frequency of a cavity submergedin liquid helium at a temperature of 2 K, and scanned the dark photon mass over a frequency rangeof 1.37 MHz centered at 1.3 GHz. Our study leveraged the superconducting radio-frequency cavity’sremarkably high quality factors of approximately 1010, resulting in the most stringent constraintsto date on a substantial portion of the exclusion parameter space on the kinetic mixing coefficientϵ between dark photons and electromagnetic photons, yielding a value of ϵ<2.2×10^(-16).

Low-Energy Supernova Constraints on Millicharged Particles

• Zuowei Liu

The hot and dense environment of the supernova core serves as an extraordinary factory for new feebly-interacting particles. Low-energy supernovae, a class of supernovae with low explosion energy, are particularly intriguing due to their stringent constraints on the energy transfer caused by new particles from the supernova core to the mantle. We investigate low-energy supernova constraints on millicharged particles by considering three production channels in the core: plasmon decay, proton bremsstrahlung, and electron-positron annihilation processes. We find that the electron-positron annihilation process, previously omitted in supernova studies on millicharged particles, is the dominant production channel in the high-mass region. By studying the energy deposition due to Coulomb scatterings with protons in the supernova mantle, we find that low-energy supernovae impose the most stringent constraints on millicharged particles in the mass range of ∼(10−200) MeV, surpassing the energy loss limit from SN1987A by nearly one order of magnitude.

Phenomenology with ALP and Dark Matter

• Xiaoping Wang (Beihang University)

The strong CP problem and dark matter candidates are two significant challenges for the Standard Model. QCD axions are regarded as the most natural solution to the strong CP problem, making the development of a UV-complete model and the precision testing of their theoretical framework critical. As potential dark matter candidates, axion-like particles (ALPs) have garnered significant attention in both particle physics and cosmology. In particular, axion dark matter with a mass below the eV scale, due to its long-wavelength nature, offers an effective solution to the small-scale structure problems in the universe. Furthermore, to account for the relic abundance of dark matter, the high particle number density of such axions exhibits the characteristics of a classical wave field. How to explore the theory and phenomenology of various axions and axion dark matter is very interesting.

New perspective of QCD cosmology with Beyond the Standard Model

• Shinya Matsuzaki (Jilin University)

This talk plans to introduce a couple of recent new phenomenologies and cosmology related to the QCD phase transition epoch, coupled to Beyond the Standard Model, in the thermal history of the universe. Baryogenesis with a QCD-induced dynamical chemical potential (a la Higgs relaxation mechanism), strong CP problem, and gravitational wave predictions will be covered in scenarios of this class, which can also be embedded into the scalegenesis to address the dynamical origin of mass based on the classical scale invariance. Typical new physics accessible at the upcoming collider experiments are to be a dark eta-prime with mass of sub GeV and leptoquarks with mass of sub GeV, or sub TeV, which depends on the type of baryogenesis. Possible issues left necessary to persist in the future will also be addressed.

Domain walls beyond the minimal scenario

• Bowen Fu (Northeastern University, Shenyang)

Domain wall is one of the topological defects that can be created during phase transitions. The minimal and most well-studied domain wall is from $Z_2$ symmetry breaking. In this talk, we will go beyond this minimal case in two ways: embedding the $Z_2$ symmetry into a $U(1)$ and generalising the abelian discrete symmetry to non-abelian ones. On the one hand, the $Z_2$ symmetry can result from a $U(1)$ symmetry at a higher scale. In such a breaking chain, the domain walls from $Z_2$ symmetry breaking form hybrid defects with the cosmic strings from $U(1)$ symmetry breaking. On the other hand, the breaking of non-abelian discrete symmetries also generates domain walls. Adopting $S_4$ as an example, we will see these non-abelian domain walls have a richer structure and thus can lead to many interesting phenomena.

Primordial black hole formation from an aborted phase transition

• Wen-Yuan Ai (King's College London)

Primordial black holes may be produced from cosmological first-order phase transitions. I will discuss a new mechanism for PBH formation based on an aborted heating phase transition during reheating. Here "heating" means that the phase transition occurs as the temperature increases during the earlier stage of reheating (when the Universe is still matter-dominated). "Aborted" means that there are bubble nucleations but the nucleation rate is so low such that there is no coalescence for these nucleated bubbles. The particular evolution of the effective potential during reheating makes the bubble expand first, then shrink, and finally disappear. However, such disappeared bubbles generate perturbed spherical regions with over-density in energy, which would accrete the surrounding matter (reheaton) and collapse into black holes.

How robust are gravitational wave predictions from first order cosmological phase transitions?

• Peter Athron (Nanjing Normal University)

The prospect of detecting Gravitational waves from first order phase transitions opens up a whole new way to test particle physics models. However in order to make use of this we need to have an understanding of the uncertainties involved involved in theoretical calculations and the reliability of commonly used approximations. I will discuss various subtle issues in the prediction of gravitational wave spectra from first order phase transitions that can significantly impact the predictions and discuss how robust the predictions are. In particular I will discuss criteria for determining if a phase transition completes, the dependence of gravitational wave predictions on the transition temperature and a variety of standard approximations.

Simulations of Bosonic Dark Matter

• 家骏 陈 (西南大学物理科学与技术学院)

This talk discusses simulations of bosonic dark matter, focusing on the condensation and evolution of halos and boson stars, as well as the polarization evolution of vector dark matter. The background section highlights the nature of cold dark matter, its problems, and possible solutions like warm dark matter, self-interacting dark matter, and ultra-light axions. It introduces axion-like particles and the mathematical framework used to model their behavior. The first part addresses the formation and evolution of halos and boson stars, with detailed discussion on condensation, growth rates, and the role of self-interaction in shaping these structures. The formation of multiple boson stars due to gravity and self-interactions is also explored. The second part explores the polarization evolution of vector dark matter. It examines how different initial conditions affect the formation of Proca stars, and how spin and polarization evolve over time. The talk shows that the density of vector dark matter correlates closely with polarization density, and that Proca stars can form due to spin in one direction, leading to a spin reversal in the outer regions.

Closing Speech