尊敬的各位专家学者及各位同学好：
2023年第九届中国LHC物理年会 The 9th China LHC Physics Workshop (CLHCP2023)由中国物理学会高能物理分会主办，上海交通大学李政道研究所/物理与天文学院承办，中国高等科学技术中心（CCAST）与北京大学高能物理中心（PKUCHEP）协办，会议日期为2023年11月16日至11月20日 (11月15日报到 )。
中国LHC物理年会（简称CLHCP）是由中国物理学会高能物理分会指导、各地学术机构轮流主办的全国性重要学术会议，聚焦于高能量与高精度前沿粒子物理实验与理论的最新研究进展，会议内容包括：上帝粒子希格斯物理、电弱物理、强子物理与味物理、重离子物理、超越标准模型的新物理、探测器与加速器技术等粒子物理高能量与高精度前沿重要基础研究热点方向。会议旨在加强理论物理学家及实验物理学家在高能量前沿、高精度前沿与实验技术前沿领域的交流与合作，引领粒子物理领域国内研究水平的共同进步、推动国内相关研究工作的国际学术影响力、为年轻学者提供交流与合作的舞台。
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会务团队：
贺刚、求芳英（上海交通大学物理天文学院粒子与核物理研究所）
汪雯、丁梦安（上海交通大学李政道研究所粒子与核物理研究部）
The charged Higgs boson plays an essential role in distinguishing between a wide variety of standard model extensions with multiple Higgs doublets. We study the prospect of a light charged Higgs boson, produced by top quark pairs at the Large Hadron Collider (LHC), and decaying into a $W$ boson and a pair of bottom quarks via an intermediate neutral Higgs boson ($H_i$). We reinterpret the cross sections of $WWbb\bar{b}\bar{b}$ final states measured by the ATLAS collaboration at LHC 13 TeV in the presence of the aforementioned decay, in a relatively wide range of Higgs masses. We find improved agreements with the data and obtain limits on the total branching ratio of the decay chain. The limits impose the strongest constraints on the parameter space of type-I two-Higgs-doublet model for most Higgs masses sampled when $H_i$ is the $CP$-odd Higgs boson $A$. We also calculate potential constraints with pseudodata in high-luminosity runs of the LHC.
We calculated partial SM NLO electroweak corrections to Higgs pair production in gluon fusion, which are proportional to triple Higgs self-interacting constant. Then we did the same calculations with the Standard Model Effective Field Theory (SMEFT) dimension-6 Higgs self-interacting operators, and calculated the cross sections corresponding to different SMEFT parameters.
We present a systematic formalism based on a factorization theorem in soft-collinear effective theory to describe non-global observables at hadron colliders, such as gap-between-jets cross sections. The cross sections are factorized into convolutions of hard functions, capturing the dependence on the partonic center-of-mass energy, and low-energy matrix elements, which are sensitive to the low scale characteristic of the veto imposed on energetic emissions into the gap between the jets. The scale evolution of both objects is governed by a renormalization-group equation, which we derive at one-loop order. By solving the evolution equation for the hard functions for arbitrary 2→M jet processes in the leading logarithmic approximation, we accomplish for the first time the all-order resummation of the so-called "super-leading logarithms" discovered in 2006, thereby solving an old problem of quantum field theory. We study the numerical size of the corresponding effects for different partonic scattering processes and explain why they are sizable for pp→2jets processes, but suppressed in H/Z+jet production. The super-leading logarithms are given by an alternating series, whose individual terms can be much larger than the resummed result, even in very high orders of the loop expansion. Resummation is therefore essential to control these effects. We find that the asymptotic fall-off of the resummed series is much weaker than for standard Sudakov form factors.
In this talk we will discuss the recent processes in the calculation of the high-order perturbative corrections to the semi-inclusive production and decay of top quarks at lepton colliders at N3LO in QCD. In particular, the talk will be focusing on the first high-precision calculation of the complete QCD corrections to the top-quark decay width $\Gamma_t$, $W$-helicity fractions and semi-inclusive distributions to the third order in the strong coupling constant $\alpha_s$. We find, in particular, that the pure $\mathcal{O}(\alpha_s^3)$ correction decreases $\Gamma_t$ by $0.8\%$ of the previous $\mathcal{O}(\alpha_s^2)$ result, exceeding considerably the error estimated by the usual scale-variation prescription. With this critical piece of correction included, we arrive at the to-date most precise theoretical prediction which meets the envisaged precision request by future hadron and lepton colliders.
In heavy quark limit, the lowest-lying charmed baryons with two light quarks can form an SU(3) triplet and sextet. The $\Xi_c$ in the SU(3) triplet and $\Xi_c'$ in the sextet have the same $J^{PC}$ quantum number and can mix due to the finite charm quark mass and the fact the strange quark is heavier than the up/down quark. We explore the $\Xi_c$-$\Xi_c'$ mixing by calculating the two-point correlation functions of the $\Xi_c$ and $\Xi_c'$ baryons from lattice QCD. Based on the lattice data, we adopt two independent methods to determine the mixing angle between $\Xi_c$ and $\Xi_c'$. After making the chiral and continuum extrapolation, it is found that the mixing angle $\theta$ is $1.2^{\circ}\pm0.1^{\circ}$, which seems insufficient to account for the large SU(3) symmetry breaking effects found in weak decays of charmed baryons.
The resummation calculation (ResBos) is a widely used tool for the simulation of single vector boson production at colliders. As the improvement over the ResBos code by increasing the accuracy from NNLL+NLO to N$^3$LL+NNLO, the nonperturbative function needs to be updated. We propose a new non-perturbative function (IFY) that includes information about the rapidity of the system. The IFY functional form was fitted to data from fixed target experiments, the Tevatron, and the LHC. We find that the non-perturbative function has mild rapidity dependence based on the results of the fit.
We present a first lattice QCD calculation of the transverse-momentum-dependent wave functions (TMDWFs) of the pion using large-momentum effective theory. Numerical simulations are based on one ensemble with 2+1+1 flavors of highly improved staggered quarks action with lattice spacing a = 0.121 fm from the MILC Collaboration, and one with 2 +1 flavor clover fermions and tree-level Symanzik gauge action generated by the CLS Collaboration with a = 0.098 fm. As a key ingredient, the soft function is first obtained by incorporating the one-loop perturbative contributions and a proper normalization. Based on this and the equal-time quasi-TMDWFs simulated on the lattice, we extract the light-cone TMDWFs. The results are comparable between the two lattice ensembles and a comparison with phenomenological parametrization is made. Our studies provide a first attempt of ab initio calculation of TMDWFs which will eventually lead to crucial theory inputs for making predictions for exclusive processes under QCD factorization.
We present FMNLO
, a framework to combine general-purpose Monte Carlo generators and fragmentation functions (FFs). It is based on a hybrid scheme of phase-space slicing method and local subtraction method, and accurate to next-to-leading order (NLO) in QCD. The new framework has been interfaced to MG5_aMC@NLO
and made publicly available in this work. We demonstrate its unique ability by giving theoretical predictions of various fragmentation measurements at the LHC, followed by comparison with the data. With the help of interpolation techniques, FMNLO
allows for fast calculation of fragmentation processes for a large number of different FFs, which makes it a promising tool for future fits of FFs. As an example, we perform a NLO fit of parton fragmentation functions to unidentified charged hadrons using measurements at the LHC. We find the ATLAS data from inclusive dijet production show a strong constraining power. Notable disparities are found between our gluon FF and that of BKK, DSS and NNFF, indicating the necessities of additional constraints and data for gluon fragmentation function.
We calculate the total cross-section and differential distributions of Higgs boson pair production and decay to $b \bar{b}\gamma \gamma$ at NLO in QCD.
We study the feasibility of observing sterile neutrino at the high energy colliders, using direct and indirect production channels in heavy meson/baryon and Higgs decays. It is found that these processes may set certain new constraints on the mass of sterile netrino in present running and next generation experiments.
The physics beyond the Standard Model (BSM) could be represented by a hidden sector at relatively low energy scales MeV-GeV and feeble couplings to SM. Their presence in our Universe would be revealed through indirect evidences such as small oscillations of SM parameters, cosmological and astrophysical considerations, and the complementary searches in accelerators. Here, I give an overview of these BSM models including axions and hidden photons.
It is important to understand the implications of current observational constraints and potential signatures on the thermal history of dark matter. Using the freeze-in/-out scenarios as templates, we revisit dark-matter production by solving the Boltzmann equations at the level of the phase-space distribution. We also investigate the current Lyman-alpha constraints on mass of the dark matter and build the connection between the mass and the production mechanism of dark matter and find that the current observation on structure formation can be imposed to constrain the decoupling temperatures and the phase-space distribution of dark matter. We further explore the potential of distinguishing different possible thermal histories of dark matter with hypothetical future observational data. This method can be more generally applied to other scenarios.
Precision prediction for top quark physics
Top quark is the heaviest particle in the standard model. Once produced, the top quark immediately decays to a W boson and a bottom quark before hadronization. Precision studies for top quark physic plays essential role in the validity of the Standard Model and exploring potential avenues for new physics. In this talk I will review recently theoretical development in top quark physics, which includes the theoretical efforts for top quark production and decay.
The Higgs boson pair production via gluon-gluon fusion and vector boson fusion in the bbμμ final state at the LHC is studied to probe the Higgs self-coupling κλ and the four-boson HHVV coupling κ2V for the first time. A cut-based analysis and a machine-learning analysis using boosted decision trees are performed with categorizations and optimizations depending on the variations of these couplings. The expected sensitivities are extracted with different integrated luminosities assumed up to the full highluminosity LHC runs. The expected upper limit at 95% confidence level on the Higgs boson pair production is calculated as 47 (28) times the Standard Model cross section using the cut-based method (boosted decision trees) for the gluon-gluon fusion production and 928 for the vector boson fusion production, assuming an integrated luminosity of 3000 fb^−1. The expected constraints on the couplings at 95% confidence level are calculated to be −13.8 < κλ < 19.1 (−10.0 < κλ < 15.5) and −3.4 < κ2V < 5.5 using the cut-based method (boosted decision trees), respectively, assuming an integrated luminosity of 3000 fb−1.
In view of both the latest LHCb measurement of $R_{K^{(*)}}$ and the new $2.8\sigma$ deviation reported by Belle II on $B^{+}\to K^{+}\nu\bar{\nu}$ decays, we present a fit to the $B$ meson anomalies for various one and two dimensional hypothesis including complex Wilson coefficients. We show in a model-independent way that the generic non-universal $U(1)^{\prime}$ extensions of the SM, without flavour violation, fail to simultaneously fit those observables and corroborate that they can modify $\mathrm{BR}(B^{+}\to K^{+}\nu\bar{\nu})$ up to only a $10\%$. In view of this deficit, we propose a new way in which those models can accommodate the data at tree level by introducing lepton flavour violating couplings and non-diagonal elements of the charged lepton mixing matrix, with implications in future charged lepton flavour violation searches.
We study probes of neutral triple gauge couplings (nTGCs) at the LHC, CEPC and SPPC. The nTGCs provide a unique window to the new physics beyond the Standard Model (SM) because they can arise from SM effective field theory (SMEFT) operators that respect the full electroweak gauge group $\mathrm{SU(2)}_{\mathrm L}^{}\!\otimes\mathrm{U(1)}_{\mathrm Y}^{}$ of the SM only at the level of dimension-8 or higher. We derive the neutral triple gauge vertices (nTGVs) generated by these dimension-8 operators in the broken phase and map them onto a newly generalized form factor formulation, which takes into account only the residual U(1)$_{\mathrm{em}}^{}$ gauge symmetry. Using this mapping, we derive new relations between the form factors that guarantee a truly consistent form factor formulation of the nTGVs and remove large unphysical energy-dependent terms. We then analyze the sensitivity reaches of the LHC, CEPC and SPPC for probing the nTGCs via both the dimension-8 nTGC operators and the corresponding nTGC form factors. We compare their sensitivities with the existing LHC measurements of nTGCs and with those of future colliders.
In this talk, we explore the potential of probing the inelastic dark matter (DM) model with an extra $U(1)_D$ gauge symmetry at the Large Hadron Collider, ForwArd Search ExpeRiment and Super Tau Charm Factory. To saturate the observed DM relic density, the mass splitting between two light dark states has to be small enough, and thus leads to some distinctive signatures at these colliders. By searching for the long-lived particle, the displaced muon-jets, the soft leptons, and the mono-photon events, we find that the inelastic DM mass in the range of $1$ MeV to $210$ GeV could be tested.
A new $U(1)_X$ gauge boson field X can have renormalizable kinetic mixing with the standard model (SM) $U(1)_Y$ gauge boson field Y. Besides the dark photon kinetic mixing $\sigma$, there could be mass mixing by introducing the additional Higgs doublet with vev engaging in $U(1)_X$ and electroweak symmetry breaking simultaneously. The Z boson interaction with SM tau lepton is modified by defining the mixing ratio parameter $\epsilon$, which shows the magnitude of the mass and kinetic mixing of dark photon. We investigate the Z boson phenomenology of dark photon model with both the kinetic mixing and mass mixing. The allowed parameter region is obtained by analyzing these constraints from the vector and axial-vector couplings $g_{V,A}^\tau$, the decay branching ratio $Br(Z\to \tau^- \tau^+)$ and tau lepton polarization in $Z\to \tau^-\tau^+$. We found that the mixing ratio plays important role in the Z boson features by choosing different $\epsilon$ values.
Further, we attempt to find the common regions to satisfy these above four bounds for $m_X>m_Z$ and $m_X
Future muon colliders with center-of-mass energy of $\mathcal{O}(1-10)$ TeV can provide a clean high-energy environment with advantages in searches for TeV-scale axion-like particles (ALPs), pseudo-Nambu–Goldstone bosons associated with spontaneously broken global symmetries, which are widely predicted in physics beyond the Standard Model (SM).
We exploit ALP couplings to SM fermions, and guided by unitarity constraints, build a search strategy focusing on the ALP decay to top quark pairs.
We present the calculation of the next-to-leading order corrections for Higgs+jet production at the Large Hadron Collider, that arise from the Higgs trilinear self-coupling ($\lambda_{HHH}$).
We use the method of large top-quark mass expansion to tackle the challenging two-loop virtual amplitude, and apply the Pad\'{e} approximation to extend the region of convergence of this expansion.
We find that the $\lambda_{HHH}$-related corrections amount to $0.66\%$ for the total cross section. For the invariant mass distribution and Higgs boson transverse momentum distribution, the corrections are mostly in the range $0.5\% \sim 0.7\%$. Our results can be used to set extra constraints on $\lambda_{HHH}$ from the experimental data.
The longitudinal spin transfer represents the probability density of producing longitudinally polarized hadrons from longitudinally polarized quarks or circularly polarized gluons. It thus was usually measured in polarized reactions or high-energy collisions where weak interaction dominates. In this work, we propose the dihadron polarization correlation as a novel probe of this quantity. Such an observable does not require the fragmenting partons to be polarized and therefore can be measured in the currently available experimental facilities, such as Belle, RHIC, Tevatron, and the LHC. We make quantitative predictions for these experiments. In light of the data already harvested, the experimental investigation of this observable provides more opportunity for the quantitative study of the longitudinal spin transfer. In particular, the measurements in $pp$ collisions can significantly constrain the fragmentation function of a circularly polarized gluon.
References
[1] Probing the longitudinal spin transfer via dihadron polarization correlations in unpolarized $e^+e^-$ and pp collisions, Hao-Cheng Zhang, Shu-Yi Wei, Phys. Lett. B 839 (2023) 137821.
[2] X. Li, Z.X. Chen, S. Cao, S.Y. Wei, arXiv:2309.09487 (2023).
We develop a hybrid scheme to renormalize quasi distribution amplitudes of a light baryon on the lattice, which combines the self-renormalization and ratio scheme. By employing self-renormalization, the UV divergences and linear divergence at large spatial separations in quasi distribution amplitudes are removed without introducing extra nonperturbative effects, while making a ratio with respect to the zero-momentum matrix element can properly remove the UV divergences in small spatial separations. As a specific application, distribution amplitudes of the Λ baryon made of uds are investigated, and the requisite equal-time correlators, which define quasi distribution amplitudes in coordinate space, are perturbatively calculated up to the next-to-leading order in strong coupling constant αs. These perturbative equal-time correlators are used to convert lattice QCD matrix elements to the continuum space during the renormalization process. Subsequently, quasi distribution amplitudes are matched onto lightcone distribution amplitudes by integrating out hard modes and the corresponding hard kernels are derived up to next-to-leading order in αs including the hybrid counterterms. These results are valuable in the lattice-based investigation of the lightcone distribution amplitudes of a light baryon from the first principles of QCD.
The hard probes, including jets and heavy flavors, play an important role in investigating the properties of quark–gluon plasma (QGP) formed in heavy-ion collisions. The positive elliptic flow of hard probes observed in semi-central Pb--Pb collisions indicates that the hard partons suffered strong interactions in the deconfined QCD medium and then obtain the collectivity. However, recent measurements show also a non-zero $v_{2}$ for high-$p_{\mathrm{T}}$ charged particles and heavy flavor hadrons in high-multiplicity p--Pb collisions for both mid and forward rapidities, whose origin is still debated.
In this contribution, we employ a multi-phase transport model (AMPT) to calculate the $v_{2}$ of jet particles and open heavy-flavour hadron decay muons in p--Pb collisions at mid and forward rapidity, respectively. The results are obtained using the two-particle correlation method and the advanced nonflow subtraction strategy. We will systematically introduce how the collectivity of hard partons are generated from parton scatterings, and then propagated to the final state in small collision systems. Comparisons with experimental results will be presented as well. This work will provide further insights into understanding the origin of elliptic anisotropy of hard probes in small collision systems, and has referential value for the future measurements.
We present the first analytic results of N3LO QCD corrections to the top-quark decay width. We focus on the dominant leading color contribution, which includes light-quark loops. At NNLO, this dominant contribution accounts for 95% of the total correction. The most precise prediction for the top-quark width is now 1.321 GeV for mt = 172.69 GeV.
To probe new physics without prior assumptions on UV models, the correlation of operators could be crucial in exposing the structure of UV completion.
When operators arise from the same heavy resonance, they are likely to correlate and their Wilson coefficients exhibit non-trivial relation, since both of them depend on the same UV parameters.
The aim of EFT analysis is to discover the correlation among operators, which might shed lights on UV completion.
For specific, if a precise measurement is consistent with the SM theory prediction, it might originate from a coherent cancellation among higher dimensional operators.
In this work, we investigate a strongly correlated cancellation of operators in electroweak scattering and attempt to expose the corresponding UV structure.
We also examine the operators correlation through a coupled channel analysis method and demonstrate that this correlation persists even when considering the uncertainties at HL-LHC.
On the other hand, since the operators connect different scattering channels through the reduction of $H$ into $v$ or $h$, the operators correlation in single top production will predict the total cross section of $thq$ production, and the correlation in $pp\to h\gamma$ can precisely examine the new physics effects of the indirect search on the weak magnetic moment $a_W$.
By tagging one or two intact protons in the forward direction, it is possible to select and measure exclusive photon-fusion processes at the LHC. The same processes can also be measured in heavy ion collisions, and are often denoted as ultraperipheral collisions (UPC) processes. Such measurements opens up the possibility to probe certain dimension-8 operators and their positivity bounds at the LHC. As an demonstration, we perform a phenomenological study on the $\gamma\gamma\to \ell^+\ell^-$ processes, and find out that the measurements of this process at the HL-LHC provides reaches on certain dimension-8 operator coefficients that are comparable to the ones at future lepton colliders. We also point out that the $\gamma q\to \gamma q$ process could potentially have better reaches on similar types of operators due to its larger cross section, but a more detailed experimental study is need to estimate the background of this process. The validity of effective field theory (EFT) and the robustness of the positivity interpretation are also discussed.
In the past few years, several indirect hints for New Physics beyond the SM arose in precision measurements, e.g., $(g-2)_\mu$ and the W-boson mass. In this work, we consider a model containing new vector-like Fermion partner gauged under a new $U(1)^\prime$ symmetry. It is found that the latest CDF $m_W$ measurement and $(g-2)_\mu$ can be simultaneously accommodated. We have also considered several other experimental constraints, including the neutrino trident production, $Z \to \mu \mu$ decay, dimuon resonance searches at the LHC, etc. Implications for the $b \to s \ell^+ \ell^-$ process will be discussed. (This work is based on 2205.02205 and 2307.05290.)
Recently, the $W$ boson mass measured by the CDF-II collaboration shows large tension with the standard model prediction and other measurements. In this work, we look into the double parton scattering (DPS) contribution in CDF-II W mass measurement. We show that the DPS process can increase the measured mass as $\Delta M_W=20-200~\mbox{MeV}$ for the missing transverse momentum fit and $\Delta M_W=0-50~\mbox{MeV}$ for the transverse mass fit. It is comparable to the W-mass tension and should be take into consideration. The DPS effect can also appears in other inclusive measurements, since it contributes $\sim10^{-2}$ events in total and cause a $\mathcal{O}(10^{-2})-\mathcal{O}(10^{-1})~\mbox{GeV}$ shift of the missing transverse momentum.
We organize massive tree-level amplitudes in Standard Model by power counting and helicity category, and match them with their high energy origins. The construction of massive amplitudes is based on the massive bootstrap method, decomposing internal and external structures, and the existing leading orders of massless-massive correspondence. For the matching of higher order components, we introduce the on-shell Higgsing mechanism first proposed by (R. Balkin et al., 2022) and further the discussion to propagators.
We present MatchingEFT.jl, an automated tool to extract hard region contribution of the tree-level and one-loop 1PI amplitude, which can be matched to the standard model effective theory (SMEFT) operator basis in ABC4EFT.
FeAnGen4EFT performs the feynman diagram generation for the specific scattering process using the designed universal feynrules output file (UFO) and Qgraf. It offers the designated Feynman diagrams' amplitudes explicitly to provide non-trivial check for the gauge invariance. It will use FORM script to process extracting hard region expansion for the output from the previous step. These results will be given in a physical basis such as P-basis and Y-basis in ABC4EFT by using the on-shell amplitude basis method for a further crosscheck. FeAmGen4SMEFT has been built with lightweight, generality, flexibility, specialization, and efficiency in mind.
These ingredients allow FeAmGen4SMEFT to have more applications beyond the matching based on the complete operator basis with the specific mass dimension offered by ABC4EFT. One of these applications includes the one-loop renormalization of arbitrary theories.
We have performed one-loop matching for some processes under the specified UV model and obtained consistent results with other papers.
In this work, we try to improve the classic asymptotic formulae to describe the probability distribution of likelihood-ratio statistical tests. The idea is to split the probability distribution function into two parts. One part is universal and described by the asymptotic formulae. The other part is case-dependent and estimated explicitly using a 6-bin model proposed in this work. The latter is similar to doing toy simulations and hence is able to predict the discrete structures in the probability distributions. The new asymptotic formulae provide a much better differential description of the test statistics. The better performance is confirmed in two toy examples.
It was found that, using nonrelativistic QCD factorization, the predicted $\chi_{cJ}$ hadroproduction cross section at large $p_T$ can be negative. The negative cross sections originate from terms proportional to plus function in ${^{3}\hspace{-0.6mm}P_{J}^{[1]}}$ channels, which are remnants of the infrared subtraction in matching the ${^{3}\hspace{-0.6mm}P_{J}^{[1]}}$ short-distance coefficients. In this article, we find that the above terms can be factorized into the nonperturbative ${^{3}\hspace{-0.6mm}S_{1}^{[8]}}$ soft gluon distribution function in the soft gluon factorization (SGF) framework. Therefore, the problem can be naturally resolved in SGF. With an appropriate choice of nonperturbative parameters, the SGF can indeed give positive predictions for $\chi_{cJ}$ production rates within the whole $p_T$ region. The production of $\psi(2S)$ is also discussed, and there is no negative cross section problem.
We investigate cosmological phase transitions in various composite Higgs models consisting of four-dimensional asymptotically-free gauge field theories. Each model may lead to a confinementdeconfinement transition and a phase transition associated with the spontaneous breaking of a global symmetry that realizes the Standard Model Higgs field as a pseudo-Nambu-Goldstone boson. Based on the argument of universality, we discuss the order of the phase transition associated with the global symmetry breaking by studying the renormalization group flow of the corresponding linear sigma model at finite temperature, which is calculated by utilizing the ε-expansion technique at the one-loop order. Our analysis indicates that some composite Higgs models accommodate phenomenologically interesting first-order phase transitions.
In this study, we use lattice to reveal nonperturbative information of the electroweak phase transition in the real-singlet extension of the Standard Model, based on the 2-loop 3D EFT framework.
Importantly, the new information is that the lattice determines the true nature of the electroweak phase transition, capable to identify it as the first order type or not, an important qualitative behavior to which perturbation theory is blind. In scenarios where perturbation theory implies a weakly first order phase transition, lattice is always more reliable than the perturbation theory. In this regime, the symmetry-breaking transition may be crossover rather than a true phase transition. On the other hand, for strong transitions, both methods yield quantitatively close results, particularly when 2-loop perturbation theory is used.
This nonperturbative framework holds potential for other Higgs-sector extensions of the SM. Besides, by holding two powerful tools, 2-loop perturbation scanning and lattice, we will explore associated phenomenology in the future.
In this study, we present a comprehensive analysis of the electroweak sphaleron formalism and its application to electroweak phase transition (EWPT) patterns in extensions of the Standard Model scalar sector with electroweak multiplets. We offer an equivalence proof for different choices for the form of sphaleron configurations; construct the previously unestablished high-dimensional $\text{SU}(2)$ sphaleron transformation matrix; investigate the scalar multiplet topology map and baryon number charge relation; and revisit the required boundary conditions needed for solving the sphaleron field equations. We then scrutinize the leading order sphaleron dynamics in the context of a multi-step EWPT. We showcase two distinct analytical approaches for extending the $\text{SU}(2)$ scalar multiplet to the standard model (SM) under differing EWPT scenarios, and perform an explicit calculation of the sphaleron energy using a septuplet example. In the context of a single-step EWPT leading to a mixed phase, we find that the additional multiplet's contribution to the sphaleron energy is negligible, primarily due to the prevailing constraint imposed by the $\rho$ parameter. Conversely, in a two-step EWPT scenario, the sphaleron energy can achieve significantly high values during the initial phase, thereby markedly preserving baryon asymmetry if the universe undergoes a first-order EWPT. In both cases, we delineate the relationship between the sphaleron energy and the parameters relevant to dark matter phenomenology.
The form factors of $B_{(s)}$ decays into P-wave excited charmed mesons (including $D^*_0(2300)$, $D_1(2430)$, $D_1(2420)$, $D^*_2(2460)$ and their strange counterparts, denoted generically as $D^{**}_{(s)}$) are systematically calculated via QCD sum rules in the framework of heavy quark effective field theory (HQEFT). We consider contributions up to the next leading order of heavy quark expansion and give all the relevant form factors, including the scalar and tensor ones only relevant for possible new physics effects. The expressions for the form factors in terms of several universal wave functions are derived via heavy quark expansion. These universal functions can be evaluated through QCD sum rules. Then, the numerical results of the form factors are presented. With the form factors given here, a model independent analysis of relevant semileptonic decays $B_{(s)} \rightarrow D^{**}_{(s)} l \bar{\nu}_l$ is performed, including the contributions from possible new physics effects. Our predictions for the differential decay widths, branching fractions and ratios of branching fractions $R(D^{**}_{(s)})$ may be tested in more precise experiments in the future.
We propose that the cascade decay $\Lambda_b \to D(\to K^+\pi^-) N(\to p\pi^-)$ may serve as the discovery channel for baryonic CP violation. This decay chain is contributed by dominantly the amplitudes with the intermediate $D$ state as $D^0$ or $\bar{D}^0$. The large weak phase between the two kinds of amplitudes suggests the possibility of significant CP violation. While the presence of undetermined strong phases may complicate the dependence of CP asymmetry, our phenomenological analysis demonstrates that CP violation remains prominent across a broad range of strong phases. The mechanism also applies to similar decay modes such as $\Lambda_b \rightarrow D(\rightarrow K^+ K^-) \Lambda$. Considering the anticipated luminosity of LHCb, we conclude that these decay channels offer a promising opportunity to uncover CP violation in the baryon sector.
CP4 3HDM is a three-Higgs-doublet model based on the CP symmetry of order 4 (CP4). Imposing CP4 leads to remarkable connections between the scalar and Yukawa sectors and unavoidably generates tree-level flavor-changing neutral couplings (FCNC). It remains unclear whether FCNC can be sufficiently suppressed in the CP4 3HDM. In this paper, we systematically explore this issue. We first develop an efficient scanning procedure which takes the quark masses and mixing as input and expresses the FCNC matrices in terms of physical quark observables and quark rotation parameters. This procedure allows us to explore the FCNC effects for all the Yukawa sectors possible within the CP4 3HDM. We find that, out of the eight possible CP4 Yukawa sectors, only two scenarios are compatible with the K, B, Bs and, in particular, D-meson oscillation constraints. The results of this work serve as clear guidelines for future phenomenological scans of the model.
We propose a new kind of CP violation effect — the double-mixing CP asymmetry — in a type of cascade decays that involves at least two mixing neutral mesons in the decay chain. It is induced by the interference between different oscillation paths of the neutral mesons in the decay process. The double-mixing CP asymmetry is of critical importance for phenomenology, providing opportunities for clean determination of CKM phase angles free of uncertainties induced by the strong dynamics. To illustrate this point, we perform a phenomenological analysis on two examples: $B^0_s \to \rho^0 K \to \rho^0 (\pi^- \ell^+ \nu_\ell)$ and $B^0 \to D^0 K \to D^0(\pi^+ \ell^- \bar{\nu}_\ell)$. Our results demonstrate that the double-mixing CP asymmetry can be numerically significant in the absence of strong phases, as shown by the former example. Additionally, the latter example showcases the direct extraction of weak and strong phases from data, without the need for theoretical inputs.