arXiv subjects

Chang-Xin Liu

Publications and source records attributed to Chang-Xin Liu.

8 recordsLinked to original sources

arXiv2026

CP-violating multi-field phase transitions and gravitational waves in a hidden NJL sector

We investigate the dynamics of a cosmological first-order phase transition (FOPT) and the associated stochastic gravitational wave background (SGWB) in a hidden strongly coupled sector described by an extended Nambu--Jona-Lasinio (NJL) model with $N_f = 3$ fermion flavors. The model incorporates a CP-violating six-fermion 't Hooft interaction, an explicit chiral symmetry breaking mass term, and chirally symmetric eight-fermion operators that stabilize the vacuum. We perform a multi-field analysis of the tunneling dynamics, going beyond conventional single-field approximations. The interplay between explicit symmetry breaking and CP violation induces a vacuum misalignment, resulting in a curved tunneling path and a spatially varying CP-violating background across the bubble wall. Through a comprehensive scan of the multi-dimensional parameter space, we find a parameter regime where the conventionally rapid transition rate of the NJL framework is drastically reduced to $β/H \sim \mathcal{O}(10^2)$. Consequently, the gravitational wave (GW) production is significantly enhanced, with the predicted SGWB peak amplitudes successfully reaching the detection sensitivity of the proposed $μ$Ares observatory. Furthermore, our analysis reveals that the macroscopic thermodynamic properties governing the SGWB are predominantly determined by the radial profile of the effective potential, rendering the resulting GW signatures remarkably insensitive to the CP-violating topological vacuum angle. Finally, the explicit symmetry breaking mass introduces a crucial energy bias between competing vacua, triggering the prompt collapse of transient domain wall configurations and thereby ensuring the cosmological viability of the model.

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arXiv2026

Renormalization and Factorization Scale-Invariant Predictions for the Higgs Rare Decay $H\to J/ψ+γ$ via the Principle of Maximum Conformality

We investigate the $J/ψ$ direct production mechanism in the rare exclusive Higgs decay $H\to J/ψ+γ$ within nonrelativistic QCD (NRQCD), which provides a clean probe for extracting the charm-quark Yukawa coupling to the Higgs boson. The Principle of Maximum Conformality (PMC) is used to remove conventional renormalization-scheme and scale ambiguities in the next-to-next-to-leading-order (N$^2$LO) perturbative QCD series. Large logarithmic contributions arising from Yukawa coupling renormalization are resummed, providing a reliable foundation for subsequent analyses. Using the experimentally measured leptonic decay width of $J/ψ$ and the N$^2$LO perturbative result, we extract the factorization-scale-dependent long-distance matrix element $\langle J/ψ({\bm ε})|ψ^{\dagger}{\bm σ}\cdot{\bm ε}χ(μ_Λ) |0\rangle$. Combining this with the factorization-scale-dependent short-distance coefficient, we obtain a factorization-scale-invariant decay width for the channel. Compared with earlier predictions in the literature, our fixed-order result for $Γ(H\to J/ψ+γ)$ is more robust and precise, with good convergence and no renormalization- or factorization-scale dependence. We find $Γ(H\to J/ψ+γ) = (6.4574^{+0.3995}_{-0.3995}) \times 10^{-11}$ GeV, where the uncertainty is the quadratic sum of contributions from $Δα_s(m_Z) = \pm 0.0009$, $ΔΓ_{J/ψ\to e^+e^-} = \pm 0.10\ \text{GeV}$, $Δ\overline{m}_c(\overline{m}_c) = \pm 0.0046\ \text{GeV}$, and the estimated magnitude of N$^3$LO contributions from Bayesian analysis. This work demonstrates for the first time how the PMC can be applied to obtain fixed-order perturbative predictions that are invariant under both renormalization and factorization scale variations.

hep-ph↗

arXiv2024

95 GeV excess in a $CP$-violating $μ$-from-$ν$ SSM

The CMS and ATLAS have recently reported their results searching for light Higgs boson with mass around 95 GeV, based on the full Run 2 data set. In the framework of the CP-violating (CPV) $μν$SSM, we discuss a $\sim$ 2.9$σ$ (local) excess at 95 GeV in the light Higgs boson search in the diphoton decay mode as reported by ATLAS and CMS, together with a $\sim$ 2$σ$ excess (local) in the $b\bar{b}$ final state at LEP in the same mass range. By introducing CPV phases as well as by mixing CP-even Higgs and CP-odd Higgs, a lighter Higgs boson in the $μν$SSM can be produced, which can account for the "di-photon excess".

hep-ph↗

arXiv2023

Lightest Higgs boson decays $h\rightarrow MZ$ in the $μ$ from $ν$ supersymmetric standard model

We study the lightest Higgs boson decays $h\rightarrow MZ$ in the $μ$ from $ν$ supersymmetric standard model ($μν$SSM), where $M$ is a vector meson $(ρ,ω,ϕ,J/Ψ,Υ)$. Compared to the minimal supersymmetric standard model (MSSM), the $μν$SSM introduces three right-handed neutrino superfields, which lead to the mixing of the Higgs doublets with the right-handed sneutrinos. The mixing affects the lightest Higgs boson mass and the Higgs couplings. In suitable parameter space, the $μν$SSM can give large new physics (NP) contributions to the signal strengths of $h\rightarrow MZ$ and $h\rightarrow γγ$, which may be detected by a 100 TeV collider or the other future high energy colliders.

hep-ph↗

arXiv2022

Muon anomalous magnetic dipole moment in the $μν$SSM

Recently, the Muon g-2 experiment at Fermilab has measured the muon anomalous magnetic dipole moment (MDM), $a_μ=(g_μ-2)/2$, which reported that the new experimental average increases the tension between experiment and the standard model (SM) prediction to 4.2$σ$. In this work, we reanalyse the muon anomalous MDM at two-loop level in the $μ$ from $ν$ Supersymmetric Standard Model ($μν$SSM) combined with the updated experimental average. The $μν$SSM can explain the current tension between the experimental measurement and the SM theoretical prediction for the muon anomalous MDM, constrained by the 125 GeV Higgs boson mass and decays, the rare decay $\bar{B}\rightarrow X_sγ$ and so on. We also investigate the anomalous MDM of the electron and tau lepton, $a_e=(g_e-2)/2$ and $a_τ=(g_τ-2)/2$, at two-loop level in the $μν$SSM. In addition, the 125 GeV Higgs boson decays to a pair of charged leptons in the $μν$SSM are also analysed.

hep-ph↗

arXiv2021

Muon $(g-2)$ in the B-LSSM

The difference between the updated experimental result on the muon anomalous magnetic dipole moment and the corresponding theoretical prediction of the standard model on that is about $4.2$ standard deviations. In this work, we calculate the muon anomalous MDM at the two-loop level in the supersymmetric $B-L$ extension of the standard model. Considering the experimental constraints on the lightest Higgs boson mass, Higgs boson decay modes $h\rightarrow γγ,\;WW,\;ZZ,\; b\bar b,\;τ\barτ$, B rare decay $\bar B\rightarrow X_sγ$, and the transition magnetic moments of Majorana neutrinos, we analyze the theoretical predictions of the muon anomalous magnetic dipole moment in the $B-L$ supersymmetric model. The numerical analyses indicate that the tension between the experimental measurement and the standard model prediction is remedied in the $B-L$ supersymmetric model.

hep-ph↗

arXiv2020

Higgs boson decay $h\rightarrow Zγ$ and muon magnetic dipole moment in the $μν$SSM

To solve the $μ$ problem and generate three tiny neutrino masses in the MSSM, the $μ$ from $ν$ Supersymmetric Standard Model ($μν$SSM) introduces three singlet right-handed neutrino superfields, which lead to the mixing of the Higgs doublets with the sneutrinos. The mixing affects the lightest Higgs boson mass and the Higgs couplings. The present observed 95\% CL upper limit on signal strength of the 125 GeV Higgs boson decay $h\rightarrow Zγ$ is 6.6, which still is plenty of space to prove the existence of new physics. In this work, we investigate the signal strength of the 125 GeV Higgs boson decay channel $h\rightarrow Zγ$ in the $μν$SSM. Besides, we consider the two-loop electroweak corrections of muon anomalous magnetic dipole moment (MDM) in the model, which also make important contributions compared with one-loop electroweak corrections.

hep-ph↗

arXiv2020

Electric dipole moments of neutron and heavy quarks in the B-L symmetric MSSM

The searching for the electric dipole moments (EDMs) of neutron ($d_n$), $b$ quark ($d_b$) and $c$ quark ($d_c$) gives strict upper bounds on these quantities. And recently, new upper bounds on $d_b$, $d_c$ are obtained by the strict limit on $d_n$. The models of new physics (NP) with additional CP-violating (CPV) sources are constrained strictly by these EDMs. In this work, we focus on the CPV effects on these EDMs in the minimal supersymmetric extension (MSSM) of the SM with local $B-L$ gauge symmetry (B-LSSM). The contributions from one-loop and some two-loop diagrams to the quark EDM are given in general form, which can also be used in the calculation of quark EDM in other models of NP. Considering the constrains from updated experimental data, the numerical results show that the two-loop corrections can make important contributions to these EDMs. Compared with the MSSM, the effects of new CPV phases and new parameters in the B-LSSM on these EDMs are also explored.

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