This study explores the diphoton and $b\bar{b}$ excesses at 95.4 GeV, as well as nano-Hertz gravitational waves originating from domain walls, within the framework of the next-to-two-Higgs-doublet model (N2HDM), which extends the two-Higgs-doublet model by introducing a real singlet scalar subject to a discrete $Z_2$ symmetry. The $Z_2$ symmetry is spontaneously broken by the non-zero vacuum expectation value of the singlet scalar, $v_s$ , which leads to the formation of domain walls. Two different scenarios are discussed: in scenario A, the 95.4 GeV Higgs boson predominantly originates from the singlet field, while in scenario B, it arises mainly from the CP-even components of the Higgs doublets. Accounting for relevant theoretical and experimental constraints, scenario A can fully account for both the diphoton and $b\bar{b}$ excesses at 95.4 GeV within the $1\sigma$ range. In the parameter space accommodating both excesses, scenario A fails to provide a valid explanation for the NANOGrav data up to $v_s=$ 1000 TeV, and the predicted gravitational wave spectrum can exceed the SKA sensitivity curve in the low frequency region. Scenario B only marginally accounts for the diphoton and $b\bar{b}$ excesses at the $1\sigma$ level, but can simultaneously explain the NANOGrav data well.

China

Haotian Xu

Yufei Wang

Xiao-Fang Han

Lei Wang

95 GeV Higgs boson and nano-Hertz gravitational waves from domain walls in the next-to-two-Higgs-doublet model * Supported by the Shandong Provincial Natural Science Foundation Projects ( ZR2024MA001, ZR2023MA038) and the National Natural Science Foundation of China (11975013)

We introduce FANG (Focused Angular $\textit{N}$ -body event Generator), a new Monte Carlo tool for efficient event generation in restricted Lorentz-Invariant Phase Space (LIPS). Unlike conventional approaches that sample the full 4$\textit{π}$ solid angle, FANG directly generates events in which selected final-state particles are constrained to fixed directions or finite angular regions in the laboratory frame. Because of the way the generator is constructed, angular constraints can be imposed directly in the laboratory frame while maintaining the correct LIPS structure, enabling differential and total cross sections or decay rates to be computed with high efficiency. The method is validated against analytic results and existing event generators, showing excellent agreement. By reducing the computational cost of full phase-space event generation by several orders of magnitude, FANG provides a robust and versatile framework applicable to particle, nuclear, and detector physics.

Israel

Itay Horin

Arik Kreisel

Or Alon

Focused angular $\textit{N}$ -body event generator (FANG)

A future $ e^+e^- $ collider could run at the $\textit{Z}$-pole to perform important electroweak (EW) precision measurements, but such a run may not be viable for a future muon collider. However, this can be compensated for by measuring other EW processes utilizing the high energy and large luminosity of the muon collider. In this paper, we consider the measurements of the vector boson fusion processes of $ WW/WZ/W\gamma $ to a pair of fermions (along with a $ \nu_{\mu}\bar{\nu}_{\mu} $ or $ \nu_{\mu}\mu^+/\bar{\nu}_{\mu}\mu^- $ pair) at a high-energy muon collider and study their potential for probing EW observables. We consider two run scenarios for the muon collider with center-of-mass energies of 10 and 30 TeV, respectively, and focus on the processes involving $ f=b,c,\tau $ and the dimension-6 operators that directly modify the corresponding fermions coupling to the $ Z/W $ bosons. The invariant mass distribution of the $ f\bar{f} $ pair helps to separate the events from the $ Z/W $ and high-energy resonances, whereas the polar angle of the outing fermion provides additional information. Through a chi-squared analysis on the binned distributions and combining the information from the $\textit{WW}$ and $ WZ/W\gamma $ fusion processes, all relevant Wilson coefficients can be constrained simultaneously. The precision surpasses the current EW measurement constraints and is even competitive with future $ e^+e^- $ colliders. Our analysis can be included in a more complete framework that is required to fully determine the potential of muon colliders in EW precision measurements.

Hao-Qiao Li

Hai-Ning Yan

Jiayin Gu

Germany

Xiao-Ze Tan

Probing $\textit{Z}$/$\textit{W}$ pole physics at high-energy muon colliders via vector-boson-fusion processes * Supported by the National Natural Science Foundation of China (NSFC) (12035008, 12375091, 12347171), and the Innovation Program for Quantum Science and Technology (2024ZD0300101). Xiao-Ze Tan also acknowledges the support from Helmholtz – OCPC (Office of China Postdoctoral Council) Postdoctoral Fellowship Program

Lepton flavor violation (LFV) offers a powerful probe of physics beyond the Standard Model, particularly in models addressing neutrino masses and the baryon asymmetry of the universe. In this study, we investigate LFV processes within the framework of type II seesaw leptogenesis, where the Standard Model is extended by an $S U(2)_L$ triplet Higgs field. We focus on key LFV processes, including $\mu^+\to e^+\gamma$ , $\mu^+ \to e^+e^-e^+$ , and $\mu \rightarrow e$ conversion in nuclei, deriving stringent constraints on the parameter space from current experimental data. We scan the 3$\textit{σ}$ range of neutrino oscillation parameters and identify the most conservative bounds consistent with existing measurements. Our results reveal that the MEG experiment currently provides the most stringent constraints in the normal ordering (NO) scenario, while the SINDRUM experiment offers comparable sensitivity in the inverted ordering (IO) case. Future experiments, such as MEG II, Mu3e, Mu2e, and COMET, are predicted to significantly improve the sensitivity, testing larger regions of the parameter space.

Chengcheng Han

Yijun Han

Sihui Huang

Zhanhong Lei

Probing type II seesaw leptogenesis through lepton flavor violation * Chengcheng Han acknowledges supports from the National Key R&D Program of China (2023YFA1606100), the Sun Yat-Sen University Science Foundation, the Fundamental Research Funds for the Central Universities at Sun Yat-sen University (24qnpy117) and the Key Laboratory of Particle Astrophysics and Cosmology (MOE) of Shanghai Jiao Tong University

We study $ \cos2\phi $ azimuthal asymmetry in doubly longitudinally polarized proton-proton Drell-Yan collisions within the transverse momentum dependent factorization framework. The asymmetry arises from the convolution of the longitudinal transversity distribution $ h_{1L}^{\perp} $ for both protons. Using the Bacchetta-Delcarro-Pisano-Radici-Signori parameterization for the nonperturbative Sudakov form factor and the Wandzura-Wilczek approximation for collinear $ h_{1L}^{\perp} $ , we predict the double spin asymmetry $ A_{LL}^{\cos2\phi} $ at RHIC and NICA kinematics. Our results demonstrate sensitivity to sea quark distributions, with the asymmetry reaching up to 25% for maximal sea quark contributions. These predictions highlight the potential of polarized Drell-Yan measurements to probe sea quark dynamics and advance our understanding of nucleon structures.

Hui Li

Ting Hu

Liang-Liang Liu

Xiao-Yu Wang

Zhun Lu

Asymmetry ${{\boldsymbol A}_{\boldsymbol{LL}}^{\bf\cos2\boldsymbol\phi}} $ in the polarized proton-proton Drell-Yan process within TMD factorization * Hui Li is supported by Fundamental Research Program of Shanxi Province (202203021222224) and Natural Science Foundation of Shanxi Normal University (JCYJ2023021). Xiao-Yu Wang is supported by the Natural Science Foundation of Henan Province (242300421377, 232300421140)

The ATLAS and CMS collaborations reported a diphoton excess in the invariant mass distribution around the 95.4 GeV with a local significance of <math><mn>3.1</mn><mi>σ</mi></math>. Moreover, there is another <math><mn>2.3</mn><mi>σ</mi></math> local excess in the <math><mi>b</mi><mover><mi>b</mi><mo>¯</mo></mover></math> final state at large electron-positron collider in the same mass region. A plausible solution is that the Higgs sector is extended to include an additional Higgs boson with a mass of 95.4 GeV. We study a complex singlet scalar extension of the two-Higgs-doublet model in which the 95.4 GeV Higgs is from the mixing of three <math><mi>C</mi><mi>P</mi></math>-even Higgs fields. In addition, the extended Higgs potential can achieve spontaneous <math><mi>C</mi><mi>P</mi></math>-violation at the finite temperature and restore <math><mi>C</mi><mi>P</mi></math> symmetry at the present temperature of the Universe. We find that the model can simultaneously explain the baryon asymmetry of the Universe, the diphoton and <math><mi>b</mi><mover><mi>b</mi><mo>¯</mo></mover></math> excesses around the 95.4 GeV while satisfying various relevant constraints including the experiments of collider and electric dipole moment.

Jing Gao

Jinghong Ma

95 GeV Higgs boson and spontaneous <math><mrow><mi>C</mi><mi>P</mi></mrow></math>-violation at the finite temperature

Combining the dark matter and muon   $ g-2 $   anomaly, we study the   $ g-2 $   breaking phase transition, gravitational wave spectra, and direct detection at the LHC in an extra   $ g-2 $   gauge symmetry extension of the standard model. The new fields include vector-like leptons (  $ g-2 $  ), the   $ g-2 $  breaking scalar S, and the gauge boson   $ g-2 $  , as well as the dark matter candidate   $ g-2 $   and its heavy partner   $ g-2 $  . A joint explanation of the dark matter relic density and muon   $ g-2 $   anomaly excludes the region where both   $ g-2 $   and   $ g-2 $   are much larger than   $ g-2 $  . In the parameter space accommodating the DM relic density and muon   $ g-2 $   anomaly, the model can achieve a first-order   $ g-2 $   breaking phase transition, whose strength is sensitive to the parameters of the Higgs potential. The corresponding gravitational wave spectra can reach the sensitivity of U-DECIGO. In addition, the direct searches at the LHC impose stringent bounds on the mass spectra of the vector-like leptons and dark matter.

Jie Wang

 (1) Breaking Phase Transition, Muon 2, Dark Matter, Collider, and Gravitational Wave  

We use the spectral lag catalog of 46 short GRBs aggregated by Xiao et al. (Astrophys J Lett 924:L29, 2022), to carry out an independent search for Lorentz invariance violation (LIV). For this purpose, we use a power-law model as a function of energy for the intrinsic astrophysical induced spectral lags. The expansion history of the universe needed for constraining LIV was obtained in a non-parametric method using cosmic chronometers. We use Bayesian model comparison to determine if the aforementioned spectral lags show evidence for LIV as compared to only astrophysically induced lags. We do not find any evidence for LIV, and obtain 95% CL lower limits on the corresponding energy scale to be  $$4 \times 10^{15}$$  <math> <mrow> <mn>4</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>15</mn> </msup> </mrow> </math>   GeV and  $$6.8 \times 10^{9}$$  <math> <mrow> <mn>6.8</mn> <mo>×</mo> <msup> <mn>10</mn> <mn>9</mn> </msup> </mrow> </math>   GeV for the linear and quadratic LIV models respectively. Our results obtained by using the flat  $$\Lambda $$  <math> <mi>Λ</mi> </math>  CDM model for characterizing the cosmic expansion history are consistent with those obtained using chronometers.

India

Shantanu Desai

Rajdeep Agrawal

Haveesh Singirikonda

Search for Lorentz invariance violation using Bayesian model comparison applied to Xiao et al. GRB spectral lag catalog

We study the CDF W-mass, muon  $$g-2$$  <math> <mrow> <mi>g</mi> <mo>-</mo> <mn>2</mn> </mrow> </math>  , and dark matter observables in a local  $$U(1)_{L_\mu -L_\tau }$$  <math> <mrow> <mi>U</mi> <msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>-</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </mrow> </math>   model in which the new particles include three vector-like leptons ( $$E_1,~ E_2,~ N$$  <math> <mrow> <msub> <mi>E</mi> <mn>1</mn> </msub> <mo>,</mo> <mspace width="3.33333pt"></mspace> <msub> <mi>E</mi> <mn>2</mn> </msub> <mo>,</mo> <mspace width="3.33333pt"></mspace> <mi>N</mi> </mrow> </math>  ), a new gauge boson  $$Z'$$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>  , a scalar S (breaking  $$U(1)_{L_\mu -L_\tau }$$  <math> <mrow> <mi>U</mi> <msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>-</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </mrow> </math>  ), a scalar dark matter  $$X_I$$  <math> <msub> <mi>X</mi> <mi>I</mi> </msub> </math>   and its partner  $$X_R$$  <math> <msub> <mi>X</mi> <mi>R</mi> </msub> </math>  . We find that the CDF W-mass disfavors  $$m_{E_1}= m_{E_2}={m_N}$$  <math> <mrow> <msub> <mi>m</mi> <msub> <mi>E</mi> <mn>1</mn> </msub> </msub> <mo>=</mo> <msub> <mi>m</mi> <msub> <mi>E</mi> <mn>2</mn> </msub> </msub> <mo>=</mo> <msub> <mi>m</mi> <mi>N</mi> </msub> </mrow> </math>   or  $$s_L=s_R=0$$  <math> <mrow> <msub> <mi>s</mi> <mi>L</mi> </msub> <mo>=</mo> <msub> <mi>s</mi> <mi>R</mi> </msub> <mo>=</mo> <mn>0</mn> </mrow> </math>   where  $$s_{L(R)}$$  <math> <msub> <mi>s</mi> <mrow> <mi>L</mi> <mo>(</mo> <mi>R</mi> <mo>)</mo> </mrow> </msub> </math>   is mixing parameter of left (right)-handed fields of vector-like leptons. A large mass splitting between  $$E_1$$  <math> <msub> <mi>E</mi> <mn>1</mn> </msub> </math>   and  $$E_2$$  <math> <msub> <mi>E</mi> <mn>2</mn> </msub> </math>   is favored when the differences between  $$s_L$$  <math> <msub> <mi>s</mi> <mi>L</mi> </msub> </math>   and  $$s_R$$  <math> <msub> <mi>s</mi> <mi>R</mi> </msub> </math>   becomes small. The muon  $$g-2$$  <math> <mrow> <mi>g</mi> <mo>-</mo> <mn>2</mn> </mrow> </math>   anomaly can be simultaneously explained for appropriate difference between  $$m_{E_1}$$  <math> <msub> <mi>m</mi> <msub> <mi>E</mi> <mn>1</mn> </msub> </msub> </math>    $$(s_L)$$  <math> <mrow> <mo>(</mo> <msub> <mi>s</mi> <mi>L</mi> </msub> <mo>)</mo> </mrow> </math>   and  $$m_{E_2}$$  <math> <msub> <mi>m</mi> <msub> <mi>E</mi> <mn>2</mn> </msub> </msub> </math>    $$(s_R)$$  <math> <mrow> <mo>(</mo> <msub> <mi>s</mi> <mi>R</mi> </msub> <mo>)</mo> </mrow> </math>  , and some regions are excluded by the diphoton signal data of the 125 GeV Higgs. Combined with the CDF W-mass, muon  $$g-2$$  <math> <mrow> <mi>g</mi> <mo>-</mo> <mn>2</mn> </mrow> </math>   anomaly and other relevant constraints, the correct dark matter relic density is mainly obtained in two different scenarios: (i)  $$X_IX_I\rightarrow Z'Z',~ SS$$  <math> <mrow> <msub> <mi>X</mi> <mi>I</mi> </msub> <msub> <mi>X</mi> <mi>I</mi> </msub> <mo>→</mo> <msup> <mi>Z</mi> <mo>′</mo> </msup> <msup> <mi>Z</mi> <mo>′</mo> </msup> <mo>,</mo> <mspace width="3.33333pt"></mspace> <mi>S</mi> <mi>S</mi> </mrow> </math>   for  $$m_{Z'}(m_S)&lt;m_{X_I}$$  <math> <mrow> <msub> <mi>m</mi> <msup> <mi>Z</mi> <mo>′</mo> </msup> </msub> <mrow> <mo>(</mo> <msub> <mi>m</mi> <mi>S</mi> </msub> <mo>)</mo> </mrow> <mo>&lt;</mo> <msub> <mi>m</mi> <msub> <mi>X</mi> <mi>I</mi> </msub> </msub> </mrow> </math>   and (ii) the co-annihilation processes for  $$min(m_{E_1},m_{E_2},m_N,m_{X_R})$$  <math> <mrow> <mi>m</mi> <mi>i</mi> <mi>n</mi> <mo>(</mo> <msub> <mi>m</mi> <msub> <mi>E</mi> <mn>1</mn> </msub> </msub> <mo>,</mo> <msub> <mi>m</mi> <msub> <mi>E</mi> <mn>2</mn> </msub> </msub> <mo>,</mo> <msub> <mi>m</mi> <mi>N</mi> </msub> <mo>,</mo> <msub> <mi>m</mi> <msub> <mi>X</mi> <mi>R</mi> </msub> </msub> <mo>)</mo> </mrow> </math>   close to  $$m_{X_I}$$  <math> <msub> <mi>m</mi> <msub> <mi>X</mi> <mi>I</mi> </msub> </msub> </math>  . Finally, we use the direct searches for  $$2\ell +E_T^{miss}$$  <math> <mrow> <mn>2</mn> <mi>ℓ</mi> <mo>+</mo> <msubsup> <mi>E</mi> <mi>T</mi> <mrow> <mi>miss</mi> </mrow> </msubsup> </mrow> </math>   event at the LHC to constrain the model, and show the allowed mass ranges of the vector-like leptons and dark matter.

Quan Zhou

The CDF W-mass, muon  $$g-2$$  <math> <mrow> <mi>g</mi> <mo>-</mo> <mn>2</mn> </mrow> </math>  , and dark matter in a  $$U(1)_{L_\mu -L_\tau }$$  <math> <mrow> <mi>U</mi> <msub> <mrow> <mo>(</mo> <mn>1</mn> <mo>)</mo> </mrow> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>-</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </mrow> </math>   model with vector-like leptons

Because both W-mass and muon   $ g-2 $   can be affected by mass splittings among extra Higgs bosons   $ g-2 $   in a two-Higgs-doublet model, we take a model with μ-τ lepton flavor violation interactions to examine the two anomalies reported by CDF II and FNAL. We obtain the following observations: (i) Combined with theoretical constraints, the CDF W-mass measurement disfavors H or A degenerating in mass with   $ g-2 $   but allows H and A to degenerate. The mass splitting between   $ g-2 $   and   $ g-2 $   must be larger than 10 GeV.   $ g-2 $   and   $ g-2 $   are favored to be smaller than 650 GeV for   $ g-2 $   GeV and allowed to have larger values with increasing   $ g-2 $   . (ii) After imposing other relevant experimental constraints, there are parameter spaces that simultaneously satisfy (at the   $ g-2 $   level) the CDF W-mass, FNAL muon   $ g-2 $  , and data on lepton universality in τ decays; however, the mass splittings among extra Higgs bosons are strictly constrained.

Fei Wang

Jin-Min Yang

Yang Zhang

Joint explanation of -mass and Muon 2 in the 2HDM  