Small neutrino masses can be generated through the well-known seesaw mechanisms, among which the type-II scenario predicts a triplet scalar with doubly charged components. Except for the Drell-Yan production at the Large Hadron Collider (LHC), the doubly charged scalars $\Delta^{\pm\pm}$ can also be produced through photon fusion along with the ultraperipheral collision of protons, from which the outgoing protons can be detected by forward detectors at the LHC, providing a promising means to explore related new physics. We study the pair production through such processes at the 14 TeV LHC, focusing on the final states of $\mu^{+}\mu^{+}\mu^{-}\mu^{-}$ and $e^{+}e^{+}e^{-}e^{-}$ under the normal hierarchy (NH) and inverted hierarchy (IH) of the neutrino mass spectra, respectively. Promising sensitivity can be reached via our proposed search strategy. At a luminosity of 36.1 fb$^{-1}$(100 fb $^{-1}$ ), $m_{\Delta}\sim430(520)$ GeV can be excluded at 95% C.L. under the NH via $\mu^{+}\mu^{+}\mu^{-}\mu^{-}$ state searching, while the mass bound can be extended to 730(880) GeV under the IH via $e^{+}e^{+}e^{-}e^{-}$ states. The exclusion limits on $m_{\Delta}$ can be improved up to 1 TeV and even higher with integrated luminosity accumulated to 3 ab $^{-1}$ .

China

Hang Zhou

Ning Liu

Search for doubly charged scalars in type-II seesaw mechanism through photon fusion at the LHC * Supported by the National Natural Science Foundation of China (12405118) and the Natural Science Foundation of Jiangsu Province (BK20230623)

We investigate the collider signatures of a maximally flavor-violating $ U(1)_{L_\mu-L_\tau} $ model, where a new gauge boson $ Z^\prime $ and scalar triplets induce lepton flavor-changing interactions in the $\textit{μ}$-$\textit{τ}$ sector. Focusing on four-lepton final states at multi-TeV lepton colliders, we conduct a detailed analysis of cross sections, asymmetries, and polarization effects. We show that the signal cross section is highly sensitive to $ m_{Z^\prime} $ and the effective parameters $ \tilde{g}/m_{Z^\prime} $ , whereas it remains largely insensitive to the triplet Yukawa couplings within the phenomenologically allowed region. The forward-backward asymmetry exhibits a characteristic monotonic dependence on $ m_{Z^\prime} $ , and beam polarization can significantly suppress the Standard Model backgrounds while enhancing new physics contributions. We find that, in the phenomenologically allowed parameter space, the predicted observables remain highly sensitive to the underlying model parameters. These results show that multi-lepton final states are powerful probes of the $ U(1)_{L\mu - L_\tau} $ framework and can offer valuable guidance for future searches at muon and electron-positron colliders.

Jianing Qin

Fei Huang

Honglei Li

Zhi-Long Han

Jin Sun

Collider probes of four-lepton final states in maximally flavor-violating ${U(1)_{L_\mu-L_\tau}} $ model * Supported by National Natural Science Foundation of China (12505112, 11805081), Shandong Province Natural Science Foundation (ZR2024QA138, ZR2022MA056) and State Key Laboratory of Dark Matter Physics, University of Jinan Disciplinary Cross-Convergence Construction Project 2024 (XKJC- 202404) and Jin Sun is supported by IBS under the project code, (IBS-R018-D1)

We investigate thermal photon production in the quark-gluon plasma (QGP) under strong magnetic fields using a magnetohydrodynamic (MHD) framework. We employ relativistic ideal fluid dynamics under the non-resistive approximation by adopting the Bjorken flow model with power-law decaying magnetic fields $ \mathbf{B}(\tau) = \mathbf{B}_0 (\tau_0/\tau)^a $ , span> $\textit{a}$ controls the decay rate, $ B_0 = \sqrt{\sigma} T_0^2 $ , and $\textit{σ}$ characterizes the initial field strength. The resulting QGP temperature evolution exhibits distinct $\textit{a}$- and $\textit{σ}$-dependent behaviors. Thermal photon production rates are calculated for three dominant processes: Compton scattering with $ q\bar{q} $ annihilation (C+A), bremsstrahlung (Brems), and $ q\bar{q} $ annihilation with additional scattering (A+S). These rates are integrated over the space-time volume to obtain the photon transverse momentum $ (p_T) $ spectrum. Our results demonstrate that increasing $\textit{a}$ enhances photon yields across all $ p_T $ , with $ a \to \infty $ (super-fast decay) providing an upper bound. For $ a = 2/3 $ , a larger $\textit{σ}$ suppresses yields through accelerated cooling, whereas for $ a \to \infty $ , a larger $\textit{σ}$ enhances yields via prolonged thermal emission. Low- $ p_T $ photons receive significant contributions from all QGP evolution stages, while high- $ p_T $ photons originate predominantly from early times. The central rapidity region $ (y=0) $ dominates the total yield. This work extends the photon yield studies to the MHD regime under strong magnetic fields, clarifying the magnetic field effects on QGP electromagnetic signatures and establishing foundations for future investigations of magnetization and dissipative phenomena.

Jie Xiong

Xiang Fan

Jing Jing

Weishan Yang

Duan She

Ze-Fang Jiang

Thermal photon emission from quark-gluon plasma: 1+1D magnetohydrodynamics results * Supported by the National Natural Science Foundation of China (NSFC) (12305138). Duan She's research is funded by the Startup Research Fund of Henan Academy of Sciences (231820058) and the 2024 Henan Province International Science and Technology Cooperation Projects (242102521068)

We investigated the effect of an isospin chemical potential ( $ \mu_{I} $ ) within the quark-meson model, which approximates quantum chromodynamics (QCD) by modeling low-energy phenomena such as chiral symmetry breaking and phase structure under varying conditions of temperature and chemical potential. Using the functional renormalization group (FRG) flow equations, we calculated the phase diagram in the chiral limit within the two-flavor quark-meson model in a finite $ \mu_{I} $ with $\textit{ρ}$ vector meson interactions. Fluctuation effects significantly decrease the critical chemical potential from the mean-field (MF) value $\mu_{I,{\rm MF}} \gt m_\rho$ to a lower value at which the $\textit{ρ}$ vector meson condensates alongside the chiral condensate once the isospin chemical potential exceeds the critical value $ \mu_{I}^{{\rm{crit}}} $ . This $\textit{ρ}$ condensation was investigated numerically for different meson coupling strengths. The $\textit{ρ}$ meson dominated region is delineated from other phases by a second-order phase transition at lower $ \mu_{I} $ and a first-order transition at slightly higher $ \mu_{I} $ .

Mohammed Osman

Defu Hou

Wentao Wang

United States

Hui Zhang

Functional renormalization group study of $\textit{ρ}$ meson condensate at a finite isospin chemical potential in the quark meson model * Supported in part by the National Key Research and Development Program of China (2022YFA1604900). This work is also partly supported by the National Natural Science Foundation of China (NSFC) (12435009, 12275104). Hui Zhang acknowledges the financial support from the Guangdong Major Project of Basic and Applied Basic Research (2020B0301030008) and the National Natural Science Foundation of China (12047523, 12105107)

In addition to the gravitational-wave (GW) tensor modes of general relativity, more general metric theories of gravity allow up to four additional polarization states. Sensitivity curves for these additional GW polarizations are key quantities for assessing how well a detector can constrain such theories. In this work, we derive analytical expressions and high-accuracy approximate formulas for the sensitivity curves for the vector-$\textit{x}$, vector-$\textit{y}$, breathing, and longitudinal modes of the second-generation time-delay interferometry (TDI). Our analysis covers the TDI Michelson, $$(\alpha ,\beta ,\gamma ),$$ Monitor, Beacon, Relay, and Sagnac combinations, together with the orthogonal $\textit{A}$, $\textit{E}$, $\textit{T}$ channels constructed from them. The validity of analytical expressions is confirmed by Monte Carlo integration. We find that, in the high-frequency limit, the sensitivity curves for the tensor and breathing modes scale as $$f^{2},$$ whereas those for the vector and longitudinal modes approach the explicit asymptotic forms $$\frac{c^{\textrm{op}}f^{2}}{\ln f}$$ and $$\frac{4c^{\textrm{op}}}{\pi ^{2} L^{2}} f,$$ respectively. In the low-frequency limit, for all GW modes, the sensitivity curves of the $$\zeta $$ combination and of the $\textit{T}$ channel scale as $$f^{-6},$$ whereas those of the other TDI combinations and of the $\textit{A}$, $\textit{E}$ channels scale as $$f^{-4}.$$ In this limit, the sensitivity curves for the tensor and vector modes coincide, and likewise for the breathing and longitudinal modes. For the breathing mode, the sensitivity curves of the $$(\alpha ,\beta ,\gamma )$$ and $$\zeta $$ combinations and of the $\textit{T}$ channel exhibit singularities at frequencies $$f = k/L$$ and do not exhibit a frequency range with nearly flat sensitivity. LISA and Taiji exhibit better sensitivity for $$f \lesssim 0.01$$ Hz due to their longer arm lengths, whereas TianQin performs better at $$f \gtrsim 0.1$$ Hz. We also highlight the advantage of utilizing the uncorrelated $\textit{A}$, $\textit{E}$, $\textit{T}$ channels to maximize the signal-to-noise ratio. These analytical formulas are useful for estimating the capability of future space-based GW detectors to constrain additional GW polarizations.

Chunyu Zhang

Analytical sensitivity curves for additional gravitational-wave polarizations of second-generation time-delay interferometry

Light polarization plays a crucial role in optical-cavity experiments; however, mirror birefringence presents a significant challenge that must be addressed carefully. In this study, a rigorous, nonperturbative framework is developed to quantify birefringence effects by incorporating variations in reflectance and polarization misalignment. We analyze the impact of this framework on the sensitivity of axionlike particle (ALP) dark matter searches. The results show that both birefringence and misalignment contribute to sensitivity degradation in the low-mass regime; however, the adverse effects of misalignment can be mitigated by selecting a postselection angle greater than the misalignment angle. Furthermore, birefringence produces an additional resonance peak in the high-mass region, which remains largely unaffected by misalignment and postselection variations. This rigorous framework underscores the importance of considering birefringence in high-precision optical-cavity experiments for ALP detection.

Japan

Tadashi Kuramoto

Yasutaka Imai

Takahiko Masuda

Yutaka Shikano

Sayuri Takatori

Satoshi Uetake

Analytical study of birefringent cavities for axionlike dark matter search

We develop a worldline-instanton approach for calculating the momentum spectrum of particles produced by gravitational fields that depend on both space and time. The instantons are open. The middle part is complex and describes the formation region, while the ends describe the trajectories of asymptotic particles.

Sweden

Philip Semrén

Greger Torgrimsson

Worldline instantons for nonperturbative particle production by space and time dependent gravitational fields

We propose a novel method to identify the two-pole structure of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Λ</mi><mo stretchy="false">(</mo><mn>1405</mn><mo stretchy="false">)</mo></math>. The two poles owe their origin to different quark flavor irreducible representations in the meson-baryon coupled-channel interactions, thus they should be individually manifested in reactions that provide good flavor eigenstate sources. Hadronic decays of charmonia into <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover><mi mathvariant="normal">Σ</mi><mi>π</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mover accent="true"><mi mathvariant="normal">Λ</mi><mo stretchy="false">¯</mo></mover><mo stretchy="false">(</mo><mn>1520</mn><mo stretchy="false">)</mo><mi mathvariant="normal">Σ</mi><mi>π</mi></math> are such reactions, and the flavor octet and singlet poles can be approximately singled out in these two decay modes. This SU(3) flavor filter works even considering the flavor symmetry breaking. With the huge charmonium data sets collected, it is therefore promising to solve the long-standing <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">Λ</mi><mo stretchy="false">(</mo><mn>1405</mn><mo stretchy="false">)</mo></math> puzzle employing the proposed flavor filter.

Ying-Bo He

Xiao-Hai Liu

Li-Sheng Geng

Feng-Kun Guo

Ju-Jun Xie

Identifying the two-pole structure of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">Λ</mi><mo stretchy="false">(</mo><mn>1405</mn><mo stretchy="false">)</mo></mrow></math> using an SU(3) flavor filter

We investigate the formation of primordial black holes (PBHs) induced by a first-order electroweak phase transition in a realistic renormalizable framework, the complex singlet extension of the Standard Model. We perform a quantitative analysis of the PBH abundance and identify parameter regions consistent with current microlensing constraints. Furthermore, we show that the same parameter space predicts observable stochastic gravitational waves within the sensitivities of future space-based detectors, as well as a sizable deviation in the Higgs triple coupling that can be probed at future lepton colliders. Our results highlight a comprehensive multimessenger framework in which PBHs, gravitational waves, and collider observations can jointly test the dynamics of a strongly first-order electroweak phase transition in the early Universe.

Fa Peng Huang

Chikako Idegawa

Aidi Yang

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

The long-distance contribution of QED corrections to the hadronic vacuum polarization is particularly challenging to compute in lattice <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>QCD</mi><mo>+</mo><mi>QED</mi></mrow></math>. Currently, it is one of the limiting factors toward matching the precision of the recent result by the Fermilab E989 experiment for the muon <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math>. In this work, we present a method for obtaining high-precision results for this contribution by reconstructing exclusive finite-volume state contributions. We find relations between the pion-photon contributions of individual diagrams and demonstrate the reconstruction method with lattice <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>QCD</mi><mo>+</mo><mi>QED</mi></mrow></math> data at a single lattice spacing of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>a</mi><mrow><mo>−</mo><mn>1</mn></mrow></msup><mo>≈</mo><mn>1.73</mn><mtext> </mtext><mtext> </mtext><mi>GeV</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><mi>π</mi></msub><mo>≈</mo><mn>275</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math>.

Germany

C. Lehner

J. Parrino

A. Völklein

Long-distance reconstruction of QED corrections to the hadronic vacuum polarization for the muon <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>g</mi><mo>−</mo><mn>2</mn></math>