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)

We present a study of the impact of data from the upcoming Electron Ion Collider (EIC) on the determination of the strong coupling within the context of the global MSHT fitting framework. To achieve this, we generate EIC electron-proton scattering pseudodata according to both conservative and optimistic experimental uncertainty projections and perform a simultaneous fit to obtain the proton PDFs and the value of the strong coupling. In the conservative case the impact is found to be moderate, but non-negligible, while in the optimistic case it is observed to be rather significant. These results therefore underline the promising potential for the EIC in the determination of the strong coupling. We in addition explore the impact of any potential tensions between the EIC data and the rest of the data in the global fit by injecting explicit inconsistencies into the pseudodata generation. This can lead to a noticeable bias in the extracted value of the strong coupling, highlighting the importance of accounting for all sources of theoretical uncertainty in the fit as well as the relevance of an enlarged, conservative, error definition in the determination of the strong coupling.

United Kingdom

L. Harland-Lang

Belgium

T. Cridge

P. Newman

R. Thorne

Germany

K. Wichmann

The impact of inclusive electron ion collider data on the strong coupling determination in a global PDF fit

The complex phases $$\phi _d$$ and $$\phi _s$$ , associated with the mixing between neutral $$B_q^0$$ and $$\bar{B}_q^0$$ mesons ( $$q\in \{d,s\}$$ ), are key observables to test the Standard Model and search for contributions from new physics. They are conventionally determined from the measurements of mixing-induced CP violation in the decays $$B_d^0\rightarrow J/\psi K^0$$ , $$B_s^0\rightarrow J/\psi \phi $$ and $$B_s^0\rightarrow D_s^+D_s^-$$ . To reach the highest possible precision on $$\phi _d$$ and $$\phi _s$$ , it is crucial that corrections from next-to-leading order effects – primarily associated with penguin decay topologies – are accounted for. The strategy adopted in this paper uses the $\textit{SU}$(3) flavour symmetry of QCD to relate the unknown contributions from penguin topologies to their counterparts in suitably-chosen control modes, where their effects are enhanced. Utilising new CP asymmetry measurements from LHCb on the decays $$B_s^0\rightarrow D_s^+D_s^-$$ , $$B_d^0\rightarrow D^+D^-$$ , $$B^+\rightarrow J/\psi K^+$$ and $$B^+\rightarrow J/\psi \pi ^+$$ , as well as from Belle-II on the decay $$B_d^0\rightarrow J/\psi \pi ^0$$ , we present the current state-of-the-art picture on controlling the penguin contributions and extract $$\phi _d$$ and $$\phi _s$$ from the corresponding observables. We explore the prospects for the end of the Belle-II and HL-LHC flavour physics programmes, and demonstrate the importance of measuring the control modes with future data.

Netherlands

Kristof Bruyn

Robert Fleischer

Eleftheria Malami

How to tame penguins: advancing to high-precision measurements of $$\phi _d$$ and $$\phi _s$$

We discuss the production of <math altimg='si10.svg'><mrow><mi>D</mi><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover></mrow></math> pairs in <math altimg='si2.svg'><mrow><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>&#8722;</mo></msup></mrow></math> collisions, where <italic>D</italic> refers to either <italic>D</italic> 0 or <math altimg='si30.svg'><msup><mi>D</mi><mo>+</mo></msup></math>. The continuum mechanism with the <italic>t</italic>/ <italic>u</italic>-channel vector-meson <italic>D</italic>* exchanges are considered. The results of the calculation depend on the parameter of the off-shell form-factor for the virtual <italic>D</italic>* mesons. The <italic>D</italic>* <italic>D&#947;</italic> coupling constants are found from the <italic>D</italic>*&#8239;&#8594;&#8239; <italic>D&#947;</italic> decays. We find relatively large contribution for the <math altimg='si4.svg'><mrow><msup><mi>D</mi><mn>0</mn></msup><msup><mrow><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover></mrow><mn>0</mn></msup></mrow></math> channel and much smaller contribution in the <math altimg='si1.svg'><mrow><msup><mi>D</mi><mo>+</mo></msup><msup><mi>D</mi><mo>&#8722;</mo></msup></mrow></math> channel. In the second case we consider also the <italic>D</italic> &#8239;&#177;&#8239; exchanges. We conclude that the bump at <math altimg='si31.svg'><mrow><msub><mi>M</mi><mrow><msup><mi>D</mi><mn>0</mn></msup><msup><mrow><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover></mrow><mn>0</mn></msup></mrow></msub><mo linebreak='goodbreak'>=</mo><mn>3.8</mn></mrow></math> GeV observed by the Belle and BaBar Collaborations has rather continuum origin than it corresponds to the broad resonance <italic>&#967;</italic> <inf><italic>c</italic>0</inf>(3860). We discuss also production of the <italic>&#967;</italic> <inf><italic>c</italic>2</inf>(3930) resonance which is a candidate for the <italic>&#967;</italic> <inf><italic>c</italic>2</inf>(2 <italic>P</italic>) state. This state can decay into both <math altimg='si10.svg'><mrow><mi>D</mi><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover></mrow></math> channels, however the branching fractions are not well known at present. From a comparison of our model results to the BaBar data we find <math altimg='si32.svg'><mrow><mi>B</mi><mo>(</mo><msub><mi>&#967;</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub><mrow><mo>(</mo><mn>3930</mn><mo>)</mo></mrow><mo>&#8594;</mo><mi>D</mi><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover><mo>)</mo><mo>=</mo><mn>0.58</mn><mo>&#177;</mo><mn>0.13</mn></mrow></math> using the two-photon width <math altimg='si33.svg'><mrow><msub><mstyle mathvariant='normal'><mi>&#915;</mi></mstyle><mrow><mi>&#947;</mi><mi>&#947;</mi></mrow></msub><mo linebreak='goodbreak'>=</mo><mn>0.544</mn></mrow></math> keV (obtained for the Buchm&#252;ller-Tye potential) evaluated within the light-front approach (NRQCD limit). Our finding of <math altimg='si34.svg'><mrow><msub><mstyle mathvariant='normal'><mi>&#915;</mi></mstyle><mrow><mi>&#947;</mi><mi>&#947;</mi></mrow></msub><mo linebreak='goodbreak'>&#215;</mo><mi>B</mi><mrow><mo>(</mo><msub><mi>&#967;</mi><mrow><mi>c</mi><mn>2</mn></mrow></msub><mrow><mo>(</mo><mn>3930</mn><mo>)</mo></mrow><mo>&#8594;</mo><mi>D</mi><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><mn>0.32</mn><mo>&#177;</mo><mn>0.07</mn></mrow></math> keV is close to the Belle and BaBar results. Realistic predictions of the differential distributions in several variables and integrated cross-sections are given for the Belle II kinematics.

Poland

Izabela Babiarz

Piotr Lebiedowicz

Wolfgang Schäfer

Antoni Szczurek

Competition of <italic>&#967;<inf>c</inf></italic>(2 <italic>P</italic>) quarkonia and continuum in <math altimg='si9.svg'><mrow><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>&#8722;</mo></msup><mo>&#8594;</mo><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>&#8722;</mo></msup><mi>D</mi><mover accent='true'><mi>D</mi><mo>&#175;</mo></mover></mrow></math>

Employing the Polyakov chiral SU(3) mean field (PCQMF) model, we investigate how momentum-space anisotropy, characteristic of quark-gluon plasma (QGP) in ultrarelativistic heavy-ion collisions (uRHIC), impacts the thermodynamic behavior and transport coefficients of strongly interacting quark matter. The momentum anisotropy is introduced via a small deformation in the momentum distribution, quantified by a spheroidal parameter <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ξ</mi></math>, which deforms the distribution functions and captures anisotropic effects to linear order. The PCQMF model captures key non-perturbative aspects of QCD, such as chiral symmetry breaking or deconfinement dynamics through Polyakov loop potential, and is extended here to accommodate momentum-space anisotropy. We compute the modifications induced by momentum-space anisotropy to key thermodynamic observables including pressure <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>p</mi></math>, energy density <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ε</mi></math>, entropy density <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>s</mi></math>, speed of sound squared <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>c</mi><mi>s</mi><mn>2</mn></msubsup></math>, and specific heat <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>c</mi><mi>v</mi></msub></math>, alongside key transport coefficients such as shear viscosity <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>η</mi></math>, bulk viscosity <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ζ</mi><mi>b</mi></msub></math>, and electrical conductivity <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>σ</mi><mrow><mi>el</mi></mrow></msub></math>. These coefficients are derived using the relativistic Boltzmann equation (RBE) under the relaxation time approximation (RTA). We find that even a weak anisotropy can lead to significant modifications in the thermodynamic response and transport behavior of quark matter. This underscores the importance of including momentum anisotropy for realistic modeling of the QCD medium across all energy regimes, from current studies at RHIC and LHC to future explorations of the high-density frontier at FAIR, NICA, and J-PARC.

India

Dhananjay Singh

Arvind Kumar

Impact of anisotropy on the QCD phase structure and transport coefficients of quark matter

Gravitational wave interferometers have studied compact object mergers and solidified our understanding of strong gravity. Their increasing precision raises the possibility of detecting new physics, especially in a neutron star binary system that may contain hidden-sector particles. In particular, a new vector force between binary constituents, giving rise to dark electromagnetic phenomena, could measurably alter the inspiral waveforms and thus be constrained by gravitational wave observations. In this work, we critically examine the mechanisms for neutron stars to acquire enough hidden-sector particles with requisite couplings to furnish a detectable signature from dark electromagnetism. In particular, we explore three plausible mechanisms for achieving a sufficient dark mass fraction, and we derive quite general limitations on the amount of charge that can be accumulated by any of these mechanisms. We demonstrate that the repulsive nature of vector forces imposes stringent constraints on any putative particle physics model or astrophysical environment which could give rise to such gravitational signatures. We argue that absent an extreme fine-tuning of parameters, such signatures are well out of reach of any current or near-future gravitational wave observatory.

Ian Harris

Canada

Yonatan Kahn

Stringent constraints on gravitational wave signatures of dark electromagnetism in neutron star binaries

The <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mn>0</mn></msup></math> bosons produced in electron-positron collisions at the potential Future Circular Collider (FCC-ee) provide unique opportunities for flavor physics. The nonzero polarization of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi mathvariant="normal">Λ</mi><mi>b</mi><mn>0</mn></msubsup></math> baryons produced in <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mn>0</mn></msup></math> decays enables access to a much larger set of observables than at the LHC, where the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi mathvariant="normal">Λ</mi><mi>b</mi><mn>0</mn></msubsup></math> baryons are produced unpolarized. This paper presents a toy angular analysis of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi mathvariant="normal">Λ</mi><mi>b</mi><mn>0</mn></msubsup><mo stretchy="false">→</mo><mrow><mi mathvariant="normal">Λ</mi><mo stretchy="false">(</mo><mo stretchy="false">→</mo><mi>p</mi><msup><mi>π</mi><mo>−</mo></msup><mo stretchy="false">)</mo><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup></mrow></math> decays using simulation samples of collisions at the FCC-ee reconstructed using the IDEA detector concept and assuming a dataset of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>6</mn><mo>×</mo><msup><mn>10</mn><mn>12</mn></msup></math> <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>Z</mi><mn>0</mn></msup></math> bosons. While the statistical sensitivity achieved for individual angular observables is not expected to significantly exceed that from the LHCb Upgrade II experiment, the addition of the polarized observables leads to a significant improvement of the knowledge on the Wilson coefficients <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>C</mi><msup><mn>9</mn><mrow><mo stretchy="false">(</mo><mo>′</mo><mo stretchy="false">)</mo></mrow></msup></msub></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>C</mi><mrow><msup><mn>10</mn><mrow><mo stretchy="false">(</mo><mo>′</mo><mo stretchy="false">)</mo></mrow></msup></mrow></msub></math>.

Anja Beck

Mero Elmarassy

Asher Sabbagh

Michal Kreps

Eluned Smith

Constraints on new physics from decays of polarized <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi mathvariant="normal">Λ</mi><mi>b</mi><mn>0</mn></msubsup></math> baryons at the FCC-ee