We constructed a four-Higgs-doublet model (4HDM) invariant under $\textit{D}$ $_{5}$ symmetry and investigated its complete neutral vacuum structure in detail. Assuming explicit CP conservation in the scalar potential, we examined whether CP symmetry can be spontaneously broken. We provided a complete list of all possible real and complex vacua, along with the constraints on the potential parameters required for each vacuum solution to exist. We also discussed the positive-definiteness conditions that the Hessian must satisfy for each vacuum to be a local minimum of the potential. The results show that, after spontaneous symmetry breaking, some complex vacua lead to spontaneous CP violation in the potential, whereas the remaining complex vacua still preserve CP conservation. Among these CP-violating complex vacua, one can be regarded as the most general form. Furthermore, we discussed the relationship between real and complex vacua.

China

Dong-Ping Fu

Michihisa Takeuchi

Spontaneous CP violation in the $\textit{D}$ $_{5}$-symmetric four-Higgs-doublet models * Supported by the Fundamental Research Funds for the Central Universities, the One Hundred Talent Program of Sun Yat-sen University, China, and the Guangdong Natural Science Foundation (2026A1515012641)

Hadron-hadron interactions, being nonperturbative in nature, play a significant role in addressing phenomenological questions in particle physics. Femtoscopy is a powerful tool in heavy-ion collision experiments, enabling the extraction of hadron-hadron interactions via momentum-correlation functions (CFs). These CFs are typically expressed as a convolution of source functions and hadron-hadron wave functions, with the latter encoding information about the interactions. However, source functions remain poorly constrained and are commonly approximated by a Gaussian form. Reconstructing source functions from experimental correlation data constitutes an 'inverse problem.' To address this, we propose a toy model based on Tikhonov regularization. Using a square-well potential with four distinct strengths, we calculate the CFs for inputs of single Gaussian source functions and mixed Gaussian source functions. The resulting CFs are then used to reconstruct the source functions via Tikhonov regularization. Our results show that the Gaussian source function can be successfully reconstructed, highlighting the potential of this approach for extracting realistic source functions from hadron pairs of interest.

Ao-Sheng Xiong

Qi-Wei Yuan

Ming-Zhu Liu

Fu-Sheng Yu

Zhi-Wei Liu

Li-Sheng Geng

Solving the inverse source problem in femtoscopy with a toy model * Supported in part by the Fundamental and Interdisciplinary Disciplines Breakthrough Plan of the Ministry of Education of China (JYB2025XDXM204) and the National Natural Science Foundation of China (W2543006, 12435007). Ming-Zhu Liu acknowledges support from the National Natural Science Foundation of China (12575086). Zhi-Wei Liu acknowledges support from the National Natural Science Foundation of China (12405133) and from the Shenzhen Science and Technology Program (ZDSYS20230626091501002). Fu-Sheng Yu and Ao-Sheng Xiong acknowledge support from the Scientific Research Innovation Capability Support Project for Young Faculty (ZYGXQNJSKYCXNLZCXM-P2) and from the Fundamental Research Funds for the Central Universities (lzujbky-2023-stlt01, lzujbky-2024-oy02, lzujbky-2025-eyt01)

We study the equation of state (EoS) of QCD matter in a bottom-up holographic setup that combines an Einstein-Maxwell-dilaton (EMD) sector with an improved Karch-Katz-Son-Stephanov (KKSS) flavor action. In the probe approximation, we perform an inverse reconstruction of the model functions by parameterizing them with neural networks and solving the EMD equations via a differentiable ODE solver (a neural ODE framework), calibrating the model to a reference thermodynamic table for $(2+1)$ -flavor QCD at finite temperature and finite baryon chemical potential. The reconstructed model functions are then parameterized and kept fixed across thermodynamic states. Next, viewing the EMD sector as an effective description of pure Yang-Mills theory, we fix its parameters by fitting the $\mu_B=0$ lattice pure-glue EoS using a hybrid optimization strategy. Finally, we go beyond the probe limit and solve the coupled EMD+KKSS equations with back-reaction, using the pure-glue-calibrated EMD sector as a fixed input and varying the KKSS couplings to compare with the $\mu_B=0$ two-flavor lattice EoS. We find a visible mismatch and a high-temperature behavior in which the back-reacted dimensionless ratios approach a nearly $\beta_1$ -insensitive plateau close to the pure-glue baseline, providing a simple structural diagnostic for the present flavor-sector truncation.

Yutian Deng

Mei Huang

Lin Zhang

Holographic QCD equation of state constrained by lattice QCD: neural-ODE for probe-limit and a back-reaction test * Start-up funding from Sun Yat-sen University (SYSU) (Y. Deng and L. Zhang); National Natural Science Foundation of China (NSFC) (12235016) (L. Zhang and M. Huang) and 12221005 (M. Huang)

In this work, we present the first computation of the full one-loop electroweak radiative corrections to the process $ \mu^- \mu^+ \to W^\pm W^\mp \to hh $ within the Standard Model (SM). Building upon this, we investigate neutral scalar pair production via vector boson fusion at multi–TeV muon colliders in the framework of the Two-Higgs-Doublet Model (2HDM). In our phenomenological analysis, we introduce an enhancement factor, defined as the ratio of the cross section for SM-like Higgs pair production in the 2HDM to the corresponding SM prediction. This factor is systematically evaluated across the allowed regions of parameter space in both Type-X and Type-Y 2HDMs. Our results indicate that, within the viable Type-X parameter space, this factor can reach a value of 3, whereas it remains between 0.91 and 0.95 across the allowed parameter space of the Type-Y scenario. We observe that the enhancement factor exhibits distinct behaviors in the Type-X and Type-Y 2HDMs. This feature provides a promising opportunity to discriminate between the two scenarios through precision measurements of double Higgs production at future multi–TeV colliders. Furthermore, we perform a detailed scan of the cross sections for both CP-odd and CP-even Higgs pair production over the viable parameter spaces of the Type-X and Type-Y 2HDMs. In the Type-Y scenario, at a center-of-mass (CoM) energy $ \sqrt{s} = 10\; \text{TeV} $ and an integrated luminosity of $ {\cal{L}} = 10000\; \text{fb}^{-1} $ , both CP-odd and CP-even Higgs pair production in the $ t\bar{t}b\bar{b} $ final state, with subsequent top-quark decays into leptons and bottom quarks, can be probed with a statistical significance exceeding the $ 2\sigma $ level at several viable parameter points.

Vietnam

Khiem Hong Phan

Quang Hoang-Minh Pham

Neutral scalar pair production via $\textit{W}$-boson fusion at multi–TeV muon colliders * This work is supported by the Vietnam National Foundation for Science Technology Development (NAFOSTED) (103.01-2023.16)

In this work, we focus on the possible linear relationship between short-range correlations (SRCs) and the EMC effect for partons in nuclei. First, we test a linear relationship pertaining to gluons in bound nuclei; it is manifested as a correlation between the slope of the reduced cross-section ratio in deep inelastic scattering (DIS) and the cross-section of sub-threshold $ J/\psi $ photoproduction. For comparison, results from four different global analysis groups of nuclear parton distribution functions (nPDFs) are utilized. These results show a good linear correlation between the gluons in bound nuclei and the slope of the reduced cross-section ratio, consistent with the possible presence of nuclear effects in the gluon distributions. Second, we investigate the linear relationship of quarks in the proton-induced Drell-Yan process. The corresponding results for quarks show strong sensitivity to the parameterizations forms adopted by the different groups. These findings enhance our understanding of the substructure in bound nuclei and provide a valuable reference for future global fitting of nPDFs.

Shu-Man Hu

Wei Wang

Ji Xu

Xing-Hua Yang

Shuai Zhao

Testing a linear relation: short-range correlations and the EMC effect for gluons and quarks in nuclei * Supported in part by the National Natural Science Foundation of China (12125503, 12335003, 12105247, 12305106, 12475098)

We investigate the discovery potential of the $T_{bc}$ state with $J^P = 0^+$ in proton-proton ( $pp$ ) collisions at LHCb at a center-of-mass energy of $\sqrt{s} = 13~{\rm{TeV}}$ . The study focuses on the decay channel $T_{bc} \to B^- D^+$ . A phenomenological approach is employed to construct the background model based on the associated production of $\textit{B}$ and $\textit{D}$ mesons, incorporating previously published LHCb results. Background processes are simulated using ${\mathtt{MadGraph5\_aMC@NLO}}$ and ${\mathtt{Pythia8.3}}$ . We explore the parameter space of the $T_{bc}$ mass, width, production cross section, and the effective double-parton scattering cross section ( $\sigma_{{\rm{eff}}}$ ) relevant for the $B D$ meson background. The integrated luminosity required for a $5\sigma$ discovery at LHCb is evaluated under various assumptions. In particular, we consider three representative $T_{bc}$ production cross section scenarios: an optimistic estimate of $103~{\rm{nb}}$ , an intermediate value of $18~{\rm{nb}}$ obtained by scaling from the $T_{cc}^+$ production cross section, and a conservative lower bound of $0.3~{\rm{nb}}$ . We find that a $5\sigma$ observation is achievable for a production cross section of $103~{\rm{nb}}$ , which is expected to be within reach during Run4. In contrast, the more realistic cross section estimate of $18~{\rm{nb}}$ requires the full Run5 dataset ( $300~{\rm{fb}}^{-1}$ ) under the most favorable parameter choices. For the conservative scenario, no significant signal would be observable even with $300~{\rm{fb}}^{-1}$ . In addition, we estimate the minimum observable $\sigma(T_{bc}) \times {\cal{B}}(T_{bc} \to $ $ B^- D^+)$ for a $5\sigma$ discovery under different luminosity scenarios, providing guidance for future experimental searches at LHCb.

Mingjie Feng

Yiming Li

France

Hua-Sheng Shao

Prospects for discovering strongly decaying doubly heavy T$_{bc}$ tetraquark states at LHCb * Mingjie Feng and Yiming Li is Supported by the National Natural Science Foundation of China (NSFC) (2175245, 12188102, W2443008). Hua-Sheng Shao is Supported by the European Research Council (101041109, 'BOSON') and the French National Research Agency (grant ANR-20-CE31-0015, 'PrecisOnium')

Semileptonic $$b\rightarrow c\tau \bar{\nu }_{\tau }$$ decays are powerful probes of non-Standard-Model effects within an effective-field-theory (EFT) framework, but fully exploiting them in current and future data demands combinations that maximise sensitivity while controlling biases from Standard-Model-based modelling and from theory inputs that are shared, and therefore correlated, across analyses in different experiments. We present a first sensitivity study of a $\textit{combined}$ extraction of Wilson coefficients in $$\bar{B}\rightarrow D^{(*)}\tau \bar{\nu }_{\tau }$$ decays using LHCb- and Belle II-like analysis configurations. Detector simulations for signal and backgrounds are typically generated under Standard Model assumptions; if non-SM contributions are present, this can bias the fitted Wilson coefficients. In addition, hadronic inputs such as form-factor parameters of signal and background components are common across analyses, requiring a consistent treatment of fully correlated effects in combinations. To avoid repeating large-scale detector simulation for each EFT hypothesis, we use event-by-event reweighting to map simulated samples to arbitrary combinations of Wilson coefficients. We then compare a simultaneous fit across multiple $$\bar{B}\rightarrow D^{(*)}\tau \bar{\nu }_{\tau }$$ channels and datasets with a combination based on post-fit averages. Sharing Wilson coefficients and common form-factor parameters in the simultaneous fit reduces model-induced biases and improves sensitivity relative to independent fits, providing a robust and scalable strategy for precision EFT constraints in $$b\rightarrow c\tau \bar{\nu }_{\tau }$$ transitions using forthcoming LHCb and Belle II datasets.

Germany

Johannes Albrecht

Florian Bernlochner

Marco Colonna

Lorenz Gärtner

Switzerland

Abhijit Mathad

United Kingdom

Biljana Mitreska

Markus Prim

Ilias Tsaklidis

Joint LHCb–Belle II prospects to constrain new physics in $$B\rightarrow D^{(*)}\tau \nu $$

We report the results of the second iteration of an experiment searching for neutron-hidden-neutron oscillations in a beam of ultracold neutrons, conducted at the PF2 facility of the Institut Laue Langevin (ILL). Oscillations were tested via neutron disappearance as a function of an applied magnetic field, in the context of a phenomenological two-parameter model assuming zero hidden potentials. The magnetic field was varied in a step-wise manner in order to resonantly enhance the oscillation probability at different mass splittings ( <italic>&#948;m</italic>) across a 60&#8211;1550 <math altimg='si8.svg'><mrow><mi mathvariant='normal'>p</mi><mrow><mi mathvariant='normal'>e</mi><mi mathvariant='normal'>V</mi></mrow></mrow></math> range. No evidence for neutron disappearance is observed and conservative limits on the neutron-hidden-neutron oscillation period ( <math altimg='si1.svg'><msub><mi>&#964;</mi><mrow><mi>n</mi><msup><mi>n</mi><mo>&#8242;</mo></msup></mrow></msub></math>) have been set at 95 % confidence level: <math altimg='si9.svg'><mrow><msub><mi>&#964;</mi><mrow><mi>n</mi><msup><mi>n</mi><mo>&#8242;</mo></msup></mrow></msub><mo linebreak='goodbreak'>&gt;</mo><mn>200</mn></mrow></math> ms for | <italic>&#948;m</italic>|&#8239;&#8712;&#8239;[60, 400] <math altimg='si8.svg'><mrow><mi mathvariant='normal'>p</mi><mrow><mi mathvariant='normal'>e</mi><mi mathvariant='normal'>V</mi></mrow></mrow></math> and <math altimg='si10.svg'><mrow><msub><mi>&#964;</mi><mrow><mi>n</mi><msup><mi>n</mi><mo>&#8242;</mo></msup></mrow></msub><mo linebreak='goodbreak'>&gt;</mo><mn>100</mn></mrow></math> ms for | <italic>&#948;m</italic>|&#8239;&#8712;&#8239;[400, 1550] <math altimg='si8.svg'><mrow><mi mathvariant='normal'>p</mi><mrow><mi mathvariant='normal'>e</mi><mi mathvariant='normal'>V</mi></mrow></mrow></math>.

Gaby Brenot

Benoit Clément

Hanno Filter-Pieler

Daniel Galbinski

Tobias Jenke

Thomas Lefort

Anthony Lejuez

Guillaume Pignol

Stephanie Roccia

William Saenz-Arevalo

Further search for magnetic-field-induced neutron disappearance in an ultracold neutron beam

We study neutrino-induced charged-current coherent pion production (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>ν</mi></mrow><mrow><mi>μ</mi></mrow></msub><mrow><mi>CC</mi><mo>−</mo><mi>Coh</mi></mrow><mi>π</mi></mrow></math>) as a tool for constraining the neutrino flux at the Deep Underground Neutrino Experiment (DUNE). The neutrino energy and flavor in the process can be directly reconstructed from the outgoing particles, making it especially useful to specifically constrain the muon neutrino component of the total flux. The cross section of this process can be obtained using the Adler relation with the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>π</mi></math>-Ar elastic scattering cross section taken either from external data or, as we explore, from a simultaneous measurement in the DUNE near detector. We develop a procedure that leverages <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>μ</mi></msub><mrow><mi>CC</mi><mo>−</mo><mi>Coh</mi></mrow><mi>π</mi></math> events to fit for the neutrino flux while simultaneously accounting for relevant effects in the cross section. We project that this method has the statistical power to constrain the uncertainty on the normalization of the flux at its peak to a few percent. This study demonstrates the potential utility of a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>μ</mi></msub><mrow><mi>CC</mi><mo>−</mo><mi>Coh</mi></mrow><mi>π</mi></math> flux constraint, though further work will be needed to determine the range of validity and precision of the Adler relation upon which it relies, as well as to measure the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>π</mi></math>-Ar elastic scattering cross section to the requisite precision. We discuss the experimental and phenomenological developments necessary to unlock the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>ν</mi><mi>μ</mi></msub><mrow><mi>CC</mi><mo>−</mo><mi>Coh</mi></mrow><mi>π</mi></math> process as a “standard candle” for neutrino experiments.

United States

Mun Jung Jung

Vishvas Pandey

Gray Putnam

David W. Schmitz

Neutrino-induced charged-current coherent pion production for constraining the muon neutrino flux at DUNE

We investigate the atmospheric production and subsequent detection of sub-GeV dark mesons within the framework of a confining dark sector coupled to the Standard Model (SM) via a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><msub><mo stretchy="false">)</mo><mi mathvariant="normal">D</mi></msub></math> vector portal. High-energy cosmic-ray interactions in the atmosphere produce dark quarks through proton bremsstrahlung, rare decays of Standard Model mesons, and Drell-Yan processes, which subsequently hadronize into dark mesons. We adopt a modified quark combination model to describe the nonperturbative dark hadronization process, allowing for a detailed event-level characterization of the dark meson flux. We simulate the flux and the interactions of these relativistic dark mesons in the Jiangmen Underground Neutrino Observatory (JUNO) using the genie generator, considering both elastic scattering off nuclei and deep inelastic scattering channels. Adopting a large-energy-singles-inspired conservative signal definition with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>15</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi><mo>&lt;</mo><msub><mi>E</mi><mrow><mi>vis</mi></mrow></msub><mo>&lt;</mo><mn>100</mn><mtext> </mtext><mtext> </mtext><mi>MeV</mi></math> and vetoing events containing final-state neutrons, we derive projected 90% C.L. sensitivities to the coupling strength between the dark gauge boson and the SM sector for a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>20</mn><mtext> </mtext><mtext> </mtext><mi>kton</mi><mo>·</mo><mi>year</mi></math> exposure. For the representative benchmark masses <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>m</mi><msup><mi>Z</mi><mo>′</mo></msup></msub><mo>=</mo><mn>0.001</mn></math>, 0.01, and 0.1 GeV, the projected JUNO reach corresponds to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msubsup><mi>g</mi><mrow><mi>SM</mi></mrow><mn>90</mn></msubsup><mo>=</mo><mn>6.48</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>7.75</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>5</mn></mrow></msup></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>2.37</mn><mo>×</mo><msup><mn>10</mn><mrow><mo>−</mo><mn>4</mn></mrow></msup></math>, respectively. This reach is found to be only mildly sensitive to order-one variations of the hadronization parameter, as illustrated by the choices <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>κ</mi><mi>β</mi></msub><mo>=</mo><mn>1</mn><mo>/</mo><mn>3</mn></math>, 1, and 3.

Zirong Chen

Dan Chi

Jinmian Li

Junle Pei

Search for cosmic-ray-produced dark mesons via the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>U</mi><mo stretchy="false">(</mo><mn>1</mn><msub><mo stretchy="false">)</mo><mi mathvariant="normal">D</mi></msub></math> portal at JUNO