Thu·Jan 22, 2026Thursday·January 22, 2026

1. 01*

   Gravitational Waves in an A4 Neutrino Mass Model

   Mu-Chun Chen🇺🇸 · Harold J. Matias🇺🇸 · Cameron Moffett-Smith🇺🇸

   The A4 flavor symmetry has provided tremendous insight into the flavor structure of the lepton sector of the Standard Model, predicting a very good approximation to neutrino mixing angles, Tri-Bimaximal Mixing. A4 is spontaneously broken by a scalar called the flavon, and when this happens a number of degenerate vacua can form, resulting in so-called domain walls. These objects are not observed and hence need to be annihilated. This is usually done by explicitly breaking A4 by adding a bias term to the scalar potential. In this paper, we construct a new model invariant under A4 and Z4, which creates cosmologically viable domain walls, lifts the degeneracy of the vacuum giving a natural mechanism for domain walls to annihilate, as well as predicts realistic neutrino mixing angles; all utilizing cross couplings between flavons. The annihilation of the domain walls, with proper choice of wall tension and the consequent bias term, leads to a gravitational wave signal that is potentially detectable in near future gravitational wave experiments, and interestingly intersects with the observed Pulsar Timing Array signal.

   hep-ph5 citations
2. 02*

   Weak boson probes of Higgs unitarity restoration at 10 TeV parton colliders

   Christoph Englert🇬🇧 · Wrishik Naskar🇩🇪 · Andrew D. Pilkington🇬🇧 · Michael Spannowsky🇬🇧

   Higgs coupling deviations, at levels accessible to the high-luminosity LHC, can imply a phenomenological no-lose theorem for the next generation of collider facilities. Correlating Higgs coupling deviations from the SM expectation in the gauge boson sector with high-scale unitarity requirements, we estimate and compare the sensitivity that can be expected at a future hadron collider (operating at 100 TeV centre-of-mass energy) and a 10 TeV muon collider. Both muon and hadron colliders offer discovery potential for mass scales up to $\mathcal{O}(6\text{TeV})$ where unitarity violation induced by (sub)percent Higgs coupling modifications is mended. We comment on how an intermediate precision FCC-ee programme can corroborate such deviations.

   hep-phhep-exPLB(2026)·0 citations
3. 03*

   How large are curvature perturbations from slow first-order phase transitions? A gauge-invariant analysis

   Xiao Wang🇦🇺 · Csaba Balázs🇦🇺 · Ran Ding🇨🇳 · Chi Tian🇨🇳

   When strongly supercooled cosmological first-order phase transitions (FOPTs) are sufficiently slow, super-horizon inhomogeneities can be generated. We compute these super-horizon curvature perturbations by employing a gauge-invariant, multi-fluid formalism. By resolving the gauge ambiguities inherent in conventional separate-universe simulations, we demonstrate that Primordial Black Holes are unlikely to be produced by these super-horizon inhomogeneities. We also derive a fitting formula for the resulting curvature perturbations and discuss potential observational constraints on FOPTs imposed by limits on primordial curvature perturbations and associated scalar-induced gravitational waves.

   hep-phPRD(2026)·11 citations
4. 04*

   Neutrino production mechanisms in strongly magnetized quark matter: Current status and open questions

   Igor A. Shovkovy🇺🇸 · Ritesh Ghosh🇺🇸

   We review the main neutrino emission mechanisms operating in dense quark matter under strong magnetic fields, with particular emphasis on conditions expected in the interiors of compact stars. We discuss the direct Urca and neutrino synchrotron processes in unpaired quark matter, incorporating the effects of Landau-level quantization. For the direct Urca process, the quantization of the electron energy spectrum plays a critical role, whereas quark quantization can often be neglected at sufficiently high baryon densities. The resulting field-dependent neutrino emissivity is anisotropic and exhibits an oscillatory behavior as a function of magnetic-field strength. We explore the implications of these effects for magnetar cooling and for possible anisotropic neutrino emission that could contribute to pulsar kicks. In addition, we review the $\nu \bar{\nu }$ synchrotron emission process, which, although subdominant, provides valuable insights into the interplay between magnetic fields and weak interactions in dense quark matter. Overall, our analysis highlights the nontrivial influence of strong magnetic fields on neutrino production in magnetized quark cores, with potential consequences for the thermal and dynamical evolution of compact stars.

   hep-phastro-ph.HEnucl-thUniverse(2026)·2 citations
5. 05*

   Symmetry Nonrestoration in the Pati-Salam Model

   N. Okada🇺🇸 · A. Stern🇺🇸

   We demonstrate that symmetry need not be restored in the Pati-Salam model, so that $SU(2{)}_L\otimes SU(2{)}_R\otimes SU(4{)}_c$ remains broken to the Standard Model group at temperatures above the Pati-Salam symmetry breaking scale. Including the leading finite-temperature corrections, suitable quartic couplings prevent a restoration transition, thereby avoiding the thermal production of 't Hooft-Polyakov monopoles after inflation, even if the reheating temperature is very high. This removes monopole-based constraints on the Pati-Salam symmetry breaking scale.

   hep-phgr-qchep-th0 citations
6. 06*

   Elastic lepton-proton two-photon exchange scattering: An exact HB$\chi$PT analysis including hadronic effects at NNLO

   Rakshanda Goswami🇮🇳 · Pulak Talukdar🇮🇳 · Bhoomika Das🇮🇳 · Udit Raha🇮🇳 · Fred Myhrer🇺🇸

   We present an exact analytical evaluation of the two-photon exchange (TPE) correction to the elastic lepton-proton differential scattering cross section at low-energies within the framework of heavy-baryon chiral perturbation theory. Our analysis focuses on the kinematic regime relevant to the ongoing MUSE experiment, and we therefore restrict the intermediate states to the dominant elastic channel. All loop integrals are evaluated analytically without approximations. Radiative and chiral recoil contributions of the proton are included, retaining kinematical and dynamical TPE corrections to the cross section through next-to-next-to-leading order [i.e., $\mathcal{O}(\alpha /M^2)$] accuracy in the recoil expansion where $M$ is the proton mass. At this chiral order, pion-loop contributions demonstrate that structure-dependent TPE effects arise through the proton form factors. Our analytical results for the scattering cross section reveal non-vanishing residual proton structure effects of $\mathcal{O}(\alpha /M^2)$, despite substantial cancellations between TPE box and crossed-box contributions. Such effects were entirely absent at this accuracy in our earlier analysis based on the soft-photon approximation. Although the next-to-leading-order contributions are numerically sizable, the next-to-next-to-leading-order TPE corrections are found to be small, thereby indicating that the chiral expansion exhibits reasonably good perturbative convergence.

   hep-phnucl-th0 citations
7. 07*

   Long-Lived Oscillons as Closed Domain Walls in the ${\mathbb{Z}}_2$-Symmetric Two-Higgs-Doublet Model

   Zhaoyu Meng🇨🇳

   We identify an oscillatory solution that exists as a long-lived, bubble-like closed domain wall in the two-Higgs-doublet model (2HDM) under a ${\mathbb{Z}}_2$ symmetry constraint, and these structures emerge naturally during the late stages of domain wall decay. \\ \\ The longevity of these structures is attributed to a potential landscape characterized by two distinct vacuum regions, the oscillating region lies in one vacuum, while the constant outer region lies in the other. The lifetime of the structure depends on the parameter in the Lagrangian, we identify a specific parameter space where radiation is suppressed, the solution exhibits a maximum lifetime that goes up to infinity. \\ \\ The simpler two-complex-field system is first used to introduce the mathematical requirements of the structure before extending it to the more physical but complex 2HDM. Further Numerical verification via Floquet analysis shows these structures are stable under perturbation.

   hep-ph1 citation
8. 08*

   Systematic study of the strong decays of the $P_c$ states and their possible isospin cousins via the QCD sum rules

   Xiu-Wu Wang🇨🇳 · Xin Li🇨🇳 · Zhi-Gang Wang🇨🇳

   In the present work, the strong decays of the discovered $P_c(4380)$, $P_c(4440)$, $P_c(4457)$ and their possible isospin cousins are systematically studied via the assignment that they are the meson-baryon molecular states. In detail, the strong decay constants, partial decay widths of their decay channels are calculated under the framework of QCD sum rules. The decay withes of the discovered $P_c(4380)$, $P_c(4440)$ and $P_c(4457)$ are in good agreement with the experiments. The predictions of the decays of these three related possible isospin cousins are presented which would shed light for their findings in experiment, in return, this may testify the assignments of the discovered $P_c$ states.

   hep-phCPC(2026)·1 citation
9. 09*

   Phenomenology of a double dilaton soft-wall model: Alpha strong from Ricci flow and pion Form Factors at intermediate-energy region

   Héctor Cancio🇪🇸 · Pere Masjuan🇪🇸

   Through a holographic model of QCD, we present a phenomenological approach to study the running of the strong coupling constant \alpha_s in both non-perturbative and perturbative regimes. The renormalization of the metric tensor, driven by the Ricci Flow, and the breaking of conformal and chiral symmetries -- thanks to introducing a double dilaton model and large-$N_c$ corrections -- allow us to relate the existence of an infrared fixed point in the coupling constant with a smooth matching to pQCD well above 2 GeV. This is done through a model with two fit parameters and one matching point. The proposed dilaton model yields linear Regge trajectories and decay constants for scalar, vector, and tensor meson families similar to their experimental counterparts. We finally study neutral and charged pion form factors to show an application of the running coupling constant obtained.

   hep-phJ.Subatomic Part.Cosmol.(2026)·0 citations
10. 10*

    Testing the three massive neutrino paradigm: Constraints on Neutrino Properties and Interactions from Recent Experimental Data

    João Paulo Pinheiro🇪🇸

    Neutrino physics offers unique insights into phenomena beyond the Standard Model (BSM). This thesis presents phenomenological investigations organized around three pillars: consolidation of the three-flavor oscillation paradigm, exploration of new physics viability, and precise determination of solar neutrino fluxes. The theoretical framework introduces massive neutrinos, leptonic mixing, and flavor transitions, followed by experimental results emphasizing Borexino and NOvA data analyses. The first pillar establishes the three-flavor framework through global analysis of solar, atmospheric, reactor, and accelerator data, providing updated determinations of mixing angles (${\theta }_{12}$, ${\theta }_{13}$, ${\theta }_{23}$) and mass-squared differences ($\Delta m_{21}^2$, $\Delta m_{31}^2$), while quantifying ambiguities in mass ordering and ${\theta }_{23}$ octant. The second pillar investigates Non-Standard Interactions (NSI) with electrons and quarks, combining Borexino data with COHERENT's CE$\nu$NS measurements to establish bounds on propagation and detection couplings, excluding viable NSI parameter regions including potential LMA-D solutions. The third pillar advances solar neutrino physics through precision flux determinations, integrating pp-chain and CNO-cycle measurements. Results show preference for high-metallicity Standard Solar Models and incompatibility between $3+1$ mixing parameters favored by Gallium experiments and solar observations. This synthesis guides future experiments toward resolving mass ordering, CP violation, and dark sector interactions.

    hep-phastro-ph.SRhep-ex1 citation
11. 11*

    Central exclusive production of $\eta$ and ${\eta }^{\prime }$ mesons in diffractive proton-proton collisions at the LHC and the nature of the pomeron

    Piotr Lebiedowicz🇵🇱 · Otto Nachtmann🇩🇪 · Antoni Szczurek🇵🇱

    Central exclusive production (CEP) of $\eta$ and ${\eta }^{\prime }$ mesons in proton-proton collisions at high-energies is discussed. At the LHC the main mechanism for the production of these mesons should be double-pomeron ($\mathrm{I}\mathrm{P}$-$\mathrm{I}\mathrm{P}$) exchange, that is, the fusion reactions $\mathrm{I}\mathrm{PI}\mathrm{P}\to \eta ,{\eta }^{\prime }$. We show that for a scalar pomeron these fusion reactions are not possible. In contrast, in the tensor-pomeron model CEP of $\eta$ and ${\eta }^{\prime }$ mesons via double-pomeron exchange is allowed. We discuss these reactions for the c.m. energy $\sqrt{s}=29.1$ GeV realised at the WA102 experiment and for $\sqrt{s}=13$ TeV corresponding to the LHC experiments. Cross sections and distributions are presented and discussed.

    hep-phPoS(2026)·0 citations
12. 12*

    Semileptonic decays $D_{(s)}\to {\eta }^{(\prime )}{\ell }^{+}{\nu }_{\ell }$ from QCD Light-Cone Sum Rules

    Xiao-En Huang🇨🇳 · Shan Cheng🇨🇳 · De-Liang Yao🇨🇳

    In light of recent precision measurements from BESIII, we reanalyze the $D,D_s\to {\eta }^{(\prime )}$ transition form factors using QCD light-cone sum rules, incorporating high-twist contributions and well-established next-to-leading-order QCD corrections. Our analysis confirms the chiral enhancement effect arising from twist-3 light-cone distribution amplitudes of the pseudoscalar mesons, and demonstrates a rapid convergence of the operator product expansion. The resulting high-accuracy form factors enable us to determine the optimal $\eta$-${\eta }^{\prime }$ mixing parameters from the precise experimental data for the $D,D_s\to {\eta }^{(\prime )}{\ell }^{+}{\nu }_{\ell }$ (with $\ell =e,\mu$) differential decay rates. We find that the BESIII data strongly favor a set of mixing parameters, characterized by small decay constants and a large mixing angle, in the quark flavor basis. Notably, the light-cone-sum-rule predictions for the decays $D\to {\eta }^{(\prime )}{\ell }^{+}{\nu }_{\ell }$, induced by weak $c\to d$ current, reach a precision comparable to the BESIII experimental results. Nevertheless, further refined measurements and more accurate form-factor determinations will be essential to scrutinize the potential role of gluonic components in charmed meson semileptonic decays.

    hep-phhep-exPRD(2026)·1 citation
13. 13*

    Top quark FCNC in Randall-Sundrum models: post-LHC allowed rates and searches at $e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$ colliders

    Sagar Airen🇺🇸 · Roberto Franceschini🇮🇹

    We present the sensitivity to Flavor Changing Neutral Currents (FCNC) in interactions involving the top quark at future $e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$ machines. We consider the $Ztc$ vertex as well as four-fermion contact interactions involving top and charm quarks. To incorporate limits from (HL-)LHC we consider FCNC from Randall-Sundrum models and we recast LHC searches for the resonances that at the microscopic level give rise to the FCNC effects. We determine the maximal strength of the effective FCNC couplings $Ztc$ coupling allowed by LHC. We find that the LHC currently improves on the limit set by previous machines, e.g. LEP indirect sensitivity to heavy vectors. Future improvements of direct searches at HL-LHC may reach a level equivalent to $BR(t\to cZ)\simeq 10^{-6}$. We explore the possibility to probe even smaller FCNC coupling strength using an $e^{+}{e}^{-}$ machine at center-of-mass energy suitable for a Higgs factory $E_{cm}\in$ [200,240] GeV or to probe contact interactions involving top and charm flavors at a high-energy muon collider at $E_{cm}=10$ TeV.

    hep-phhep-ex2 citations
14. 14*

    Combined constraints on dark photons from high-energy collisions, cosmology, and astrophysics

    A. W. Romero Jorge🇩🇪 · L. Sagunski🇩🇪 · Guan-Wen Yuan🇮🇹 · T. Song🇩🇪 · E. Bratkovskaya🇩🇪

    We investigate a dark sector coupled to the Standard Model (SM) through a kinetically mixed dark photon $U$ associated with a new $U(1{)}^{\prime }$ gauge symmetry. Kinetic mixing $\epsilon$ induces an effective coupling to the electromagnetic current, while $U$ interacts with stable dark matter (DM) $\chi$ via a dark gauge coupling $g_{\chi }$. Our analysis is based on the parton-hadron-string dynamics (PHSD) transport approach, extended to include dark photon production and decay into dileptons ($U\to e^{+}{e}^{-}$). In PHSD, dark photons are produced in high-energy collisions through Dalitz decays of light mesons (${\pi }^0,\eta ,{\eta }^{\prime },\omega$), Delta-resonances ($\Delta \to NU$), direct vector meson decays ($\rho ,\omega ,\varphi \to U$), kaon decays, and $q\bar{q}\to U$ annihilation. Building on previous PHSD benchmarks against dilepton data, we extract upper limits on ${\epsilon }^2(m_U,m_{\chi },{\alpha }_{\chi })$ in both the visible regime ($m_U<2m_{\chi }$), where $U\to e^{+}{e}^{-}$ dominates, and the invisible regime ($m_U>2m_{\chi }$), where $U\to \chi \bar{\chi }$ is kinematically open. Cosmological and astrophysical constraints are incorporated in two complementary ways. First, we compute the velocity-dependent self-interaction cross section $\sigma /m_{\chi }$ for Yukawa-mediated SIDM and confront it with bounds from dwarf galaxies, galaxy groups, and clusters. Second, we determine thermal relic target curves by computing the relic abundance and requiring ${\Omega }_{\mathrm{DM}}{h}^2\simeq 0.12$, consistent with \textit{Planck} measurements of the cosmic microwave background. Combining PHSD limits on ${\epsilon }^2$ with relic density and self-interaction requirements, we exclude regions of the $(m_{\chi },m_U)$ plane for each DM realization (Dirac, Majorana, or complex scalar) and identify benchmark scenarios in which heavy-ion, cosmological, and astrophysical constraints are simultaneously satisfied.

    hep-phastro-ph.COnucl-thPRD(2026)·3 citations
15. 15*

    The Hadron-Parton Bridge, From the QCD Vacuum to Partons

    Edward Shuryak🇺🇸 · Ismail Zahed🇺🇸

    Quantum Chromodynamics (QCD) exhibits complementary descriptions of hadrons: a rest-frame picture based on confinement, chiral symmetry breaking and interquark forces, and a high-energy light-front picture expressed through parton distributions (PDFs,TMDs,GPDs) and form factors. This review develops a unified framework that connects these two domains. It is based mostly on multiple studies by the authors in the past few years. Using the Instanton Liquid Model (ILM) to capture essential nonperturbative features of the QCD vacuum, we derive effective interactions for mesons, baryons, and multiquark states, construct their wave functions in hyperspherical coordinates, and boost them to the light front. The resulting light-front Hamiltonians, incorporating both perturbative and instanton-induced dynamics in the Wilsonian spirit, provide realistic nonperturbative inputs for computing PDFs, DAs, GPDs, quasi-distributions, and gravitational form factors at a well-defined low scale. The connection to perturbative QCD is then established by matching gradient-flow-renormalized operators and LF wave functions to the standard $\overline{\mathrm{MS}}$ scheme. Perturbative DGLAP and ERBL evolution then connects these predictions to experimentally accessible regimes. % This approach is applied to quarkonia, glueballs, light mesons, baryons, tetraquarks, pentaquarks, and higher multiquark hadrons, yielding consistent descriptions of both their spectra and partonic structure. Special emphasis is placed on the energy-momentum tensor and the mechanical properties of hadrons, which emerge naturally from the same dynamical ingredients. Overall, the framework demonstrates a clear continuity between hadronic spectroscopy and partonic observables, offering a coherent multiscale picture of hadron structure rooted in the underlying dynamics of QCD.

    hep-ph9 citations
16. 16*

    Chemical evolution of antimatter domains in early Universe

    A.I.Dembitskaia · Stephane Weiss · M. Yu. Khlopov🇫🇷 · M.A.Krasnov

    According to modern physics, our Universe is baryon-asymmetric. That phenomenon can not be described in the frameworks of the Standard Model of particle physics. Globally, the Universe consists of baryon matter. However, some scenarios can lead to the existence of local antimatter domains. In the research, the chemical evolution of such an isolated antimatter domain, surrounded by baryonic matter, is studied. The size of the domain is estimated according to the conditions of its survival in baryon surrounding, and the process of annihilation at its border is taken into account.

    hep-phastro-ph.CO0 citations
17. 17*

    Reassessing CP Violation in the C2HDM with Machine Learning

    Rafael Boto🇩🇪 · Karim Elyaouti🇩🇪 · Duarte Fontes🇩🇪 · Maria Gonçalves🇩🇪 · Margarete Mühlleitner🇩🇪 · Jorge C. Romão🇵🇹 · Rui Santos🇵🇹 · João P. Silva🇵🇹

    We provide a study of the parameter space of the complex 2-Higgs Doublet Model (C2HDM), focusing on signs of large CP-violating couplings of the 125 GeV Higgs boson with the fermions. The study is performed utilizing Machine Learning (ML) techniques developed recently for parameter space exploration, including an Evolutionary Strategy Algorithm and Novelty Reward. We give particular attention to the electron electric dipole moment (eEDM). We confirm that the recently found kite diagrams are crucial for the outcome of the analysis. Moreover, their use also mitigates the dependence of the results on the scale and scheme choice of the masses in the loop diagrams. We furthermore point out that, already at the current level of experimental precision, the Barr-Zee diagrams with charm quark loops must be taken into account. The combined use of kite diagrams and ML techniques allows for the resurrection of large fermion CP-odd couplings for Type-II and Flipped C2HDM when the 125 GeV Higgs coincides with the second lightest neutral scalar. This arises due to cancellations, typically of the per-mil order, which, moreover, will still be possible for a foreseeable eEDM precision down to $10^{-33}$ e.cm. For these cases, the constraints on the CP-odd couplings arises from the precision LHC measurements.

    hep-ph4 citations
18. 18*

    Bhabha scattering at future colliders with BHLUMI/BHWIDE

    Wiesław Płaczek (1)🇵🇱 · Maciej Skrzypek (2)🇵🇱 · Bennie F. L. Ward (3)🇺🇸 · Scott A. Yost (4) ((1) Jagiellonian University, Krakow, Poland, (2) Institute of Nuclear Physics, Polish Academy of Sciences, Krakow, Poland, (3) Baylor University, Waco, USA, (4) The Citadel, Charleston, USA)🇺🇸

    In this paper, we briefly present the Monte Carlo event generators BHLUMI and BHWIDE for small and large angle Bhabha scattering, respectively, and discuss possible ways of their improvements in order to satisfy precision needs of future electron-positron colliders.

    hep-phActa Phys.Polon.Supp.(2026)·3 citations
19. 19*

    Single-wave solutions of the neutrino fast flavor system. Part I. Mechanical properties

    Damiano F. G. Fiorillo🇩🇪 · Georg G. Raffelt🇩🇪

    A dense neutrino plasma can exhibit collective flavor evolution caused by neutrino--neutrino refraction. Recently, a new class of exact nonlinear inhomogeneous solutions was discovered: single-wave (SW) solutions of the fast flavor system. The key property is that the flavor occupation numbers remain homogeneous, whereas the field of flavor coherence varies spatially with a single wave vector. The equations of motion for this structure resemble those of a collection of classical spins, in analogy with the homogeneous slow and fast flavor cases. In contrast, the SW system is not integrable (it does not possess Gaudin invariants) so that, while two-beam pendulum solutions are inevitable, they do not extend to a multi-angle system. We develop a taxonomy of all known nonlinear collective flavor solutions, explaining the overlap between categories and their differences.

    hep-phastro-ph.COastro-ph.HEJHEP(2026)·4 citations
20. 20*

    Exploring Quantumness at Long-Baseline Neutrino Experiments

    Murshed Alam🇺🇸 · Vedran Brdar🇺🇸 · Dibya S. Chattopadhyay🇺🇸

    Violations of classicality can be probed through measurements performed on a system at different times, as proposed by Leggett and Garg. Specifically, violations of Leggett-Garg inequalities suggest the presence of quantum effects in macroscopic systems. Long-baseline neutrino experiments provide some of the longest available propagation distances over which such tests can be performed. Previous studies of Leggett-Garg tests in the neutrino sector have largely focused on showing that the oscillation probabilities can violate classical bounds for certain parameter choices. In this work, we develop a more complete and data-driven framework that treats both the distributions representing the classical and quantum behavior, as well as the experimental uncertainties. We consider MINOS, T2K, NOvA, as well as the upcoming DUNE, and present the respective statistical significance for distinguishing quantum behavior from classical scenarios at these long-baseline neutrino experiments. Among them, we find that T2K yields the most significant violation of classicality, at the level of $\sim 14\sigma$, with NOvA and projections for DUNE also resulting in a significance of more than $5\sigma$.

    hep-phhep-exquant-phJHEP(2026)·5 citations
21. 21*

    Differentiable quantum-trajectory simulation of Lindblad dynamics for QGP transport-coefficient inference

    Lukas Heinrich🇩🇪 · Tom Magorsch🇩🇪

    We study parameter estimation for the transport coefficients of the quark-gluon plasma by differentiating open-quantum-system-based Monte Carlo simulations of quarkonium suppression. The underlying simulator requires solving a Lindblad equation in a large Hilbert space, which makes parameter estimation computationally expensive. We approach the problem using gradient-based optimization. Specifically, we apply the score-function gradient estimator to differentiate through discrete jump sampling in the Monte Carlo wave-function algorithm used to solve the Lindblad equation. The resulting stochastic gradient estimator exhibits sufficiently low variance and can still be estimated in an embarrassingly parallel manner, enabling efficient scaling of the simulations. We implement this gradient estimator in the existing open-source quarkonium suppression code QTraj. To demonstrate its utility for parameter estimation, we infer the two transport coefficients $\hat{\kappa }$ and $\hat{\gamma }$ using gradient-based optimization on synthetic nuclear modification factor data.

    ↳ physics.comp-phhep-exhep-phnucl-ex+10 citations
22. 22*

    Amplifying the Cosmological Collider with Ghost Spectators

    Matheus Curado Ferreira🇧🇷 · F. T. Falciano🇧🇷 · Guilherme L. Pimentel🇮🇹

    Ghost inflation is a well-known framework in which cosmological fluctuations can generate enhanced primordial non-Gaussianity, typically of the equilateral type. In its original form, however, it is in tension with current observational constraints. Here we instead consider a setup in which a standard inflaton drives the background evolution, while excitations of a ghost condensate act as spectator fields that interact with the inflaton. This proposal fits naturally within the cosmological collider program: the exchanged particle has a modified dispersion relation, $\omega \propto k^2$. We show that this ghost-inspired dynamics weakens the usual Boltzmann suppression, similarly to models with a very small effective sound speed, yielding an enhanced bispectrum signal relative to standard cosmological collider scenarios. At the same time, the horizon-crossing scale remains a free parameter of the theory. As a result, the model shares features of both the de Sitter bootstrap and boostless frameworks. Finally, we derive the differential equations governing cosmological correlators in the ghost-collider setup. Their structure reflects the quadratic momentum dependence of the dispersion relation and distinguishes this scenario from conventional relativistic cases.

    ↳ hep-thgr-qchep-phJCAP(2026)·4 citations
23. 23*

    Thermodynamics of ideal spin fluids and pseudo-gauge ambiguity

    Jay Armas🇳🇱 · Akash Jain🇬🇧

    Conserved currents of relativistic spin fluids derived from microscopic models are known to violate local thermodynamic relations. We present a systematic analysis of pseudo-gauge improvements in ideal spin hydrodynamics and identify a family of pseudo-gauges where standard thermodynamic relations are satisfied. We quantify pseudo-gauge ambiguities in the spin equation of state and derive universal thermodynamic relations that apply to conserved currents in any pseudo-gauge. As an application, we extract the thermodynamic variables and equations of state for free Dirac fermions and scalar fields.

    ↳ hep-thhep-phnucl-th8 citations
24. 24*

    Benchmarking neutrino-nucleus quasielastic scattering model predictions against a missing energy profile obtained using a monoenergetic neutrino beam

    Jake McKean🇬🇧 · Laura Munteanu🇨🇭 · Seisho Abe🇯🇵

    We examine three exclusive nuclear ground state shell models implemented in the NEUT neutrino event generator and benchmark them against the recent JSNS${}^2$ measurement of missing energy using a monoenergetic neutrino source. The nature of the measurement allows a detailed investigation of nuclear ground-state modeling using a neutrino source, and gives access to a direct measurement of the neutron spectral function in a ${}^{12}$C nucleus. The NEUT intranuclear cascade and nuclear deexcitation \textsc{NucDeEx} are used to simulate inelastic final-state interactions and nuclear deexcitations respectively. We find that the spectral function (SF) models perform better than relativistic mean field models in modeling both the ground state and the tail of the missing energy distribution when the NEUT cascade and nuclear excitation channels are turned on. We also find that taking into account the missing energy threshold for single nucleon knockout interactions results in all nuclear models being accepted based on the obtained $p$-values.

    ↳ hep-exhep-phnucl-thPRD(2026)·3 citations
25. 25*

    $H$ dibaryon and its cousins from SU(6)-constrained baryon-baryon interaction

    Tao-Ran Hu🇨🇳 · Feng-Kun Guo🇨🇳

    We constrain the $S$-wave baryon-baryon interaction using SU(6) symmetry within a nonrelativistic effective field theory. The most general leading-order Lagrangian contains two independent parameters, which we determine using physical $NN$ and lattice QCD $\Omega \Omega$ scattering lengths. This framework allows for parameter-free predictions in the strangeness $S=-2$ sector relevant to the $H$ dibaryon. Solving the coupled-channel scattering problem, we identify two bound states below the $\Lambda \Lambda$ threshold, one deeply bound and one shallow, along with resonances near the $\Sigma \Sigma$ and ${\Sigma }^{\ast }{\Sigma }^{\ast }$ thresholds. We demonstrate that these poles result in distinct enhancements in $\Lambda \Lambda$ invariant mass distributions, suggesting that the $H$ dibaryon exists as a multichannel bound state and providing clear signatures for experimental verification.

    ↳ nucl-thhep-exhep-lathep-ph+12 citations
26. 26*

    Gravitational form factors of the proton in the improved holographic QCD model

    Antti Hippeläinen🇫🇮 · Niko Jokela🇫🇮 · Matti Järvinen🇰🇷

    We compute the gluonic contribution to the gravitational form factors of the proton using the improved holographic QCD model, in which the proton is described in terms of bulk Dirac fermions. Model parameters are constrained using lattice and phenomenological input, allowing us to obtain estimates for the gravitational form factors and to compare them with results from other approaches. The resulting gluonic contribution to the $\mathcal{D}(t)$ form factor is found to exhibit an infrared pole in our framework. Using the extracted form factors, we analyze mechanical properties of the proton, including pressure and shear distributions. We obtain estimates of ${\rho }_{\text{mech}}=0.95$ fm and ${\rho }_{\text{mass}}=0.61$ fm for the mechanical and the mass radii of the proton, respectively, which are similar to other nonperturbative studies.

    ↳ hep-thhep-ph4 citations
27. 27*

    Shear and bulk viscosities of the gluon plasma across the transition temperature from lattice QCD

    Heng-Tong Ding🇨🇳 · Hai-Tao Shu🇨🇳 · Cheng Zhang🇨🇳

    We investigate the temperature dependence of the shear viscosity ($\eta$) and bulk viscosity ($\zeta$) of the gluon plasma using lattice QCD over the range 0.76--2.25$T_c$, extending from below the transition temperature $T_c$ across the transition region and into the deconfined phase. At each temperature, we employ three large, fine lattices, which enables controlled continuum extrapolations of the energy-momentum tensor correlators. Using gradient flow together with a recently developed blocking technique, we achieve percent-level precision for these correlators, providing strong constraints for a model-based spectral analysis. Since the inversion to real-time information is intrinsically ill posed, we extract viscosities by fitting spectral functions whose ultraviolet behavior is matched to the best available perturbative result, while the infrared region is described by a Lorentzian transport peak. The dominant modeling uncertainty associated with the transport peak width is bracketed by varying it over a physically motivated range set by thermal scales. We find that the shear-viscosity-to-entropy-density ratio, $\eta /s$, exhibits a minimum near the transition temperature $T_c$ and increases for $T>T_c$, whereas the bulk-viscosity-to-entropy-density ratio, $\zeta /s$, decreases monotonically over the entire temperature range studied.

    ↳ hep-lathep-phnucl-thPRD(2026)·3 citations
28. 28*

    Five-point partial waves, splitting constraints and hidden zeros

    Arnab Priya Saha🇮🇳 · Aninda Sinha🇮🇳

    We introduce a partial-wave basis for the double residues of five-point tree amplitudes involving identical external scalar particles, decomposing them into exchanges of definite spin at each internal channel. We verify this basis using massive spinor-helicity building blocks and by matching the resulting partial-wave coefficients against the tree-level five-point Veneziano amplitude at fixed mass levels. As an application, we express five-point splitting constraints -- the reduction of the five-point amplitude to products of four-point amplitudes on special kinematic loci -- as linear relations among the five-point partial-wave coefficients. At low mass levels these constraints, together with spin truncation, fix the full five-point partial-wave data in terms of the four-point coefficients and imply simple compatibility conditions; remarkably, imposing two independent splitting loci also forces the residue to vanish on their intersection, making the associated hidden zero manifest in partial-wave space. We also show that once both channels allow spin-2 exchange a genuine kernel can remain, indicating the need for additional higher-point input to achieve complete rigidity.

    ↳ hep-thhep-phJHEP(2026)·6 citations
29. 29*

    DAMSA Experiment Conceptual Design White Paper

    Prithak Bhattarai🇺🇸 · Andrew Brandt🇺🇸 · Alan Bross🇺🇸 · Bradley Brown🇺🇸 · Samriddha Chakraborty🇺🇸 · Haohui Che🇺🇸 · Bhupal Dev🇺🇸 · Bhaskar Dutta🇺🇸 · Juan V. Estrada🇺🇸 · Eric Garcia🇺🇸 · Anthony Gomez🇺🇸 · Gajendra Gurung🇺🇸 and 32 other authors

    DAMSA (DArk Messenger Searches at an Accelerator) is a novel short-baseline accelerator experiment aimed at probing short-lived physics processes, including searches for evidence of a dark sector of particle physics and well-motivated Standard Model signals. Motivated by open questions in neutrino physics and the absence of conclusive evidence for conventional weakly interacting massive particles, DAMSA targets MeV-to-sub-GeV dark-sector messengers with feeble couplings that can be produced in abundance at the PIP-II LINAC. By employing an ultra-short baseline of order one meter, DAMSA is uniquely positioned to overcome the beam-dump "ceiling" that limits sensitivity to promptly decaying particles in longer-baseline experiments. The conceptual design emphasizes a beam-dump production scheme combined with a compact detector optimized for rare decays while mitigating intense neutron-induced backgrounds inherent to high-power proton beams. To validate the experimental strategy and detector technologies, the Little DAMSA Path-Finder (LDPF) proof-of-concept experiment is proposed, focusing on axion-like particles decaying to two photons and operating with 300 MeV electron beams at FAST. Successful realization of LDPF will establish the feasibility of the DAMSA approach, enabling a broad and powerful program to explore short-lived new physics and precision Standard Model processes in a previously inaccessible regime. This conceptual design document outlines the technical details of DAMSA's physics goals, the beam facility proposals, key experimental challenges and how to overcome them, and the proposed experimental staging campaigns.

    ↳ hep-exhep-ph4 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.