Fri·May 1, 2026Friday·May 1, 2026

1. 01*

   Mesogenesis through the Ephemeral Dark Decay of Beauty

   Hooman Davoudiasl🇺🇸 · Rachel Houtz🇺🇸 · Seyda Ipek🇨🇦

   Mesogenesis provides a path for generating the baryon asymmetry of the Universe, using only the CP violation furnished by the Standard Model in the decay of $B$ mesons. While this is an intriguing possibility, it is largely constrained by the data on $B$ meson branching fractions into baryons and missing energy carried into the dark sector. We point out that it is possible to make this branching fraction dominant only in the early Universe, through an ultralight scalar coupled to the dark sector and the Standard Model leptons. A scenario is examined where the thermal density of muons in the early Universe temporarily lowers the mass of a dark fermion, allowing for efficient $B$ meson decays. This `dark' decay channel is shut off later when the muon number density falls, making the scenario compatible with flavor data. Our model can be consistent with the LHC constraints on color-charged heavy bosons required to implement Mesogenesis; such states may be discovered in the future runs as their masses cannot be far above the current bounds. We also outline other possible signals, which can arise in future displaced vertex searches, long range force searches, and observations of neutron star binary mergers.

   hep-ph1 citation
2. 02*

   Rydberg states of muonic helium in quantum electrodynamics

   A. V. Eskin🇷🇺 · A. P. Martynenko🇷🇺 · F. A. Martynenko🇷🇺 · D. K. Pometko🇷🇺

   The variational method is used to study the energy levels of muonic helium $({\mu }^{-}{e}^{-}He)$ with an electron in the ground state and a muon in an excited state with principal and orbital quantum numbers $n\sim l+1\sim 14$. The variational wave functions are chosen in the Gaussian form. The matrix elements of the Hamiltonian in the nonrelativistic approximation, as well as corrections for the vacuum polarization and relativism, are calculated analytically. A series of energies of the Rydberg muon states is obtained, which can be studied experimentally.

   hep-ph0 citations
3. 03*

   Optimised Inference of Quantum Phenomena in High-Energy Collider Experiments

   Hai-Chau Nguyen🇩🇪 · Gilberto Tetlalmatzi-Xolocotzi🇩🇪 · Carmen Diez Pardos🇩🇪 · Otfried Gühne🇩🇪 · Matthias Kleinmann🇩🇪

   Entanglement, a fundamental phenomenon of quantum theory, has recently been observed in processes in high-energy physics. This opens new avenues for probing quantum effects in relativistic regimes, but also poses conceptual and technical challenges. We develop a general framework based on shadow tomography techniques for characterising spin-spin correlations in collider experiments. This improves the analysis of spin-spin entanglement, where relativistic motion couples spin and momentum and the momenta of the investigated particles are not under experimental control. As a proof of concept we illustrate the application of our formalism to top quark pair production at the Large Hadron Collider at CERN. The framework, however, is general and flexible and can be readily applied to more complex final states and systems with more particles.

   hep-phhep-exquant-ph2 citations
4. 04*

   Planar master integrals for two-loop NLO electroweak light-fermion contributions to $gg\to ZH$

   Shu-Xiang Li🇨🇳 · Ren-You Zhang🇨🇳 · Xiao-Feng Wang🇨🇳 · Pan-Feng Li🇨🇳 · Xiang-Jie Wei🇨🇳 · Yi Wang🇨🇳 · Yi Jiang🇨🇳 · Qing-hai Wang🇨🇳

   For the two-loop next-to-leading-order electroweak (NLO EW) corrections to $gg\to ZH$, the light-fermion contributions can be classified into eight distinct topologies. Using the canonical differential-equations method, we perform an analytic computation of the master integrals (MIs) associated with the four planar topologies. Canonical bases are constructed using the Magnus-expansion method, and the resulting alphabets consist of algebraic symbol letters involving nontrivial radicals. We develop a systematic framework for identifying the radical structures of the canonical MIs, enabling their organization into suitable subsystems and, whenever possible, their representation in terms of Goncharov polylogarithms (GPLs) up to $\mathcal{O}({ϵ}^4)$. Only a few MIs at $\mathcal{O}({ϵ}^3)$ and $\mathcal{O}({ϵ}^4)$ are instead represented as one-fold integrals over GPLs, due to the presence of nested square roots that obstruct the simultaneous rationalization of all radicals.

   hep-ph2 citations
5. 05*

   Electroweak Baryogenesis from Collapsing Domain Walls

   Yang Bai🇺🇸 · Kun-Feng Lyu🇺🇸 · Yue Zhao🇨🇳

   We propose a novel mechanism for electroweak baryogenesis in which collapsing domain walls formed by an axion-like field replace the bubble walls in a strong first-order electroweak phase transition. The axion-like particle coupling to the Higgs mass term allows domain walls to separate regions with distinct electroweak phases, while the electroweak crossover induces a potential-energy bias that triggers their collapse. The directed wall motion, through the axion-like particle coupling to the electroweak topological term, acts as an effective baryon chemical potential and generates an asymmetry via electroweak sphaleron processes. We show that the observed baryon asymmetry can be obtained from either late-time entropy injection or sphaleron suppression in a weakly broken electroweak domain. The wall collapse also produces a stochastic gravitational-wave background with features distinct from standard electroweak-scale first-order-transition spectra.

   hep-ph3 citations
6. 06*

   Constraints on a Light Singlet Scalar from Combined Exotic Higgs Decays

   F. Azari🇮🇷 · M. Haghighat🇮🇷

   We investigate the phenomenology of the Standard Model extended by a real gauge-singlet scalar field, focusing on exotic Higgs decay channels. For a light scalar mass in the range \(0 < m_{\phi} < 40\) GeV, the Higgs boson can decay to both two and three scalar final states. We derive analytical expressions for these decay rates and impose a global constraint on the model parameters by requiring that their sum does not exceed the total Standard Model Higgs boson decay width. This requirement translates into a fourth-order inequality with respect to the singlet vacuum expectation value, \(v_{\phi}\). We demonstrate that satisfying this inequality imposes an upper bound of \(\cos \theta < 0.12 - 0.13\) across the entire mass range, providing a complementary constraint to existing direct search limits. Utilizing stronger independent constraints on the mixing (e.g., \(\cos \theta < 0.1\)), we then predict upper bounds on the individual exotic decay rates as a function of \(m_{\phi}\) as \(\Gamma_{h \rightarrow \phi \phi} < 0.06\) MeV and \(\Gamma_{h \rightarrow \phi \phi \phi} < 5 \times 10^{- 6}\) MeV, respectively.

   hep-phhep-thPhys.Scripta(2026)·0 citations
7. 07*

   Low mass scalars at $e^{+}{e}^{-}$ colliders

   Tania Robens🇭🇷

   I briefly discuss the search for low mass scalars at Higgs factories as well as available models that render such scalars feasible, where I focus on new developments since the review presented in arXiv:2205.09687 (see also arXiv:2504.11969 for a recent update).

   hep-phEur.Phys.J.Plus(2026)·2 citations
8. 08*

   A theoretical account of tiny multi-Higgs vacuum expectation values from non-invertible symmetry

   Takaaki Nomura🇨🇳 · Hiroshi Okada🇨🇳

   We propose a novel mechanism to explain the naturally small vacuum expectation values (VEVs) of exotic multi-Higgs fields by employing non-invertible symmetries. Specifically, we introduce an $SU(2{)}_L$ quartet $H_4$ and a quintet $H_5$ within the framework of the minimal Fibonacci fusion rule (FFR). This non-invertible symmetry strictly forbids the generation of tree-level VEVs for these exotic fields. However, once the symmetry is broken, these VEVs are generated radiatively at the one-loop level.This mechanism is highly minimal, as it requires no additional loop-inducing particles. We demonstrate that for various benchmark energy scales, the resulting VEVs are naturally suppressed to the order of $10^{-3}-10^{-2}$ GeV, satisfying experimental constraints from the $\rho$ parameter. Finally, we illustrate the phenomenological viability of this setup by applying it to three representative neutrino mass models: the type-III seesaw, the Dirac neutrino seesaw, and the inverse seesaw mechanisms.

   hep-ph1 citation
9. 09*

   Dark photon search status in $\tau -c$ energy region

   Zhijun Li🇨🇳 · Zhengyun You🇨🇳

   The dark photon plays an important role as a portal to dark matter and has been extensively studied on both experimental and theoretical frontiers. However, as no signals have been observed, the whereabouts of the dark photon remain a long-standing open question. With the proposal of a future $\tau -c$ facility, this proceeding reviews and summarizes the current experimental status of the dark photon in the $\tau -c$ energy region, which is expected to provide a reference for future searches. The experimental status indicates that the dark photon in the $\tau -c$ energy region remains highly promising, highlighting the requirement for larger data samples or new methods to further investigate the benchmarks related to the observed cosmic dark matter.

   hep-phhep-ex0 citations
10. 10*

    Theoretical and Experimental Constraints in the $\mu$--$\tau$ Four-Lepton Sector of the SMEFT: implications to neutrino self interactions

    Aadarsh Singh🇮🇳 · G. D'Ambrosio🇮🇹 · Sudhir K. Vempati🇮🇳

    We study the dimension-six SMEFT four-lepton operators in the $\mu$--$\tau$ sector. These operators control both charged-lepton scattering and neutrino self-interactions, the latter being weakly constrained by direct laboratory probes despite their importance for cosmological tensions. We compare three classes of constraints on the Warsaw-basis coefficients $[C_{\ell \ell }{]}_{2222}$, $[C_{\ell \ell }{]}_{2233}$, and $[C_{\ell \ell }{]}_{2332}$. We use perturbative unitarity from $2\to 2$ partial-wave analysis, spin-summing positivity sum rules, and the experimental bounds from NA64$\mu$ and the global fit~\cite{Falkowski:2017pss}. We find that the global fit dominates for $[C_{\ell \ell }{]}_{2222}$ and $[C_{\ell \ell }{]}_{2332}$, while NA64$\mu$ provides the leading bound on $[C_{\ell \ell }{]}_{2233}$, with the unitarity line for this direction entering the range of collider energies near $200\mathrm{GeV}$. Renormalization-group running between $1\mathrm{GeV}$ and $30\mathrm{TeV}$ modifies these coefficients by up to $10\%$. Translating these bounds onto the effective four-neutrino coupling $G_{\mathrm{eff}}$, we find values many orders of magnitude smaller than the strongly interacting regime motivated by the Hubble tension; this excludes heavy-mediator UV completions of strong ${\nu }_{\mu }$--${\nu }_{\mu }$ and ${\nu }_{\mu }$--${\nu }_{\tau }$ self-interactions within the validity of the dimension-six SMEFT and in the absence of tuned cancellations between operators, while leaving the cosmologically motivated light-mediator scenarios unconstrained by this analysis. Finally, we comment on the bounds these coefficients place on a leptophilic $L_{\mu }-L_{\tau }$ $Z^{\prime }$ UV completion. Our SMEFT-based current and projected NA64$\mu$ bounds reproduce the dedicated $Z^{\prime }$ analyses already available in the literature.

    hep-phastro-ph.COhep-exPRD(2026)·1 citation
11. 11*

    Strangeness enhancement in pp collisions from string closepacking in Pythia 8.3

    Javira Altmann · Lorenzo Bernardinis🇮🇹 · Peter Skands🇦🇺 · Valentina Zaccolo🇮🇹

    Measurements at LHC show an increased production of strange hadrons with charged multiplicity in pp collisions, which is not described by the Lund String Model (with the Monash tune) implemented in PYTHIA. This work investigates string closepacking, a mechanism invoked during hadronization where overlapping strings create a background field that increases the effective string tension. This reduces strangeness suppression, effectively enhancing production. The model also incorporates an option for "popcorn destructive interference", which suppresses baryon production, to address the non-strange $p/\pi$ ratio, utilizing color algebra arguments; and an option for "strange junctions", which enhances strangeness specifically within the baryon sector. The Trieste tunes of this model to LHC data are presented. The closepacking model is in qualitative agreement with many of the salient particle ratios, although the ${\Xi }_c/D$ ratio and the shape of $p_{\perp }$ spectra remain challenging to account for. Overall, the closepacking model with the Trieste tunes provides a competitive description of enhanced strangeness production in pp collisions, improving upon existing PYTHIA models while avoiding excessive proton yields.

    hep-ph0 citations
12. 12*

    Stochastic Axion Mixing: A General Mechanism Beyond Decay Constant Constraints

    Hai-Jun Li🇨🇳

    We propose a novel and generalized mechanism, dubbed stochastic axion mixing. In a multi-axion framework, this mixing occurs naturally provided that the masses of all ultra-light axion-like particles (ALPs) are distinct and lighter than the zero-temperature mass of the QCD axion. Crucially, this mechanism is independent of the relative magnitudes of the axion decay constants. In contrast to the conventional maximal mixing scenario -- which strictly relies on specific decay constant hierarchies -- stochastic mixing represents a significantly broader formalism. Notably, maximal mixing emerges as a specific subset of stochastic mixing under restrictive conditions. This new mechanism offers profound implications for axion cosmology.

    hep-phastro-ph.CO1 citation
13. 13*

    Electromagnetic response of a relativistic drifting plasma

    Ashes Modak🇮🇳 · Anowar Shaikh🇮🇳 · Manu Kurian🇮🇳 · Binata Panda🇮🇳 · Sadhana Dash🇮🇳

    We investigate the charge transport properties of a relativistic drifting plasma using the kinetic theory within the relaxation time approximation. The collective drift induced by electromagnetic fields is described in terms of a suitably modified distribution function. The analysis is done for both constant and time dependent field configurations. For constant electromagnetic fields, we obtain the Hall drift current that arises from the transverse motion of charged particles in electric and magnetic fields. Extending the framework to time dependent electric fields, we show that their temporal variations give rise to polarization drift, which significantly alters the structure of the induced current and introduces additional components along both the conventional drift and polarization directions. We present a quantitative estimate of the Hall drift and polarization induced contributions in the quark gluon plasma and study the temperature dependence of the associated charge transport coefficients in the QCD.

    hep-phPRD(2026)·0 citations
14. 14*

    Thermal Spectra Without Detailed Balance

    Xingjian Lu🇨🇳 · Shuzhe Shi🇨🇳

    A thermal spectrum is often taken as a signature that the emitted probe has reached detailed balance with the surrounding medium. We show that this interpretation is not generally valid by studying how the microscopic emission kernel determines the macroscopic spectrum. In $3+1$ dimensions, a simple thermal spectrum can be generated without probe thermalization when the relevant kernel belongs to a thermally degenerate class. A representative case is realized when the differential cross section depends on the scattering angle but carries no additional dependence on the Mandelstam variable $s$, as in low-energy Thomson scattering. Our results provide a kernel-based criterion for distinguishing genuine probe--medium exchange equilibrium from thermal spectra produced by the structure of the emission kernel itself.

    hep-phhep-thnucl-th1 citation
15. 15*

    $b\to c$ semileptonic sum rule: orbitally excited hadrons

    Motoi Endo🇯🇵 · Syuhei Iguro🇯🇵 · Satoshi Mishima🇯🇵

    We study semileptonic sum rules for $b\to c\tau \overline{\nu }$ transitions involving orbitally excited charm hadrons. Starting from the amplitude-level relation implied by the heavy quark symmetry, we construct sum rules relating these decays. We then examine deviations from the small-velocity limit. Our numerical analysis shows that the deviations generally increase once excited hadrons are involved, with tensor contributions often inducing sizable effects. At present, however, the relevant form factors are not yet sufficiently constrained. Further improvements in the hadronic inputs are essential for these sum rules to yield robust predictions for the corresponding lepton-universality ratios.

    hep-phhep-ex3 citations
16. 16*

    The status of theory in the electroweak sector: Radiative corrections, salient features, approximations

    Stefan Dittmaier🇩🇪

    Electroweak radiative corrections form a crucial ingredient in modern precision calculations for particle processes at high-energy colliders such as the Large Hadron Collider. The salient features of electroweak corrections as well as currently used techniques and concepts for their calculation are reviewed. Recent progress in this enterprise is illustrated in a discussion of electroweak multi-gauge-boson production processes: massive di-boson production, vector-boson scattering, and massive tri-boson production.

    hep-ph2 citations
17. 17*

    Semi-analytic bounds on axion-like-particle supernovae emission

    Ana Luisa Foguel🇧🇷 · Eduardo S. Fraga🇧🇷

    Core-collapse supernovae provide natural laboratories for the production of new light particles. In particular, axion-like particles (ALPs) can be constrained via SN1987A cooling arguments. However, significant astrophysical and nuclear uncertainties imply that such bounds may vary strongly depending on modeling choices, even when expensive simulations are employed. In this context, semi-analytic methods offer a simple and fast alternative for deriving new-physics constraints. Building on a previous semi-analytic framework, in which proto-neutron star (PNS) observables are expressed in terms of six global PNS parameters, we include a finite ALP mass in the calculation and derive bounds in the axion-nucleon coupling versus mass plane. The obtained bounds are in good agreement with previous results from numerical simulations, demonstrating the robustness of the method. We also illustrate the sensitivity of the bounds to different PNS parameter calibrations, nuclear effects and cooling exclusion criteria.

    hep-phastro-ph.HE0 citations
18. 18*

    Phenomenology of $f_2(1270)$ photoproduction at energies measured with the CLAS facility

    K. E. S. Mendes🇧🇷 · D. T da Silva🇧🇷 · M. L. L. da Silva🇧🇷

    We investigate the photoproduction of the tensor meson $f_2(1270)$ on the proton within a Regge-based framework, focusing on the reaction $\gamma p\to p{f}_2(1270)$ in the few-GeV energy region. The production mechanism is modeled through the exchange of vector-meson Regge trajectories in the $t$-channel, including both $\rho$ and $\omega$ exchanges with phenomenologically motivated couplings. The scattering amplitudes are derived using Reggeized propagators and effective hadronic vertices, allowing for the calculation of differential cross sections in the narrow-width approximation. We further extend the analysis to the ${\pi }^{+}{\pi }^{-}$ invariant mass distribution by incorporating a relativistic Breit--Wigner description of the $f_2(1270)$ resonance.

    hep-phhep-ex0 citations
19. 19*

    New gravitational-wave templates for metastable cosmic strings: Loop breaking versus network collapse

    Doa Hashemi Asl🇩🇪 · Kai Schmitz🇩🇪

    Metastable cosmic strings are a common prediction of grand unified theories and act as a source of a gravitational-wave background (GWB) that can explain the 2023 pulsar timing array (PTA) signal. In this paper, we revisit the GWB signal from metastable strings, emphasizing the need to carefully distinguish between two different time scales: (i) t_LB, the time scale of loop breaking because of spontaneous monopole nucleation on closed string loops, and (ii) t_NC, the time scale of network collapse when string segments attached to monopoles begin to enter the Hubble horizon. We discuss under which conditions these two time scales are similar or far apart from each other and illustrate the resulting consequences for the GWB signal. In doing so, we generalize the description of the GWB signal from metastable strings to a three-parameter model in terms of the string tension G\mu and the time scales t_LB and t_NC, which allows us to unify the modeling of standard metastable strings with what is known as quasi-stable strings. In the limit of a large t_LB/t_NC ratio, we, moreover, derive a compact analytical expression for the predicted GWB spectrum in excellent agreement with numerical results in the literature. We thus conclude that our new templates for the GWB spectrum from metastable strings can be readily used in the analysis of future PTA data sets.

    hep-phastro-ph.COgr-qcPRD(2026)·5 citations
20. 20*

    Simplified approach to extracting nucleon transversity in collinear factorization using near-side energy-energy correlators

    Zhong-Bo Kang🇺🇸 · Andreas Metz🇺🇸 · Daniel Pitonyak🇺🇸 · Congyue Zhang🇺🇸

    We develop a novel strategy for accessing the transversity parton distribution function (PDF) of the nucleon within collinear factorization using near-side energy-energy correlators in the dihadron fragmentation framework. We show how this removes the complications of previous approaches that must model either intrinsic parton transverse momentum or resonances in the invariant mass distribution of a final-state dihadron. We present leading-order analytical results for transverse-spin observables in semi-inclusive deep-inelastic scattering and electron-positron annihilation, highlighting their close similarity to the expressions one uses in extracting (un)polarized PDFs and (single-hadron) fragmentation functions in collinear factorization. We make predictions for kinematics relevant for existing and future facilities that demonstrate the feasibility of an energy-energy correlator program in extracting the transversity PDF.

    hep-phhep-exnucl-exnucl-th6 citations
21. 21*

    Mapping data sensitivities in global QCD analysis with linear response and influence functions

    Richard Whitehill🇺🇸

    Global QCD analyses provide the primary framework for extracting hadron structure from experimental data, yet the mechanisms by which data constrain non-perturbative functions remain difficult to interpret due to the high dimensionality and complexity of these fits. Here we develop a framework based on linear response and influence functions, which are gradient-based sensitivity measures that directly quantify how experimental information propagates to fitted quantities and observables. These quantities cleanly expose how data locally determines the central values and uncertainties of quantum correlation functions, as well as the correlations between them, providing a transparent and general framework for diagnosing information flow in inverse problems in QCD.

    hep-ph1 citation
22. 22*

    Deeply virtual pion production through two-loop order

    Wen Chen🇨🇳 · Feng Feng🇨🇳 · Yu Jia🇨🇳 · Qin-Tao Song🇨🇳 · Guang Tang🇨🇳 · Zhe-Yu Wang🇨🇳

    Deeply virtual meson production (DVMP) is among the most prominent channels to extract the nucleon's generalized parton distributions (GPDs) at $ep$ scattering facilities such as {\tt JLab} and the upcoming {\tt EIC/EicC} experiments, which plays a vital role in unravelling the three-dimensional internal structure of nucleon. In this work we calculate for the first time the next-to-next-to-leading order (NNLO) QCD radiative corrections to the DV$\pi$P processes ${\gamma }_L^{\ast }p\to {\pi }^{+}n$ and ${\gamma }_L^{\ast }p\to {\pi }^{0}p$ in the generalized Bjorken limit $Q^2\gg |t|,{\Lambda }_{\text{QCD}}^2$, accurate at the leading twist within collinear factorization framework. The impact of the two-loop QCD corrections appears to be positive and substantial, including which considerably improves the agreement between the perturbative QCD prediction and the available {\tt JLab} data. In addition to the differential longitudinal DV$\pi$P cross section, we also study the impact of the two-loop QCD corrections on the transverse single-spin asymmetries (TSSA) in some benchmark kinematics at {\tt JLab}, {\tt EIC} and {\tt EicC}.

    hep-phhep-exhep-latnucl-ex+11 citation
23. 23*

    Baryonic Bound States in the Non-Local NJL Model

    Arpan Chatterjee🇪🇪 · Stefan Groote🇪🇪

    Baryons, as three-quark bound states, require a covariant treatment in the intermediate-energy regime where perturbative QCD is no longer applicable and where nonperturbative correlations dominate. This article reformulates the content of the CERN Baltic Conference 2025 presentation on baryonic bound states in the non-local Nambu--Jona-Lasinio (NJL) model. We review how the relativistic Faddeev approach reduces the three-body quark problem to an effective quark--diquark bound-state problem, describe the scalar and axial-vector diquark channels, and show how the resulting quark--diquark Bethe--Salpeter equation can be written as an eigenvalue problem for the baryon mass. The non-local NJL framework, motivated by QCD-based nonlocal interactions and Dyson--Schwinger considerations, provides a compact description in which baryon masses and form factors are extracted from the numerical solution of coupled integral equations.

    hep-phnucl-th0 citations
24. 24*

    A Model of Annihilogenesis

    Arvind Rajaraman🇺🇸 · Alexander Stewart🇺🇸 · Tim M.P. Tait🇺🇸

    We present an explicit model of leptogenesis via annihilogenesis in which two right-handed Majorana neutrinos couple to the Standard Model lepton doublets and Higgs, and acquire a large mass shift during a strong first-order phase transition of an additional scalar singlet. As bubbles of true vacuum expand, the ${\chi }_a$ are reflected off the walls and confined to shrinking pockets of false vacuum, where the density grows and the dominant CP-violating process is the $2\to 4$ annihilation ${\chi }_1{\chi }_1\to L_1{L}_1{\Phi }^{\ast }{\Phi }^{\ast }$. Interference between tree-level $W$ and $B$ exchange and one-loop diagrams containing the heavier ${\chi }_2$ produces a CP asymmetry $ϵ$, which we evaluate numerically and find to lie in the range $|ϵ|\sim 10^{-9}$--$10^{-7}$ for $\mathcal{O}(1)$ Yukawa couplings. Electroweak sphalerons convert the resulting lepton asymmetry into a baryon asymmetry $Y_{\Delta B}$ that reproduces the observed value across a broad region of parameter space, with little sensitivity to the bubble-wall velocity or initial pocket size. The Majorana mass that controls $ϵ$ is the residual mass of ${\chi }_1$ inside the collapsing pockets rather than its post-transition value, so the usual relation between the singlet mass and the Standard Model active neutrino masses is relaxed. As a result, the upper bound on $|ϵ|$ from the largest light-neutrino mass that constrains standard thermal leptogenesis does not apply, and the lower limits on the right-handed-neutrino scale and the reheating temperature are relaxed.

    hep-ph0 citations
25. 25*

    The neutral scalars of type-II 2HDM+S under the LHC

    Cheng Li🇨🇳 · Juxiang Li🇨🇳 · Shufang Su🇺🇸 · Wei Su🇨🇳

    The 2HDM+S is a singlet extension of the Two-Higgs-Doublet Model (2HDM), which offers rich collider phenomenology. In this paper, we parametrize the 2HDM+S with the Higgs masses and mixing angles, which provide a model-independent framework to study the collider signature. Under five benchmark scenarios, we obtain the 95\% C.L. exclusion regions in the Type-II 2HDM+S parameter space by incorporating the SM-like 125~GeV Higgs precision measurements, beyond the Standard Model Higgs direct searches, $Z$-pole precision measurements and $B$-physics observables. We present the results in the Higgs boson masses vs $\tan \beta$, Higgs boson masses vs mixing angles, $\tan \beta$ vs mixing angles and doublet Higgs boson masses vs singlet Higgs boson mass parameter space. We explore the complementarity between direct and indirect Higgs searches, as well as conventional Higgs search channels and exotic Higgs search channels. Compared to the 2HDM scenarios, we find that exotic channels such as $A/H\to Z{h}_S/Z{A}_S$ can probe large part of the parameter spaces, especially for moderate $1<\tan \beta <7$ region where the conventional channels in the 2HDM cannot contribute much.

    hep-ph0 citations
26. 26*

    Pre-inflationary QCD axion stars after moduli domination

    Edward Hardy🇬🇧 · Noelia Sánchez González🇬🇧 · Henry Stubbs🇬🇧 · Lorenzo Tranchedone🇬🇧

    The growth of adiabatic density perturbations during an era of early matter domination induces $\mathcal{O}(1)$ fluctuations in pre-inflationary QCD axion dark matter across a broad, string-theory-motivated parameter space. Remarkably, at $\Lambda$CDM matter-radiation equality the scale of these perturbations coincides with the quantum Jeans scale, so they collapse to solitonic ``axion stars''. These axion stars have densities up to $10^4{\mathrm{eV}}^4$, and, including their surrounding halos, they contain as much as $50\%$ of dark matter. Direct searches for a smooth axion background can be suppressed, but transient enhancements or indirect astrophysical signals at axion masses $m_a\lesssim 10^{-5}\mathrm{eV}$ would point to a non-standard cosmological history.

    hep-phastro-ph.COhep-thPRD(2026)·2 citations
27. 27*

    Quarkonium $p_{\mathrm{T}}$ spectra in heavy--ion collisions at LHC energies within a hydrodynamic core--corona framework

    Biswarup Paul🇮🇳

    We present a systematic study of the transverse momentum ($p_{\mathrm{T}}$) spectra of charmonium (J/$\psi$, $\psi (2S)$) and bottomonium (${\rm Y}(nS)$) states in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV within an analytical relativistic hydrodynamics framework. The medium evolution is described assuming cylindrical symmetry with boost-invariant longitudinal expansion and Hubble-like transverse flow. Quarkonium spectra are evaluated using the Cooper-Frye formalism on a constant-temperature freeze-out hypersurface, supplemented by a core--corona approach to include both thermal and non-thermal contributions. The model describes the measurements from ALICE and CMS over a broad $p_{\mathrm{T}}$ range. For charmonium, both the spectra and the $\psi (2S)$/J/$\psi$ ratio are well reproduced, while deviations at high $p_{\mathrm{T}}$ for J/$\psi$ indicate additional hard production mechanisms. In the bottomonium sector, the ${\rm Y}(nS)$ spectra and their yield ratios are successfully described, consistent with the expected sequential suppression pattern. These results demonstrate that an analytical hydrodynamic approach combined with a core-corona framework provides a unified and transparent description of quarkonium production in heavy--ion collisions at LHC energies.

    ↳ nucl-thhep-phnucl-ex0 citations
28. 28*

    Primordial black hole dark matter from axion inflation

    Gabriele Franciolini🇮🇹 · Nadir Ijaz🇮🇹 · Marco Peloso🇮🇹

    We revisit the production of primordial black holes (PBHs) by a U(1) gauge field with a pseudo-scalar coupling to the inflaton. We improve upon the existing literature by working in the homogeneous backreaction regime with numerically computed gauge mode functions, adopting state-of-the-art PBH abundance calculations, and incorporating the uncertainty in the statistics of $\delta \rho$. We find that PBHs can account for all of the dark matter in the asteroidal mass range, even when the inflaton gradient energy density is highly subdominant ($10^{-4}$--$10^{-3}$ of the kinetic energy), supporting the validity of the backreaction scheme. This mechanism also unavoidably generates a stochastic gravitational wave background with an amplitude that will be measured at LISA and that will allow to indirectly discriminate between different statistics of $\delta \rho$.

    ↳ astro-ph.COhep-phhep-th5 citations
29. 29*

    Gravitational wave constraints on the Paneitz operator

    Robin Valtin🇩🇪 · Alexander Ganz🇩🇪 · Guillem Domènech🇩🇪

    The Paneitz operator is a dimension-4 conformally invariant fourth-order differential operator that has recently attracted attention for possible cancellations of the vacuum energy. We show that, in four dimensions, the Paneitz operator acting on a scalar field falls within the class of extended mimetic gravity theories. Thus, it exhibits the usual instabilities of mimetic gravity. Assuming such instabilities are cured by higher derivative terms, we derive constraints on the Paneitz operator from a modified propagation speed of gravitational waves, after including the Einstein-Hilbert action in the mimetic gravity formulation.

    ↳ gr-qcastro-ph.COhep-phEPL(2026)·0 citations
30. 30*

    A Cosmological Uncertainty Relation and Late-Universe Acceleration

    Savvas M. Koushiappas🇺🇸

    We propose that the size of the universe and its expansion rate cannot be simultaneously specified with arbitrary precision--a quantum mechanical uncertainty encoded via a deformed commutation relation for the scale factor. This deformation introduces a geometric correction to the Friedmann equation, where the resulting cosmological dynamics are governed entirely by the sign and magnitude of a single free exponent. For a positive exponent, the model predicts late-time dark energy with $w>-1$, leaving a distinct expansion history that is testable by current and next-generation large-scale structure surveys. Conversely, a sufficiently negative exponent yields a nonsingular classical bounce, resolving the big bang singularity. Notably, the model requires no exotic particles or fields and preserves a scale-invariant primordial power spectrum. Rather than operating at the Planck length, this deformation naturally manifests as a horizon-scale phenomenon set by the cosmological horizon. Within this framework, cosmic acceleration emerges as the macroscopic imprint of quantum gravity at the cosmological horizon.

    ↳ astro-ph.COgr-qchep-phhep-thPRD(2026)·0 citations
31. 31*

    Some Properties and Uses of the Species Scale

    Luis E. Ibáñez🇪🇸

    The 'Species Scale' has proved to be an important concept when studying consistent effective actions in Quantum Gravity. This is a short summary of my contribution to the Corfu Summer Institute in September 2025, in which I covered two topics, both related in different ways to the fact that the Species Scale is moduli dependent. In the first, based on work done in collaboration with C. Aoufia and A. Castellano, we show how the one-loop Wilson coefficients ${\mathcal{F}}_n^{(d)}$ multiplyiing BPS protected ${\mathcal{R}}^{2n}$ operators obey Laplace-like eigenvalue differential equations of the form ${\mathcal{D}}_{\mathcal{M}}^2{\mathcal{F}}_n^{(d)}={\eta }_d{\mathcal{F}}_n^{(d)}$. This is true both for $n=2$ with 32 and 16 SUSY generators in 10,9,8 dimensions and theories with 8 SUSY generators in 6,5,4 dimensions $(n=1)$. We argue that this fact is at the root of some Swampland conjectures put forward in the past, like bounds on the dumping rates for the tower scales and the exponential behaviour in the Swampland Distance Conjecture. For the second topic, based on work done in collaboration with G.F. Casas, we discuss the one loop potential of the no-scale moduli in GKP-like Type IIB 4d orientifolds. To compute this potential we sum both over light and heavy (tower) modes using the Species Scale as a UV cut-off. We find a generic form $V_{1-loop}\sim g^2{m}_{3/2}^2{M}_p^2(g^{i\bar{i}}({\partial }_i\Lambda )({\partial }_{\bar{i}}\Lambda ))/{\Lambda }^2$, with $\Lambda$ the Species Scale. This has minima at the $desert$ $points$ in moduli space and exponentially decreases at large moduli, with a dS hill in between. We argue that this potential may lead to the stabilisation of some or all Kahler moduli at the desert points in 4d Type IIB orientifolds of phenomenological interest.

    ↳ hep-thhep-phPoS(2026)·1 citation
32. 32*

    Chiral Symmetry and Its Restoration in QCD

    Teiji Kunihiro🇯🇵

    We first note the peculiar property of the pion as the pseudoscalar particle, which play the essential role in realizing the basic properties of the nuclear matter such as the density/energy saturations. Then, we introduce the notion of chirality using the Dirac equation, and show how chiralities are mixed in the massive Dirac field with an emphasis on the similarity with the Bogoliubov-Valatin theory of superconductivity. After noting the approximate chiral symmetry in QCD in the light quark sector, we introduce the notion of the spontaneous symmetry breaking, and the Nambu-Goldstone theorem. A remark is given on the U(1)${}_A$ anomaly and its physical consequences. Several chiral quark models of the Nambu-Jona-Lasinio type are introduced with an emphasis to the relevance to QCD, and discuss some consequences of the models. A three-flavor linear sigma model with the determinant term is examined, and discuss the origin of the mass term of the ${\eta }^{\prime }$ meson. A parity-doublet model for nucleons is introduced, and the current active effort is described to construct the equation of state of nuclear and neutron-star matter incorporating the parity-doubling in the baryon sector and the occurrence of the restoration of chiral symmetry in the QCD matter. An intuitive account is given on how the chiral condensate may be reduced on the basis of Hellmann-Feynman theorem. We describe some experiments to explore the chiral restoration in hot and/or dense medium, such as the pionic atoms, lepton-pair production in relativistic-heavy-ion collisions, an attempt to produce ${\eta }^{\prime }$-mesonic nuclei, and so on.

    ↳ nucl-thhep-exhep-phnucl-ex0 citations
33. 33*

    Hadron properties at finite temperature

    Juan M. Torres-Rincon🇪🇸 · Glòria Montaña🇪🇸

    This review provides an overview of thermal effects on hadron properties, focusing on the theoretical frameworks used to describe in-medium modifications of masses, decay widths, and spectral functions. We examine the application of finite-temperature quantum field theory -- specifically the imaginary-time formalism (ITF) -- to analyze both light- and heavy-hadron sectors. For light hadrons, we discuss the role of chiral symmetry restoration and the different definitions of thermal masses in effective field theories, like chiral perturbation theory. In the heavy-flavor sector, we review recent progress in describing open-heavy mesons and quarkonia using self-consistent unitarized approaches and nonrelativistic effective field theories. All these results are complemented by analyses of recent lattice-QCD calculations using the Euclidean formulation of QCD at finite temperature, relevant to extract screening masses and reconstructed spectral functions. Finally, we discuss the phenomenological impact of the thermal modifications on experimental observables in relativistic heavy-ion collisions, including numerical simulations, dilepton spectra, transport coefficients, and hadron femtoscopy. By combining phenomenological considerations with robust theoretical tools, this review provides a coherent picture of how thermal effects emerge in the hadronic phase and how they can be systematically studied within controlled frameworks. Ultimately, the discussion serves as a bridge between experimental observations in relativistic heavy-ion collisions and fundamental developments in finite-temperature QCD and effective field theories for hadronic systems.

    ↳ nucl-thhep-lathep-ph1 citation
34. 34*

    Topological Susceptibility and QCD at Finite Theta Angle

    Claudio Bonanno🇨🇭 · Claudio Bonati🇮🇹 · Massimo D'Elia🇮🇹

    In this chapter we provide a pedagogical introduction to the main theoretical aspects related to topology and $\theta$-dependence in Quantum Chromo-Dynamics (QCD), and to their phenomenological relevance in the Standard Model (${\eta }^{\prime }$ physics, neutron electric dipole moment) and beyond (strong CP problem and the axion solution). We then provide an overview of the main analytic predictions for $\theta$-dependence obtained using several different approaches (chiral effective theories, large-$N$ arguments, semiclassical methods) and their regimes of validity, as well as a selection of the most recent numerical results about QCD topology obtained via Monte Carlo simulations of the lattice-discretized theory.

    ↳ hep-lathep-phhep-th4 citations
35. 35*

    The DAMSA Experiment

    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/beam dump experiment aimed at probing short-lived physics processes, including searches for evidence of a dark sector of particle physics and well-motivated rare 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 a beam dump/target. By employing an ultra-short baseline, DAMSA is uniquely positioned to overcome the beam-dump "ceiling" that limits sensitivity to fast 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 DAMSA Path-Finder (DPF) proof-of-concept experiment is also proposed, focusing on axion-like particles decaying to two photons, as the benchmark physics case and operating with 8 GeV electron beams at SLAC Linac-to-ESA (LESA) facility. Successful realization of DPF 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 paper outlines the technical details of DAMSA's physics goals, key experimental challenges, and how to overcome them.

    ↳ hep-exhep-ph1 citation
36. 36*

    Towards Systematics of Calabi-Yau Landscape for String Cosmology

    George K. Leontaris🇬🇷 · Pramod Shukla🇮🇳

    In this review, we discuss the relevance and impact of studying Calabi-Yau threefolds in the context of global model building in string phenomenology. First, taking a phenomenologist-friendly approach, we review how the topologies of the various divisors and curves of the compactifying CY threefolds play a crucial role for generating the various ``suitable" classes of effective scalar potentials, within the framework of the popular moduli stabilization schemes such as KKLT and LVS. Subsequently, we discuss the impact of the specifics of the CY threefold geometries in the minimal LVS inflationary models such as fibre inflation, in particular, along the challenges such as the inflaton field-range bound. In this regard, we discuss a multi-field approach in which several fibre moduli assist to drive successful inflation having a sufficient number of efolds, without getting close to their individual Kähler cone boundaries.

    ↳ hep-thhep-ph1 citation
37. 37*

    Covariant Locally Localized Gravity and vDVZ Continuity

    Hao Geng🇺🇸 · Moritz Merz🇺🇸 · Lisa Randall🇺🇸

    The Karch-Randall braneworld concerns the physics of an AdS${}_d$ brane embedded in an ambient gravitational AdS${}_{d+1}$ spacetime. The gravitational theory induced on the AdS${}_d$ brane has a very light but massive graviton. It has been established that the zero graviton mass limit of the $d$-dimensional graviton propagator is smooth at tree-level. Furthermore, this smoothness was conjectured to persist to the quantum level. This conjecture suggests that the massive graviton on the AdS${}_d$ brane is due to spontaneous symmetry breaking, which is consistent with its holographic dual description. In this letter, we show that the zero mass limit of the partition function is a theory of a massless graviton and a decoupled massive vector. The zero mass limit is not the basic Randall-Sundrum II model, but a theory with these additional decoupled vector degrees of freedom coupled only to gravity. The proof relies on deriving the fully covariant description of the $d$-dimensional gravity theory which enables us to compute the one-loop partition function. At the end, we comment on the implications of this result to the physics of entanglement islands.

    ↳ hep-thgr-qchep-ph0 citations
38. 38*

    Probing Jet-Medium Interactions in Heavy-Ion Collisions Using Energy-Energy Correlators

    Rushil Saraswat · Aditya Prasad Dash🇺🇸 · Huan Zhong Huang🇺🇸 · Gang Wang🇨🇳 · Xin-Nian Wang🇨🇳 · Zhong Yang🇨🇳

    Energy-energy correlators (EECs) provide a sensitive probe of both perturbative and nonperturbative dynamics in relativistic heavy-ion collisions. Jet-medium interactions enhance particle multiplicity within the jet cone, which must be properly accounted for when extracting the EEC of jet shower hadrons in experiments. To address this issue, we develop an augmentation method that exploits momentum conservation between the near-side and away-side regions, using $\gamma$-jet events with 0-10\% centrality in Pb+Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV simulated with the CoLBT-hydro model. This approach yields an experimentally reconstructed EEC that shows improved agreement with the EEC of hadrons originating primarily from jet parton splittings. Comparing EECs of jets from Pb+Pb and p+p collisions with different matching conditions can be sensitive to jet medium interaction dynamics, and provide a novel means to test the scenario of jet energy loss in the QGP, followed by fragmentations outside the QGP.

    ↳ nucl-thhep-phnucl-ex0 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.