Fri·Feb 20, 2026Friday·February 20, 2026

1. 01*

   Probing Ultralight Dark Matter at the Mega-Planck Scale with the Thorium Nuclear Clock

   Jason Arakawa🇺🇸 · Jack F. Doyle🇺🇸 · Elina Fuchs🇩🇪 · Jacob S. Higgins🇺🇸 · Fiona Kirk🇩🇪 · Kai Li🇺🇸 · Tian Ooi🇺🇸 · Gilad Perez🇮🇱 · Wolfram Ratzinger🇮🇱 · Marianna S. Safronova🇺🇸 · Thorsten Schumm🇦🇹 · Jun Ye🇺🇸 · Chuankun Zhang🇺🇸

   Ultralight dark matter is expected to induce oscillations of nuclear parameters. These oscillations are characterized by extremely weak couplings or high suppression scales, with the Planck scale - the characteristic scale of quantum gravity - serving as a natural benchmark. Probing this phenomenon requires systems with exceptional sensitivity to shifts in nuclear energies. The uniquely low-energy nuclear isomeric transition in ${}^{229}$Th provides such sensitivity: it directly probes the nuclear interaction and, owing to a near cancellation between electromagnetic and nuclear contributions, its response to changes in nuclear structure is greatly amplified. We devise and perform a new type of ultrasensitive search for dark matter which uses the precision nuclear spectroscopy at JILA to set the strongest bounds in the mass range $10^{-21}\mathrm{eV}\lesssim m_{\mathrm{DM}}\lesssim 10^{-19}\mathrm{eV}$. Our results probe effective interaction scales exceeding $10^6$ times the Planck scale (the Mega-Planck scale) and establish the ${}^{229}$Th system as the leading probe of dark matter couplings to the nuclear sector.

   hep-phnucl-exphysics.atom-ph12 citations
2. 02*

   Rescuing Overabundant Dark Matter with a Strongly First Order Phase Transition in the Dark Sector

   Peisi Huang🇺🇸 · Anibal D. Medina🇦🇷 · Carlos E. M. Wagner🇺🇸

   We consider a dark sector consisting of fermionic dark matter (DM) charged under a broken dark $U(1{)}_D$ gauge symmetry, interacting with the Standard Model through kinetic mixing. In such models, the DM annihilation cross section is typically suppressed by the small kinetic mixing and or a heavy mediator, often leading to an overabundant relic density. We show that the observed DM abundance can be achieved if the dark Higgs undergoes a strong first order phase transition after DM freeze-out. In this scenario, the relic abundance is set by thermal freeze-out in the symmetric phase and subsequently reduced by entropy injection from the phase transition, rather than by annihilation in the broken phase. We find that to reproduce the observed relic abundance, the required phase transition is generically supercooled. The resulting stochastic gravitational wave signal lies within the sensitivity of future experiments, providing a complementary probe of this framework. Moreover, a strongly supercooled phase transition can potentially account for the NANOGrav signal for DM masses below $O(10)$ GeV.

   hep-phastro-ph.COhep-thPRD(2026)·3 citations
3. 03*

   New Physics and Symmetry Tests with Polarized Photon Fusion and Dipole Moments

   Fang Xu🇨🇳

   We discuss new-physics searches and symmetry tests with dipole moments, emphasizing the role of polarization observables. As a primary benchmark, we consider polarized photon fusion in the $e^{+}{e}^{-}$ environment of the Super Tau-Charm Facility (STCF) and study $\gamma \gamma \to {\tau }^{+}{\tau }^{-}$ in the nearly back-to-back region, where a transverse-momentum-dependent (TMD) description provides a convenient framework for organizing polarization effects. We show that linearly polarized photons induce characteristic azimuthal asymmetries in the ${\tau }^{+}{\tau }^{-}$ kinematics, enabling polarization-based observables that enhance sensitivity to the $\tau$ electromagnetic dipole form factors. Moreover, $CP$-even and $CP$-odd dipole interactions can be disentangled through distinct angular structures, offering a systematic path to probe $\tau$ dipole moments with improved precision at future lepton colliders. As an illustration, we obtain an improved $2\sigma$ reach on the anomalous magnetic dipole moment, $-4.6\times 10^{-3}<\mathrm{Re}(a_{\tau })<7.0\times 10^{-3}$, reaching a precision level close to the Standard Model expectation. To place these prospects in a broader context, we briefly summarize the experimental status of dipole-moment measurements across different fermionic systems and highlight their complementarity in constraining new physics. We illustrate this interplay with supersymmetric scenarios featuring $R$-parity violation, in which loop-induced dipole moments provide correlated probes of $CP$-conserving and $CP$-violating interactions. Taken together, polarized photon fusion and precision dipole measurements constitute a coherent program for testing fundamental symmetries and exploring physics beyond the Standard Model.

   hep-phhep-exPoS(2026)·0 citations
4. 04*

   Relativistic corrections to gluon fragmentation into the ${}^3{P}_J^{[1,8]}$ states

   Zhi-Guo He🇨🇳 · Bernd A. Kniehl🇩🇪 · Peng Zhang🇮🇳

   We compute relativistic corrections to the gluon fragmentation functions to ${}^3{P}_J^{[1,8]}$ Fock states of heavy quarkonium within non-relativistic QCD factorization framework. We find that, at $\mathcal{O}(v^2)$ sub-leading order, the $S$-$D$ mixing effect must be taken into account to absorb the infrared divergence of spin-triplet $P$-wave production within full QCD into the NRQCD long-distance matrix elements. Unlike the $S$-wave case, we find that the short-distance coefficients of the fragmentation functions at leading and sub-leading order are no longer proportional to each other. However, upon convolution with the gluon production cross section, their ratios are almost constant across the whole $p_T$ region. We find the relativistic corrections to be negative and substantial, which makes them a non-negligible ingredient in the study of $J/\psi$ production at the LHC.

   hep-ph1 citation
5. 05*

   Regge trajectories for the doubly heavy triquarks $((Qq){\bar{Q}}^{\prime })$

   Xin-Ru Liu🇨🇳 · Qi Liu🇨🇳 · He Song🇨🇳 · Jiao-Kai Chen🇨🇳

   We attempt to apply the Regge trajectory approach to the doubly heavy triquarks $((Qq){\bar{Q}}^{\prime })$ $(Q,Q^{\prime }=b,c;q=u,d,s)$. We propose the Regge trajectory relations for the doubly heavy triquarks, and then employ them to crudely estimate the spectra of the triquarks $((cu)\bar{c})$, $((cu)\bar{b})$, $((cs)\bar{c})$, $((cs)\bar{b})$, $((bu)\bar{c})$, $((bu)\bar{b})$, $((bs)\bar{c})$, and $((bs)\bar{b})$. The $\lambda$-trajectories and the $\rho$-trajectories are investigated. The triquark Regge trajectory becomes a new and very simple approach for estimating the spectra of triquarks. It also provides a simple method to investigate the $\rho$-mode and $\sigma$-mode excitations of pentaquarks and hexaquarks in the triquark picutre. Moreover, the spin-averaged masses of the ground states of pentaquarks $(\bar{c}(cu))(cu)$, $(\bar{b}(bu))(bu)$ and $(\bar{c}(cu))(bu)$ are estimated, which are consistent with other theoretical predictions.

   hep-ph3 citations
6. 06*

   Decoding the near-threshold $X_{0,1}(4140)$ and $X_1(4685)$ states via OZI-suppressed coupled-channel scattering

   Mao-Jun Yan🇨🇳

   To decode the near-threshold dynamics of the $X_{0,1}(4140)$ and $X_1(4685)$ states, we investigate the OZI-suppressed $\{D_s{\bar{D}}_s,J/\psi \varphi ,D_s^{\ast }{\bar{D}}_s^{\ast }\}$ coupled-channel scattering in $B\to D_s{\bar{D}}_{s}K$ decays using the effective range expansion. We demonstrate that the $X_0(4140)$, associated with a dip in the lineshape, corresponds to a dynamically generated pole near the $J/\psi \varphi$ threshold. The single-channel $J/\psi \varphi$ scattering length is extracted to be $1.11\pm 0.65\mathrm{fm}$, yielding an effective scattering length of $0.12_{-0.10}^{+0.20}+i0.78_{-0.40}^{+0.20}\mathrm{fm}$ when coupled channels are included. By treating the spin-spin interaction as a subleading effect, we predict a $J^{PC}=1^{++}$ virtual state near the $J/\psi \varphi$ threshold, which naturally resolves the empirical ambiguities surrounding the $X_1(4140)$ width. Extending this framework via heavy quark spin symmetry, we further interpret the $X_1(4685)$ as a $\psi (2S)\varphi$ hadronic molecule. Ultimately, these findings highlight how the $X(4140)$ family and $X_1(4685)$ serve as unique theoretical windows into the Fierz rearrangement and OZI suppression mechanisms in low-energy strong interactions.

   hep-phPRD(2026)·0 citations
7. 07*

   Strangeness is the key: from $\bar{K}N$ to ${\bar{D}}_{s}DK$

   Li-Sheng Geng🇨🇳 · Ming-Zhu liu🇨🇳 · Jia-Ming Xie🇨🇳

   The kaon, the lightest hadron containing a strangeness quark, is very peculiar. It is a Nambu-Goldstone boson, but significantly heavier than the pion. As a result, its interaction with a matter particle, such as the nucleon or a heavy-light meson, such as the $D$ meson, is completely determined by chiral dynamics and much stronger than its pion cousin. The strong attractive interaction has brought us many surprises and is manifested in the peculiar nature of many particles, such as the mysterious $\Lambda (1405)$ and $D_{s0}^{\ast }(2317)$. These two particles can be understood as $\bar{K}N$ and $DK$ hadronic molecules, respectively. They also imply the existence of three-body hadronic molecules that await future discovery. In this talk, I review some recent developments in our understanding of hadronic interactions involving the kaon.

   hep-phhep-exhep-lat0 citations
8. 08*

   Quantum interferometric probe of neutron--hidden neutron oscillations

   Antonio Capolupo🇮🇹 · Gabriele Pisacane🇮🇹 · Aniello Quaranta🇮🇹 · Peter Böni🇩🇪

   The nature of dark matter remains an outstanding problem in particle physics and cosmology. Hidden-sector extensions of the Standard Model predict a neutral partner of the neutron, whose weak mixing with ordinary neutrons induces oscillations between visible and dark baryonic states. We show that macroscopic quantum interferometry provides a direct and experimentally accessible probe of this phenomenon. In particular, a Mach--Zehnder interferometer with very cold neutrons converts neutron--hidden neutron oscillations into measurable phase-dependent intensity modulations. By combining controlled phase shifts with tunable magnetic fields and material potentials, the setup enables a resonant exploration of the hidden-sector parameter space. We find that existing cold-neutron facilities can probe mixing amplitudes down to ${ϵ}_{n{n}^{\prime }}\sim 10^{-14}\mathrm{eV}$ for mass splittings $\delta m\sim 10^{-9}\mathrm{eV}$, accessing a previously unexplored region of parameter space relevant to baryonic dark matter scenarios. These results establish neutron interferometry as a precision laboratory tool for testing hidden-sector physics.

   hep-ph0 citations
9. 09*

   Tri-Resonant Leptogenesis in a Non-Holomorphic Modular A${}_4$ Scotogenic Model

   Tapender🇮🇳 · Surender Verma🇮🇳

   We investigate low-scale baryogenesis \textit{via} tri-resonant leptogenesis within the scotogenic model with a scalar dark matter embedded in non-holomorphic modular $A_4$ symmetry framework. The model naturally accommodates three nearly degenerate right-handed (RH) neutrinos when they are assigned to the triplet representation of $A_4$. The near degeneracy originates from treating the symmetric contribution to the Majorana mass matrix, arising from the $3\otimes 3$ decomposition of $A_4$, as a small perturbation to the dominant singlet contribution. Generalized CP (gCP) symmetry is imposed in the model, rendering the complex modulus $\tau$ as the sole source of CP violation. In particular, for the inverted hierarchy (IH), the predicted $3\sigma$ range of ${\theta }_{23}$ lies in the lower octant close to maximal value while CP phase ${\delta }_{\mathrm{CP}}$ and the Majorana phase ${\alpha }_{21}$ are predicted to lie close to $0^{\circ }$ or $360^{\circ }$. Also, in this case, predicted values of $m_{ee}$ and ${\sum }_i{m}_i$ can be tested and constrained by future neutrinoless double beta decay $(0\nu \beta \beta )$ experiments, as well as by cosmological observations, particularly DESI+BAO and Planck data. In fact DESI+BAO disallows IH in the model. We further show that successful baryogenesis can be achieved for both normal hierarchy (NH) and inverted hierarchy (IH) of light neutrino masses with RH neutrino masses as low as $537\mathrm{GeV}$ rendering this scenario experimentally testable. For NH, RH neutrino mass degeneracy of $\mathcal{O}(10^{-7}-10^{-6})$ is required, while for IH a stronger degeneracy of $\mathcal{O}(10^{-8})$ is needed. Remarkably, in the NH case, successful baryogenesis can occur even in the deep washout regime with decay parameters of $\mathcal{O}(10^5)$ owing to the tri-resonant enhancement of the CP asymmetry and the inclusion of flavor effects.

   hep-phEPJC(2026)·8 citations
10. 10*

    Ultralight Dark Matter Detection with a Ferromagnet Lattice

    Dongyi Yang🇨🇳 · Xiao Yang🇨🇳 · Chenxi Sun🇨🇳 · Jianwei Zhang🇨🇳

    A levitated ferromagnet provides an exceptionally sensitive probe of ultralight dark matter (ULDM) through measuring weak magnetic-like field signals. We propose a ferromagnet lattice magnetometer that coherently combines multiple levitated ferromagnets to enhance effective sensitivity. By replacing a single ferromagnet with a lattice, we increase the total polarized spin while preserving the intrinsic dynamical response of each constituent ferromagnet. We show that magnetic dipole-dipole interactions within the lattice can be dynamically suppressed through a high-frequency magnetic field, rendering the system effectively noninteracting, at the cost of only a moderate reduction in signal amplitude due to the distinct renormalization of linear and quadratic spin responses. We analyze the noise properties of the lattice and demonstrate that collective readout leads to favorable scaling with the number of ferromagnets. Interpreted in terms of axion-electron, dark photon, and axion-photon couplings, our results yield projected sensitivities that significantly exceed existing single-ferromagnet implementations. In particular, for axion-photon interactions, we find a nontrivial lattice-induced enhancement of the signal itself, leading to sensitivities that surpass existing constraints over a broad mass range.

    hep-phhep-ex3 citations
11. 11*

    Toward Precision Helicity PDFs from Global DIS and SIDIS Fits with Projected EIC Measurements

    HAPS Collaboration: Hamzeh Khanpour🇵🇱 · Maryam Soleymaninia🇮🇷 · Majid Azizi🇮🇷 · Michael Klasen🇩🇪 · Hadi Hashamipour🇮🇹 · Maral Salajegheh🇩🇪 · Ulf-G. Meißner🇩🇪

    We present a new global determination of the helicity-dependent parton distribution functions (PDFs) of the proton, based on inclusive deep-inelastic scattering (DIS) and semi-inclusive DIS (SIDIS) data within a consistent next-to-leading order (NLO) QCD framework. In addition to existing measurements, we incorporate simulated pseudodata for the future Electron-Ion Collider (EIC), considering two beam-energy configurations, $E_e\times E_p=5\times 41\mathrm{Ge}{\mathrm{V}}^2$ and $18\times 275\mathrm{Ge}{\mathrm{V}}^2$, corresponding to an extended kinematic reach down to $x\sim 10^{-5}$. We focus on longitudinal double-spin asymmetries $A_1^h$ for charge-separated pion and kaon production in SIDIS off a longitudinally polarized proton target. These projected measurements significantly improve the flavor separation of sea-quark polarized PDFs ($\Delta \bar{u}$, $\Delta \bar{d}$, $\Delta s$) and reduce the uncertainties on both quark and gluon helicity distributions, with the largest impact at small $x$. Polarized PDFs are extracted using a neural-network parametrization and a Monte Carlo replica methodology to propagate experimental uncertainties, while theoretical constraints such as positivity are imposed during the fit. We demonstrate that the inclusion of EIC pseudodata leads to a substantially more precise determination of polarized PDFs, with the largest impact in the small-$x$ region. The resulting polarized PDF sets are provided in the LHAPDF format.

    hep-phhep-exPRD(2026)·4 citations
12. 12*

    Chiral symmetry restoration effects onto the meson spectrum from a Dyson-Schwinger and Bethe-Salpeter approach

    Reinhard Alkofer🇦🇹 · Christian S. Fischer🇩🇪 · Fabian Zierler🇬🇧

    Light meson spectra are studied in a Dyson-Schwinger/Bethe-Salpeter approach to QCD. By varying the interaction strength of three sets of models for the quark-antiquark interaction, the transition from the chiral symmetric to the chirally broken regime in the vacuum is studied. The simplest type of these models leads to degenerate meson spectra for a large domain of the strength parameter. The more sophisticated and thus more realistic models show significantly smaller parameter domains for which degenerate meson spectra are obtained. The underlying mechanism for obtaining and then lifting degeneracies is traced back to the location of the quark propagators' poles, in particular, whether they are beyond or within the domain of integration in the Bethe-Salpeter equation. In view of this mechanism the potential relation of the obtained degeneracies to the dynamical emergence of symmetries is discussed, adding thereby another point of view on the conjectured chiral spin symmetry of QCD in the temperature domain right above the crossover.

    hep-phnucl-thPRD(2026)·5 citations
13. 13*

    Neutral Scalar Signatures at a Muon Collider in the $Z_3$ symmetric Three Higgs Doublet Model

    Baradhwaj Coleppa🇮🇳 · Akshat Khanna🇮🇳

    Extending the scalar sector of the Standard Model is a well-motivated approach to exploring physics beyond the Standard Model. In this work, we investigate the phenomenology of the Three Higgs Doublet Model at a future muon collider. The scalar spectrum of the 3HDM comprises three CP-even Higgs bosons, two CP-odd Higgs bosons, and a pair of charged Higgs states. Focusing on Higgs pair production via muon-antimuon annihilation, we study the production and decay of neutral scalar states through the process ${\mu }^{+}{\mu }^{-}\to {\varphi }_i{\varphi }_j$, assuming a mass hierarchy in which the SM-like CP-even Higgs is the lightest state. We analyze several benchmark scenarios leading to $b\bar{b}b\bar{b}$ and $b\bar{b}t\bar{t}$ final states, and perform a cut-and-count analysis at a center-of-mass energy of $\sqrt{s}=3$ TeV. Our results demonstrate that a future muon collider provides a sensitive and promising environment to probe extended Higgs sectors, with neutral scalar states in the mass range of $200-400$ GeV being discoverable with $5\sigma$ significance for integrated luminosities of $\mathcal{O}(1-4{\mathrm{ab}}^{-1})$.

    hep-ph3 citations
14. 14*

    Hyperon longitudinal polarization and vector meson spin alignment in a thermal model for heavy-ion collisions

    Soham Banerjee🇮🇳 · Samapan Bhadury🇮🇳 · Wojciech Florkowski🇵🇱 · Amaresh Jaiswal🇮🇳 · Radoslaw Ryblewski🇵🇱

    The concept of a common local spin equilibrium for both spin-1/2 and spin-1 particles is incorporated into a thermal model of particle production in heavy-ion collisions at the top RHIC energies. We show that an effective spin polarization tensor leading to a correct description of the longitudinal spin polarization of $\Lambda$ hyperons simultaneously yields a positive alignment of vector mesons ($\varphi$ and $K^{\ast 0}$) that grows monotonically with transverse momentum and centrality. Similar trends can be seen in the data, suggesting a possible common mechanism for longitudinal spin polarization and alignment. However, model calculations are insufficient to explain the data in a fully quantitative way. The correlation found between the magnitude of the $\Lambda$ longitudinal polarization and vector meson alignment suggests further more elaborate investigations of this issue.

    hep-phhep-thnucl-thActa Phys.Polon.B(2026)·1 citation
15. 15*

    Non-perturbative effects and soft-gluon dynamics in low-$p_T$ Drell-Yan production

    D. Subotić🇲🇪 · H. Jung🇧🇪 · A. V. Kotikov🇷🇺 · N. Raičević🇲🇪

    The transverse-momentum spectrum of Drell--Yan lepton pairs at small \ptll\ probes non-perturbative QCD effects, including intrinsic partonic transverse momentum and initial-state soft-gluon radiation. The novel \pythiaPB\ approach, which implements the Parton Branching (\PB ) framework in \pythia\ while employing the same evolution ingredients, is used to study this spectrum in the low-\ptll\ region. This framework is particularly well suited for such investigations, as it allows for a systematic treatment of the dominant non-perturbative effects and their interplay. We examine in detail the implementation of primordial transverse momentum in \pythiaPB . With an improved recoil treatment, we determine the width of the intrinsic-\kt\ distribution and find a \sqrts\ dependence that is steeper than in \PB , but much flatter than in \pythia . We identify the origin of these differences. Furthermore, different treatments of the strong coupling at low scales are investigated and confronted with available experimental data. We find that, at the highest centre-of-mass energy considered, the low-\ptll\ Drell--Yan spectrum becomes sensitive to the transition between the perturbative and non-perturbative regimes.

    hep-phEPJC(2026)·0 citations
16. 16*

    Compact Representation of Particle-Collision Events for Physics-Informed Machine Learning

    Wasikul Islam🇺🇸 · Sergei Chekanov🇺🇸

    We introduce a compact, physics-driven event representation, RMM-C46, designed to compress the high-dimensional rapidity mass matrix (RMM) into a low-dimensional, interpretable feature set suitable for physics-informed machine learning (ML) and quantum computing applications. The full RMM encodes detailed pairwise correlations among jets, b-jets, leptons, photons, and missing transverse energy but contains more than a thousand values per event, making it computationally heavy for large-scale training and incompatible with current low-qubit quantum devices. The proposed RMM-C46 input space for ML preserves the physical block structure of the RMM through aggregated invariant mass, rapidity difference, and transverse energy components, reducing the size of the original RMM by over an order of magnitude while maintaining interpretability. Applied to simulated proton-proton collisions at centre-of-mass energy of 13.6 TeV, these representations match or exceed the discriminative performance of the full RMM in both supervised and unsupervised ML tasks. Their compactness, stability, and physics transparency also make them naturally compatible with near-term quantum machine learning architectures. RMM-C46 provides a scalable, efficient, and quantum-ready alternative to the full RMM for next-generation collider physics analyses.

    hep-phhep-ex0 citations
17. 17*

    Lecture Notes: Probing ultralight axion-like particles with quantum technology

    Sreemanti Chakraborti🇬🇧

    We review the physics of ultralight axion-like particles (ALPs) as dark matter candidates and the experimental strategies used to search for them with precision and quantum technologies. In the ultralight regime, the enormous occupation number of the dark matter field motivates a classical description in terms of a coherently oscillating background, leading to distinctive, time-dependent signatures in laboratory observables. We discuss the effective field theory framework governing ALP interactions with Standard Model fields, and show how different operators give rise to qualitatively different experimental signals. The lecture notes cover both conversion-based searches enabled by the axion-photon coupling, such as haloscopes and helioscopes, and precision experiments sensitive to oscillations of fundamental constants and material properties. These include atomic and nuclear clocks, optical cavities, laser and unequal time-delay interferometers, and mechanical or solid state resonators. Emphasis is placed on the physical origin of the sensitivity of each platform, the role of coherence, bandwidth, and noise, and the complementarity between different technologies across a wide range of ALP masses. Together, these approaches provide broad and overlapping coverage of ultralight dark matter parameter space and define a rapidly evolving experimental programme with strong discovery potential.

    hep-phPoS(2026)·0 citations
18. 18*

    Stochastic galactic supernova flux of semi-relativistic particles

    David Alonso-González🇪🇸 · David Cerdeño🇪🇸 · Marina Cermeño🇪🇸 · Andres D. Perez🇦🇷

    New exotic particles with MeV masses, such as axion-like particles or light dark matter, can be emitted from core-collapse supernovae (SNe) with semi-relativistic velocities. Due to their speed dispersion, they would arrive at Earth as an extended packet with a time spread that can be as large as tens of millennia for typical detectors. It has been argued in the literature that the superposition of packets from all galactic SNe would give rise to a smooth and stationary diffuse flux that could be observable on terrestrial experiments. In this article, we critically examine this hypothesis by carrying out a numerical simulation of the galactic history of SN explosions. We show that, although the particle packets do overlap, due to the short observational time window, each of them only contributes with a very narrow range of energies and with an intensity that depends on the SN distance. As a consequence, the energy dependence of the resulting flux is extremely sensitive to the stochastic nature of the SN population and far from smooth. This has profound implications for the expected signature in terrestrial experiments, which displays a spectral shape that is not properly described by the smooth approximation. We develop a numerical tool to compute this stochastic galactic flux for generic semi-relativistic particles, which also allows us to explore sub-MeV particles, where the smooth diffuse flux approach does not hold. To test this framework, we revisit existing bounds on axion-like particles and fermionic dark matter, finding weaker constraints than previously reported.

    hep-phastro-ph.CO2 citations
19. 19*

    Light dark sector via thermal decays of Dark Matter: the case of a 17 MeV particle coupled to electrons

    Marco Graziani🇮🇹

    Recent experimental observations, most notably those reported by the ATOMKI and Positron Annihilation into Dark Matter Experiment (PADME) collaborations, have hinted anomalies that may indicate the presence of a new resonance with a mass around $17\text{MeV}$, potentially interacting with both nucleons and electrons. Since 2020, ATOMKI has observed this resonance in nuclear transitions from excited to ground states in ${}^8\mathrm{Be}$, ${}^4\mathrm{He}$, and ${}^{12}\mathrm{C}$. More recently, in 2025, PADME, operating at the Laboratori Nazionali di Frascati, has also hinted a similar excess, in this case in the $e^{+}{e}^{-}$ final-state events originating from positron annihilation on fixed-target atomic electrons of Carbonium. This concordance strengthens the case for a common underlying origin, potentially involving a new boson, conventionally referred to as $X_{17}$. Despite these intriguing developments, the global experimental landscape remains highly dynamic, particularly in light of recent MEG~II constraints, and a definitive confirmation or exclusion of the $X_{17}$ hypothesis is still lacking. Within this evolving and exciting context, this thesis investigates whether a hypothetical $17\text{MeV}$ particle, coupled to electrons as suggested by the PADME observations, could function as a mediator between the Standard Model and previously unexplored hidden sectors. Such a mediator could, in principle, offer a novel pathway toward addressing one of the principal outstanding inconsistencies of the Standard Model: the nature and origin of dark matter.

    hep-phastro-ph.CO0 citations
20. 20*

    Revisiting the Higgs-mass calculation in the scale-invariant THDM

    Pietro Slavich🇫🇷

    We revisit the one-loop calculation of the Higgs-mass spectrum of the scale-invariant THDM, relying on a direct calculation of the relevant Feynman diagrams. We highlight a number of incorrect assumptions in earlier calculations that relied on the effective-potential approach. In contrast with the earlier findings, we show that the one-loop corrections can have an effect of $\mathcal{O}(10\%)$ on the predictions for the BSM-Higgs masses, and they can also induce non-negligible mixing between the SM-like and BSM states in the neutral-scalar sector.

    hep-phPRD(2026)·2 citations
21. 21*

    Generating the fermion mass hierarchy at the TeV scale

    Nima Arkani-Hamed🇺🇸 · Carolina Figueiredo🇺🇸 · Lawrence J. Hall🇺🇸 · Claudio Andrea Manzari🇺🇸

    We propose a class of theories to generate quark and lepton mass matrices where the scale of new physics is at the TeV scale, without inducing the large flavor and CP violating processes that are often thought to relegate the origin of flavor to energies above $\sim 100$ TeV. The models have new vector-like leptons and quarks, with mass mixings to each other and Yukawa couplings to light Standard Model fields encoded in "chains" reminiscent of dimensional deconstruction. Locality in the chains both generates the hierarchical Standard Model Yukawa matrices, and ensures that CP and flavor violating effects are small, even with the vector-like particles at the TeV scale. A simple extension also generates neutrino masses, whose tiny size is parametrically related to the square of the electron Yukawa coupling. We outline the essential features of these models, explain how fermion mass hierarchies and mixing angles emerge, and explore their phenomenological implications. This framework can be tested both in the final run of the LHC as well as at possible future colliders operating at the 10 TeV scale, and we identify some of the distinctive experimental signatures associated with the production and decay of the new vector-like fermions.

    hep-phhep-exhep-th14 citations
22. 22*

    Minimal Dark Matter: Generalized Framework and Direct-Detection Sensitivity

    Spencer Griffith🇺🇸 · Juri Smirnov🇬🇧 · Laura Lopez-Honorez🇧🇪 · John F. Beacom🇺🇸

    Minimal electroweak dark matter models are compelling due to their simplicity, though calculations of their freezeout abundance are complicated by nonperturbative effects due to Sommerfeld enhancement and bound-state formation. It has been shown that all individual multiplet scenarios beyond the doublet lead to direct-detection signals above the neutrino floor and thus within the reach of next-generation experiments. If no signals are found, would minimal dark matter be excluded? Yes for the simplest models, but it has been unknown for the important extension of two multiplets coupled by Higgs interactions (Higgs-coupled minimal dark matter). We present a generalized framework for calculating nonperturbative effects for such models that also covers the case of individual multiplets. In this framework, we calculate nonperturbative effects on freezeout as well as the prospects for direct detection, correcting shortcomings and omissions in the literature. Importantly, for the mixed Majorana (odd) and Dirac (even) multiplet combination 3M2D (and marginally the 5M4D), we find that the predicted direct-detection signals can extend below the neutrino floor. Fully testing minimal dark matter will thus require more than direct-detection experiments.

    hep-phastro-ph.COPRD(2026)·3 citations
23. 23*

    Testing the cosmic distance-duality relation with localized fast radio bursts: a cosmological model-independent study

    Jéferson A. S. Fortunato · Surajit Kalita · Amanda Weltman🇿🇦

    We test the Etherington cosmic distance-duality relation (CDDR), by comparing Type Ia supernova (SNIa) luminosity-distance information from the Pantheon+ compilation with an angular-diameter-distance reconstructed from localized Fast Radio Bursts (FRBs). The core of our methodology is a data-driven reconstruction from FRBs using artificial neural networks (ANNs): we infer a smooth mean extragalactic dispersion-measure relation and use its redshift derivative to recover $H(z)$ and hence $D_{\mathrm{A}}^{\mathrm{FRB}}(z)$ without assuming a parametric form for the expansion history. Possible deviations from CDDR are parameterized through three one-parameter models of $\eta (z)\equiv D_{\mathrm{L}}/[(1+z{)}^2{D}_{\mathrm{A}}]$. We implement two complementary likelihoods: (i) a direct approach using individual SNIa with the full Pantheon+ covariance, and (ii) a machine-learning approach in which we reconstruct the SN Hubble diagram on the FRB redshift grid, propagating SN and FRB uncertainties into non-diagonal covariance matrices via Monte Carlo and bootstrap realizations. Within the FRB reconstruction, we anchor the mean extragalactic dispersion measure at $z=0$, which yields a data-driven constraint on the average host/near-source contribution ${\mathrm{DM}}_{\mathrm{host}}=128.8\pm 34.1\mathrm{pc}\mathrm{c}{\mathrm{m}}^{-3}$ ($3\sigma$ of statistical confidence). We find that both likelihood implementations give consistent posteriors and no statistically significant evidence for departures from CDDR at the current precision.

    ↳ astro-ph.COhep-ph3 citations
24. 24*

    Inflationary Reheating to Preheating - A Personal Account

    Robert Brandenberger (McGill)🇨🇦 · Jennie Traschen (Univ. of Massachusetts)🇺🇸

    This is a personal account of the early work that led to what is now known as the ``preheating stage" of inflationary cosmology. The broader applicability of the underlying instability mechanisms in cosmology are indicated.

    ↳ astro-ph.COgr-qchep-phhep-thUniverse(2026)·4 citations
25. 25*

    Breit corrections to moderately charged ions in all-orders calculations

    Andoni Skoufris · Benjamin M. Roberts🇦🇺

    The atomic properties of heavy, moderately-charged ions are important for a wide variety of applications, including precision tests of fundamental physics and for the study and development of atomic and nuclear clocks. In these systems it is known that relativistic effects, such as the Breit interaction and radiative quantum electrodynamics corrections, are important for an accurate understanding of atomic properties. It is also known that inclusion of correlations alongside the Breit effect is crucial. In this work we include the Breit interaction into all-orders calculations of energy levels and fine structure intervals of ions in the Cs and Fr isoelectronic sequences. This requires modifying the electron Green's function to account for Breit within the all-orders correlation potential method, which sums dominating series of perturbation diagrams exactly using a Feynman diagram technique. We find that Breit corrections to the energies of moderately ionized ions along these sequences are very large, particularly for the f states. We also observe a significant deviation from experiment for these levels. Incorporating Breit into the all-orders correlation potential provides a significant additional contribution beyond including Breit at the second-order level alone. While this does not resolve the disagreement in the energy levels, it does substantially improve the fine-structure intervals beyond what is achieved by including Breit only at second order. Furthermore, we include the frequency-dependent Breit interaction into the Dirac-Fock procedure, and find that this does not significantly modify the energy levels at this order of approximation.

    ↳ physics.atom-phhep-phPRA(2026)·0 citations
26. 26*

    Spectra and elliptic flow of light hadrons in an expanding fire-cylinder model for the RHIC Beam Energy Scan

    Anand Rai🇮🇳 · Ashutosh Dwibedi🇮🇳 · Sabyasachi Ghosh🇮🇳

    We investigate the transverse momentum spectra ($p_T$) and elliptic flow ($v_2$) of ${\pi }^{\pm }$, $K^{\pm }$, $p$, and $\bar{p}$ produced in peripheral Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=7.7$, 11.5, 19.6, 27, and 39 GeV in the Beam Energy Scan (BES) Program at the Relativistic Heavy Ion Collider (RHIC). The analysis is carried out within an expanding elliptic fire-cylinder model that incorporates longitudinal expansion and anisotropic transverse flow. Particle production at kinetic freeze-out is obtained using a local equilibrium distribution function with a blast-wave-like fluid velocity profile derived from the expansion dynamics of the elliptic fire-cylinder. The model parameters governing the collective expansion are first constrained by fitting the midrapidity $p_T$ spectra of ${\pi }^{\pm }$ and are then applied, without further adjustment, to $K^{\pm }$, $p$, and $\bar{p}$. The model provides a consistent description of the $p_T$ spectra and reproduces the qualitative behavior of the elliptic flow for all considered particle species.

    ↳ nucl-thhep-phNPA(2026)·1 citation
27. 27*

    Schwarzian Theory and Cosmological Constant Problem

    Jun Nian🇨🇳

    Observational data in cosmology indicate a small, positive, and nonvanishing cosmological constant that dominates the energy budget of the present universe. The origin of the cosmological constant from a quantum perspective remains unresolved, with a discrepancy of approximately 120 orders of magnitude between its observed value and theoretical estimates. Motivated by earlier work of Gibbons, we analyze the cosmological constant problem within a quantum-gravitational framework based on Schwarzian theory and its ensemble averaging. We then derive the phenomenological value of the dark energy density and obtain the corresponding equation of state. In this model, the cosmological constant arises from the ensemble average of time-reparametrization modes.

    ↳ hep-thastro-ph.COgr-qchep-ph0 citations
28. 28*

    Non-BPS Monopoles and Dyons via Resurgent Transseries

    Gerald V. Dunne🇺🇸 · Evan Shinn🇺🇸

    Radially symmetric non-BPS 't Hooft-Polyakov monopoles and dyons are constructed as resurgent transseries: infinite sums of exponentially decaying terms, each multiplied by a factorially divergent fluctuation factor. All higher exponential terms are explicitly expressed in terms of the leading order solutions. In the BPS limit all fluctuation terms truncate.

    ↳ hep-thhep-phmath-phmath.MPPRD(2026)·2 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.