Thu·Dec 18, 2025Thursday·December 18, 2025

1. 01*

   Three-dimensional imaging of hadrons with hard exclusive reactions: advances in experiment, theory, phenomenology, and lattice QCD

   M. Boër🇺🇸 · A. Camsonne🇺🇸 · M. Constantinou🇺🇸 · H.S. Jo🇰🇷 · K. Joo🇺🇸 · K. Semenov-Tian-Shansky🇰🇷 · H.-D. Son🇰🇷 · P. Sznajder🇵🇱 · C. Van Hulse🇪🇸 · E. Voutier🇫🇷 · J. Wagner🇵🇱 · A. Afanasev🇺🇸 and 28 other authors

   Generalized Parton Distributions (GPDs) have emerged as a powerful framework for exploring the internal structure of hadrons in terms of their partonic constituents. Over the past three decades, the field has witnessed significant theoretical and experimental advancements. The interpretation of GPDs in impact parameter space offers a vivid three-dimensional visualization of hadron structure, correlating longitudinal momentum and transverse spatial distributions, thereby enabling tomographic imaging of hadrons. Furthermore, the link between GPDs and the matrix elements of the QCD energy-momentum tensor provides access to fundamental properties of hadrons, including spin decomposition and internal pressure distributions. Notably, recent analyses of Deeply Virtual Compton Scattering (DVCS) data have enabled the empirical extraction of the quark pressure profile inside the proton. Motivated by the rapidly evolving experimental landscape, this white paper provides a timely and focused overview of recent developments in GPD theory, phenomenology, and lattice QCD studies. Its scope is shaped by the needs and opportunities of forthcoming experimental programs, and it highlights advances that are particularly relevant for the next generation of dedicated measurements, including the extended Jefferson Lab 12 GeV program and its potential 22 GeV upgrade, J-PARC, COMPASS/AMBER, LHC ultra-peripheral collisions, and the future electron-ion colliders EIC and EicC.

   hep-phhep-exhep-latnucl-ex+114 citations
2. 02*

   Crossover or First-Order: Impacts of Regularization

   Xin-Peng Li🇨🇳 · Hao-Ran Zhang🇨🇳 · Zhu-Fang Cui🇨🇳 · Thomas Klähn🇺🇸

   The equation of state of hot, dense nuclear matter plays a fundamental role in many areas. However, owing to the nonperturbative nature of strong interactions, a reliable treatment is still under debate. We use a symmetry-preserving treatment of a vector\,$\otimes$\,vector contact interaction to study related issues at nonzero temperature or quark chemical potential, and carefully compare a noncovariant and a covariant regularization scheme. The numerical results show that the character of the phase transition depends sensitively on the regularization scheme and parameter choices.

   hep-phnucl-th1 citation
3. 03*

   The domain of soft hadrons in transverse momentum space in high energy collisions

   Jun Song🇨🇳 · Hai-hong Li🇨🇳 · Feng-lan Shao🇨🇳

   By studying experimental data for invariant transverse momentum distribution $f(p_T)$ of hadrons in high energy $pp$, $p$A and AA collisions, we find two characteristic $p_T$ points relating to the behavior of ${\left[\ln f(p_T)\right]}^{{}^{\prime \prime }}$, i.e., the second derivative of the logarithm of hadronic $p_T$ spectrum with respect to $p_T$. One point is $p_0$ at which ${\left[\ln f(p_T)\right]}^{{}^{\prime \prime }}$ is zero and another point is $p_1$ at which ${\left[\ln f(p_T)\right]}^{{}^{\prime \prime }}$ reaches maximum. \bz{The hadronic distribution can be classified into three kinetic regions, i.e., soft region $0<p_T<p_0$ dominated by hadrons from soft parton system, hard region $p_T>p_1$ dominated by hadrons from high energy partonic jet, and the transition region $p_0<p_T<p_1$ of above two sources of hadron production.} Using rich data of hadronic $p_T$ spectra at RHIC and LHC, we carry out a systematical analysis for $p_0$ and $p_1$ of kaon, $K^{\ast }$, $\varphi$ and baryons such as $p$, $\Lambda$, $\Xi$, $\Omega$ in $pp$, $p$-Pb and heavy-ion collisions, and show their dependence on hadron species, collision energy, collision centrality and/or charged-particle multiplicity. We also study the correlation between $p_0$ of hadrons and their average transverse momentum $⟨p_T⟩$, and find a difference between $p_0$-$⟨p_T⟩$ correlation of baryons and that of mesons which can be understood by quark combination mechanism at hadronization. The systematic comparison for $p_0$-$⟨p_T⟩$ correlation of kaon, $\varphi$, $p$ and $\Lambda$ in $pp$, $p$-Pb, Pb-Pb and Au+Au collisions at RHIC and LHC energies indicates that $p_0$ is a sensitive physical quantity of reflecting the production property of soft hadrons in high energy collisions.

   hep-phnucl-thPRD(2025)·1 citation
4. 04*

   Axion-like Particle Search with a Light-Shining-Through-Walls Setup at a $\gamma$-$\gamma$ Collider

   Zi-Yao Yan🇨🇳 · Jie Feng🇨🇳

   In this work, we have explored a practical extension of the conventional light-shining-through-walls technique by making direct use of the high-intensity $\gamma$-ray beam available at a $\gamma$-$\gamma$ collider. The energetic and highly collimated photon flux produced via inverse Compton scattering naturally provides an efficient ALP production stage, while the addition of a regeneration region downstream enables a complete LSW configuration without introducing new experimental complexities. This approach therefore represents an experimentally simple and infrastructure-compatible method for enhancing laboratory sensitivity to axion-like particles. Under conservative assumptions, we find that one year of operation can probe ALP-photon couplings down to $g_{a\gamma \gamma }\simeq 3.82\times 10^{-5}\mathrm{Ge}{\mathrm{V}}^{-1}$ for $m_a\lesssim 0.1\mathrm{eV}$ when an additional magnetic region is included upstream of the beam dump, improving upon previous laboratory LSW limits by up to an order of magnitude.

   hep-phEur.Phys.J.ST(2026)·2 citations
5. 05*

   Selected decays of $B_s$ meson in covariant confined quark model

   Stanislav Dubnička🇸🇰 · Anna Zuzana Dubničková🇸🇰 · Mikhail A. Ivanov🇷🇺 · Andrej Liptaj🇸🇰

   We present a study of various $B_s$ meson decays, including hadronic and semileptonic final states with different spins and diagram topologies. The covariant confined quark model is employed to describe hadronic effects, and our analysis serves as a broad test of the current understanding of the underlying dynamics within the Standard Model. The level of agreement with experimental data varies across channels: it is good for the semileptonic decays $B_s^0\to D_s^{-}{\mu }^{+}{\nu }_{\mu }$ and $B_s^0\to K^{-}{\mu }^{+}{\nu }_{\mu }$; acceptable for the hadronic modes $B_s^0\to D_s^{-}{D}^{+}$ and $B_s^0\to K^{-}{\pi }^{+}$; marginal for $B_s^0\to D_s^{-}{\pi }^{+}$, $B_s^0\to D_s^{-}{\rho }^{+}$, and $B_s^0\to \varphi J/\psi$; and significantly discrepant for $B_s^0\to \varphi \overline{D^0}$ and $B_s^0\to \varphi {\eta }_c$. We argue that the observed inconsistencies may arise from the breakdown of naive factorization and unaccounted long-distance effects. In particular, the channels $B_s^0\to D_s^{-}{\pi }^{+}$ and $B_s^0\to D_s^{-}{\rho }^{+}$ are theoretically among the cleanest nonleptonic decays, yet they exhibit persistent discrepancies also reported by other theoretical groups.

   hep-phEPJA(2026)·1 citation
6. 06*

   Statistical repulsion on hyperons in two-color dense QCD

   Masato Nagatsuka🇯🇵 · Toru Kojo🇯🇵

   We investigate the onset of hyperons in baryonic (diquark) matter in two-color QCD (QC${}_2$D) by introducing heavy quark doublets that emulate strange quarks. An even number of flavors is required to avoid the sign problem in lattice Monte Carlo simulations. To explore QC${}_2$D matter containing both light and heavy quarks, we construct a model in which quarks interact with light-light, light-heavy (hyperonic), and heavy-heavy diquarks via Yukawa couplings. As the quark chemical potential increases, the light diquarks condense first and form baryonic matter, and this onset density can be understood in hadronic terms. In contrast, the onset density of hyperons is substantially higher than that estimated from the hadronic sector of the model. This shift reflects an effective repulsion among baryons induced by the pre-occupied light quarks. The Pauli blocking of light quarks suppresses the attractive diquark correlations responsible, in vacuum, for making hyperons lighter than the sum of the constituent light and heavy quark masses. Implications for three-color QCD are also briefly discussed.

   hep-phhep-latnucl-thPRD(2026)·2 citations
7. 07*

   The effective charm mass from the excited charmonium leptonic decays

   V. Sauli🇨🇿

   We use the covariant four-dimensional Bethe-Salpeter (BS) equation to determine the effective charm quark mass. The scale dependence of the effective charm quark mass is determined using experimentally known spin-one charmonium spectra and leptonic decay constants. The infrared finite, massive-like effective QCD running charge is used to solve the Bethe-Salpeter equation to achieve this. The obtained effective charm quark mass values run from 1.1 GeV for the $J/Psi$ meson to 1.5 GeV for its higher radial excitations. These values are substantially smaller than those extracted in the perturbative MS renormalization scheme, but they agree with the semi-perturbative solution of the quark Schwinger-Dyson equation in the momentum subtraction scheme. Within the interaction entirely governed by QCD running coupling, the sliding scale charm quark mass is crucial for the correct determination of leptonic decays. Notably, for leptonic decay constants of excited states, this is the first time the theory based on Bethe-Salpeter equation has met the precision of the experimental data.

   hep-ph1 citation
8. 08*

   Hybrid Type-I and Type-II Leptogenesis in Minimal Renormalizable $\mathrm{SO}(10)$

   Gayatri Ghosh🇮🇳

   We investigate flavoured hybrid leptogenesis in a minimal renormalizable $\mathrm{SO}(10)$ framework in which both Type-I and Type-II seesaw interactions contribute to the generation of the cosmological baryon asymmetry. We consider a regime where heavy Majorana neutrinos and electroweak scalar triplets are independently quasi-degenerate, leading to resonant enhancement in each sector, while additional CP-violating contributions arise from loop-induced interference between fermionic and scalar interactions. These hybrid contributions vanish if either sector is absent, providing a genuinely new source of CP violation beyond conventional single-sector leptogenesis. The evolution of the lepton asymmetry is studied using a flavour-covariant density-matrix formalism that consistently incorporates flavour coherence, spectator effects, and washout processes. We show that the observed baryon asymmetry, $Y_B\simeq 8.7\times 10^{-11}$, can be reproduced for representative parameter regions with heavy mass scales of $10^{10}$--$10^{12},\mathrm{GeV}$ and perturbative Yukawa couplings. To characterize the flavour structure of the hybrid interference terms, we introduce the scalar quantity [ J_{\rm hybrid}={\rm Im}!\left[\mu,{\rm Tr}!\left(fY_\nu^\dagger Y_\nu\right)\right], ] which provides a compact parametrization of the flavour contractions entering the hybrid amplitudes in the flavour basis adopted here. We emphasize that it serves as a convenient diagnostic of the hybrid interference terms rather than a complete basis-independent measure of CP violation. The same interactions responsible for baryogenesis can also induce charged-lepton flavour violation and electric dipole moments, linking neutrino mass generation, grand unification, and future precision searches for CP violation.

   hep-ph0 citations
9. 09*

   An Extra-Dimensional Axion in a 5D Warped Orbifold GUT

   Gongjun Choi🇺🇸 · Tony Gherghetta🇺🇸

   We study the QCD axion arising from the 5th component of a bulk $U(1)$ gauge field in a five-dimensional warped grand unified theory, and determine the viable range of the axion decay constant $f_a$. Unlike flat extra dimensions, where gauge couplings run quickly above the Kaluza--Klein (KK) scale, the logarithmic running in warped geometries permits substantially smaller $f_a$ while preserving perturbative gauge coupling unification. However, bulk tree-level contributions to the gauge coupling -- interpreted holographically as CFT renormalization -- place a lower bound on $f_a$. We find that the conventional QCD axion window $10^9\mathrm{GeV}\lesssim f_a\lesssim 10^{12}\mathrm{GeV}$ is readily compatible without losing perturbativity, provided the AdS curvature is near the Planck scale. Thus, the 5D warped orbifold GUT naturally accommodates a high-quality QCD axion in a grand unified theory that provides an effective description of string-theoretic warped flux compactifications, admitting complementary geometric and holographic descriptions of the axion.

   hep-phhep-thJHEP(2026)·6 citations
10. 10*

    Fermionic Electroweak Two-Loop Corrections to Drell-Yan and Related Processes

    Ayres Freitas🇺🇸 · E. Jackson Wallace🇺🇸

    We perform a complete calculation of the next-to-next-to-leading order (NNLO) electroweak fermionic corrections to fermion-pair production processes, where "fermionic" refers to contributions with closed fermion loops. We did this via a semi-numerical technique that uses dispersion relations for the fermion sub-loop in two-loop box and vertex diagrams and dispersion relations and Feynman parameters for vertex diagrams with fermionic triangle sub-loops. UV and IR divergences are treated with suitable subtraction terms. We present numerical results for the cross-sections of $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}/u\bar{u}/d\bar{d}$ and differential distributions at representative center-of-mass energies. The NNLO corrections are found to modify the NLO cross-section on the order of 1%.

    hep-phJHEP(2026)·4 citations
11. 11*

    Cosmological Neutron Stars Produce Diffuse Axion X-Ray Signatures

    Orion Ning🇺🇸 · Kailash Raman🇺🇸 · Benjamin R. Safdi🇺🇸

    Axion-like particles can be abundantly produced through scattering processes in the cores of neutron stars (NSs). If they are ultralight ($m_a\lesssim 10^{-4}$ eV), then they can efficiently convert to detectable photons in the external NS magnetospheres, and if they are heavy ($m_a\gtrsim 1$ eV), then they can decay into photons before reaching Earth. In this work, we search for the resulting X-ray signatures from both of these channels summing over the $\text{cosmological}$ NS population. We compare the predicted axion-induced X-ray signal to the cosmic X-ray background today as measured by a number of instruments such as NuSTAR, HEAO, Swift, and INTEGRAL. We model the axion-induced signal using NS cooling simulations and magnetic field evolution models. We find no evidence for axions and derive strong constraints for both ultralight and heavy axion scenarios, covering new parameter space for the axion-photon and axion-nucleon couplings. Our results rule out the axion-explanation of the Magnificent Seven X-ray excess from nearby isolated NSs.

    hep-phastro-ph.COastro-ph.HE5 citations
12. 12*

    Reusable theory representations for colliders: a demonstrator SMEFT foundation model

    Supratim Das Bakshi🇺🇸 · T.J. Hobbs🇺🇸 · Brandon Kriesten🇺🇸

    We develop a demonstrator foundation model for collider-scale explorations of the Standard Model Effective Field Theory (SMEFT), constructed from contrastive representations of theoretically simulated neutral-current Drell-Yan cross sections. Using a controlled sampling of the Warsaw-basis dimension-6 Wilson-coefficient space at $O({\Lambda }^{-2})$, we generate a corpus of high-resolution differential distributions in $m_{\ell \ell }$ and $p_T$, augmented by physics-motivated Monte Carlo replicas with correlated uncertainties. A minimally parameterized encoder network is trained with a supervised contrastive loss to produce a low-dimensional latent manifold on which SMEFT-induced deformations of the Drell-Yan spectrum acquire a well-defined geometric structure. We analyze the resulting embedding and demonstrate that (i) latent directions correlate with characteristic SMEFT shape distortions, including energy-growing four-fermion contributions and electroweak vertex corrections; (ii) clusters in the embedding correspond to families of Wilson-coefficient configurations with similar phenomenological impact; and (iii) the learned representation supports downstream tasks such as classification with uncertainty quantification, anomaly detection, and nearest-neighbor retrieval. While restricted to leading-order SMEFT and simplified uncertainty modeling, this study provides the first step toward a reusable, physics-aligned foundational representation for the theory of New-Physics searches at high-energy colliders. We outline extensions towards a complete global analyses, including multi-process training corpora, higher-order corrections, and multi-objective pretraining.

    hep-ph0 citations
13. 13*

    Kination and the Inert Doublet Model

    Geneviève Bélanger🇫🇷 · Nicolás Bernal🇦🇪 · Andreas Goudelis🇫🇷 · Alexander Pukhov🇷🇺

    The inert doublet model is a two-Higgs-doublet extension of the standard model that provides a minimal and versatile framework for frozen-out dark matter. Assuming standard cosmology, if the dark matter mass ranges between approximately 120 GeV and 500 GeV then it turns out to be underabundant, as gauge interactions render its annihilation too efficient. In this work, we show that this mass window becomes allowed in cosmological scenarios where dark matter freeze-out occurs during a period with a stiff equation of state, $w>1/3$, such as kination. This predictive setup satisfies all current experimental constraints while remaining within the reach of upcoming detection efforts.

    hep-phastro-ph.CO3 citations
14. 14*

    Weak Charge Form Factor Determination at the Electron-Ion Collider

    Hooman Davoudiasl🇺🇸 · Hongkai Liu🇺🇸 · Sonny Mantry🇺🇸 · Ethan T. Neil🇺🇸

    Determining the weak charge form factor, $F_W(Q^2)$, of nuclei over a continuous range of momentum transfers, $0\lesssim Q^2\lesssim 0.1$ GeV${}^2$, is essential for mapping out the distribution of neutrons in nuclei. The neutron density distribution has significant implications for a broad range of areas, including studies of nuclear structure, neutron stars, and physics beyond the Standard Model. Currently, our knowledge of $F_W(Q^2)$ comes primarily from fixed target experiments that measure the parity-violating asymmetry in coherent elastic electron-ion scattering. Fixed target experiments, such as CREX and PREX-1,2, have provided high-precision weak charge form factor extractions for the ${}^{48}\mathrm{Ca}$ and ${}^{208}\mathrm{Pb}$ nuclei, respectively. However, a major limitation of fixed target experiments is that they each provide data only at a single value of $Q^2$. With the proposed Electron-Ion Collider (EIC) on the horizon, we explore its potential to impact the determination of the weak charge form factor. While it cannot compete with the precision of fixed target experiments, it can provide data over a wide and continuous range of $Q^2$ values, and for a wide variety of nuclei. We show that with data corresponding to an integrated luminosity of $\mathcal{L}\sim$ 500/$A$ fb${}^{-1}$, where $A$ is the nucleus atomic weight, the EIC can significantly impact constraints by lifting degeneracies in theoretical models of the neutron density distribution. Ensuring EIC detector coverage at low $Q^2$ and large negative pseudorapidities will be essential for such $F_W(Q^2)$ measurements.

    hep-phhep-exnucl-exnucl-thPRD(2026)·3 citations
15. 15*

    Renormalization of general Effective Field Theories: Renormalization of fermionic operators

    Renato M. Fonseca🇪🇸 · Pablo Olgoso🇮🇹 · José Santiago🇪🇸

    Renormalization group equations play a central role in effective field theories, both maintaining perturbative control and allowing one to determine the correct low-energy phenomenology. In this work, we complete the one-loop renormalization of the recently developed general effective field theory up to mass dimension six by providing the beta functions for physical fermionic operators. Together with Ref. [1], our results allow one to renormalize any effective theory up to dimension six at one loop using only a group-theoretical calculation.

    hep-phhep-thJHEP(2026)·4 citations
16. 16*

    HEPTAPOD: Orchestrating High Energy Physics Workflows Towards Autonomous Agency

    Tony Menzo🇺🇸 · Alexander Roman🇺🇸 · Sergei Gleyzer🇺🇸 · Konstantin Matchev🇺🇸 · George T. Fleming🇺🇸 · Stefan Höche🇺🇸 · Stephen Mrenna🇺🇸 · Prasanth Shyamsundar🇺🇸

    Many theoretical and experimental workflows in high-energy-physics (HEP) stand to benefit from recent advances in transformer-based large language models (LLMs). While early applications of LLMs focused on text generation and code completion, modern LLMs now support orchestrated agency: the coordinated execution of complex, multi-step tasks through tool use, structured context, and iterative reasoning. We introduce the HEP Toolkit for Agentic Planning, Orchestration, and Deployment (HEPTAPOD), an orchestration framework designed to integrate external LLMs into general HEP workflows spanning theoretical calculations, simulation, and data analysis. The framework enables LLMs to interface with domain-specific tools and to construct and manage diverse HEP pipelines while preserving transparency, reproducibility, and human oversight. To demonstrate these capabilities, we present a representative case study in the context of a Beyond the Standard Model (BSM) Monte Carlo signal validation that spans model generation, event simulation, and analysis within an established, reproducible workflow. HEPTAPOD provides a structured and auditable layer between human researchers, LLMs, and computational infrastructure, establishing a foundation for human-in-the-loop, agent-assisted workflows across high-energy physics.

    hep-phhep-ex22 citations
17. 17*

    Characteristic features of the resonant trident process in the field of a strong monochromatic electromagnetic wave

    S.P. Roshchupkin🇷🇺 · M.V. Shakhov🇷🇺

    The characteristic features of the resonant trident process (Oleinik resonances) have been theoretically studied in a wide range of frequencies and intensities of a circularly polarized strong electromagnetic wave. The resonant trident process is defined by two characteristic quantum energies: the characteristic energy of the nonlinear Compton effect and the characteristic energy of the nonlinear Breit-Wheeler process. These characteristic energies depend significantly on the frequency and intensity of the wave, as well as on the angle between the momenta of the initial electrons and the electromagnetic wave. The resonant trident process is effective when the energy of the initial electrons is greater than or on the order of magnitude of the corresponding characteristic energies. It is shown that quantum entanglement of final particles takes place in this resonant process. An important aspect of the resonant trident process is the equality of the energies of the electron and positron pairs. Analytical expressions for the differential rates of the resonant trident process on the energy of final particles are obtained. The corresponding analytical expressions for full rates have also been obtained. It is shown that the rate data of the resonant trident process in the field of optical and X-ray wave frequencies significantly exceed the corresponding rate of the non-resonant trident process. Results obtained can be used in experiments at leading laser centers, as well as to explain QED processes in strong X-ray fields near neutron stars and magnetars.

    hep-phphysics.plasm-ph0 citations
18. 18*

    Heisenberg-Euler and the Quantum Dilogarithm

    Gerald V. Dunne🇺🇸

    A dispersion integral representation of the Heisenberg-Euler QED effective lagrangian is derived, with Faddeev's quantum dilogarithm as a generalized Borel kernel. The nonperturbative imaginary part of the effective lagrangian is expressed as the quantum dilogarithm, while the real part has the form of a dispersion integral involving both the quantum dilogarithm and its modular dual, a manifestation of electromagnetic duality. The Heisenberg-Euler effective lagrangian generates all one-loop QED scattering amplitudes in a constant external field, with the Lorentz invariants of the constant background electromagnetic field playing the role of the Mandelstam variables in conventional QED dispersion theory.

    ↳ hep-thhep-phmath-phmath.MPPRD(2026)·6 citations
19. 19*

    ANUBIS: Projected Sensitivities and Initial Results from the proANUBIS demonstrator with Run 3 LHC data

    Théo Reymermier🇫🇷 · Oleg Brandt🇬🇧 · Anna Mullin🇬🇧 · Paul Swallow🇬🇧 · Michael Revering🇬🇧 · Cayetano Fernandez Ruiz🇬🇧

    Despite the success of the Standard Model (SM) there remains behaviour it cannot describe, in particular the presence of non-interacting Dark Matter. Many models that describe dark matter can generically introduce exotic Long-Lived Particles (LLPs). The proposed ANUBIS experiment is designed to search for these LLPs within the ATLAS detector cavern, located approximately 20-30 m from the Interaction Point (IP). A prototype detector, proANUBIS, has taken data within the ATLAS detector cavern since 2024, corresponding to 104 $f{b}^{-1}$ of pp data. We report on the potential sensitivity of ANUBIS to a selection of LLP models, i.e. Higgs Portal and Heavy Neutral Leptons, as well as future planned studies. Additionally, we will show the first results of the proANUBIS demonstrator, and how it will be used to study the expected backgrounds for the ANUBIS detector.

    ↳ hep-exhep-phnucl-exPoS(2026)·0 citations
20. 20*

    Observation of partonic collectivity via $p_{\mathrm{T}}$-differential radial flow fluctuations in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV

    Rohit Agarwala🇮🇳 · Dipankar Basak🇮🇳 · Kalyan Dey🇮🇳

    We report the observation of partonic radial collectivity in Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}=200$~GeV via the $p_{\mathrm{T}}$-differential flow observable $v_0(p_{\mathrm{T}})$ using the \texttt{AMPT} String Melting model. For inclusive charged hadrons, we establish three signatures of collectivity: long-range pseudorapidity correlations, the factorization of two-particle correlations, and a centrality-independent scaling of $v_0(p_{\mathrm{T}})$ normalized by its $p_{\mathrm{T}}$-integrated value $v_0$, analogous to anisotropic flow. For identified particles (${\pi }^{\pm },K^{\pm },p+\overline{p}$), the $v_0(p_{\mathrm{T}})$ spectra show mass ordering at low-$p_{\mathrm{T}}$ and meson-baryon separation at intermediate-$p_{\mathrm{T}}$. In \textit{central} collisions, $v_0(p_{\mathrm{T}})/n_q$ exhibits robust \textit{Number of Constituent Quark} (NCQ) scaling with $(m_{\mathrm{T}}-m_0)/n_q$, a scaling that breaks down in \textit{peripheral} collisions and is more precise at RHIC than at LHC energies, consistent with earlier $v_2$ studies. These findings provide strong evidence that radial collectivity originates predominantly at the partonic stage, extending the paradigm of quark-level dynamics from anisotropic to isotropic flow.

    ↳ nucl-exhep-ph1 citation
21. 21*

    Accurate neural network emulator for primordial light element abundances

    Fan Zhang🇨🇳 · Hang Diao🇨🇳 · Bohua Li🇨🇳 · Joel Meyers🇺🇸 · Paul R. Shapiro🇺🇸

    Big-Bang Nucleosynthesis (BBN) predictions of primordial light-element abundances offer a powerful probe of early-Universe physics. However, high-accuracy numerical BBN calculations have become a major computational bottleneck for large-scale cosmological inferences due to the complex nuclear network. Here we present BBNet, a fast and accurate deep learning emulator for primordial abundances. The training data are generated by full numerical calculations using two public BBN codes, PArthENoPE and AlterBBN, modified to accommodate extended cosmologies that include dark radiation and a stiff equation of state. The network employs a residual multi-head architecture to capture convoluted physical relationships. BBNet produces primordial helium-4 and deuterium abundances with negligible errors in milliseconds per sample, achieving a speed-up of up to $10^4$ times relative to first-principles solvers while remaining unbiased over wide parameter ranges. Therefore, our emulator can supersede traditional simplified numerical prescriptions that compromise accuracy for speed. Based on extensive assessments of its performance, we conclude that BBNet is an optimal solution to the theoretical prediction of primordial element abundances. It will serve as a reliable tool for precision cosmology and new-physics searches.

    ↳ astro-ph.COastro-ph.HEgr-qchep-phPRD(2026)·0 citations
22. 22*

    First measurement of the Hubble constant from gravitational wave-galaxy cross-correlations

    Isabela Santiago de Matos🇬🇧 · Charles Dalang🇬🇧 · Tessa Baker🇬🇧 · Raul Abramo🇧🇷 · João Ferri🇧🇷 · Miguel Quartin🇧🇷

    We measure for the first time the Hubble constant ($H_0$) from the cross-correlation of galaxies and gravitational waves (GW), by applying the $\text{Peak Sirens}$ method. This method consists of finding the peak of the 3D angular cross-spectrum $C_{\ell }(z,D_L)$ between the galaxy redshifts ($z$) and the GW luminosity distances ($D_L$). Using two GW events from the GWTC-3.0 catalog and the GLADE+ galaxy catalog, we make the first detection of the cross-correlation peak at $5.9\sigma$ confidence. This signal comes mostly from the best localized event in the catalog, GW190814, which alone provides a $3.4\sigma$ significance. Adding also the multimessenger event GW170817, but without using its known redshift, we find $H_0=67_{-15}^{+18}$ km s${}^{-1}$Mpc${}^{-1}$ and the first observational constraint on the GW bias, $b_{\mathrm{gw}}<4.3$ at 95\% CI. These measurements set the stage for future novel cosmological constraints with this technique.

    ↳ astro-ph.COgr-qchep-ph11 citations
23. 23*

    The art of simulating the early Universe. Part II. Non-canonical cases & gravitational waves

    Jorge Baeza-Ballesteros🇩🇪 · Daniel G. Figueroa🇪🇸 · Adrien Florio🇩🇪 · Joanes Lizarraga🇪🇸 · Nicolás Loayza🇪🇸 · Kenneth Marschall🇪🇸 · Toby Opferkuch🇮🇹 · Ben A. Stefanek🇪🇸 · Francisco Torrentí🇪🇸 · Ander Urio🇪🇸

    We present a discussion on lattice techniques for the simulation of non-canonical field theory circumstances, complementing our previous monograph (arXiv:2006.15122) on canonical cases. We begin by reviewing basic aspects of lattice field theory, including symplectic and non-symplectic evolution algorithms. We then introduce lattice implementations of non-canonical interactions, considering scalars with a non-minimal coupling to gravity, ${\varphi }^{2}R$, non-minimal scalar kinetic theories, ${\mathcal{G}}_{ab}(\{{\varphi }_c\}){\partial }_{\mu }{\varphi }^a{\partial }^{\mu }{\varphi }^b$, and axion-like particle (ALP) interactions with Abelian gauge fields, $\varphi F_{\mu \nu }{\tilde{F}}^{\mu \nu }$. Next, we discuss methods to set up special field configurations, including the creation of cosmic defect networks towards scaling (e.g. cosmic strings and domain walls), field configurations based on arbitrary power spectra or spatial profiles, and probabilistic methods as required e.g. for thermal configurations. We further extend the notion of non-canonical theories, discussing the discretization of scalar field dynamics in $d+1$ dimensions, with $d\ne 3$. Unrelated to non-canonical aspects, we also discuss implementation(s) of gravitational wave (GW) dynamics on the lattice. This document represents the theoretical basis for the non-canonical field theory aspects (interactions, initial conditions, dimensionality) and GW dynamics implemented in $\mathcal{C}$osmo$\mathcal{L}$attice v2.0, to be released in 2026.

    ↳ astro-ph.COgr-qchep-phJCAP(2026)·11 citations
24. 24*

    Note on bulk viscosity as an alternative to dark energy

    P. P. Avelino🇵🇹 · A. R. Gomes🇧🇷 · D. A. Tamayo🇵🇹

    Bulk viscosity, which characterizes the irreversible dissipative resistance of a fluid to volume changes, has been proposed as a potential mechanism for explaining both early- and late-time accelerated expansion of the Universe. In this work, we investigate two distinct physical scenarios for the origin of bulk viscosity: (1) nonminimal interactions between two fluids, and (2) elastic collisions in an ideal gas. In both cases, we demonstrate that while the associated energy-momentum exchange can significantly influence fluid dynamics, overall energy-momentum conservation precludes such exchange from having any direct gravitational effect in the context of General Relativity. In case (1), we show that the standard bulk viscous energy-momentum tensor can be obtained for the two-fluid system only at the cost of the violation of all classical energy conditions: null, weak, dominant, and strong. In case (2), we consider a single fluid composed of point particles undergoing instantaneous, energy- and momentum-conserving collisions, and find that the proper pressure remains strictly non-negative, with the equation-of-state parameter confined to the interval $[0,1/3]$. In both scenarios, achieving a sufficiently negative effective pressure to drive cosmic acceleration requires assumptions that compromise the physical viability of the model. Our results highlight some of the key physical challenges involved in modeling dark energy through bulk viscous effects.

    ↳ astro-ph.COgr-qchep-phhep-thPRD(2025)·3 citations
25. 25*

    Observational constraints on the spin/anisotropy of the CCOs of Cassiopeia A, Vela Jr. and G347.3-0.5 and a single surviving continuous gravitational wave candidate

    Jing Ming🇩🇪 · Maria Alessandra Papa🇩🇪 · Heinz-Bernd Eggenstein🇩🇪 · Bernd Machenschalk🇩🇪 · J. Martins🇩🇪 · B. Steltner🇩🇪 · B. McGloughlin🇩🇪 · V. Dergachev🇩🇪 · R. Prix🇩🇪 · M. Bensch🇩🇪

    We carry out the deepest and broadest search for continuous gravitational-wave signals from three neutron stars at the center of the supernova remnants Cassiopeia A, Vela Jr., and G347.3-0.5. This search was made possible by the computing power shared by thousands of Einstein@Home volunteers. After the initial Einstein@Home search, which used O3a data, we perform a multi-stage follow-up of the most promising $\approx$ 45 million signal candidates. In the last stages, we use independent data (O3b and O4a) to further investigate the remaining candidates from the previous stages. We set the most stringent constraints to date on the gravitational-wave amplitude, equatorial ellipticity, r-mode saturation amplitude, and -- for the first time -- the neutron-star crustal anisotropy. For spin periods lower than 2 ms we constrain the ellipticity to be smaller than $4\times 10^{-7}$ for all targets. We exclude crustal anisotropy values larger than $5\times 10^{-3}$ for spin periods between 1.3--100 ms. Only one candidate -- from the G347.3 search -- survives all follow-ups. We illustrate properties of this candidate. Investigations on new data will aid in clarifying its nature. Such ``new" data already exist, O4b and O4c, and would be optimal for this purpose, but they are not publicly accessible at the time of writing. In the appendix we provide our estimate of the candidate phase parameters, which are useful for others to carry out checks on the new data.

    ↳ gr-qchep-phApJ(2026)·8 citations
26. 26*

    Observable Gravitational Wave Strain at Second Order

    Guillem Domènech🇩🇪 · Shi Pi🇨🇳 · Ao Wang🇨🇳

    There is currently no rigorous definition of gravitational wave strain at second order in cosmological perturbation theory. The usual association of gravitational waves with transverse and traceless fluctuations of the metric on spatial hypersurfaces becomes ambiguous at second order, as it inherently depends on the spacetime slicing. While this poses no practical issues in linearized gravity, it presents a fundamental problem for secondary gravitational waves, especially notorious for gravitational waves induced by primordial fluctuations. We compute, for the first time, the observable gravitational wave strain at second order, as measured by geodesic observers that emit and receive electromagnetic signals, thereby settling the debate on gauge ambiguities. Working in a gauge invariant fashion, we find that the measured gravitational wave strain coincides with the transverse-traceless components in the Newton gauge.

    ↳ gr-qcastro-ph.COhep-phhep-thPRL(2026)·10 citations
27. 27*

    Charged black holes in the 1/N expansion

    Georges Obied🇬🇧 · Mario Reig🇬🇧

    We study some implications of $SU(N)\times U(1)$ theories coupled to gravity in the large-$N$ limit. We find that in theories with quarks transforming as $q\sim (\mathbf{N},1)$, black holes (BH) with charge larger than a critical value approach extremality $(M_{\mathrm{BH}}=\sqrt{2}{M}_{\mathrm{Pl}}{Q}_{\mathrm{BH}})$ as they evaporate. This occurs because BHs in this theory can only lose charge by emitting baryons, a process suppressed by a combinatoric factor $e^{-N\log N}$. Once extremality is reached the BH evolution halts for exponentially long times, ${\tau }_{\mathrm{BH}}\gtrsim e^{N\log N}$, without being protected by any symmetry. At times $t\gg {\tau }_{\mathrm{BH}}$ the BH forms a cloud of deconfined quarks around it, a \textit{quark corona}. The quarks are connected to the horizon by strings extending throughout distances that can be much larger than the inverse of the confinement scale, ${\Lambda }_N^{-1}$. Strikingly, due to energy conservation, these long strings cannot break even for light quarks. These effects can be further enhanced in clockwork-like theories based on Yang-Mills sectors of the type, $SU(N_1)\times SU(N_2)\times ...\times U(1)$. As an application to phenomenology, we give examples where BHs as light as one gram survive until today without evaporating, opening up regions of parameter space for primordial BH dark matter previously excluded by Hawking evaporation. This result relies only on large-$N$ combinatorics and is independent of the radiation mechanism from the BH, particle masses, and confinement scale. The theories we discuss pass non-trivial tests imposed by Swampland conjectures, including completeness of the spectrum as well as the weak gravity conjecture.

    ↳ hep-thgr-qchep-ph0 citations
28. 28*

    Dark Acoustic Oscillations as an Early-Universe Explanation of the DESI Anomaly

    Mathias Garny🇩🇪 · Florian Niedermann🇸🇪 · Martin S. Sloth🇩🇰

    DESI DR2 data have been widely interpreted as evidence for late-time evolving dark energy (DE) with an apparent phantom crossing. Here we investigate an alternative explanation, based on early-Universe physics. If dark acoustic oscillations (DAO) are close in scale to baryon acoustic oscillations (BAO), they can bias the extraction of the BAO scale from the peak in the galaxy correlation function. This leads to an apparent shift in the inferred distance if the superposition of BAO and DAO features is misinterpreted as being due to BAO only. Taking this shift into account, we find that a DAO with percent-level amplitude can reconcile DESI DR2 with Planck 2018 as well as Pantheon+ supernovae data, with fit improvement at a similar level as compared to evolving DE. Notably, a DAO feature with the required properties has been predicted in a previously proposed scenario that resolves the Hubble tension via a pre-recombination decoupling of dark matter and dark radiation (DRMD). The presence of a DAO feature close to the BAO peak can be scrutinized with future full-shape galaxy clustering data from DESI and Euclid.

    ↳ astro-ph.COhep-phPRD(2026)·8 citations
29. 29*

    Modeling the frequency-domain ringdown amplitude of comparable-mass mergers with greybody factors

    Romeo Felice Rosato🇮🇹 · Sophia Yi🇺🇸 · Emanuele Berti🇺🇸 · Paolo Pani🇮🇹

    It was recently shown that, in a binary coalescence, the greybody factor of the remnant black hole modulates the post-merger ringdown signal. In this work, we demonstrate that a simple four-parameter model based on the greybody factor accurately reproduces the frequency-domain amplitude of a large set of comparable-mass, aligned-spin numerical relativity waveforms from the SXS catalog, achieving mismatches of order $\mathcal{O}(10^{-5})$ and improving existing models by roughly two orders of magnitude. We also identify the optimal initial frequency for applying the model in the frequency domain and provide analytical fits of the model parameters in terms of the progenitor masses and aligned spins. Our results pave the way for new consistency tests of the ringdown phase, complementary to traditional black hole spectroscopy.

    ↳ gr-qcastro-ph.HEhep-phPRD(2026)·5 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.