Fri·Jan 30, 2026Friday·January 30, 2026

1. 01*

   MadAgents

   Tilman Plehn🇩🇪 · Daniel Schiller🇩🇪 · Nikita Schmal🇩🇪

   We uncover an effective and communicative set of agents working with MadGraph. Agentic installation, learning-by-doing training, and user support provide easy access to state-of-the-art simulations and accelerate LHC research. We show in detail how MadAgents interact with inexperienced and advanced users, support a range of simulation tasks, and analyze results. In a second step, we illustrate how MadAgents automatize event generation and run an autonomous simulation campaign, starting from a pdf file of a paper. The updated Claude Code implementation includes a self-improvement loop.

   hep-ph25 citations
2. 02*

   Constraining dimension-6 SMEFT with higher-order predictions for $pp\to tW$

   Nikolaos Kidonakis🇺🇸 · Kaan Şimşek🇺🇸

   We study single-top production in association with a $W$ boson at the Large Hadron Collider (LHC) as a probe of dimension-6 Standard Model effective field theory (SMEFT) at leading order, next-to-leading order, and approximate next-to-next-to-leading order accuracy in quantum chromodynamics (QCD). The process is sensitive to operators that modify the top-quark weak and chromomagnetic dipole interactions, and we perform three-parameter linear and quadratic SMEFT fits using doubly differential top-quark distributions in transverse momentum and rapidity for the Run II and Run III configurations at the LHC. We provide a detailed account of the uncertainties and quantify the impact of the different uncertainty components across bins and perturbative orders. We find that effective scales up to 2 TeV can be probed in nonmarginalized fits, while in marginalized fits the corresponding scales are around 0.5 and 1.5 TeV for linear and quadratic fits, respectively.

   hep-phPRD(2026)·1 citation
3. 03*

   Medium separation scheme effects on the magnetized and cold two-flavor superconducting quark matter

   Francisco X. Azeredo🇧🇷 · Dyana C. Duarte🇧🇷 · Ricardo L. S. Farias🇧🇷

   We analyze the impact of the Medium Separation Scheme (MSS) on two-flavor color superconducting (2SC) dense quark matter under the influence of a constant external magnetic field. The effects of the proper treatment of the model divergences are examined through a comparison of different approaches, including the combined implementation of the Magnetic Field Independent Regularization (MFIR) and the MSS, as well as the standard use of smooth form factors. Our findings for the Nambu--Jona-Lasinio model emphasize the critical role of properly separating medium effects from vacuum contributions in the model. The combined MFIR-MSS scheme suppresses spurious unphysical oscillations, often misinterpreted in the literature as de Haas--van Alphen oscillations, and ensures the correct high-density behavior of the diquark condensate. Furthermore, within the MSS framework, the magnetization remains positive across the explored parameter space, in sharp contrast with the behavior obtained in the traditional approach.

   hep-phhep-lathep-thnucl-thPRD(2026)·4 citations
4. 04*

   Nucleon axial-vector form factor and radius from radiatively-corrected antineutrino scattering data

   Oleksandr Tomalak🇨🇳 · Aaron S. Meyer🇺🇸 · Clarence Wret🇬🇧 · Tejin Cai🇺🇸 · Richard J. Hill🇺🇸 · Kevin S. McFarland🇺🇸

   The nucleon axial-vector form factor, $G_A$, is critical to determine the electroweak interactions of leptons with nucleons. Important examples of processes influenced by $G_A$ are elastic (anti)neutrino-nucleon scattering and muon capture by the proton. Sparse experimental data results in a large uncertainty on the momentum dependence of $G_A$ and has motivated the consideration of new experimental probes and first-principles lattice quantum chromodynamics (QCD) evaluations. The comparison of new and precise theoretical predictions for $G_A$ with future experimental data necessitates the application of radiative corrections to experimentally-observable processes. We apply these corrections in the extraction of $G_A$ and the associated axial-vector radius from the recent MINERvA antineutrino-hydrogen data, compare the effects from radiative corrections to other uncertainties in neutrino scattering experiments, and discuss the comparison of lattice QCD evaluations to experimental measurements.

   hep-phhep-exhep-latnucl-ex+1PRD(2026)·6 citations
5. 05*

   Earth-Density Effects in Long Baseline Neutrino Experiments

   Tia Pandit🇮🇳 · Bipin Singh Koranga🇮🇳

   Earth matter density uncertainties play a non trivial role in three flavor neutrino oscillations in matter, particularly for the muon to electron appearance channel that underpins CP violation measurements in long baseline experiments. We demonstrate that when realistic spatial variations of the Earths density are taken into account, the oscillation probabilities acquire additional, energy dependent structures that cannot be captured by path-averaged density approximations. We show that mismodeling of the matter density profile can introduce degeneracies that obscure genuine leptonic CP violating effects, thereby degrading parameter sensitivity and biasing the inference of the CP phase. Identifying energy regions in which CP sensitivity remains robust against matter density uncertainties is therefore essential. These considerations indicate that marginalization over a single effective density parameter is insufficient for next generation precision measurements and motivate the incorporation of spatially resolved Earth density profiles in the analysis frameworks of future long-baseline neutrino oscillation experiments.

   hep-phPRD(2026)·4 citations
6. 06*

   Measurements of $H\to W^{+}{W}^{-}$ in the Fully Leptonic Decay Mode at the FCC-ee

   Kael Kemp🇦🇺 · Aman Desai🇦🇺 · Paul Jackson🇦🇺

   The expected precision on measuring the $\sigma (e^{+}{e}^{-}\to ZH)\times Br(H\to W^{+}{W}^{-})$ in the fully leptonic decay mode at the Future Circular Collider (FCC) is presented. We consider two FCC-ee scenarios: $\sqrt{s}=240$ GeV centre-of-mass energy with a luminosity of 10.8${\mathrm{ab}}^{-1}$ and $\sqrt{s}=365$ GeV centre-of-mass energy with a luminosity of 3.12${\mathrm{ab}}^{-1}$. Our results indicate that a relative uncertainty of 2.9\% and 6.8\% can be achieved on measurements of $\sigma (e^{+}{e}^{-}\to ZH)\times Br(H\to W^{+}{W}^{-})$ in the fully leptonic decay mode at $\sqrt{s}=240$ GeV and $\sqrt{s}=365$ GeV, respectively.

   hep-ph2 citations
7. 07*

   Scaling Properties of Two-Particle-Two-Hole Responses in Asymmetric Nuclei for Neutrino Scattering within the Relativistic Mean-Field Framework

   V.L. Martinez-Consentino🇪🇸 · J. E. Amaro🇪🇸 · J. Segovia🇪🇸

   We perform a systematic analysis of the nuclear dependence of two-particle-two-hole meson-exchange current contributions to inclusive lepton-nucleus scattering within the relativistic mean-field framework. We present microscopic calculations of nuclear responses for a set of 17 nuclei, ranging from helium to uranium, using a model with different Fermi momenta for protons and neutrons. We propose a novel scaling prescription based on the two-particle phase space and key nuclear parameters. The resulting description is accurate over a wide range of nuclear targets, with typical deviations below 10\%, and allows for a separate treatment of the different emission channels. In addition, a consistent benchmark against electron-scattering data is provided. The parametrization presented provides a practical framework for extending the responses to different nuclear targets in neutrino event generators.

   hep-phnucl-thUniverse(2026)·5 citations
8. 08*

   Lepton sourced baryon asymmetry in the fourth generation model

   Hsiang-nan Li🇹🇼

   We demonstrate that the observed baryon asymmetry in the Universe can be accommodated in the extended Standard Model with sequential fourth generation fermions (SM4). We first construct the dimension-6 effective operators of the type $-i({\Phi }^{†}\Phi ){\bar{F}}_L\Phi f_R$ induced by fourth generation quarks, which carry the $CP$ violation (CPV) source from the $4\times 4$ Cabibbo-Kobayashi-Maskawa (CKM) matrix, $\Phi$ ($F_L$, $f_R$) being a Higgs double (left-handed fermion doublet, right-handed fermion singlet). The required inputs of the fourth generation fermion masses were derived in our previous dispersive analyses on heavy quark decays and neutral meson mixing. The similar framework allows the determination of the $4\times 4$ CKM matrix elements $V_{i{b}^{\prime }}$, $i=u$, $c$ and $t$, such that the strength of the CPV source can be evaluated unambiguously. The dimension-6 operators associated with fourth generation leptons, as implemented into the formalism for the electroweak baryogenesis in the literature, lead to the baryon-over-entropy ratio ${\eta }_B\approx 10^{-10}$.

   hep-phJHEP(2026)·1 citation
9. 09*

   Chiral-odd generalized parton distributions of spin-1/2 baryons

   Navpreet Kaur🇮🇳 · Monika Randhawa🇮🇳 · Harleen Dahiya🇮🇳

   We present the tomographical structure of baryons by studying the nonforward matrix elements of lightlike correlation functions of the tensor current. At the leading twist, with the tensor current, four chiral-odd distributions are in count. We calculate these distributions in a diquark spectator model with light-front formalism by considering purely transverse momentum transfer, i.e., zero skewness. Predictions for the nucleons and light hyperons are studied, emphasizing the difference arising from their different quark flavors.

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

    Gravitational form factors of baryons in a spectator diquark model

    Navpreet Kaur🇮🇳 · Harleen Dahiya🇮🇳

    Energy momentum tensor (EMT) expresses the interaction between the gravitation and the matter fields, in which the scattering off the graviton is a natural but infeasible probe. However, the EMT can be accessed indirectly through electromagnetic interactions in quantum chromodynamics. The matrix elements of the local EMT operator are parameterized by gravitational form factors, which are subsequently related to the generalized parton distributions. Within the diquark spectator model, we investigate the gravitational form factors of baryons. We consider all the feasible pairs of quark-diquark systems to understand the behavior of each constituent quark flavor of strange and non-strange baryons.

    hep-phJ.Subatomic Part.Cosmol.(2026)·0 citations
11. 11*

    The $\Omega (2380)$ as a partner of the $\Omega (2012)$

    Yi-Yao Li🇨🇳 · Albert Feijoo🇪🇸 · Eulogio Oset🇪🇸

    We present a study of the $\Omega (2380)$ resonance and show that it is consistent with a dynamically generated state arising from the ${\bar{K}}^{\ast }{\Xi }^{\ast }$, $\omega \Omega$, and $\varphi \Omega$ interactions. In this picture, the $\Omega (2380)$ is analogous to the $\Omega (2012)$, which is generated from the $\bar{K}{\Xi }^{\ast }$ and $\eta \Omega$ channels. The resulting mass, total width, and partial decay widths into the $\bar{K}{\Xi }^{\ast }$ and ${\bar{K}}^{\ast }\Xi$ channels are compatible with the available experimental data. We also discuss possible experimental observables that could provide further insight into the nature of this state.

    hep-phnucl-thPRD(2026)·3 citations
12. 12*

    Understanding the 1P- and 2S-wave nucleon resonances within the extended Lee-Friedrichs Model

    Yu-Hui Zhou🇨🇳 · Hui-Hua Zhong🇨🇳 · Zhi-Yong Zhou🇨🇳 · Xian-Hui Zhong

    We present a unified desciption of the low-lying $1P$- and $2S$-wave nucleon resonance within the framework of an extended Lee-Friedrichs scheme. By incorporating the coupled-channel dynamics between bare quark-model states and the $\pi N$, $\pi \Delta$ and $\eta N$ meson-baryon continua, we examine the mass shifts and structural properties of these excited states. We demonstrate that when the model parameters are calibrated to match the $1P$-wave spectrum and their widths, the pole associated with the bare $2S$ state is naturally shifted downward to the mass region of physical Roper resonance--$N(1440)$, thereby offering a dynamical explanation for the long-standing level-inversion problem. An approximate analysis of compositeness and elementariness reveals that the Roper resonance contains a significant meson-baryon continuum states, consistent with the picture of a bare core heavily dressed by meson-baryon cloud. Simultaneously, the pole positions and properties of five $1P$-wave resonances--$N(1535)$, $N(1650)$, $N(1520)$, $N(1700)$ and $N(1675)$ are successfully reproduced. Our results highlight the essential role of coupled-channel effects in shaping the nucleon spectrum and provide a consistent microscopic insight into the interplay between internal quark degrees of freedom and external hadronic fields.

    hep-phPRD(2026)·1 citation
13. 13*

    From LUXE to Future Colliders: Probing Strong-Field QED and Beyond

    Ivo Schulthess🇩🇪

    Strong-field quantum electrodynamics offers a unique window into non-perturbative phenomena such as vacuum pair production, in which electron--positron pairs are created from the vacuum in the presence of intense electromagnetic fields. The LUXE experiment at DESY is designed to probe this regime using collisions between a high-intensity laser and the 16.5 GeV electron beam of the European XFEL. Future accelerator infrastructures, such as linear colliders, could extend these studies to even higher intensity and energy scales. Additionally, high-energy photons produced in such interactions can be used in beam-dump experiments to search for new physics.

    hep-phhep-exEur.Phys.J.Plus(2026)·1 citation
14. 14*

    $f$-Mode oscillations and the gravitational response of compact stars with analytic equations of state

    Kilar Zhang🇨🇳 · Alessandro Parisi🇮🇹 · C. Vásquez Flores🇧🇷 · C.Henrique Lenzi🇧🇷 · Chian-Shu Chen🇹🇼

    We use a simple holographic model to study the property of cold and dense neutron stars (NSs) and deconfined QCD matter. With the aim of investigating the global properties of compact stars, such as the total gravitational mass and radius, the equation of states (EOS) of neutron stars and quark stars (QSs) are used to solve the Tolman-Oppenheimer-Volkov (TOV) equations for stellar structure. Additionally, we investigate the tidal deformabilities and $f$-mode oscillation for these two different compact stars. Our main conclusion is that, by using a holographic equation of state, it is possible to obtain neutron matter and quark matter properties and that it is also possible to extend the procedure to astrophysical applications.

    hep-phastro-ph.HEastro-ph.SRgr-qc0 citations
15. 15*

    Discovery prospects of a singly-charged scalar at $\mu$TRISTAN

    Joseph George🇮🇳 · Nobuchika Okada🇺🇸 · Dibyashree Sengupta🇮🇹 · Sudhir K. Vempati🇮🇳

    In this article, we study the associated production of a singly-charged (${\Delta }^{+}$) scalar along with a $W^{+}$ boson in the newly proposed ${\mu }^{+}{\mu }^{+}$ collider (also known as $\mu$TRISTAN) at $\sqrt{s}=2$ TeV. Such a singly-charged scalar is naturally accommodated in an extremely well-motivated neutrino mass model, namely, the Type-II seesaw model. This model, beside providing a viable explanation of neutrino mass generation, also allows for lepton flavor violating (LFV) processes. Since LFV processes are not allowed in the Standard Model (SM), we focus on the discovery prospect of the singly-charged scalar in the Type-II seesaw model at $\mu$TRISTAN through a LFV process, owing to the advantage of this process being free of any SM background. Additionally, this article also proposes a method to indicate if the underlying theory follows a Normal or an Inverted hierarchy depending on the distribution of lepton flavors in the final state.

    hep-phPRD(2026)·1 citation
16. 16*

    All-order prescription for facet regions in massless wide-angle scattering

    Yao Ma🇨🇭

    We take a step toward answering a long-standing question in the asymptotic expansion of Feynman integrals: how to systematically determine the regions in the Expansion-by-Regions technique for multiscale processes? Focusing on generic massless wide-angle scattering, we provide an all-order momentum-space prescription for facet regions, which generally dominate -- and in most cases exhaust -- the contributions in a given asymptotic expansion. This extends the Euclidean-space picture, where regions correspond to specific subgraphs, to the complexities of Minkowski space. Our results are derived from a novel analytical approach combining graph theory and convex geometry; as a key byproduct, we uncover for the first time the algebraic structure underlying momentum modes (collinear, soft, and their hierarchies).

    hep-phhep-th7 citations
17. 17*

    Azimuthal angular entanglement between decaying particles in ultra-peripheral ion collisions

    Spencer R. Klein🇺🇸

    Ultra-peripheral collisions (UPCs) involving relativistic heavy ions are a unique laboratory to study quantum correlations. The intense electromagnetic fields generate high rates of photonuclear interactions, including events involving multiple photon exchange. Multiple photon exchange can result in the production of multiple vector mesons and/or nuclear excitations. These interactions share a common impact parameter, so the photons have the same linear polarization. The shared polarization entangles the particles, leading to unique quantum correlations. The decays of these vector excitations are sensitive to this polarization, allowing for the study of these correlations. This letter will compare classical and quantum calculations of the correlations between these azimuthal directions. The two approaches predict vert different angular correlations. The differences are akin to those seen with polarized photons in tests of Bells inequality. Uniquely, UPC photoproduction can produce final states containing three or more particles, all entangled with the same polarization. These more complex states exhibit additional unique phenomenology, allowing new tests of multi-particle entanglement.

    hep-phnucl-exnucl-thquant-ph1 citation
18. 18*

    Axions on a Hyperbolic Ride: Geometric Suppression of CMB Isocurvature and a Blue-Tilted Spectrum

    Sai Chaitanya Tadepalli🇺🇸

    CMB limits on cold-dark-matter isocurvature are often interpreted as excluding the simultaneous realization of high-scale inflation and large QCD axion decay constants in pre-inflationary Peccei--Quinn (PQ) scenarios. This conclusion can be evaded by exploiting \emph{field-space geometry}. For a minimal complex PQ scalar with a $U(1)$-symmetric potential and a nonlinear sigma-model kinetic term $d{\sigma }^2=d{R}^2+f^2(R)d{\theta }^2$, the observable axion fluctuation is $\delta \theta \sim H_{\inf }/f(R)$, so an enhanced effective decay constant $f(R)$ suppresses isocurvature without explicit PQ breaking, extreme radial displacements, or additional couplings. We specialize to a hyperbolic metric $f(R)\propto \sinh (R/L)$ with curvature scale $L$. The same geometry also induces a time-dependent $\mathcal{O}(H_{\inf })$ effective mass for the canonical axial mode during radial slow-roll, and fixing the tilt and running of isocurvature. Thus, CMB-scale isocurvature is suppressed while a characteristic blue-tilted spectrum is generated. As a result, inflationary Hubble scales as large as $H_{\inf }\sim 10^{13}\mathrm{GeV}$ can be compatible with $f_a\sim 10^{14}$--$10^{16}\mathrm{GeV}$, reopening parameter space usually regarded as excluded. We present `observable' benchmarks and a semi-analytic template that relates the scale-dependence of isocurvature to the geometric lever arm $R/L$, providing a direct phenomenological probe on PQ field-space geometry.

    hep-phastro-ph.COPRD(2026)·3 citations
19. 19*

    Proposal to Search for the CP Violating Electromagnetic Vacuum Angle at the Event Horizon Telescope

    Willy Fischler🇺🇸 · Tom Banks🇺🇸

    We examine the possibility that evidence for a non-zero value of the CP violating $\frac{e^2}{32{\pi }^2}{\theta }_{EM}\int d^{4}x\vec{E}\cdot \vec{B}$ coupling might be extracted from Event Horizon Telescope observations of the black holes SgA* and M87*. The Fischler-Kundu\cite{FK} effect predicts a universal Hall current in the relaxation of charge falling onto the black hole horizon. We argue that this leads to a non-zero value of a certain CP-violating observable $\mathcal{C}$, defined below. The effect can be masked by parity violating plasma currents. In particular, evidence for polarization flips \cite{flip} in the signals from M87* indicate strong plasma effects in the data. We suggest that time averaging the data over periods including the flip might leave over a residual that would be an indicator of the FK signal. In addition, similarities in the polarization patterns between the two very different black holes, and a part of the signal that is uniform in frequency, might enable us to distinguish the universal topological signal from source and frequency dependent plasma effects. Current data does not appear to be sufficient to perform such a test.

    ↳ astro-ph.HEhep-phhep-th0 citations
20. 20*

    A Universal CMB $B$-Mode Spectrum from Early Causal Tensor Sources

    Kylar Greene🇰🇷 · Aurora Ireland🇺🇸 · Gordan Krnjaic🇺🇸 · Yuhsin Tsai🇺🇸

    Many early universe scenarios predict post-inflationary tensor perturbations from causality-limited, sub-horizon sources. While the microphysical details may differ, as long as these sources are bounded in duration and correlation length, their tensor power spectra exhibit a universal scaling behavior at small wavenumber: $P_h(k)\propto k^3$, corresponding to white noise on super-horizon scales at the time of production. If these early causal tensor sources (ECTs) exclusively produce gravitational waves before redshift $z\sim 10^5$, this scaling is realized on all of the scales observed in the cosmic microwave background (CMB), and thus yields a universal multipole distribution for the $B$-mode angular power spectrum. Unlike the scale-invariant distributions of inflationary $B$ modes, ECTs generically predict enhanced power on small scales and suppressed power on large scales, which allows these source classes to be distinguished given measurements over a sufficient range of angular scales. In this paper, we introduce a unified framework for characterizing ECTs and demonstrate how their universal infrared scaling manifests in low-frequency observables, including CMB $B$ modes and stochastic gravitational wave spectral densities. We illustrate this mapping with representative case studies of this universality class involving first-order phase transitions, topological defects, and enhanced scalar perturbations, which source tensor modes at second order in perturbation theory.

    ↳ astro-ph.COgr-qchep-phPRD(2026)·4 citations
21. 21*

    The Silver Blaze Problem in QCD

    Thomas D. Cohen🇺🇸

    This article provides a pedagogical introduction to the Silver Blaze problem. This problem refers to the difficulty of reconciling to perspectives on QCD with a chemical potential. The first is the phenomenological fact that at $T=0$ QCD remains in its ground state -- the vacuum -- with all physical observables unchanged whenever the magnitude of a chemical potential is less than some critical value. The second is the fact that in functional integral treatments, the inclusion of any nonzero chemical potential changes all eigenvalues of the Dirac operator for every gauge configuration, leading to a natural expectation that the functional determinants also changes, which leads to the expectation that physical observables should be altered. The problem amounts to explaining why nothing happens below the critical chemical potential. By focusing on the eigenvalues of ${\gamma }_0$ times the Dirac operator rather than the Dirac operator itself, it is possible to show that for QCD with two flavors and identical quark masses, an isospin chemical potential with a magnitude less than $m_{\pi }$ (and no baryon chemical potential), or a baryon chemical potential of less than $\frac{3}{2}{m}_{\pi }$ (and no isospin chemical potential), the functional integerals at $T=0$ themselves remain unchanged in all configurations that contribute to the functional integral with non-vanishing weight. However, for ${\mu }_{\mathrm{crit}}{\mu }_B>\frac{3}{2}{m}_{\pi }$, the Silver Blaze phenomenon arises due to functional determinants having nontrivial phases that lead to cancellations between different gauge configurations. The mechanism leading to such cancellations remains unknown.

    ↳ nucl-thhep-lathep-ph3 citations
22. 22*

    Background instability of quintessence model in light of entropy and distance conjecture

    Min-Seok Seo🇰🇷

    We apply the covariant entropy bound argument supporting the de Sitter swampland conjecture to the quintessence model, to find out the condition for the background to be unstable. More concretely, the background is unstable when the matter entropy given by the species number of the effective field theory increases more rapidly than the geometrical entropy proportional to the apparent horizon area, since it contradicts the covariant entropy bound. The rapid increase in the matter entropy is proposed by the distance conjecture, which states that the time evolution of some scalar field along the geodesic in the field space brings about the descent of a tower of states from UV. From this, we find that for the quintessence model, the unstable background admits the event horizon of finite size, and the converse is also true when the string tower is taken into account. Here, the presence of the event horizon implies that the trans-Planckian modes can be classicalized, violating the trans-Planckian censorship bound. We also point out that the scale separation between the Kaluza-Klein mass scale and the Hubble parameter can be realized when the product between the increasing rates of the matter and the geometrical entropies is bounded from below, which is consistent with the AdS distance conjecture. Our study suggests that various swampland conjectures can be comprehensively understood in the language of the entropy.

    ↳ hep-thgr-qchep-phFortsch.Phys.(2026)·0 citations
23. 23*

    Chemical potential differentials in the QCD phase diagram from heavy-ion isobar collisions

    Joaquin Grefa🇺🇸 · Chun Yue Tsang🇺🇸 · Rajesh Kumar🇺🇸 · Veronica Dexheimer🇺🇸 · Claudia Ratti🇺🇸 · Zhangbu Xu🇺🇸

    Temperature and baryon, charge, and strangeness chemical potentials characterize QCD matter under extreme conditions. Differences between these chemical potentials and their ratios probe conserved-charge correlations and the system's response in the multidimensional QCD phase diagram. We extract these quantities from STAR Ru+Ru and Zr+Zr isobar collisions using a Bayesian thermal analysis of hadron yields, which substantially reduces systematic uncertainties, and compare them with Taylor-expanded lattice-QCD and Chiral Mean Field model predictions. Isobar collisions thus emerge as a precision probe of four-dimensional QCD thermodynamics.

    ↳ nucl-thhep-exhep-lathep-ph+15 citations
24. 24*

    Realizing the phantom-divide crossing with vector and scalar fields

    Shinji Tsujikawa🇯🇵

    In generalized Proca theories, characterized by a vector field with broken $U(1)$ gauge invariance, late-time cosmic acceleration can be realized with a dark energy equation of state in the regime $w_{\mathrm{DE}}<-1$. In such scenarios, however, a phantom-divide crossing, as recently suggested by DESI observations, is not achieved without encountering theoretical inconsistencies. We incorporate a canonical scalar field with a potential, in addition to the vector field, and show that the phantom-divide crossing from $w_{\mathrm{DE}}<-1$ to $w_{\mathrm{DE}}>-1$ can occur at low redshifts. We propose a minimal model that admits such a transition and identify the region of parameter space in which all dynamical degrees of freedom in the scalar, vector, and tensor sectors are free from ghost and Laplacian instabilities. We further investigate the evolution of linear cosmological perturbations by applying the quasi-static approximation to modes well inside the Hubble radius. The dimensionless quantities $\mu$ and $\Sigma$, which characterize the growth of matter perturbations and the bending of light rays, respectively, depend on the sound speed $c_{\psi }$ of the longitudinal scalar perturbation associated with the vector field. Since $c_{\psi }$ is influenced by the transverse vector mode, the model exhibits sufficient flexibility to yield values of $\mu$ and $\Sigma$ close to 1. Consequently, unlike theories such as scalar Galileons, the present model can be consistent with observations of redshift-space distortions and integrated Sachs-Wolfe-galaxy cross-correlations.

    ↳ astro-ph.COgr-qchep-phhep-thJCAP(2026)·7 citations
25. 25*

    Cone-Dependent Jet Collisional Energy Loss in Finite QCD Medium

    Magdalena Djordjevic🇷🇸 · Bojana Ilic🇷🇸 · Marko Djordjevic🇷🇸

    We derive a compact HTL-resummed expression for the leading-order jet collisional energy loss in a finite-size, finite-temperature QCD medium. Defining the jet energy inside a cone of radius $R$, we obtain the out-of-cone elastic energy loss with an explicit separation between contributions from the primary jet parton and recoiling medium partons. The result reproduces the known partonic limit as $R\to 0$, vanishes for $R\to \pi$, and applies to both light- and heavy-flavor jets. Numerically, the elastic component shows a pronounced non-linear $R$ dependence relative to the radiative baseline, and its importance increases with $R$, becoming comparable to or exceeding the radiative contribution for sufficiently large jet radii. The path-length dependence remains close to linear for all $R$, while the medium-response contribution can exceed $10\%$ for realistic jet radii.

    ↳ nucl-thhep-phPLB(2026)·2 citations
26. 26*

    Gravitational amplitudes in the Regge limit: waveforms, shock waves and unitarity cuts

    Francesco Alessio🇮🇹 · Vittorio Del Duca🇮🇹 · Riccardo Gonzo🇬🇧 · Emanuele Rosi🇮🇹

    Motivated by recent progress in the high-energy description of gravitational scattering, we develop a systematic Regge-theory framework for $2\to 2+n$ amplitudes describing the scattering of two massive particles with $n$ graviton emissions, including spin effects. Working in the ultra-relativistic limit at leading logarithmic accuracy, the massive result smoothly reduces to its massless counterpart. We describe both quantum (Regge trajectory and BFKL $t$-channel evolution) and classical ($s$-channel multi-$H$ evolution) contributions using both an exponential representation of the S-matrix and a shock-wave formalism in light-cone quantisation. In the latter approach, gravitational Wilson lines evolve in rapidity space under a boost-invariant Hamiltonian, providing a space-time realisation of the high-energy dynamics and making contact with recent effective field theory descriptions in the forward limit. As an application, we compute the leading-logarithmic contribution to the massive spinless $2\to 2$ amplitude at 5PM-2SF order, recovering the previously determined massless result, and derive the tree-level $2\to 3$ amplitude and its associated scattering waveform for Kerr black holes in the ultra-relativistic limit.

    ↳ hep-thgr-qchep-ph9 citations
27. 27*

    Celestial energy-energy correlation in Yang-Mills theory and gravity

    HongYi Ruan🇨🇳 · YiZhe Zheng🇨🇳 · Hua Xing Zhu🇨🇳

    We introduce the celestial energy-energy correlator (cEEC), an infrared and collinear safe observable that makes the celestial conformal symmetry of four-dimensional scattering manifest. The cEEC is defined as a correlation function of average null energy operators measured on boost eigenstates and takes the form of a four-point function in a fictitious two-dimensional conformal field theory on the celestial sphere. An important feature of the cEEC is that it smoothly interpolates between different key regimes of perturbative gauge theory and gravity, such as the collinear limit, the Sudakov limit, and the Regge limit. We compute the cEEC to the first nontrivial order in $\mathcal{N}=4$ super Yang-Mills theory, pure Yang-Mills theory, Einstein gravity, and $\mathcal{N}=8$ supergravity. In $\mathcal{N}=8$ supergravity, the cEEC is uniquely determined by celestial symmetries and boundary data, demonstrating that bootstrap methods can yield closed-form results for this class of observables.

    ↳ hep-thhep-phPRD(2026)·6 citations
28. 28*

    Numerical simulations of primordial black hole formation via delayed first-order phase transitions

    Zhuan Ning🇨🇳 · Xiang-Xi Zeng🇨🇳 · Rong-Gen Cai🇨🇳 · Shao-Jiang Wang🇨🇳

    We perform fully nonlinear, spherically symmetric numerical simulations of superhorizon false-vacuum-domain (FVD) collapse in a coupled gravity-scalar-fluid system to study primordial black hole (PBH) formation during delayed first-order phase transitions (FOPTs). Using adaptive mesh refinement to resolve the bubble wall, we identify three dynamical outcomes: type B (supercritical) PBHs with an interior baby universe and a bifurcating trapping horizon, type A (subcritical) PBHs with an apparent horizon formed by direct wall collapse, and dispersal with no PBH formation. To separate these three cases, we evaluate two commonly used PBH-formation criteria: the time scale ratio $t_{\mathrm{H}}/t_{\mathrm{V}}$ (horizon crossing time versus vacuum-energy domination time) and the local density contrast $\delta (t_{\mathrm{H}})$ at horizon crossing. For the parameter space explored, we find that $t_{\mathrm{H}}/t_{\mathrm{V}}$ is a more robust predictor of outcome: type B PBHs form when $t_{\mathrm{H}}/t_{\mathrm{V}}\gtrsim 1$ (critical range $\sim 1.1-1.6$ in our survey), type A PBHs arise when $t_{\mathrm{H}}/t_{\mathrm{V}}$ is below this threshold but remains above a lower bound (typical range $\sim 0.35-0.7$), and no-PBH dispersal occurs when $t_{\mathrm{H}}/t_{\mathrm{V}}$ falls below this lower bound. When a clear thin-wall FVD boundary exists, $\delta (t_{\mathrm{H}})$ can correspondingly distinguish different outcomes (roughly ${\delta }_c(t_{\mathrm{H}})\sim 1-1.7$ for type B and ${\delta }_c(t_{\mathrm{H}})\sim 0.35-0.5$ for type A), but is highly sensitive to wall structure and model details and thus less universal. These results offer new insights into the dynamics of FVD collapse, quantify practical PBH-formation thresholds, and pave the way for precise predictions of PBH abundance from delayed FOPTs.

    ↳ gr-qcastro-ph.COhep-phJCAP(2026)·22 citations
29. 29*

    Quantum fluctuations in hydrodynamics and quantum long-time tails

    Akash Jain🇬🇧

    We construct a quantum Schwinger-Keldysh (SK) effective field theory for the diffusive hydrodynamics of a conserved scalar field. Quantum corrections within the SK framework are guided by fluctuation-dissipation relations, enforced via a dynamical Kubo-Martin-Schwinger (KMS) symmetry. We find that the KMS symmetry necessarily generates fluctuation contributions in the SK effective action at all orders in the noise field, thereby giving rise to intrinsically non-Gaussian noise. We use our results to compute one-loop quantum corrections to the two-point density-density retarded correlation function, leading to a quantum generalization of hydrodynamic long-time tails. Our results apply at arbitrarily high orders in $\hslash$. The one-loop results for retarded correlation functions have been expressed in terms of a family of polynomials. We also provide a closed-form expression for the one-loop results at leading order in the wavevector expansion.

    ↳ hep-thcond-mat.stat-mechhep-phmath-ph+22 citations
30. 30*

    Neural S-matrix bootstrap II: solvable 4d amplitudes with particle production

    Mehmet Asim Gumus🇫🇷 · Damien Leflot🇫🇷 · Piotr Tourkine🇫🇷 · Alexander Zhiboedov🇨🇭

    We study a model for nonperturbative unitarization of the four-point contact scalar amplitude in four dimensions. It is defined through an infinite sum of planar diagrams, constructed using two-particle unitarity and crossing symmetry. We reformulate the problem in terms of a set of nonlinear integral equations obeyed by the single and double discontinuities of the amplitude. We then solve them using a neural-network ansatz trained by minimizing a physics-informed loss functional. We obtain a one-parameter family of amplitudes, which exhibit rich structure: sizeable particle production, nontrivial emergent Regge behavior, Landau curves, a logarithmic decay at high energy and fixed angle. Finally, we go beyond the two-particle-reducible setup by treating the multi-particle data -- supported above the multi-particle Landau curves due to multi-particle unitarity -- as a dynamical variable. We demonstrate that it can be tuned to suppress low-spin particle production -- a phenomenon we call Aks screening -- at the cost of generating larger and oscillatory double spectral density in the multi-particle region.

    ↳ hep-thhep-ph4 citations
31. 31*

    Modified Teleparallel $f(T)$ Gravity, DESI BAO and the $H_0$ Tension

    Mariam Bouhmadi-López🇪🇸 · Carlos G. Boiza🇪🇸 · Maria Petronikolou🇬🇷 · Emmanuel N. Saridakis🇬🇷

    We investigate whether late-time modifications of gravity in the teleparallel framework can impact the current tension in the Hubble constant $H_0$, focusing on $f(T)$ cosmology as a minimal and well-controlled extension of General Relativity. We consider three representative $f(T)$ parametrisations that recover the teleparallel equivalent of General Relativity at early times and deviate from it only at late epochs. The models are confronted with unanchored Pantheon+ Type~Ia supernovae, DESI DR2 baryon acoustic oscillations, compressed Planck cosmic microwave background distance priors, and redshift-space distortion data, allowing us to jointly probe the background expansion and the growth of cosmic structures. Two of the three models partially shift the inferred value of $H_0$ towards local measurements, while the third worsens the discrepancy. This behaviour is directly linked to the effective torsional dynamics, with phantom-like regimes favouring higher $H_0$ and quintessence-like regimes producing the opposite effect. A global statistical comparison shows that the minimal $f(T)$ extensions considered here are not favoured over $\Lambda$CDM by the combined data. Nevertheless, our results demonstrate that late-time torsional modifications can non-trivially redistribute current cosmological tensions among the background and growth sectors.

    ↳ gr-qcastro-ph.COhep-phhep-thUniverse(2026)·13 citations
32. 32*

    Asymptotic Freedom and Vacuum Polarization Determine the Astrophysical End State of Relativistic Gravitational Collapse: Quark--Gluon Plasma Star Instead of Black Hole

    Herman J. Mosquera Cuesta🇨🇴 · Fabián H. Zuluaga Giraldo🇨🇴 · Wilmer D. Alfonso Pardo🇨🇴 · Edgardo Marbello Santrich🇨🇴 · Guillermo U. Avendaño Franco🇺🇸 · Rafael Fragozo Larrazabal🇪🇸

    A general relativistic model of an astrophysical hypermassive extremely magnetized ultra-compact self-bound quark--gluon plasma object that is supported against its ultimate gravitational implosion by the simultaneous action of the vacuum polarization driven by nonlinear electrodynamics (NLED: light-by-light scattering) and the quantum chromodynamics (QCD) asymptotic freedom, is presented. These QCD stars can be the final figures of the equilibrium of collapsing stellar cores. Post-supernova fallback material pushes the nascent remnant beyond its stability to collapse into a hybrid hypermassive neutron star (HHMNS). Hypercritical accretion can unbind the whole HHMNS's baryons to spontaneously break away color confinement, powering a first-order hadron-to-quark phase transition to a sea of ever-freer quarks and gluons. This core is hydro-stabilized by the steady, endlessly compression-admitting asymptotic freedom state, possibly via gluon-mediated enduring exchange of color charge among bound states. The nonlinear TOV equation indicates the occurrence of hypermassive QGP/QCD stars with a wide mass spectrum ($0\lesssim$ M${}_{\mathrm{Star}}^{\mathrm{QGP}}\lesssim$\,7\,M${}_{\odot }$ and beyond), for star radii ($0\lesssim R_{\mathrm{Star}}^{\mathrm{QGP}}\lesssim 24$\,km and beyond) with B-fields ($10^{14}\le$ B${}_{\mathrm{Star}}^{\mathrm{QGP}}\le 10^{16}$\,G and beyond). Such QCD stars can emulate what the true black holes are supposed to gravitationally do in most astrophysical settings. This color quark star could be found through a search for its eternal ``yo-yo'' state gravitational-wave emission, or via lensing phenomena like gravitational rainbows, as in this scenario it is expected that the light deflection angle, directly influenced by the larger effective mass/radius and magnetic field of the deflecting object, increases as the incidence angle decreases for impact parameter lower values.

    ↳ gr-qcastro-ph.HEhep-phnucl-thUniverse(2025)·1 citation

* 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.