Mon·Sep 8, 2025Monday·September 8, 2025

1. 01*

   Exploring Scalar Leptoquarks at Muon Collider via Indirect Signatures and Right-Handed Neutrino-Assisted Decays

   Subham Saha🇮🇳 · Arvind Bhaskar🇮🇳 · P. S. Bhupal Dev🇺🇸 · Manimala Mitra🇮🇳

   Scalar leptoquarks (sLQs) appear in a wide range of ultraviolet-motivated extensions of the Standard Model and provide a natural link between the quark and lepton sectors. In this work, we investigate the discovery potential of an sLQ doublet ${\tilde{R}}_2(3,2,1/6)$ that couples to light quarks and right-handed neutrinos (RHNs) at the proposed muon collider. We analyze both indirect probes arising from $t$-channel sLQ exchange that affects the high-$p_T$ behavior of dijet spectra and direct searches exploiting pair and single production of the sLQs, incorporating the full interplay of kinematic thresholds and decay topologies. We find that indirect probes at muon colliders deliver remarkably robust sensitivity to the sLQ-quark-muon coupling over a broad mass range. Assuming a sub-$\mathcal{O}(1)$ Yukawa coupling, we achieve a $5\sigma$ sensitivity up to sLQ masses $\sim 4.0$ TeV ($7.0$ TeV) at $\sqrt{s}=5$ (10) TeV center-of-mass energy with $\mathcal{L}=3{\mathrm{ab}}^{-1}$ ($10{\mathrm{ab}}^{-1}$) integrated luminosity. Direct production channels provide complementary reach: pair production dominates below threshold, while single production, driven by the sLQ-quark-muon/RHN interaction, decisively extends the mass reach well into the multi-TeV regime. We demonstrate that with $\mathcal{O}(1)$ Yukawa couplings, the single production channel can probe sLQ masses up to $3.0$ TeV ($6.0$ TeV) for $\sqrt{s}=5$ TeV ($10$ TeV). Together, these channels enable a unified exploration of parameter space far beyond the projected capabilities of the HL-LHC, including regions where conventional charged-lepton signatures are subdominant.

   hep-ph3 citations
2. 02*

   Dark Matter in a Three-Brane Randall-Sundrum Scenario out of the Evanescent Limit

   Andrea Donini🇪🇸 · Miguel G. Folgado🇪🇸 · Alejandro Muñoz-Ovalle🇪🇸

   The Nature of Dark Matter (DM), that constitutes approximately 25\% of the energy density in the Universe, is still eluding us. An intriguing possibility is that DM does indeed interacts with SM particles only gravitationally (the only mean by which we have detected it so far), albeit in an extra-dimensional scenario yet it has not been possible to detect it by some non-gravitational means. In a three-brane Randall-Sundrum setup, with DM located on a Deep Infra-Red GeV-TeV brane, and the SM on an Infra-Red TeV-PeV one, it was shown to be possible to recover the observed DM relic abundance and somewhat relax the hierarchy problem, whilst avoiding LHC stringent bounds on DM and KK graviton masses that constrain severely similar two-brane setups. The phenomenological results, however, have been obtained under the assumption that the bulk curvatures on the left ($k_1$) and the right ($k_2$) of the intermediate IR-brane are identical, $k_2\to k_1$. Since the brane tension ${\sigma }_{\mathrm{IR}}$ of the intermediate brane is proportional to $k_2-k_1$ and, therefore, vanishes, it is clear that this limit (for which the IR-brane becomes {\em evanescent}) is unphysical. We could say that this is {\em no brane}: if the brane tension of a brane vanishes, there is no brane in the bulk (pun intended). In this paper, therefore, we study in detail the theoretical framework needed to explore this interesting phenomenological possibility, {\em out of the evanescent brane limit}. We show that most of the formulæused in the {\em evanescent limit} are still valid for $\mathcal{O}(1)$ differences between $k_1$ and $k_2$ (thus, introducing no new unjustified hierarchy in the bulk). Once the relevant couplings of radions and KK gravitons are computed, we study the (enlarged) parameter space of the model looking for the region in which the relic DM abundance is recovered.

   hep-phhep-thJHEP(2026)·4 citations
3. 03*

   Hot and dense pQCD in a very strong magnetic background

   Eduardo S. Fraga🇧🇷 · Letícia F. Palhares · Tulio E. Restrepo🇺🇸

   We compute the pressure, chiral condensate and strange quark number susceptibility from perturbative QCD up to two-loop order at finite temperature and very high magnetic fields with physical quark masses. We also discuss the case of cold and dense quark matter in the presence of a very strong magnetic field and constraints for quark magnetars.

   hep-phEPJ Web Conf.(2026)·1 citation
4. 04*

   Tribute to Henry Primakoff: Chiral Perturbation Theory Tests via Primakoff Reactions

   Murray Moinester🇮🇱

   Consider high energy (GeV) beam particles scattering from the Coulomb field of a target nucleus (Z, A). The Coulomb field acts as a target of ${\gamma }^{\ast }$ virtual photons, with the target density proportional to Z${}^2$. Henry Primakoff was the first to propose determining the lifetime of the ${\pi }^0$ meson by measuring the production cross section for the reaction $\gamma {\gamma }^{\ast }\to {\pi }^0$. This process occurs when a high-energy gamma-ray interacts with the Coulomb field. Quasi real exchanged photons (${\gamma }^{\ast }$) are identified by isolating the sharp Coulomb peak at very low values of the squared four momentum transfer t to the target nucleus. The scattering cross section via one-photon exchange is proportional to the fine-structure constant $\alpha$ and inversely proportional to t${}^2$. Since t is inversely related to the squared center-of-mass energy (s), it decreases rapidly as s increases. Consequently, despite the weakness of the electromagnetic interaction, the interaction amplitude can still be significant. We will first discuss Primakoff's scientific career and personal life. Next, we will review the Primakoff scattering experiments that measured the pion polarizability and the $\gamma \to \pi \pi \pi$ chiral anomaly amplitude at CERN COMPASS and the ${\pi }^0$ lifetime at Jefferson Laboratory (JLab). The data from these experiments are in good agreement with two-flavor (u, d) Chiral Perturbation Theory (ChPT) predictions. We explain that additional Primakoff measurements with kaons and $\eta$ mesons are needed to test how well three flavor (u, d, s) ChPT captures strange quark effects.

   hep-phhep-ex0 citations
5. 05*

   Flavour from Fractal Mass Chains

   Alejandro Ibarra🇩🇪 · Aadarsh Singh🇮🇳 · Sudhir K Vempati🇮🇳

   We explore the possibility that the underlying flavour structure of the Standard Model could be determined by mass chains on a fractal geometry. We consider, as an example, the theory space on a Sierpinski-like geometry. The fermion mass chains on a Sierpinski-like geometry with three decorations (iterations) lead to three zero modes, which can be identified with the three generations of the Standard Model. This framework also reproduces the measured charged and neutral lepton masses and mixing angles with very few parameters. We also briefly discuss the possible extension to the quark sector.

   hep-phhep-thPLB(2026)·3 citations
6. 06*

   Dissipative contributions to spin polarization

   Matteo Buzzegoli🇷🇴

   Utilizing the Zubarev non-equilibrium density operator method and a first-order gradient expansion, we provide a comprehensive classification of all possible spin polarization effects. A key finding is that, with the unique exception of those induced by the gradient of the spin potential, all first-order dissipative corrections are chiral, implying their dependence on parity-breaking interactions or chiral imbalance. The work also introduces new non-dissipative phenomena akin to the Spin Hall Effect, including the Chiral Spin Hall Effect, which offers a novel observable to probe QCD topological configurations.

   hep-phnucl-thEPJ Web Conf.(2026)·0 citations
7. 07*

   Surveying the theory space of pion dark matter

   Anja Alfano🇬🇧 · Nick Evans🇬🇧 · Suchita Kulkarni🇦🇹 · Werner Porod🇩🇪

   We use a holographic model to survey the space of strongly coupled SU(Nc) gauge dynamics with QCD-like chiral symmetry breaking pattern for quarks in the fundamental representation. We systematically identify the light degrees of freedom (rho, sigma and pi mesons) that would make up the dark sector as a function of Nf, Nc and a common quark mass scale. We identify seven distinct effective theories that are of interest to explore and make a first summary of the expected dark matter phenomenology. Amongst our results we conclude that QCD-like models where the low energy theory is described purely in terms of pions struggle to generate a large enough Mpi/fpi value so these theories will need extra relic density generation mechanisms to be viable. The largest space of models (with an intermediate quark mass) have both the sigma and rho lying below 2 Mpi and are largely unexplored in the literature so far. Regions with just one of rho or sigma light are possible in constrained parameter regions. These states aid the pion relic density generation as needed for valid theories. The sigma always lies above the pi mass becoming degenerate with the pi in the extreme walking limit.

   hep-phJHEP(2026)·10 citations
8. 08*

   Engineering Confining Dilatons: A WKB Inverse Problem in Holographic QCD

   Miguel Angel Martin Contreras🇨🇳 · Alfredo Vega🇨🇱

   This work presents a WKB-based inverse problem approach within the framework of holographic bottom-up QCD to engineer confining dilatons from hadronic mass spectra. Starting from a general parameterization of nonlinear radial Regge trajectories, $M_n^2=a(n+b{)}^{\nu }$, we apply the Rydberg-Klein-Rees (RKR) formula to derive the large-z behavior of the corresponding holographic confining potential. This potential is inversely related to the dilaton field profile, leading naturally to a non-quadratic dilaton $\Phi (z)=(\kappa z{)}^{2-\alpha }$, where the parameters ($\kappa$, $\alpha$) are uniquely determined by the spectral parameters ($a$,$\nu$). We successfully test this method by fitting the spectra of heavy quarkonia ($c\bar{c}$ and $b\bar{b}$), achieving good agreement with experimental data. Furthermore, we extend this formalism to describe the spectroscopy of tetraquark states by superimposing an additional potential term, derived from the Bethe-Salpeter equation for diquarks, onto the standard mesonic confining potential. This work establishes a powerful and flexible bottom-up framework for deriving confinement directly from spectral data, applicable to both conventional and exotic hadrons.

   hep-ph3 citations
9. 09*

   Reconstruction of the Dipole Amplitude in the Dipole Picture as a mathematical Inverse Problem

   Henri Hänninen🇫🇮 · Antti Kykkänen🇺🇸 · Hjørdis Schlüter🇫🇮

   We show that the inference problem of constraining the dipole amplitude with inclusive deep inelastic scattering data can be written into a discrete linear inverse problem, in an analogous manner as can be done for computed tomography. To this formulation of the problem, we apply standard inverse problems methods and algorithms to reconstruct known dipole amplitudes from simulated reduced cross section data with realistic precision. The main difference of this approach to previous works is that this implementation does not require any fit parametrization of the dipole amplitude. The freedom from parametrization also enables us for the first time to quantify the uncertainties of the inferred dipole amplitude in a novel more general framework. This mathematical approach to small-$x$ phenomenology opens a path to parametrization bias free inference of the dipole amplitude from HERA and Electron--Ion Collider data.

   hep-phmath-phmath.MPnucl-thPRD(2025)·4 citations
10. 10*

    Exact calculation of photon polarization observables in Bethe-Heitler process

    Yu.M. Bystritskiy🇷🇺 · V.A. Zykunov🇷🇺

    The effects of polarization transfer from the initial electron to the bremsstrahlung photon in electron-nucleus scattering (Bethe-Heitler process) are considered. The calculation is carried out without the assumption of smallness of the electron mass. A detailed comparison with previous well-known works is made. Some issues related to neglecting the electron mass are shown and commented on. The results are applicable to the modelling of polarized cross sections at low energies (even at a few electron mass scale).

    hep-phPRD(2026)·0 citations
11. 11*

    Tensor-polarized twist-3 parton distribution functions $f_{LT}(x)$ for the spin-1 deuteron by using twist-2 relations

    S. Kumano🇨🇳 · Kenshi Kuroki🇨🇳

    Tensor-polarized twist-3 parton distribution functions (PDFs) $f_{LT}(x)$ are calculated for the spin-1 deuteron by using twist-2 relations, which are similar to the Wandzura-Wilczek relation and the Burkhardt-Cottingham sum rule in the spin-1/2 nucleon, together with tensor-polarized twist-2 PDFs $f_{1LL}(x)$. The PDFs are shown for $f_{LT}(x)$ at $Q^2=2.5$ GeV${}^2$, where the tensor-polarized PDFs $f_{1LL}(x)$ are provided. The $x$-dependence of $f_{LT}(x)$ is similar to $f_{1LL}(x)$, and the magnitude of $f_{LT}(x)$ is roughly of the order of $f_{1LL}(x)$. In experiments at the Thomas Jefferson National Accelerator Facility (JLab), higher-twist effects could be sizable because $Q^2$ values are not very large in comparison with the hadronic scale of 1 GeV${}^2$. Therefore, the JLab experiments could provide a good opportunity to investigate the twist-3 distributions $f_{LT}(x)$ in addition to the twist-2 ones $f_{1LL}(x)$. Furthermore, these tensor-polarized PDFs could be investigated at future Electron-Ion Colliders (EICs) and hadron accelerator facilities such as the Fermi National Accelerator Laboratory (Fermilab), the Nuclotron-based Ion Collider fAcility (NICA), and the Large Hadron Collider (LHC).

    hep-phhep-exhep-latnucl-ex+1PLB(2026)·6 citations
12. 12*

    Dispersion relations of deeply virtual Compton scattering: investigating twist-4 kinematic power corrections

    Víctor Martínez-Fernández🇫🇷 · Cédric Mezrag🇫🇷

    In this paper we include kinematic power corrections up to twist-four to the deeply virtual Compton scattering dispersion relation. We demonstrate that, both for (pseudo-)scalar and spin-$1/2$ targets, the formal expression of the $n$-subtracted leading-twist dispersion relations is preserved. However, the expression of the subtracted constants is modified by the kinematic powers. Importantly, the minimal-subtracted dispersion relation for the helicity-conserving amplitude, previously thought to depend only on the Polyakov-Weiss $D$-term, now also depends on the double distributions $F$ and $K$. These results are consistent with the ones obtained previously in the literature. Such a mixing may be critical for the Jefferson Lab kinematic range, as it is not suppressed for typical values of $t$ and $Q^2$ in the valence region. We therefore expect a strong impact on attempts to extract pressure forces from DVCS data.

    hep-phnucl-thPRD(2026)·8 citations
13. 13*

    Relativistic spin precession in homogeneous background fields

    Yunhua Ding🇺🇸 · Alan Kostelecky🇺🇸 · Arnaldo J. Vargas🇺🇸

    The Bargmann-Michel-Telegdi equation, which describes the precession of the spin of a charged Dirac particle moving in a homogeneous electromagnetic field, is generalized to include also other homogeneous background fields. The treatment incorporates observable coefficients that govern operators of mass dimensions three through six in the underlying Dirac effective field theory. A relativistic formulation valid in arbitrary inertial frames is obtained. The results are applicable to searches for new physics beyond the Standard Model, including searches for Lorentz and CPT violation.

    hep-phPLB(2025)·3 citations
14. 14*

    Monte Carlo challenges for strong field quantum electrodynamics

    Anthony Hartin🇩🇪

    The assisted Schwinger effect, which is predicted to display non-perturbative quantum tunnelling, is expected to be produced in precision lab experiments with electron beams and intense lasers. Indeed, many novel effects predicted by a theory which incorporates the laser field exactly, can be probed experimentally with the proper application of theory and simulation. Among predicted first order effects are a rest mass shift and harmonic Compton scattering. Higher order effects include resonant transition rates which become apparent when scanned over specific kinematic parameters. The underpinning of the theory and experiment is a Monte Carlo simulation tool which precisely links experimental realities to the expected theoretical transition rates. We report on the progress of such a tool here.

    hep-phEPJ Web Conf.(2025)·1 citation
15. 15*

    Searching for a Dark Dimension Right-handed Neutrino in KATRIN

    Ignatios Antoniadis🇹🇭 · Auttakit Chatrabhuti🇹🇭 · Hiroshi Isono🇹🇭

    We study the possibility that the Right-handed neutrino is a five-dimensional state propagating along a micron size extra dimension, as required in the dark dimension proposal. We work out the signatures of R-neutrino production in KATRIN experiment and compare them with those of a sterile neutrino which manifests by a kink in the electron energy spectrum of the beta-decay at a value corresponding to the sterile neutrino mass. We explore the allowed parameter space of the compactification scale and the R-neutrino bulk mass versus the Yukawa coupling, and show that a large part of it is within KATRIN's sensitivity. When the bulk mass is much smaller than the compactification scale, several kinks could be observed corresponding to the positions of the R-neutrino Kaluza-Klein excitations, while for large bulk mass there will be effectively one kink at the position of the bulk mass.

    hep-phastro-ph.COhep-thJHEP(2026)·9 citations
16. 16*

    Spin-spin entanglement in diffractive heavy quark production

    Michael Fucilla🇵🇱 · Yoshitaka Hatta🇺🇸

    We calculate the spin density matrix of a heavy quark-antiquark pair ($b\bar{b}$, $c\bar{c}$ or $s\bar{s}$) diffractively produced in Deep Inelastic Scattering and Ultraperipheral Collisions. We show that the Pomeron exchange leaves characteristic imprints on the entanglement pattern between the quark and the antiquark. For the longitudinally polarized virtual photon, the pair always exhibits maximal entanglement and maximal violation of the Bell-CHSH inequality. For the transversely polarized photon, the pair is always entangled and Bell-violating, reaching maximal entanglement and maximal violation simultaneously when the transverse momentum approximately equals the quark mass.

    hep-phquant-phPRD(2026)·23 citations
17. 17*

    Unbinning global LHC analyses

    Henning Bahl🇩🇪 · Tilman Plehn🇩🇪 · Nikita Schmal🇩🇪

    Neural simulation-based inference has been shown to outperform traditional, histogram-based inference in numerous phenomenological and experimental studies at the LHC. So far, these analyses have focused on individual processes. We study the combination of four different di-boson processes in terms of the Standard Model Effective Field Theory. Our results demonstrate how neural simulation-based inference also wins over traditional methods for more global LHC analyses.

    hep-ph4 citations
18. 18*

    Do null defects dream of conformal symmetry?

    Rajeev S. Erramilli🇫🇷 · Justin Kulp🇺🇸 · Fedor K. Popov🇺🇸

    We initiate the study of null line defects in Lorentzian conformal field theories in various dimensions. We show that null lines geometrically preserve a larger set of conformal isometries than their timelike and spacelike counterparts, explain a connection to non-relativistic systems, and constrain correlation functions using conformal Ward identities. We argue that having conformal symmetry, and especially maximal conformal symmetry, is extremely constraining -- nearly trivializing systems. We consider the (3+1)d scalar pinning field and null Wilson line examples in depth, compare their results to ultraboosted limits of timelike and spacelike systems, and argue that shockwave-type solutions are generic. A number of physical consistency conditions compel us to consider defect correlators as distributions on a restricted subspace of Schwartz test functions. Consequently, we provide a resolution to the longstanding problem of ultraboosted limits of gauge potentials in classical electromagnetism. We briefly analyze semi-infinite sources for the scalar in ($4-ϵ$)-dimensions, consider solutions on the Lorentzian cylinder, and introduce the ''perfect null polygon'' which emerges for compatibility between Gauss' law and ultraboosted limits.

    ↳ hep-thhep-phmath-phmath.MP7 citations
19. 19*

    Spontaneous collapse effects on relativistic fermionic matter

    Y.M.P.Gomes🇧🇷

    This study expands the spontaneous collapse assumptions into the relativistic quantum field theory framework for Dirac fields. By solving Lindblad's master equation using the Keldysh formalism, the effective action is derived, which captures the dynamics of fermions with spontaneous collapse represented as an imaginary self-interaction term. Utilizing the corresponding Dyson-Schwinger equations at 1-loop approximation, the effective mass induced by the nonlinearity is computed. The findings indicate the presence of a new mechanism that introduces a qualitative change in the mass spectrum, where the particle's mass becomes complex. This mechanism, which generates a Lorentz invariance violation in the infrared regime, recovers the Lorentz invariance in the ultraviolet regime. The corresponding hydrodynamics of the system is analyzed through the Keldysh component of the propagator, and a conserved charge is found. In contrast, the energy-momentum tensor is shown to be non-conserving. This phenomenon represents a new contribution to the understanding of the spontaneous collapse and the transition from quantum to the classical realm.

    ↳ hep-thhep-phEPJC(2025)·0 citations
20. 20*

    New phases in QCD at finite temperature and chemical potential

    Masanori Hanada🇬🇧 · Jack Holden🇨🇳 · Hiromasa Watanabe🇯🇵

    Understanding the phases of quantum chromodynamics (QCD) at finite temperature and baryon density is crucial for describing matter in heavy-ion collisions and the interior of neutron stars. While the transition from the confined phase to the deconfined phase has been extensively studied at vanishing chemical potential, recent theoretical work suggests the existence of intermediate phases with partial deconfinement, where only a subset of the color degrees of freedom is deconfined. In this paper, we study the generalization of partial deconfinement in QCD in the Veneziano large-$N_{\mathrm{c}}$ limit ($N_{\mathrm{f}}/N_{\mathrm{c}}$ fixed) to finite baryon chemical potential. We find that the partially deconfined phase has finer structure, and hence that there are four phases in QCD at finite temperature and moderately large chemical potential: complete confinement, complete deconfinement, and two kinds of partial deconfinement. A key ingredient is the refined understanding of the meaning of the 'Gross-Witten-Wadia point', i.e., the opening of a gap in the distribution of Polyakov line phases: either string condensation or baryon condensation causes the GWW transition. As a by-product, we observe the emergence of the QCD critical point from the interplay between baryon condensation and partial deconfinement. While our approach is necessarily qualitative due to the fermion sign problem, it provides a unified theoretical framework for understanding the rich phase structure of dense QCD matter and offers new perspectives on the location and nature of the QCD critical point.

    ↳ hep-thhep-lathep-phnucl-thPTEP(2026)·5 citations
21. 21*

    rho-Meson Nucleon Scattering Length from CLAS Threshold Photoproduction Measurements

    Igor I. Strakovsky (GWU)🇺🇸 · Evgeny L. Isupov (MGU)🇷🇺 · Victor Mokeev (Jlab)🇺🇸 · Axel Schmidt (GWU)🇺🇸

    Extending our study of the vector meson-nucleon scattering lengths (summary is given in Ref.~\cite{Strakovsky:2021vyk}), we are focusing on the $\rho$-meson case using recent CLAS threshold data for the reaction $\gamma p\to \rho p$ within the meson-baryon reaction model~\cite{CLAS:2018drk}. The total ${\sigma }_t(\gamma p\to \rho p)$ and ${\sigma }_t(\gamma p\to \omega p)$ cross sections are close below the momentum of the vector meson in CM $q=0.2GeV/c$. Then the $\rho p$ photoproduction cross section grows rapidly. Our result for $\rho N$ scattering length is a factor of 4 smaller than the size of the hadron and the phenomenological determination of the $\omega$ nucleon scattering length using threshold photoproduction cross sections. The observed difference between $\rho N$ and $\omega N$ scattering lengths is of interest for further understanding within the hadron structure theory.

    ↳ nucl-thhep-exhep-phnucl-exPRD(2025)·5 citations
22. 22*

    Parton physics from a heavy-quark operator product expansion: Lattice QCD calculation of the fourth moment of the pion distribution amplitude

    William Detmold🇺🇸 · Anthony V. Grebe🇺🇸 · Issaku Kanamori🇯🇵 · C.-J. David Lin🇹🇼 · Robert J. Perry🇺🇸 · Yong Zhao🇺🇸

    The pion light-cone distribution amplitude (LCDA) is an essential non-perturbative input for a range of high-energy exclusive processes in quantum chromodynamics. Building on our previous work, the continuum limit of the fourth Mellin moment of the pion LCDA is determined in quenched QCD using quark masses which correspond to a pion mass of $m_{\pi }=550$ MeV. This calculation finds $⟨{\xi }^2⟩=0.202(8)(9)$ and $⟨{\xi }^4⟩=0.039(28)(11)$ where the first error indicates the combined statistical and systematic uncertainty from the analysis and the second indicates the uncertainty from working with Wilson coefficients computed to next-to-leading order. These results are presented in the $\overline{\text{MS}}$ scheme at a renormalization scale of $\mu =2$ GeV.

    ↳ hep-lathep-phnucl-thPRD(2026)·12 citations
23. 23*

    Few is different: deciphering many-body dynamics in mesoscopic quantum gases

    Juergen Berges🇩🇪 · Sandra Brandstetter🇩🇪 · Jasmine Brewer🇬🇧 · Georg Bruun · Tilman Enss🇩🇪 · Stefan Floerchinger🇩🇪 · Keisuke Fujii🇯🇵 · Maciej Galka🇩🇪 · Giuliano Giacalone🇨🇭 · Qingze Guan · Carl Heintze🇩🇪 · Lars H. Heyen🇩🇪 and 18 other authors

    Emergent macroscopic descriptions of matter, such as hydrodynamics, are central to our description of complex physical systems across a wide spectrum of energy scales. The conventional understanding of these many-body phenomena has recently been shaken by a number of experimental findings. Collective behavior of matter has been observed in \emph{mesoscopic} systems, such as high-energy hadron-hadron collisions, or ultra-cold gases with only few strongly interacting fermions. In such systems, the separation of scales between macroscopic and microscopic dynamics (at the heart of any effective theory) is inapplicable. To address the conceptual challenges that arise from these observations and explore the universality of emergent descriptions of matter, the EMMI Rapid Reaction Task Force was assembled. This document summarizes the RRTF discussions on recent theoretical and experimental advances in this rapidly developing field. Leveraging technological breakthroughs in the control of quantum systems, we can now quantitatively explore what it means for a system to exhibit behavior beyond the sum of its individual parts. In particular, the report highlights how the (in)applicability of hydrodynamics and other effective theories can be probed across three principal frontiers: the size frontier, the equilibrium frontier, and the interaction frontier.

    ↳ cond-mat.quant-gashep-phnucl-thquant-phEPJA(2026)·4 citations
24. 24*

    Gaussian curvature and Lyapunov exponent as probes of black hole phase transitions

    Shi-Hao Zhang🇺🇸 · Zi-Qiang Zhao🇺🇸 · Zi-Yuan Li🇨🇳 · Jing-Fei Zhang🇺🇸 · Xin Zhang🇺🇸

    First-order phase transitions of black holes have been extensively studied within thermodynamic frameworks, yet the corresponding evolution of spacetime geometric properties remains unclear. This paper establishes a purely differential geometric framework to probe such phase transitions by analyzing the curvature of unstable null orbits. Using the geodesic curvature of the null circular orbit in the optical metric to locate the light ring, we demonstrate that the corresponding Gaussian curvature $K$ serves as a direct geometric signature of the phase transition. During a first-order phase transition, the curve $K$ versus temperature $T$ exhibits a multivalued structure within the spinodal region, precisely mirroring the swallowtail behavior of the free energy. Numerical analysis of Hayward-Letelier-AdS black holes confirms the effectiveness of this geometric signature. Our work demonstrates that the intrinsic geometric quantities of spacetime encode the information of black hole phase transitions. These quantities serve as geometric probes of black hole phase transitions, while their discontinuity between the small and large black hole branches exhibits order parameter-like behavior. As an extension of this geometric probe, we also find that the Gaussian curvature exhibits a heat-capacity-like divergence at the second-order phase transition point. These results provide a purely geometric foundation for understanding the correspondence between thermodynamics and spacetime curvature in the null case.

    ↳ gr-qchep-phhep-thPLB(2026)·14 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.