Mon·Dec 16, 2024Monday·December 16, 2024

1. 01*

   Direct detection of boosted dark matter in two component dark matter scenario

   Keiko I. Nagao🇯🇵

   We investigate the detection of boosted dark matter in a two component dark matter model with the hidden gauge $U(1{)}_D$ symmetry. The model introduces heavy and light fermionic dark matter components, where the heavy dark matter annihilation in the Galactic center boosts the light dark matter. Directional direct detection experiments, such as NEWSdm, are suitable for testing the boosted scenario by focusing on signals from the Galactic center. We found that the expected event rate could reach up to O(10) events per year per 5 kg of the detector material.

   hep-phastro-ph.COhep-ex1 citation
2. 02*

   In-medium electromagnetic form factors of pseudoscalar mesons from the quark model

   Ahmad Jafar Arifi🇯🇵 · Parada T. P. Hutauruk🇰🇷 · Kazuo Tsushima🇧🇷

   We explore the modifications of hadron structure in a nuclear medium, focusing on the spacelike electromagnetic form factors (EMFFs) of light and heavy-light pseudoscalar mesons. By combining the light-front quark model (LFQM) with the quark-meson coupling (QMC) model, which reasonably reproduces EMFFs in free space and the saturation properties of nuclear matter, respectively, we systematically analyze the in-medium EMFFs and charge radii of mesons with various quark flavors. Our findings show that the EMFFs of charged (neutral) mesons exhibit a faster fall-off (increase) with increasing four-momentum transfer squared and nuclear density. Consequently, the absolute value of the charge radii of mesons increases with nuclear density, where the rate of increase depends on their quark flavor contents. We observe that the EMFFs of pions and kaons undergo significant modifications in the nuclear medium, while heavy-light mesons are only slightly modified. By decomposing the quark flavor contributions to EMFFs, we show that the medium effects primarily impact the light-quark sector, leaving the heavy-quark sector nearly unaffected. The results of this study further suggest the importance of the medium effects at the quark level.

   hep-phnucl-thPRD(2025)·8 citations
3. 03*

   Searching for neutral state in the rare decay $J/\psi \to e^{+}{e}^{-}\varphi$

   Ahmed Rashed🇺🇸

   We investigate the decay process $J/\psi \to e^{+}{e}^{-}\varphi$, where the relatively clean electromagnetic (EM) transitions dominate at leading order at the tree level, while hadronic contributions arise only through hadronic loop transitions. The branching ratio of $J/\psi \to e^{+}{e}^{-}\varphi$ was estimated to be approximately $2.28\times 10^{-8}$ keV where the hadronic effects are negligible compared to the EM contributions. The upper limit on the branching fraction was set to be $B(J/\psi \to e^{+}{e}^{-}\varphi )<1.2\times 10^{-7}$ by BESIII collaboration. In this paper we investigate the existence of a neutral state such as dark photon and dark $Z$. Our analysis shows that the constraints on the dark photon and dark $Z$ are stringent in the way that large enhancement to the SM branching ratio up to the present experimental limit is not possible. Therefore, observing a signal for the dark photon and dark $Z$ in this decay channel is changeable.

   hep-ph0 citations
4. 04*

   Photon-induced neutron, proton and alpha evaporation from heavy nucleus

   P. Jucha🇵🇱 · K. Mazurek🇵🇱 · M. Klusek-Gawenda🇵🇱 · M. Ciemala🇵🇱 · A. Szczurek🇵🇱 · Yuliia Shevchuk · S. Słotwiński

   In ultraperipheral heavy-ion collisions (UPCs) at the Large Hadron Collider (LHC) Pb nuclei are excited through interactions induced by strong electromagnetic fields. The expected excitation energy could reach hundreds MeV, which leads to the subsequent emission of various particles, including neutrons, protons, and alpha particles. To accurately describe deexcitation of nuclei, we have developed two novel approaches. The first method utilizes the Heavy Ion Phase Space Exploration (HIPSE) model to simulate pre-equilibrium emissions and to estimate the excitation energy of the remaining nucleus. Our second approach introduces a new technique for modeling the excitation energy of the nucleus. This method consists of a two-component function to represent the excitation energy distribution more precisely, accounting for the energy loss due to the interaction between photons and quasi-deuteron. Both of these modeling techniques are integrated with the results produced by the GEMINI++ generator, which implements the Hauser-Feshbach formalism to simulate the statistical decay of excited nuclei. The alternative calculations are done with EMPIRE platform. Using these approaches, we obtained the cross sections for the emission of neutrons, protons, and alpha particles resulting from UPC at the LHC. Our results were compared with the experimental data of the ALICE group on neutron and proton multiplicities.

   hep-phnucl-thActa Phys.Polon.Supp.(2025)·1 citation
5. 05*

   Two portals to GeV sterile neutrinos : dipole versus mixing

   Enrico Bertuzzo🇮🇹 · Michele Frigerio🇫🇷

   Massive sterile neutrinos, also known as heavy neutral leptons, can have a mixing with active neutrinos, $\theta$, as well as a dipole coupling to the photon, $d$. We study the interplay between these two portals, considering the production from meson decays of sterile neutrinos with mass $0.1$ GeV $\lesssim M_N\lesssim 10$ GeV, at beam-dump facilities such as NA62 and SHiP, and at the FASER2 experiment. These sterile neutrinos can be long-lived and decay into a photon in a distant detector, via the dipole operator. We find that all these experiments will be sensitive to values of $d$ which are presently unconstrained. The experimental reach varies strongly with the mass $M_N$ and the mixing $\theta$, and one observes specific correlations with the flavour of active neutrinos. The SHiP experiment will mark a jump in sensitivity: (i) it will probe a sterile dipole as small as $d\sim 10^{-8}$ GeV${}^{-1}$, thus testing new physics well above the electroweak scale; (ii) it may detect the active-sterile dipole to the level predicted by electroweak loops, if $\theta$ is close to the present bound.

   hep-phSciPost Phys.(2025)·5 citations
6. 06*

   The bremsstrahlung-like production of the massive spin-2 dark matter mediator

   I. V. Voronchikhin🇷🇺 · D. V. Kirpichnikov🇷🇺

   The link between Standard Model (SM) particles and dark matter (DM) can be introduced via spin-2 massive mediator, G, that couples to photon and charged leptons. Moreover, in a mediator mass range from sub-MeV to sub-GeV, fixed-target facilities such as NA64e, LDMX, NA64$\mu$, M${}^3$, and E137, can potentially probe such particle of the hidden sector via the signatures that are described by the bremsstrahlung-like process involving tensor mediator. We compare numerically the Weizsaker-Williams (WW) approximation and the exact tree-level (ETL) approach for the bremsstrahlung-like mediator production cross section by choosing various parameters of the fixed-target experiments. In addition, we derive novel constraints on spin-2 DM mediator parameter space from the data of the E137 fixed-target experiment. In particular, we demonstrate that the E137 experiment has been ruled out the the couplings of the spin-2 mediator at the level of $8\times 10^{-8}\text{mbox}{GeV}^{-1}\lesssim c_{ee}^{\mathrm{G}}\lesssim 10^{-5}\text{mbox}{GeV}^{-1}$ for the typical masses in the range $100\text{mbox}MeV\lesssim m_{\mathrm{G}}\lesssim 800\text{mbox}MeV$, that corresponds to the statistics of $1.87\times 10^{20}$ electrons accumulated on target. The latter implies its universal coupling to photons and leptons, $c_{ee}^{\mathrm{G}}=c_{\gamma \gamma }^{\mathrm{G}}$.

   hep-phEPJC(2025)·8 citations
7. 07*

   QCD Axion Dark Matter from level crossing with refined adiabatic condition

   Kai Murai🇯🇵 · Yuma Narita🇯🇵 · Fuminobu Takahashi🇯🇵 · Wen Yin🇯🇵

   We investigate the level-crossing phenomenon in two-axion systems, where the mass eigenvalues intersect as the mass of one axion increases with the cooling of the universe. This phenomenon can significantly alter the abundance of axions in the early universe. Our study focuses on its impact on the QCD axion and an axion-like particle, identifying viable regions of axion mass and decay constant that explain the observed dark matter. We demonstrate the equivalence of two different bases for describing the axion system in the existing literature. Furthermore, we derive an improved expression for the adiabatic condition that overcomes limitations in earlier formulations. This new formulation is basis-independent, and we numerically validate its effectiveness. Our analysis reveals specific relations between axion masses and axion-photon couplings within the viable region. These relations could potentially serve as a smoking gun signal for this scenario if confirmed experimentally. We also find that, using the chiral perturbation model, the thermal friction on the QCD axion might be significantly larger than previously estimated. Additionally, we show that a simple model with axion mixing can naturally realize either a heavier or lighter QCD axion.

   hep-phastro-ph.COJHEP(2025)·22 citations
8. 08*

   Low-scale seesaw with flavour and CP symmetries $–$ from colliders to leptogenesis

   Marco Drewes🇧🇪 · Yannis Georis🇧🇪 · Claudia Hagedorn🇪🇸 · Juraj Klaric🇳🇱

   We consider an extension of the Standard Model with three right-handed neutrinos, endowed with a flavour symmetry $G_f$, $G_f=\Delta (3n^2)$ or $G_f=\Delta (6n^2)$, $n\ge 2$, and CP. For large active-sterile mixing, we study the properties of the (nearly mass-degenerate) heavy neutrinos, such as their lifetimes and branching ratios. In doing so, we examine the four different cases, called Case 1) through Case 3 b.1), that lead to distinct lepton mixing patterns, all potentially compatible with current data. Furthermore, we comprehensively explore for each case the region of parameter space in which a sufficient amount of baryon asymmetry of the Universe can be generated via leptogenesis, while being testable at accelerator-based and potentially also precision flavour experiments.

   hep-ph10 citations
9. 09*

   Sensitivity to $\mathcal{C}\mathcal{P}$-violating effective couplings in the top-Higgs sector

   Víctor Miralles🇬🇧 · Yvonne Peters🇬🇧 · Eleni Vryonidou🇬🇧 · Joshua K. Winter🇬🇧

   The observed baryon asymmetry of the Universe requires new sources of charge-parity ($\mathcal{C}\mathcal{P}$) violation beyond those in the Standard Model. In this work, we investigate $\mathcal{C}\mathcal{P}$-violating effects in the top-Higgs sector using the Standard Model Effective Field Theory (SMEFT) framework. Focusing on top-pair production in association with a Higgs boson and single top-Higgs associated production at the LHC, we study $\mathcal{C}\mathcal{P}$ violation in the top-Higgs Yukawa coupling and other Higgs and top interactions entering these processes. By analysing $\mathcal{C}\mathcal{P}$-sensitive differential observables and asymmetries, we provide direct constraints on $\mathcal{C}\mathcal{P}$-violating interactions in the top-Higgs sector. Our analysis demonstrates how combining $t\bar{t}h$ and $thj$ production can disentangle the real and imaginary components of the top-Yukawa coupling, offering valuable insights into potential sources of $\mathcal{C}\mathcal{P}$ violation. The sensitivity of these observables to SMEFT operators provides model-independent constraints on the parameter space, advancing the search for new physics in the top-Higgs sector.

   hep-phhep-exJHEP(2025)·11 citations
10. 10*

    Neutrino-Portal Dark Matter Detection Prospects at a Future Muon Collider

    Jyotismita Adhikary🇵🇱 · Kevin J. Kelly🇺🇸 · Felix Kling🇩🇪 · Sebastian Trojanowski🇵🇱

    With no concrete evidence for non-gravitational interactions of dark matter to date, it is natural to wonder whether dark matter couples predominantly to the Standard Model (SM)'s neutrinos. Neutrino interactions (and the possible existence of additional neutrinophilic mediators) are substantially less understood than those of other SM particles, yet this picture will change dramatically in the coming decades with new neutrino sources. One potential new source arises with the construction of a high-energy muon collider (MuCol) -- due to muons' instability, a MuCol is a source of high-energy collimated neutrinos. Importantly, since the physics of muon decays (into neutrinos) is very well-understood, this leads to a neutrino flux with systematic uncertainties far smaller than fluxes from conventional high-energy (proton-sourced) neutrino beams. In this work, we study the capabilities of a potential neutrino detector, "MuCol$\nu$," placed ~100 m downstream of the MuCol interaction point. The MuCol$\nu$ detector would be especially capable of searching for a neutrinophilic mediator $\varphi$ through the mono-neutrino scattering process ${\nu }_{\mu }N\to {\mu }^{+}\varphi X$, exceeding searches from other terrestrial approaches for $m_{\varphi }$ in the ~few MeV -- ten GeV range. Even with a 10 kg-yr exposure, MuCol$\nu$ is capable of searching for well-motivated classes of thermal freeze-out and freeze-in neutrino-portal dark matter.

    hep-phhep-exPRD(2025)·13 citations
11. 11*

    Toward a foundation model for heavy-ion collision experiments based on point-cloud diffusion

    Manjunath Omana Kuttan🇩🇪 · Kai Zhou🇩🇪 · Jan Steinheimer🇩🇪 · Horst Stoecker🇩🇪

    A novel point cloud diffusion model for relativistic heavy-ion collisions, capable of ultra-fast generation of complete, event-by-event collision output, is introduced. When trained on UrQMD cascade simulations, the model generates realistic collision event output containing 26 distinct hadron species, as a list of particle momentum vectors along with their particle ID. From solving inverse problems to accelerating model calculations or detector simulations, the model can be a promising general purpose tool for heavy-ion collisions beneficial to both theoretical studies and experimental applications.

    hep-phhep-exnucl-exnucl-thPRC(2025)·8 citations
12. 12*

    Real-Time Simulation of Asymmetry Generation in Fermion-Bubble Collisions

    Marcela Carena🇺🇸 · Ying-Ying Li🇨🇳 · Tong Ou🇺🇸 · Hersh Singh🇺🇸

    Motivated by the out-of-equilibrium dynamics during an early-universe first-order phase transition, we perform real-time simulations of fermion-bubble scattering in $1+1$ dimensions. This nonequilibrium process can generate a charge-conjugation $\mathsf{C}$ asymmetry outside the bubble wall, induced by the complex fermion mass profile. The resulting $\mathsf{C}$ asymmetry is the 1+1-dimensional analog of the $\mathsf{CP}$ asymmetry in 3+1 dimensions, a key ingredient in baryon asymmetry generation at the electroweak scale. Using tensor network methods, we track the real-time evolution of the $\mathsf{C}$ asymmetry in the charge density as the fermion interacts with the bubble wall, a regime inaccessible to analytic calculations. We further introduce two observables to quantify the asymmetry in the asymptotic region where reflected particles are well separated from the scattering point: one based on the net charge outside the bubble wall, and the other on the spatial displacement between the reflected particle and antiparticle wavepackets. Our study represents a first step toward nonperturbative, real-time computations of $\mathsf{CP}$ asymmetry in 3+1 dimensions for electroweak baryogenesis.

    hep-phhep-latPRD(2026)·9 citations
13. 13*

    Minimal Electroweak Baryogenesis via Domain Walls

    Jacopo Azzola🇩🇪 · Oleksii Matsedonskyi🇩🇪 · Andreas Weiler🇩🇪

    The Standard Model extended by a real scalar singlet $S$ with an approximate ${\mathbb{Z}}_2$ symmetry offers a minimal framework for realizing electroweak baryogenesis (EWBG) during a first-order electroweak phase transition. In this work, we explore a novel mechanism where spontaneous ${\mathbb{Z}}_2$ breaking enables EWBG via domain walls separating two distinct phases of the $S$ field. These domain walls feature restored (or weakly broken) EW symmetry in their cores and sweep through space, generating the baryon asymmetry below the temperature of EW symmetry breaking. We identify the key conditions for the existence of EW-symmetric domain wall cores and analyze the dynamics required for wall propagation over sufficient spatial volumes. Additionally, we outline the CP-violating sources necessary for baryogenesis under different regimes of domain wall evolution. The parameter space accommodating this mechanism spans singlet masses from sub-eV to 15 GeV, accompanied by a non-vanishing mixing with the Higgs boson. Unlike the standard realization of EWBG in the minimal singlet-extended SM, which is notoriously difficult to test, our scenario can be probed by a wide range of existing and upcoming experiments, including fifth force searches, rare meson decays, and EDM measurements.

    hep-phastro-ph.COJHEP(2025)·16 citations
14. 14*

    Neutrinoless double beta decay with light sterile neutrinos: the contact terms

    Vincenzo Cirigliano🇺🇸 · Wouter Dekens🇺🇸 · Sebastián Urrutia Quiroga🇺🇸

    We study neutrinoless double-beta decay in extensions of the Standard Model that include $n$ right-handed neutrino singlets, with masses $m_s$ below the GeV scale. Generalizing recently developed matching methods, we determine the $m_s$ dependence of the short-range $nn\to pp$ couplings that appear to leading order in the chiral effective field theory description of neutrinoless double beta decay. We focus on two scenarios, corresponding to the minimal $\nu$SM and left-right symmetric models. We illustrate the impact of our new results in the case of the $\nu$SM, showing a significant impact on the neutrinoless double-beta decay half-life when $m_s$ is in the 200-800 MeV range.

    hep-phnucl-thJHEP(2025)·10 citations
15. 15*

    Aspen Open Jets: Unlocking LHC Data for Foundation Models in Particle Physics

    Oz Amram🇺🇸 · Luca Anzalone🇮🇹 · Joschka Birk🇩🇪 · Darius A. Faroughy🇺🇸 · Anna Hallin🇩🇪 · Gregor Kasieczka🇩🇪 · Michael Krämer🇩🇪 · Ian Pang🇺🇸 · Humberto Reyes-Gonzalez🇩🇪 · David Shih🇺🇸

    Foundation models are deep learning models pre-trained on large amounts of data which are capable of generalizing to multiple datasets and/or downstream tasks. This work demonstrates how data collected by the CMS experiment at the Large Hadron Collider can be useful in pre-training foundation models for HEP. Specifically, we introduce the AspenOpenJets dataset, consisting of approximately 178M high $p_T$ jets derived from CMS 2016 Open Data. We show how pre-training the OmniJet-$\alpha$ foundation model on AspenOpenJets improves performance on generative tasks with significant domain shift: generating boosted top and QCD jets from the simulated JetClass dataset. In addition to demonstrating the power of pre-training of a jet-based foundation model on actual proton-proton collision data, we provide the ML-ready derived AspenOpenJets dataset for further public use.

    hep-phcs.LGhep-exstat.MLMach.Learn.Sci.Tech.(2025)·29 citations
16. 16*

    Neutrinos from explosive transients at the dawn of multi-messenger astronomy

    Irene Tamborra🇩🇰

    With the advent of time-domain astronomy and the game-changing next generation of telescopes, we have unprecedented opportunities to explore the most energetic events in our Universe through electromagnetic radiation, gravitational waves, and neutrinos. These are elementary particles, which exist in three different flavors and change the latter as they propagate in the dense core of astrophysical sources as well as en route to Earth. To capitalize on existing and upcoming multi-messenger opportunities, it is crucial to understand: 1. the role of neutrinos in explosive transient sources as well as in the synthesis of the elements heavier than iron; 2. the impact of neutrino physics on the multi-messenger observables; 3. the information on the source physics carried by the detectable neutrino signal. In this review, the status of this exciting and fast-moving field is outlined, focusing on astrophysical sources linked to collapsing massive stars and neutron-star mergers. In light of the upcoming plethora of multi-messenger data, outstanding open issues concerning the optimization of multi-messenger detection strategies are discussed.

    ↳ astro-ph.HEhep-exhep-phNature Rev.Phys.(2025)·29 citations
17. 17*

    Lorentz and CPT violation and the hydrogen and antihydrogen molecular ions I -- rovibrational states

    Graham M. Shore🇬🇧

    The extremely narrow natural linewidths of rovibrational energy levels in the molecular hydrogen ion ${\text{H}}_2^{+}$, and the prospect of synthesising its antimatter counterpart ${\overline{\text{H}}}_2^{-}$, make it a promising candidate for high-precision tests of fundamental symmetries such as Lorentz and CPT invariance. In this paper, we present a detailed analysis of the rovibrational spectrum of the (anti-)hydrogen molecular ion in a low-energy effective theory incorporating Lorentz and CPT violation. The focus is on the spin-independent couplings in this theory, for which the best current bounds come from measurements of the 1S-2S transition in atomic hydrogen and antihydrogen. We show that in addition to the improvement in these bounds from the increased precision of the transition frequencies, potentially reaching 1 part in $10^{17}$, rovibrational transitions have an enhanced sensitivity to Lorentz and CPT violation of $O(m_p/m_e)$ in the proton (hadron) sector compared to atomic transitions.

    ↳ physics.atom-phhep-phPRD(2025)·8 citations
18. 18*

    ATLAS EFT Results in the Top Quark Sector

    Dongwon Kim (for the ATLAS Collaboration)🇸🇪

    With no direct evidence for new physics at the TeV scale, deviations from the Standard Model (SM) can be explored systematically through Effective Field Theories (EFTs) such as the Standard Model EFT (SMEFT). SMEFT extends the SM by introducing higher-dimensional operators parametrized by Wilson coefficients, offering a framework to probe beyond the SM (BSM) effects. This contribution highlights three recent analyses using the ATLAS Run-2 dataset at a center-of-mass energy of $\sqrt{s}$ = 13 TeV with an integrated luminosity of 140 ${\text{fb}}^{-1}$. Combined measurements improve the sensitivity to Wilson coefficients by reducing degeneracies and tightening constraints, exploring the potential of SMEFT in the top quark sector.

    ↳ hep-exhep-phSciPost Phys.Proc.(2026)·1 citation
19. 19*

    Searching for long-lived dark scalars at the FCC-ee

    Giulia Ripellino🇸🇪 · Magdalena Vande Voorde🇸🇪 · Axel Gallén🇸🇪 · Rebeca Gonzalez Suarez🇸🇪

    This paper investigates the search for long-lived dark scalars from exotic Higgs boson decays at the Future Circular Collider in its $e^{+}{e}^{-}$ stage, FCC-ee, considering an integrated luminosity of 10.8 ${\text{ab}}^{-1}$ collected during the ZH run at a center-of-mass energy $\sqrt{s}=240$ GeV. The work considers $Zh$ events where the $Z$ boson decays leptonically and the Higgs boson $h$ decays into two long-lived dark scalars $s$ which further decay into bottom anti-bottom quark pairs. The analysis is performed using a parametrized simulation of the IDEA detector concept and targets dark scalar decays in the tracking volume, resulting in multiple displaced vertices in the final state. The sensitivity towards long-lived dark scalars at FCC-ee is estimated using an event selection requiring two opposite-charge, same-flavor leptons compatible with the $Z$ boson, and at least two displaced vertices in the final state. The selection is seen to efficiently remove the Standard Model background, while retaining sensitivity for dark scalar masses between $m_s=20$ GeV and $m_s=60$ GeV and mean proper lifetimes $c\tau$ between approximately 10 mm and 10 m The results show that the search strategy has potential to probe Higgs to dark scalar branching ratios as low as $10^{-4}$ for a mean proper lifetime $c\tau \approx 1$ m. The results provide the first sensitivity estimate for exotic Higgs decays at FCC-ee with the IDEA detector concept, using the common FCC framework.

    ↳ hep-exhep-phJHEP(2025)·16 citations
20. 20*

    The Equivalence Theorem at work: manifestly gauge-invariant Abelian Higgs model physics

    Bram Boeykens🇧🇪 · David Dudal🇧🇪 · Thomas Oosthuyse🇧🇪

    We reconsider the Equivalence Theorem from an algebraic viewpoint, using an extended BRST symmetry. This version of the Equivalence Theorem is then used to reexpress the Abelian Higgs model action, originally written in terms of undesirable gauge variant field excitations, in terms of gauge-invariant, physical variables, corresponding to the Fröhlich-Morchio-Strocchi composite operators in the original field formulation. Although the ensuing action encompasses an infinite number of vertices and appears to be nonrenormalizable from the powercounting viewpoint, it nevertheless is renormalizable, thanks to the hidden equivalence with the original model. Hence, manifestly gauge-invariant computations are possible. We present an explicit illustration in terms of the gauge-invariant scalar field, its Green's function and corresponding pole mass.

    ↳ hep-thhep-phPRD(2025)·1 citation
21. 21*

    Path integral measure and cosmological constant

    C. Branchina🇮🇹 · V. Branchina🇮🇹 · F. Contino🇮🇹 · A. Pernace🇮🇹

    Considering (euclidean) quantum gravity in the Einstein-Hilbert truncation, we calculate the one-loop effective action ${\Gamma }_{\mathrm{grav}}^{1l}$ using a spherical background. Usually, this calculation is performed resorting to proper-time regularization within the heat kernel expansion and gives rise to quartically and quadratically UV-sensitive contributions to the vacuum energy ${\rho }_{\mathrm{vac}}=\frac{{\Lambda }_{\mathrm{cc}}}{8\pi G}$, with ${\Lambda }_{\mathrm{cc}}$ and $G$ cosmological and Newton constant, respectively. We show that, if the measure in the path integral that defines ${\Gamma }_{\mathrm{grav}}^{1l}$ is correctly taken into account, and the physical UV cutoff ${\Lambda }_{\mathrm{cut}}$ properly introduced, ${\rho }_{\mathrm{vac}}$ presents only a (mild) logarithmic sensitivity to ${\Lambda }_{\mathrm{cut}}$. We also consider a free scalar field and a free Dirac field on a spherical gravitational background, and find that the same holds true even in the presence of matter. These results are found without resorting to any supersymmetric embedding of the theory, and shed new light on the cosmological constant problem.

    ↳ hep-thgr-qchep-phPRD(2025)·15 citations
22. 22*

    Partially Coherent X-Ray Oscilex Radiation from a FEL-Modulated Positron Bunch during Its Planar Channeling in a Crystalline Undulator

    Hayk L. Gevorgyan · Lekdar A. Gevorgian🇺🇸

    The radiation emitted at zero angle by a microbunched positron bunch undergoing planar channeling in a crystalline undulator (CU) is studied. The bunch energy is assumed to be far above the threshold for radiation generation in the dispersive CU medium. Besides the usual ``hard'' undulator radiation produced by channeling oscillations (channeling undulator radiation) and by the CU bending (crystalline undulator radiation), a ``soft'' medium-polarization component also appears at zero angle due to the oscillations that excite atomic electrons. We refer to this soft component as Oscilex (oscillationally-excited) radiation. Since the two types of oscillations have different frequencies, they yield two distinct frequency components of both undulator and Oscilex radiation. The Oscilex frequencies are set by the plasma frequency and the characteristic oscillation frequency and are, to high accuracy, independent of the positron energy. The CU period is chosen so that the radiation wavelength is not shorter than the microbunch length, ensuring coherent emission from microbunches and partially coherent Oscilex emission from the full bunch. Analytical expressions are obtained for the spectral line shapes and the number of photons of spontaneous Oscilex radiation. For partially coherent emission, Gaussian distributions are used for both the bunch and microbunches. Gain factors for the two Oscilex components, including longitudinal form-factors, and the total number of partially coherent photons are derived. A positron bunch with LCLS parameters, modulated by SASE XFEL, channeling between (1 1 0) planes of a periodically bent diamond crystal is analyzed. The number of spontaneously emitted Oscilex photons exceeds the number of positrons by $1\text{div}2$ orders of magnitude, and the gain factors reach $10^3\text{div}10^4$.

    ↳ physics.acc-phhep-exhep-phphysics.class-ph+11 citation
23. 23*

    Black holes and gravitational waves from phase transitions in realistic models

    Marek Lewicki🇵🇱 · Piotr Toczek🇵🇱 · Ville Vaskonen🇪🇪

    We study realistic models predicting primordial black hole (PBH) formation from density fluctuations generated in a first-order phase transition. We show that the second-order correction in the expansion of the bubble nucleation rate is necessary for accurate predictions and quantify its impact on the abundance of PBHs and gravitational waves (GWs). We find that the distribution of the fluctuations becomes more Gaussian as the second-order term increases. Consequently, models that predict the same PBH abundances can produce different GW spectra.

    ↳ astro-ph.COhep-phPhys.Dark Univ.(2025)·34 citations
24. 24*

    Is inflationary magnetogenesis sensitive to the post-inflationary history ?

    Konstantinos Dimopoulos🇬🇧 · Anish Ghoshal🇵🇱 · Theodoros Papanikolaou🇮🇹

    Considering inflationary magnetogenesis induced by time-dependent kinetic and axial couplings of a massless Abelian vector boson field breaking the conformal invariance we show in this article that, surprisingly, the spectral shape of the large-scale primordial magnetic field power spectrum is insensitive to the post-inflationary history, namely the barotropic parameter ($w$) and the gauge coupling functions of the post-inflationary era.

    ↳ astro-ph.COhep-phPRD(2025)·7 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.