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Physics High Energy Physics (Phenomenology)

hep-ph Watch High Energy Physics (Phenomenology)

Tuesday 29 September

High Energy Physics (Phenomenology)

Imprints of Left-Right Symmetry breaking in Gravitational Wave Spectroscopy: A non-minimal case study

Abdul Rahaman Shaikh, Nandini Das, Rathin Adhikari et al. (+1 more)

We investigate the dynamics of cosmological phase transition in the framework of a non-minimal version of Left-Right symmetric gauge model. At a high energy scale, this framework having the symmetry $SU(2)_L \otimes SU(2)_{R} \otimes U(1)_R \otimes U(1)_L$, is stemmed out from the Grand Unifying group $E_6$. Rich scalar sector of this model offers interesting opportunity for studying first order phase transition which can be the source of stochastic gravitational waves. Taking into account the theoretical and experimental constraints applicable to this model, we look for benchmark parameters where first order phase transition could be observed during the breaking of $SU(2)_{R} \otimes U(1)_R \otimes U(1)_L$ down to $U(1)_Y$, at an energy scale of tens of TeVs or higher. Our investigation reveals the possibility of strong first order phase transition over a large region of parameter space. We also discuss the production of stochastic gravitational waves arising from such strong first order phase transition. Our results present clear, testable predictions that fall directly within the sensitivity bands of ongoing and next-generation gravitational-wave observatories like LISA, DECIGO, AEDGE and $\mu$ARES.
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All authors Abdul Rahaman Shaikh, Nandini Das, Rathin Adhikari, Anindya Datta

High Energy Physics (Phenomenology) · Cross-listed from astro-ph.HE

HESS J1507-622: A Plausible Young Galactic Kilonova Remnant

Prantik Sarmah, Xilu Wang, Myles Carley et al. (+3 more)

HESS J1507$-$622 is an unusual TeV gamma-ray source in the H.E.S.S. Galactic Plane Survey, distinguished by its off-plane location ($b \simeq -3.5^{\circ}$) and compact angular extent ($\sim 0.3^{\circ}$). Its location and morphology challenge conventional pulsar wind nebula and supernova remnant interpretations, and the absence of a detected shell or associated pulsar leaves its origin unresolved. Here, we propose that HESS J1507$-$622 is a young Galactic kilonova remnant with gamma-ray emission of leptonic origin. In this scenario, the source's off-plane location is naturally explained by the natal kick imparted to the progenitor binary neutron star system. We demonstrate that a leptonic kilonova remnant model can successfully reproduce the observed GeV-TeV flux via inverse-Compton scattering from shock-accelerated electrons, while the corresponding synchrotron emission remains below current X-ray and radio upper limits. Based on the source's energetics and angular size, we infer a distance of 3.8-14.3 kpc and an age of 0.2-3.0 kyr. Importantly, our analysis favors a kilonova remnant younger than 1 kyr. The lack of a historical naked-eye record can be explained by the transient's rapid fading, far-southern declination, and potential line-of-sight extinction. We further assess the detectability of unique multi-wavelength signatures that could confirm this hypothesis. We find promising prospects for detecting the unique MeV gamma rays from the decay of $r$-process radioisotopes using future observatories, alongside complementary low-energy signatures from thermal dust emission and a possible optical light echo. These distinct signals offer definitive tests of the kilonova remnant interpretation and motivate targeted observations with current and future facilities.
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All authors Prantik Sarmah, Xilu Wang, Myles Carley, Shu-Xu Yi, Ming-Yu Ge, Rebecca Surman

High Energy Physics (Phenomenology)

A Partial Wave Formalism for High-Energy Meson Electroproduction

Dillon Leahy, Derek Glazier, Vincent Mathieu et al. (+7 more)

We present a comprehensive partial-wave analysis formalism for meson electroproduction based on reflectivity amplitudes. By applying parity-based symmetries, we construct a fully diagonalized framework that relates complex production amplitudes to measurable spherical harmonic moments and Spin Density Matrix Elements. We demonstrate that, under the assumption of high-energy Regge factorization, longitudinal and transverse cross sections can be natively separated without requiring beam-energy-varying Rosenbluth separations. We validate this inversion methodology through numerical closure tests and apply it to existing unpolarized $\rho^0$ and $\omega$ electroproduction data from HERMES and COMPASS. The extracted amplitudes align with $s$-channel helicity conservation expectations for the $\rho^0$, while clearly isolating the large unnatural-parity pion exchange contribution in $\omega$ production without model-dependent background approximations. Finally, we systematically generalize the formalism to include initial target and recoil baryon polarization, establishing the rigorous observables required for complete amplitude extraction, no longer requiring any factorisation assumptions. This unified framework directly supports upcoming spectroscopy and nucleon structure programs at CLAS12, GlueX, and the future Electron-Ion Collider.
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All authors Dillon Leahy, Derek Glazier, Vincent Mathieu, Marco Filippini, David Ireland, Glòria Montaña, Alessandro Pilloni, Bhawani Singh, Charlie Velasquez, Daniel Winney

High Energy Physics (Phenomenology)

Constraints on Complex Electroweak WIMPs from Solar Capture

Juan P. Luengas, Maxim Pospelov and Harikrishnan Ramani

One of the most convincing realizations of particle dark matter is provided by models based on electroweak multiplets. The lightest neutral state of such a multiplet can be a stable Majorana fermion or a real scalar, and its phenomenology is governed by two parameters: the dark matter mass and the mass splitting $\{m_\chi,\delta\}$. The sub-MeV range for $\delta$ is particularly important as it allows for a large inelastic scattering cross section. In this paper, we analyze solar capture, energy loss, and annihilation of scalar and fermionic electroweak multiplet dark matter, generalizing earlier results for the Higgsino to other representations. We find that, while the case of a doublet is somewhat special, higher representations behave in a self-similar way. For the higher multiplets, IceCube results constrain the splitting to $\delta \gtrsim 350$ keV for all dark matter masses up to $100$ TeV. Assuming thermal freeze-out and a Standard Halo Model velocity distribution, this rules out most models of electroweak dark matter as a possible origin of the single high-recoil event reported by the LZ collaboration. We also show that a high-velocity tail in the dark matter distribution, such as that induced by the Large Magellanic Cloud, raises the splitting preferred by the LZ event above the solar bounds for many of the multiplets.
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High Energy Physics (Phenomenology)

How collective modes terminate in the dispersion relation of neutrino plasmas

Damiano F. G. Fiorillo

Neutrino plasmas support flavor waves, collective oscillations of flavor, that neutrinos can resonantly emit or absorb when they fulfill the Cherenkov condition. For massless neutrinos, this condition leads to singular features in the dispersion relation: Landau-damped modes, for example, disappear abruptly as their phase velocity approaches the speed of light. We investigate how these singularities change when nonzero neutrino masses introduce a spread in velocities. We classify singular behavior of the frequency as a function of wavevector into i) degeneracy points, where two modes merge, and ii) abrupt mode termination, when the frequency approaches a branch cut of the flavor dielectric function. For each class, we derive a local expansion and determine where such behavior can occur. Degeneracy points, frequently encountered in axially symmetric dispersion relations in the fast limit, are not generic. Nonzero neutrino masses lift the degeneracy along the symmetry axis; in three-dimensional wavevector space, there might still be degeneracy lines, not necessarily intersecting the symmetry axis. Abrupt mode termination, instead, persists generically, except for special energy distributions which are entire functions. As a byproduct of this study, we show that a collisionless plasma with a Lorentzian neutrino-frequency distribution is exactly equivalent to a monochromatic one with an effective collision rate. Approximating a general frequency distribution by a sum of Lorentzians therefore substantially simplifies the dispersion relation.
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High Energy Physics (Phenomenology)

Searching for BSM Experimental Signatures with Large Lagrangian Models

Ibrahim Elsharkawy, Victoria Knapp-Perez, Wahid Bhimji et al. (+1 more)

The search for physics Beyond the Standard Model (BSM) is generally limited not by the supply of theory descriptions but by the lack of discriminating experimental observations. A case in point is dark matter, where the overwhelming gravitational evidence only goes so far in distinguishing between models within a vast theory space. Exploring the space of testable model signatures may help identify overlooked experimental observables and indicate the utility of future experiments. A challenge is designing a search through model signatures outside what is found in the literature. Our primary contribution is hAIthem, a framework that combines the self-guided exploration of reinforcement learning (RL) with the broad literature-derived knowledge of LLMs. We build an RL agent that learns to find which portions of a theory's high-dimensional parameter space are not excluded under some subset of constraints by playing a Battleship-style "game" against a suite of phenomenology tools. The agent is built as a Large Lagrangian Model (LLaM), an autoregressive transformer that reads a tokenized Lagrangian, is pretrained at scale (here on ~1 billion tokens from ~10,000 Lagrangians), and is fine-tuned in a live environment. The framework then constructs a decision tree that separates RL-found regions using observables computed with established tools, and passes the remaining degenerate regions to a set of LLM agents that compete to produce realistic signatures. In this proof of concept, RL-search outperforms an evolutionary-algorithm baseline, finding more viable regions with greater physical diversity. In a restricted space of single dark scalar multiplet models, we find that hAIthem proposes interesting combinations of previously studied observables, such as the application of a halo-independent kinematic ratio to paleo-detectors.
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All authors Ibrahim Elsharkawy, Victoria Knapp-Perez, Wahid Bhimji, Aishik Ghosh

High Energy Physics (Phenomenology) · Cross-listed from astro-ph.CO

Close Pulsar Pairs See Dark Matter Substructure through the Gravitational-Wave Background

Abhiram Cherukupalli, Vincent S. H. Lee, Kim V. Berghaus et al. (+1 more)

Pulsar timing arrays detect signals from dark matter substructure, but a nanohertz gravitational-wave background (GWB) severely degrades their sensitivity. We show that timing pulsar pairs separated by sub-parsec distances avoids this degradation. The GWB imprints nearly the same perturbation on both pulsars and is suppressed in the difference of their residuals, whereas a nearby dark matter subhalo perturbs the two differently and survives. We find that an array with pulsar pairs separated by $0.1\,\mathrm{pc}$ improves the sensitivity to subhalos of order $\sim10^{-6}$ solar masses by more than an order of magnitude, relative to an otherwise identical array of widely separated pulsars. Dense globular clusters naturally host many such pairs, though the baryonic environment must be separated from a dark matter substructure signal.
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All authors Abhiram Cherukupalli, Vincent S. H. Lee, Kim V. Berghaus, Kathryn M. Zurek

High Energy Physics (Phenomenology) · Cross-listed from hep-th

Detectors in Nonrelativistic Conformal Field Theories

Cyuan-Han Chang, Subham Dutta Chowdhury, Ian Moult et al. (+1 more)

Correlations in asymptotic fluxes provide one of the primary experimental means of studying physical systems. In the context of relativistic QFT, the formalization of such experiments in terms of detector operators has led to significant progress. Motivated by these successes, in this paper we initiate a study of detector operators in nonrelativistic conformal field theories (NRCFTs). In NRCFTs, fluxes are distributed in both angle and velocity, making the natural detector operator the energy flux differential in velocity, $\mathcal{E}_v(\hat{n})$. We provide non-perturbative definitions of these operators in NRCFTs, and study their symmetries and algebra. We calculate one-point functions of these detector observables in a variety of few and many body states of representative NRCFTs, including free fermions, as well as fermions at unitarity. In interacting three-body states, they exhibit a remarkably rich behavior reflective of the Efimov three-body wave-function, including the formation of an enhanced "jet" structure due to the presence of resonant interactions. We use these detectors to derive a nonrelativistic generalization of the Hofman-Maldacena conformal collider bounds by arguing for positivity of $\mathcal{E}_v(\hat{n})$, and imposing this in spin 1 states. We outline a number of future directions for the study of detectors in NRCFTs, and discuss how they can be measured in a variety of experimental platforms from cold atoms to low energy neutron experiments.
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All authors Cyuan-Han Chang, Subham Dutta Chowdhury, Ian Moult, Dam Thanh Son

High Energy Physics (Phenomenology) · Cross-listed from hep-th

CMB Injection Bounds on Moduli Fields

Naman Agarwal, Andrew R. Frey, Ratul Mahanta et al. (+3 more)

Light scalar fields with gravitational strength interactions (moduli) are ubiquitous in string, supergravity, and extra-dimensional models. If produced in the early universe with lifetimes exceeding the epoch of recombination, slowly decaying moduli inject energetic particles into the Standard Model plasma, leaving distinct imprints on the cosmic microwave background (CMB). In this paper we systematically derive CMB injection bounds on light moduli ($10^3\ {\rm eV}\leq m_{\rm{mod}}\leq 10^8\ {\rm eV}$) across the primary cosmological production channels: vacuum misalignment, heavy scalar/inflaton decay, thermal emission from the primordial plasma including production from a Hagedorn phase of hot strings. We show that these injection bounds impose stringent constraints that are complementary to both the standard cosmological moduli problem and fifth force bounds.
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All authors Naman Agarwal, Andrew R. Frey, Ratul Mahanta, Anshuman Maharana, Fernando Quevedo, Gonzalo Villa

High Energy Physics (Phenomenology) · Cross-listed from astro-ph.CO

Gravitational-wave dark sirens as astrophysical probes: inferring galaxy-merger relations and identifying individual hosts

Alessandro Agapito and Michele Mancarella

Gravitational-wave (GW) “dark siren” techniques, namely the statistical association of GW events with a galaxy catalog, have so far been used as a cosmological tool. Yet this association carries distinctive astrophysical information that remains unused—specifically, how compact binaries populate galaxies and the identities of individual hosts. In this work, we turn the dark-siren program into an astrophysical probe by inferring both simultaneously within a single hierarchical framework. The method reduces the many potential hosts to a compact, probabilistically ranked target list, providing a direct follow-up decision tool. Applied blindly to GW170817, it recovers NGC~4993 as the highest-ranked host and constrains the galaxy luminosity weighting, mildly favoring non-uniform host weights. Fixing the galaxy weighting can instead degrade host identification and even favor the wrong host. This framework recasts dark sirens as a potentially unique probe of the astrophysics of electromagnetically dark compact-binary mergers.
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High Energy Physics (Phenomenology) · Cross-listed from cs.LG

Dimensionally consistent surrogate modelling through dimensional analysis and harmonic expansions

Ernest Tarrus and Hector Gisbert

Dimensional homogeneity is a fundamental constraint on physically meaningful models, requiring invariance under changes of units. We present a data-driven method for constructing surrogate models that satisfy this constraint at the level of the hypothesis class. Starting from a dimension matrix of measured variables, the method derives Buckingham $\Pi$-groups, constructs admissible dimensional prefactors, and approximates the remaining dimensionless dependence using truncated harmonic expansions on normalized invariant domains. Once the prefactor and dictionary are fixed, the coefficients are obtained from a regularized linear regression problem. We test the approach on the simple pendulum, Planck's black-body law, the double-pendulum Lyapunov field, and an experimental COBE/FIRAS black-body spectrum dataset. The results show that dimensional constraints improve conditioning, robustness to noise, and sample efficiency relative to unconstrained baselines, while the choice of dictionary becomes important in non-periodic or multi-invariant settings. The learned expressions are explicit and inexpensive to evaluate, which makes them useful as surrogate models for structured physical problems.
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High Energy Physics (Phenomenology)

Self-interacting $O(N)$ scalar dark matter multiplet in a Higgs-portal model with a light scalar mediator

U-Rae Kim, Jungil Lee and Soo-hyeon Nam

We investigate self-interacting dark matter in an $O(N)$-symmetric real scalar multiplet model with Higgs-portal interactions involving the Standard Model Higgs and a real singlet scalar. After spontaneous breaking of the singlet $\mathbb{Z}_2$ symmetry, the singlet scalar mixes with the SM Higgs boson. We focus on the regime where the resulting light scalar serves as a mediator, leading to sizable and velocity-dependent self-interactions. We impose constraints from Higgs measurements, rare $B$-meson decays, the dark matter relic abundance, spin-independent direct-detection searches, and scalar coupling perturbativity. We find viable parameter regions in which destructive interference between scalar-mediated scattering amplitudes suppresses the direct-detection cross section while allowing self-interactions relevant to dwarf-galaxy scales. Among these viable parameter regions, a subset also satisfies electroweak vacuum stability up to the Planck scale. Finally, we show that future long-lived-particle searches can probe part of the viable parameter space, providing complementary tests of Higgs-portal self-interacting dark matter with a light scalar mediator.
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High Energy Physics (Phenomenology)

The new LHCb beauty-strange state as the bottom partner of the $D_{s0}^*(2317)$: a LQCD constrained coupled-channel chiral analysis

Miguel Albaladejo, Pablo Encarnación, Albert Feijoo et al. (+1 more)

The LHCb Collaboration has observed a narrow state in the $\bar{B}_s^0\pi^0$ spectrum, about 74 MeV below the $B^-K^+$ threshold, which is the natural candidate for the bottom partner of the $D_{s0}^*(2317)$. Such a state had been predicted as a $\bar{B}K$ bound state by unitarized heavy-meson chiral perturbation theory with lattice-QCD input. We analyze the LHCb spectrum with these coupled-channel amplitudes, including isospin breaking through the physical meson masses, $\pi^0$-$\eta$ mixing, and $m_u\neq m_d$ in the chiral amplitudes, thereby allowing the $\bar{B}_{s0}^*$ to decay through its only open strong channel, $\bar{B}_s^0\pi^0$. With the parameters fixed by lattice QCD and no experimental input from the LHCb measurement, the predicted state lies within 1.1-1.7 standard deviations of the observed peak. Adjusting a single parameter, the spectrum is described as well as with the zero-width limit of the LHCb analysis. The new state thus emerges naturally from these amplitudes, with a large $\bar{B}K$ component and an isospin-violating width of tens of keV, and its $J^P=1^+$ heavy-quark spin partner is predicted with a precision comparable to that of the measured mass.
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All authors Miguel Albaladejo, Pablo Encarnación, Albert Feijoo, Juan M. Nieves

High Energy Physics (Phenomenology)

Two Feynman integral families for vector boson fusion at NNLO QCD

Linus Götzfried and Andreas von Manteuffel

We consider a planar and a non-planar two-loop Feynman integral family arising in non-factorisable quantum chromodynamics corrections to Higgs-boson production via vector boson fusion. We construct basis integrals which fulfil canonical differential equations with respect to seven variables for the external kinematics and an internal mass. One of the integral families involves nested square roots. We present strategies for deriving canonical master integrals, $\mathrm{d}\log$ forms and analytic continuation for such cases. Including also families with crossed massless legs, we express the $\varepsilon$-expanded integrals in terms of an algebraically independent function basis. For their evaluation, we employ numerical integration of the differential equations.
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High Energy Physics (Phenomenology)

One-loop QCD amplitudes for vector-boson-fusion Higgs-boson production to higher orders in $\epsilon$

Konstantin Asteriadis, Linus Götzfried and Andreas von Manteuffel

We consider one-loop QCD corrections to Higgs-boson production via vector-boson fusion at hadron colliders. As an input for future exact NNLO computations, we derive the one-loop helicity amplitudes to higher orders in the dimensional regulator. We present a direct calculation of the amplitudes with spinor-helicity techniques and different $\gamma_5$ schemes. In addition, we compare this approach to a projector-based calculation. In order to derive analytical results to higher orders in $\epsilon$, we calculate the pentagon master integrals by the method of $\epsilon$-factorised differential equations and express them in terms of an algebraically independent set of basis functions.
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High Energy Physics (Phenomenology)

The $\psi$(2S) state as a subthreshold pole in electron positron annihilation into $D\bar D$ final states

Peter Lichard

By performing a fit to the merged BES 2008 and BESIII 2024 $e^+e^-\to D\bar D$ cross-section data, we find that the $\psi(2\mathrm S)$ subthreshold pole influences this process markedly. The statistical significance of the $\psi(2\mathrm S)$ as a subthreshold pole is 8$\sigma$. A fit assuming it and seven resonances excels with the fit quality characterized by $\chi^2/\mathrm{DOF}=240.4/284$, which means a $p$-value of 97%. The interference of resonances with the continuum provided by the subthreshold pole changes their shapes, positions, and widths.
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High Energy Physics (Phenomenology) · Cross-listed from math-ph

Breaking the Spin Degeneracy for Distributions of Off-Diagonal Scattering Matrix Elements in the Case of Symplectic Symmetry

Nils Gluth and Thomas Guhr

Recently derived exact expressions for the distributions of scattering matrix elements show that all combinations of ingoing and outgoing spin orientations are equally distributed. We propose a model suitable for experimental realization that breaks this degeneracy by introducing a spin preference in the channels. With the help of supersymmetry we derive a corresponding nonlinear sigma model. We exactly calculate the distributions of real and imaginary part in first order of the parameter measuring the preference. Quite remarkably, while breaking the spin degeneracy leads to different distributions for the favored and unfavored spin orientation, the real and imaginary parts of these altered distributions are the same as in the case of unbroken spin degeneracy.
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High Energy Physics (Phenomenology)

Heavy quark energy loss in the Bayesian-inference-improved CUJET model

Yu Guo, Jinfeng Liao and Shuzhe Shi

We compute jet quenching observables–the nuclear modification factor $R_{AA}$ and elliptic anisotropy coefficient $v_2$–for open-heavy flavor mesons with high transverse momentum in an improved CUJET model, in which the strong coupling parameter as well as the temperature-dependent fraction of chromo-magneto monopoles are extracted through Bayesian inference using high-$p_T$ light-hadron $R_{\mathrm{AA}}$ and $v_2$ measurements from RHIC and the LHC. We show in this work that such a Bayesian-inference-improved CUJET model provides a good description of available high-$p_T$ charm- and bottom-hadron observables based on the same posterior parameters. The corresponding heavy-quark spatial diffusion parameter, $2\pi T D_s$, is also computed, which is broadly consistent with current phenomenological and lattice-QCD constraints. These results support a universal description for the medium modification of high-$p_T$ light- and heavy-flavor energy loss and indicate an important role played by the chromo-magnetic degrees of freedom near the confinement transition region of quantum chromodynamics (QCD).
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High Energy Physics (Phenomenology)

Muon-to-positron conversion from local dimension-nine operators: pion-pole-improved nuclear multipoles

Yi Liao and Hao-Lin Wang

We begin a systematic study of neutrinoless muon-to-positron conversion, $\mu^-+(A,Z)\to e^++(A,Z-2)$, which violates lepton number by two units and changes charged-lepton flavor. This first paper in a series constructs nuclear operators for local dimension-nine interactions containing a scalar or pseudoscalar lepton bilinear and two contracted vector or axial quark currents. The covariant nucleon currents are built with all six vector and axial form factors. For the working nuclear operator we neglect second-class currents and adopt a pion-pole-improved reduction: non-pole recoil terms generated by the displayed one-body currents are retained through second order in inverse nucleon mass, whereas the pion-pole longitudinal axial current is kept intact before the two currents are contracted. We preserve the two independent momentum transfers at the nucleon vertices and the Coulomb-shifted spatial phase of the outgoing positron. Starting from the spacetime transition element, we show explicitly how the interaction-coordinate integral fixes the sum, but not the sharing, of the two current momenta. Unequal form-factor arguments then generate relative-coordinate multipoles absent in the usually used common-momentum approximation. We give an exact recoupling into two-body nuclear tensors and specialize it to the phenomenologically important $0^+\to0^+$ transition. In this case the external nuclear rank is zero and all magnetic sums collapse, although finite-momentum internal orbital and spin tensors remain. The result is expressed in a form directly contractible with charge-changing two-body transition densities. General six-form-factor currents, arbitrary nuclear angular momenta, and power-counting qualifications are collected in appendices.
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High Energy Physics (Phenomenology)

A Full Reproduction of the Godfrey–Isgur Relativized Quark Model

Mikhail Mikhasenko

The relativized quark model of Godfrey and Isgur (1985) remains a reference for meson spectroscopy four decades after its publication, yet despite its impact the calculation behind it has never been publicly available. I present an independent reproduction of the whole paper, released as the open-source Julia package GIModel.jl with companion packages for transition observables and for the comparison with the original. The published parameters are used without refitting, and the paper's three-stage harmonic-oscillator algorithm is cross-checked with an independent finite-difference solver. All 209 levels of the paper's spectrum figures are reproduced within the precision of the printed diagrams. The strong-decay, radiative, annihilation, and electromagnetic tables are reproduced with median model-to-paper ratios between 0.97 and 1.06, and the $1P$ mixing angles agree with the values the authors revised after 1985. With the calculation open, the model's own wavefunctions become available for decay amplitudes and structure visualization. The package, its teaching material, and its agent-accessible interface make the model a baseline for experimental questions and theoretical extensions.
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High Energy Physics (Phenomenology) · Cross-listed from hep-th

Reconciling Inflation with the Festina Lente Bound through Affleck-Dine Baryogenesis

Kazuto Nakamura and Masaki Yamada

The Festina-Lente bound is a swampland conjecture motivated by the behavior of charged BHs in dS spacetime, which imposes a constraint on the masses of charged particles. Although relatively weak in the present-day Universe, it can severely constrain inflation. We clarify its underlying assumptions and show that breaking all gauge symmetries during inflation, with gauge boson masses above the Hubble scale, provides a natural way to evade these constraints. We catalogue single flat directions in the Minimal Supersymmetric Standard Model that completely break its continuous gauge group, together with pairs that achieve complete breaking only when both directions are excited and simultaneously satisfy F- and D-flatness. With suitable lifting operators, such condensates can also generate the baryon asymmetry through the Affleck-Dine mechanism. Within this classification, all single-direction monomials that admit complete breaking carry nonzero $B-L$, providing candidates for Affleck-Dine baryogenesis. We further show that, in this setting, a large condensate compatible with the observed baryon asymmetry and isocurvature constraints readily satisfies the Festina-Lente bound, establishing a natural connection between the FL bound and Affleck-Dine baryogenesis.
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High Energy Physics (Phenomenology)

A glueball puzzle explained in terms of $\phi h_1(1380)$ dynamics: Aka $X(2370)$

K. P. Khemchandani, A. Martinez Torres and E. Oset

We study the interaction of $\phi$ with $h_1(1380)$, considering the latter as a $K^*\bar K$ molecular state, and find the generation of a state with the same quantum numbers, together with a mass and width compatible with the experimental results, as those of $X(2370)$, recently advocated as a candidate for a glueball. Within our description, the suppressed decay modes of $X(2370)$ to $\gamma \omega$, $\omega \phi$ and $K^*\bar K$, reported in the experimental paper as clues to its glueball nature, are naturally explained. Conversely, the non $K^* \bar K$ decay to $K \bar K \pi$ (the latter being the invariant mass where the resonance is observed) is shown to be largely enhanced due to the combination of a triangle singularity and the presence of $K(1630)$ in the $\rho \phi \to \bar K$ vertex involved in the triangle loop.
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High Energy Physics (Phenomenology)

Bound-state decay of a charged scalar particle in an external Coulomb field

Andrzej Czarnecki and Artem O. Davydov

We determine the decay rate $\Gamma$ of a scalar particle bound to a light nucleus, numerically and analytically. As a model system, we consider a negatively charged kaon in the ground state of a hydrogen-like ion decaying into charged and neutral scalar pions, $K^-\to \pi^-\pi^0$. All particles are assumed point-like; the nucleus is infinitely heavy. The partial wave expansion converges slowly, as in a recent analysis of the bound-muon decay. To overcome this difficulty, we introduce a subtraction method: the free $\pi^-$ contribution is evaluated separately, while the partial-wave sum is used only for the Coulomb distortion. The ratio of bound-to-free decay rates, $\Gamma/\Gamma_0$, is found for light nuclei, $1\leq Z\leq 10$. The numerical calculation is complemented by a diagrammatic small-$\alpha Z$ expansion. We find $ \Gamma/\Gamma_0 = 1-(\alpha Z)^2/2 + 17(\alpha Z)^4/24 +\mathcal{O}((\alpha Z)^5)$, in agreement with the all-orders numerical calculation at low $Z$.
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High Energy Physics (Phenomenology) · Cross-listed from astro-ph.CO

Carving out the Multifield Cosmological Collider Landscape

Denis Werth

We show that inflation with a large number of fields, as predicted by concrete ultraviolet embeddings, generically produces almost-local cosmological collider signals in the bispectrum squeezed limit. We construct the most general boost-breaking mixings between the curvature perturbation and $N_{\rm f}$ additional fields, and extract the late-time scaling dimensions that dictate the soft limits of cosmological correlators. For a handful of fields, an enhanced squeezed limit (with potential oscillations) is a fine-tuned signal. At large $N_{\rm f}\sim100$, however, mixings generically drive the scaling dimensions toward the unitarity boundary. We show that this is a direct consequence of extreme value statistics and random-matrix universality, turning an almost-local bispectrum shape into a generic prediction for almost any masses and mixings.
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High Energy Physics (Phenomenology)

The four-loop quark-to-quark splitting function in QCD

Thomas Gehrmann, Andreas von Manteuffel, Vasily Sotnikov et al. (+1 more)

The scale evolution of parton distributions is governed by splitting functions. We compute the four-loop pure-singlet contribution to the quark-to-quark splitting function in perturbative QCD. Together with the known non-singlet contribution, our result completes the quark-to-quark splitting function at this order. We confirm previous partial results and obtain, for the first time, a fully analytic expression valid for all momentum fractions. We examine its behavior at small momentum fractions and provide precise numerical representations suitable for parton evolution.
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All authors Thomas Gehrmann, Andreas von Manteuffel, Vasily Sotnikov, Tong-Zhi Yang

High Energy Physics (Phenomenology)

Decaying Dark Matter for the Exothermic Recoil at LZ

Yongsoo Jho, Sanghwan Kim and Seong Chan Park

The LUX-ZEPLIN (LZ) experiment has reported a single nuclear-recoil candidate at $248\pm23\,(\mathrm{stat})\pm23\,(\mathrm{sys})$ keV. We suggest that it comes from a GeV-scale dark state $\chi_1$ that downscatters exothermically, $\chi_1A\to\chi_2A$, and is continuously replenished in the halo by the slow decay $\chi_0\to\chi_1\chi_1$ of a long-lived parent. Because the recoil energy is supplied by the mass splitting rather than by the halo velocity, the event is a narrow line with no low-energy tail. Kinematics requires $m_{\chi_1}\gtrsim247$ MeV and fixes the splitting for each $m_{\chi_1}$. The same line should appear at 700$-$810 keV in argon for $m_{\chi_1}=0.3-10$ GeV. Normalizing to one LZ event also fixes the local rate of the radiative decay $\chi_1\to\chi_2\gamma\gamma$, up to the mediator's photon coupling. A rough $\gamma$-ray estimate then requires this coupling to be $\lesssim10^{-2}$ of a proton-loop reference at $m_{\chi_1}=10$ GeV, but $\lesssim10^{-9}$ at 0.3 GeV, which favours daughters near 10 GeV.
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High Energy Physics (Phenomenology)

Resummation-scale effects in DIS PDF fits with xFitter

Francesco Giuli

Renormalisation-group evolution enters PDF determinations through the running coupling and the splitting functions. At fixed perturbative order, the solution of the evolution equations is not unique beyond the nominal accuracy, and this residual freedom can be probed through resummation-scale variations. This contribution summarises an NNLO study of this effect in inclusive HERA DIS fits performed with the xFitter fitting framework. The induced shifts are sizeable in a low-scale baseline fit, especially for the gluon and sea PDFs, and can affect LHC and FCC top-quark pair predictions at the few-percent level. Raising the PDF starting scale and applying a higher DIS virtuality cut considerably reduces the effect, a conclusion also supported by treating the resummation scale as a free parameter constrained directly by the data.
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High Energy Physics (Phenomenology)

Endothermic Dark Matter at LZ from a Decaying Parent

Yongsoo Jho, Sanghwan Kim and Seong Chan Park

The LUX-ZEPLIN experiment has reported a nuclear-recoil candidate near 248 keV. We investigate a decay source for an endothermic interpretation: a long-lived dark parent produces energetic ground-state particles that upscatter on xenon. The parent mass fixes the injection energy, while its lifetime determines the absolute flux through the Galactic dark-matter column density. We include the Doppler broadening from parent and observer motion and use exact scattering kinematics with natural xenon isotopes. For a scalar contact interaction, a benchmark with a 10 MeV incident state and a 506 MeV parent gives an efficiency-weighted recoil spectrum peaked at 248.5 keV. One event in a specified high-energy window requires $\tau_X \simeq 4.4 \times 10^{20}$ s $f_X [\sigma_{\text{ref}}/(10^{-36} \text{cm}^2)]$, with a normalization sensitive to the nuclear response. We quantify the accompanying elastic-scattering requirement and the target-dependent thresholds. The calculation identifies a decay realization of the boosted flux and the portal conditions needed to preserve the recoil signal; a detector-level fit and ultraviolet-specific constraints remain necessary for a complete experimental assessment.
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High Energy Physics (Phenomenology) · Cross-listed from hep-th

The Stieltjes Bootstrap for Feynman Integrals

Hadrien Brochet, Maximilian Haensch, Johannes Henn et al. (+4 more)

We prove that scalar Feynman integrals are Stieltjes functions in each kinematic variable $-p_i\cdot p_j$, as well as in the particle masses, for arbitrary loop order, arbitrary numbers of external legs, and arbitrary internal masses, whenever a certain exponent condition is satisfied. The proof rests on a canonical decomposition of the second Symanzik polynomial with manifestly non-negative coefficients indexed by spanning two-forests. We present a dedicated analysis of the case in which the kinematic variables satisfy relations, as frequently happens in physical applications. We argue that integration-by-parts relations allow the selection of master-integral bases in which every element is a Stieltjes function. The Stieltjes property guarantees the convergence of Padé approximants and provides determinantal (Hankel) constraints on the Taylor coefficients of master integrals that go beyond previously known complete-monotonicity bounds. We develop a numerical strategy that combines these Stieltjes constraints with differential equations to determine the master integrals in the Euclidean region via semidefinite optimization. We demonstrate this approach on the pedagogical example of the six-dimensional massive box integral, and then apply it to the calculation of previously unknown three-loop two-mass integrals needed for three-loop electroweak corrections to the $Z$- and Higgs-boson self-energies.
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All authors Hadrien Brochet, Maximilian Haensch, Johannes Henn, Benjamin Hollering, Prashanth Raman, Qinglin Yang, Simone Zoia

High Energy Physics (Phenomenology) · Cross-listed from astro-ph.HE

Search for dark matter annihilation in the Sun using the full ANTARES dataset

A. Albert, S. Alves, M. André et al. (+133 more)

Weakly Interacting Massive Particles (WIMPs) are among the most popular candidates for particle dark matter. In certain scenarios, WIMPs could be gravitationally captured into massive celestial objects and then annihilate into Standard Model particles, possibly leading to the emission of neutrinos. The ANTARES neutrino telescope, located in the Mediterranean Sea, is sensitive to neutrinos with energies ranging from a few tens of GeV to the TeV scale, making it well suited to search for the annihilation of WIMPs with masses below a few TeV/c$^2$. One of the closest potential astrophysical sources of neutrinos from WIMP annihilations is the Sun. In this work, a search for high-energy neutrinos originating from the Sun, using the full dataset recorded by ANTARES from 2007 to 2022 was conducted. The analysis yielded no significant evidence for a neutrino excess over the expected background, and upper limits on the WIMP-proton interaction cross section have been obtained, for both spin-dependent and spin-independent processes. These limits are valid for dark matter masses ranging from 35 GeV/c$^2$ to 10 TeV/c$^2$ for the annihilation benchmark channels WIMP$+$WIMP $\longrightarrow$ $b\bar{b},\tau^+\tau^-, W^+W^-$, assuming a 100$\%$ branching ratio for each of these channels. These results improve on those previously obtained by the ANTARES Collaboration by a factor of two-three and are consistent with those reported by other experiments in direct and indirect searches for dark matter.
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All authors A. Albert, S. Alves, M. André, M. Ardid, S. Ardid, J.-J. Aubert, J. Aublin, B. Baret, S. Basa, Y. Becherini, B. Belhorma, F. Benfenati, V. Bertin, S. Biagi, J. Boumaaza, M. Bouta, M.C. Bouwhuis, H. Brânzaş, R. Bruijn, J. Brunner, J. Busto, B. Caiffi, D. Calvo, S. Campion, A. Capone, L. Caramete, F. Carenini, J. Carr, V. Carretero, T. Cartraud, S. Celli, M. Chabab, T. Chiarusi, M. Circella, J.A.B. Coelho, A. Coleiro, R. Coniglione, P. Coyle, A. Creusot, A. F. Díaz, B. De Martino, C. Distefano, I. Di Palma, C. Donzaud, D. Dornic, D. Drouhin, T. Eberl, A. Eddymaoui, T. van Eeden, D. van Eijk, S. El Hedri, A. Enzenhöfer, P. Fermani, G. Ferrara, F. Filippini, L.A. Fusco, S. Gagliardini, J. García-Méndez, C. Gatius Oliver, P. Gay, N. Geißelbrecht, H. Glotin, R. Gozzini, R. Gracia Ruiz, K. Graf, C. Guidi, L. Haegel, H. van Haren, A.J. Heijboer, Y. Hello, L. Hennig, J.J. Hernández-Rey, J. Hößl, F. Huang, G. Illuminati, B. Jisse-Jung, M. de Jong, P. de Jong, M. Kadler, O. Kalekin, U. Katz, A. Kouchner, I. Kreykenbohm, V. Kulikovskiy, R. Lahmann, M. Lamoureux, A. Lazo, D. Lefèvre, E. Leonora, G. Levi, S. Le Stum, S. Loucatos, J. Manczak, M. Marcelin, A. Margiotta, A. Marinelli, P. Migliozzi, A. Moussa, R. Muller, S. Navas, E. Nezri, B. Ó Fearraigh, E. Oukacha, A.M. Păun, G.E. Păvălaş, S. Peña-Martínez, M. Perrin-Terrin, P. Piattelli, C. Poirè, T. Pradier, N. Randazzo, D. Real, G. Riccobene, A. Romanov, A. Sánchez Losa, A. Saina, F. Salesa Greus, D. F. E. Samtleben, M. Sanguineti, P. Sapienza, F. Schüssler, J. Seneca, M. Spurio, Th. Stolarczyk, M. Taiuti, Y. Tayalati, B. Vallage, G. Vannoye, V. Van Elewyck, S. Viola, D. Vivolo, J. Wilms, S. Zavatarelli, A. Zegarelli, J.D. Zornoza, J. Zúñiga