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Physics High Energy Physics (Phenomenology)

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Friday 11 September

High Energy Physics (Phenomenology)

Gauge-invariant Higgs mechanism via gradient-flow regularization

We provide a manifestly gauge-invariant description of the Higgs mechanism in the Standard Model, casting it not as the breaking of a local symmetry, but as a smooth, analytic crossover from a high-temperature symmetric phase to a low-temperature Higgs phase. Taking the vacuum expectation value of a gauge-invariant local scalar operator and constructing composite quasi-particle states from the original fields of the Lagrangian usually introduces contact-term divergences. Previous attempts to circumvent this issue via bilocal operators remain unsatisfactory. Here we demonstrate that the gradient flow at a flow time $t$ provides a clean, structurally sound, and Lorentz-covariant regularization that permits a consistent, renormalon-free matching onto the standard $\overline{\text{MS}}$ scheme at a scale $\mu \sim 1/\sqrt{2t}\gg m_t$. Beyond its theoretical appeal, this construction clarifies a number of conceptional and practical questions. We demonstrate the utility of this framework at the one-loop level, thereby establishing the foundation for future electroweak precision physics in this approach.
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High Energy Physics (Phenomenology) · Cross-listed from astro-ph.CO

Probing Inflationary Origins of Primordial Black Holes with LIGO–Virgo–KAGRA O1–O4a data

Large primordial curvature perturbations not only produce primordial black holes (PBHs) but also inevitably source a scalar-induced stochastic gravitational-wave background upon horizon reentry. We analyze the combined LIGO–Virgo–KAGRA O1–O4a data to constrain two representative inflationary mechanisms for generating such perturbations: ultra-slow-roll inflation and an inflationary phase transition. Detecting no evidence for either scenario, we place 95% credible upper limits on the curvature-spectrum amplitude across the frequency range accessible to ground-based interferometers. Translated into the PBH context, these limits already exceed conventional constraints, probing abundance fractions far below unity. Our results remain robust even when the PBHs themselves are too rare to be directly detected or have evaporated. This work demonstrates that stochastic gravitational-wave observations offer a powerful and complementary probe of small-scale inflationary physics and PBH formation, with upcoming interferometers promising to extend sensitivity to a wider range of inflationary epochs and PBH masses.
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All authors Haipeng An, Huai-Ke Guo, Mai Qiao, Lian-Tao Wang, Chen Yang, Yue Zhao

High Energy Physics (Phenomenology)

Supernova cooling from neutrinophilic dark matter

Core-collapse supernova serve as a powerful laboratory for testing physics beyond the Standard Model (BSM), particularly regarding new, light states interacting feebly with SM particles. In this work, we investigate for the first time the production of dark matter (DM) via the neutrino-neutrino scattering processes inside a core-collapse supernova, which contributes to the excessive cooling. By incorporating state-of-the-art supernova simulation data , we derive stringent and robust limits on sub-GeV dark matter with effective couplings to neutrinos. We find that the existing and projected constraints from indirect detection are quite weak. Our supernova cooling bounds on DM-neutrino reference cross section can improve indirect detection limits more than ten orders of magnitude for DM masses below $\mathcal{O}(100)$ MeV, and it can also provide strong complementarity with other cosmological constraints. Our results highlight the exceptional sensitivity of core-collapse supernova to feebly interacting particles and motivate future supernova neutrino observations as a powerful probe of light dark sectors.
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High Energy Physics (Phenomenology)

Reconstructing the Dark Matter Equation of State with Compact Object Inspirals

We investigate the gravitational wave (GW) signatures of compact binaries embedded in extended dark matter (DM) configurations in hydrostatic equilibrium. If a neutron star is surrounded by a sufficiently massive and extended envelope, an inspiraling companion experiences dynamical friction (DF) in addition to the standard GW energy loss. We show that this environmental effect can be isolated through a GW observable, the $D$-function, which directly characterizes the additional dissipative power induced by the surrounding medium. Since the density of the envelope is directly determined by the DM equation of state together with the stellar boundary conditions, the frequency dependence of the $D$-function provides direct information about the macroscopic properties of the dark sector. We develop a regression-based framework to reconstruct both the density profile and the DM equation of state over the density range probed by observations of the GW inspiral. Using representative DM models as benchmarks, we demonstrate that the method accurately recovers the input equation of state while remaining largely independent of the microscopic realization of DM. Our results show that future GW observations of compact binaries can provide a probe of the equation of state of DM.
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High Energy Physics (Phenomenology)

Associated $W$ + charm production: indications for PDF analysis

The strange quark and antiquark contents of the proton remain weakly constrained compared to the other light quarks, particularly the asymmetry between the two. Production of a $W^\mp$ boson in association with a charmed meson $D^{(*)\pm}$ could provide additional constraints in future fits of parton distribution functions. We calculate this process in general-mass variable-flavor-number scheme at next-to-leading order in perturbative Quantum Chromodynamics. We investigate the production ratio between events with oppositely charged $W$ bosons, in which various theoretical uncertainties largely cancel while sensitivity to PDFs remains. We compare our predictions for this quantity with the recent ATLAS data at $\sqrt{s} = 13$ TeV and find that CT18ANLO, which sets the strangeness asymmetry to zero, yields good agreement with the data while MSHT20NLO and NNPDF4.0NLO, which have positive strangeness asymmetry in the relevant range of momentum fraction $x$, show more tension with the data. An approximate PDF-level analysis of the production ratio indicates that this tension could be attributed to a too large strangeness asymmetry.
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High Energy Physics (Phenomenology) · Cross-listed from hep-ex

The DALI Haloscope: A Magnetized Phased Array Coupled to a Semi-Open Fabry–Pérot Resonator

DALI is an axion haloscope consisting of a magnetized phased array backed by a conducting mirror and coupled in the near field to a semi-open Fabry–Pérot resonator. The applied static magnetic field makes both the dielectric interfaces and the conducting mirror sensitive to axion-induced electromagnetic conversion. Each interface acts as a radiating surface, and the resulting fields are projected onto the mode collected by the resonator and delivered to the receiver. We derive the detected power in terms of the power available from the magnetized mirror, the coherent contribution of the dielectric interfaces, the transverse mode overlap, the loaded quality factor, and the receiver-coupling coefficient. This formulation separates two distinct enhancement mechanisms. The dielectric-interface emissions may add coherently, producing a dielectric boost, while the semi-open Fabry–Pérot resonator provides enhancement through resonant storage of the coupled electromagnetic field. These contributions depend differently on the dielectric thicknesses, spacings, and resonant mode, and should therefore be evaluated independently. The same assembly can operate between the limits of a coherently boosted dielectric haloscope and a mirror-sourced, resonantly enhanced Fabry–Pérot haloscope. This combined architecture offers a flexible approach to resonant axion searches at frequencies for which conventional closed microwave cavities become increasingly limited in conversion volume.
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All authors Javier De Miguel, Antonios Gardikiotis, Eduardo David González-Carretero, Elvio Hernández-Suárez, Roger J. Hoyland, Enrique Joven, Abaz Kryemadhi, Marios Maroudas, Chiko Otani, J. Alberto Rubiño-Martín, Yannis K. Semertzidis, Michael E. Tobar, Konstantin Zioutas

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

Constraints on Galactic Dark Photons from a DALI Prototype

An analysis of 36 hours of data from a DALI haloscope reveals no statistically significant excess attributable to dark-photon dark matter. We therefore set new constraints in the 6.88691–6.91792 GHz band, reaching a dark-photon-to-photon kinetic mixing strength of $\chi\lesssim 6.8\times10^{-14}$ at $28.54 \, \mu\mathrm{eV}$. To our knowledge, this result established the strongest laboratory-based exclusion limit in this frequency range.
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All authors Javier De Miguel, Antonios Gardikiotis, Elvio Hernández-Suárez, Roger J. Hoyland, Enrique Joven, Abaz Kryemadhi, Haroldo Lorenzo-Hernández, Marios Maroudas, Chiko Otani, J. Alberto Rubiño-Martín, Yannis K. Semertzidis, Michael E. Tobar, Konstantin Zioutas

High Energy Physics (Phenomenology) · Cross-listed from gr-qc

Intrinsic pressure anisotropy in spherical Proca stars

Pressure anisotropy in relativistic stars is commonly prescribed through a phenomenological closure, obscuring its microscopic origin and relation to stress-energy conservation. Here it is derived directly from the minimally coupled Einstein-complex-Proca theory. For spherical Proca stars, the principal-pressure difference admits an exact on-shell form whose sign is controlled solely by the local mass-shell threshold. The stress is radially dominated in the core, reverses on a surface of fixed gravitational redshift, and becomes tangentially dominated in the envelope. At the first mass maximum, the fractional anisotropy reaches about 21% near the density maximum, whilst the region beyond the reversal contains about 9% of the mass. Its exact atmospheric limit is approximately 24%, equal in magnitude and opposite in sign to the scalar-boson-star limit. Because the usual local fluid variables remain non-zero at the crossing, no sign-definite closure constructed from them can reproduce the profile. These results identify an intrinsically vectorial stress reversal, generated without additional interactions, and provide a first-principles benchmark for anisotropic bosonic compact objects.
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High Energy Physics (Phenomenology)

Comparision of modeling of prompt photon production in proton-proton collisions at energies NICA $\sqrt{s}$ =10 GeV in PYTHIA and calculations using FeynCalc

The process of prompt photon production in proton-proton collisions at energies of $\sqrt{s}$=10 GeV at the NICA accelerator complex, modulated using PYTHIA 8.316 and calculated in FeynCalc. The main focus is on three main subprocesses: Compton scattering of a quark-gluon $qg \rightarrow q\gamma$, annihilation of a quark-antiquark pair $q\bar{q} \rightarrow g\gamma$ and bremsstrahlung of quarks $qq \rightarrow qq\gamma$. Main statistical parameters: number of produced prompt photon on photon energy, rapidity and invariant mass photon pairs are determined. The distribution of the number of produced photons by energy$ E_{\gamma } $ and rapidity photons can be mathematically described by the logarithmic-normal and normal law, correspondingly. The analysis shows that Compton scattering of a quark-gluon $qg \rightarrow q\gamma$ makes a dominant contribution to the total cross section of the process, accounting for 51.27%, while the contributions of annihilation of quark-antiquark pair $q\bar{q} \rightarrow g\gamma$ and bremsstrahlung of quarks $qq \rightarrow qq\gamma$, correspondingly are is 47.22% and 0.003%. The difference between the results obtained from the PYTHIA modeling and those calculated by FeynCalc is explained. The use of modern modeling tools such as PYTHIA not only improves the accuracy of experimental predictions, but also plays a key role in the development of new technologies for particle detection and data analysis.
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All authors Mohsun R.Alizada, Azar I.Akhmedov, Sarhaddin K.Abdullayev, Mejid Sh.Gojayev, Mammed R.Rajabov

High Energy Physics (Phenomenology)

Phase Structure and Gravitational-Wave Phenomenology of a Thermal First-Order Phase Transition

We investigate the phase structure and gravitational-wave (GW) phenomenology of a cosmological first-order phase transition described by the finite-temperature effective potential $V(\phi,T)=D(T^2-T_0^2)\phi^2-ET\phi^3+\lambda\phi^4/4$. We derive the critical temperature and the broken-phase order parameter and identify the dimensionless combination $E^2/(D\lambda)$ that controls the critical-temperature shift. We then construct a dense numerical atlas containing $30\,000$ parameter points and map the resulting transition parameters onto the characteristic GW frequency and peak amplitude. The scan resolves the multidimensional correlations among $T_*$, $\alpha$, $\beta/H_*$, $v_w$, $f_{\rm peak}$ and $\Omega_{\rm GW}^{\rm peak}h^2$. The present analysis is phenomenological: $T_*$ is defined by the prescription $T_*=0.95T_c$, while $\beta/H_*$ and $v_w$ are treated as scan inputs. Consequently, the resulting GW signals are not interpreted as first-principles predictions. We identify the additional ingredients required for a predictive calculation, including the thermal bounce action, nucleation and percolation temperatures, the transition duration and a microscopic treatment of bubble-wall friction. The resulting framework provides a systematic numerical characterization of the connection between the phase structure of the finite-temperature potential and the corresponding phenomenological GW parameter space.
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High Energy Physics (Phenomenology)

Observables in exclusive heavy quarkonium electroproduction at NLO and prospects for the EIC

We perform various phenomenological studies of exclusive heavy-quarkonium electroproduction in $ep$ collisions that are relevant for both the existing measurements from HERA and the forthcoming Electron-Ion Collider (EIC). We provide quantitative predictions at next-to-leading order (NLO) in perturbative QCD (pQCD) for various observables accessible at HERA for $J/\psi$ electroproduction that serve as valuable benchmarks across a broad range of photon virtualities $Q^2$ and $\gamma^* p$ centre-of-mass energies. We then discuss how the forthcoming EIC will complement existing measurements and end by advocating the need for a dedicated and systematic resummation framework for $J/\psi$ electroproduction at large $Q^2$.
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High Energy Physics (Phenomenology)

Minimal Flavoured DFSZ Axion Models: Predictive Yukawa Textures and Flavour Constraints

We study a predictive class of flavoured DFSZ axion models in which the Peccei–Quinn symmetry is fully horizontal and the domain wall number is unity. These Minimal F-DFSZ models simultaneously resolve the strong CP problem and avoid the post-inflationary domain wall problem, while enforcing a predictive set of texture-zero quark mass matrices. Remarkably, the entire quark Yukawa sector can be reconstructed in terms of the measured quark masses and Cabibbo–Kobayashi–Maskawa parameters. We derive analytic expressions for the resulting flavour-violating Higgs and axion couplings, thereby making explicit how the new-physics effects are determined by Standard Model observables. We then analyse the full flavour phenomenology of the framework and obtain bounds on the scale of new physics from precision flavour observables.
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High Energy Physics (Phenomenology)

Comprehensive study of spectroscopic properties of $D_{(s)}$ mesons

We decode the excited open charm mesons $D$ ($c\bar{q}$, $q=u,d$) and charm strange $D_s$ ($c\bar{s}$) families within a nonrelativistic quark-antiquark potential model based on the Cornell (Coulomb plus linear) potential supplemented by a Gaussian smeared spin-spin interaction. With only seven parameters determined by fitting the ground state masses, the numerically solved Schrödinger equation reproduces the masses of essentially every confirmed $D$ and $D_s$ state to better than $1\%$. The same wave functions are then employed to get a complete decay analysis including pseudoscalar and vector decay constants ($f_D = 231.8$~MeV, $f_{D_s} = 252.2$~MeV, the latter within $0.4\%$ of the world average), leptonic branching fractions reproducing the measured $\mu\nu$ and $\tau\nu$ modes, electromagnetic $E1$/$M1$ widths, and all kinematically open strong channels in heavy quark effective theory (HQET). Going beyond width ratios, we extract the full set of HQET couplings $g_H$, $g_S$, $g_T$, $g_X$, $g_Y$, $g_Z$, and $g_R$ directly from the measured total widths and convert our predictions into absolute widths. The $D$ and $D_s$ sector extractions of each coupling agree ($g_T = 0.42$ vs. $0.39$, $g_X = 0.22$ vs. $0.21$, $g_Y = 0.39$ vs. $0.40$), a nontrivial test of heavy quark flavor symmetry, while the pure $c\bar{s}$ picture demands a $1^3P_0$ width nearly two orders of magnitude above the observed $D_{s0}^*(2317)$ bound demanding it to be of exotic nature. Linear and parallel Regge trajectories in the $(J,M^2)$ and $(n_r,M^2)$ planes, with slopes $\alpha \simeq 0.55-0.65$~GeV$^{-2}$ and $\beta \simeq 0.36 - 0.39$~GeV$^{-2}$, identify the assignments of $D_J(3000)^0$, $D_J^*(3000)^0$, and $D_2^*(3000)^0$ as the $3^1S_0$, $3^3S_1$, and $3^3P_2$ states. Our predictions provide concrete, testable targets for LHCb, BESIII, and Belle~II.
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All authors Janki. J. Patel, Dhaval Achary, Dhruvesh Maiya, Keval Gandhi, Nakul R. Soni, Jignesh N. Pandya

High Energy Physics (Phenomenology)

Leptogenesis Determined By Low Energy Parameters

We study thermal leptogenesis in three predictive type-I seesaw models in which the neutrino Dirac mass matrix is equal to the mass matrix of up-type quarks, or down-type quarks, or charged leptons. In this framework, the seesaw relation permits a full reconstruction of the heavy right-handed neutrino mass matrix from low-energy neutrino parameters, which greatly reduces the parameter freedom. A systematic numerical scan based on density matrix Boltzmann equations is performed to examine whether the observed baryon asymmetry of the Universe can be obtained. Successful leptogenesis occurs for normal ordering of light neutrino masses with nonzero Majorana phases. In this case, viable solutions are found in model B, associated with down-type quarks, and model C, associated with charged leptons. Both point to a close-mass pair of heavy neutrinos satisfying $|M_i-M_j|/M_i<10^{-3}$, while remaining outside the conventional quasi-degenerate resonant regime. Four representative benchmark points are selected to show the evolution of the asymmetry and the impact of different treatments of spectator effects. Neutrinoless double beta decay is further studied for all parameter points that can generate an acceptable baryon asymmetry $\eta_B = (6.12 \pm 0.20)\times 10^{-10}$. The predicted effective Majorana mass for certain cases can be probed by next generation experiments with sub-10 meV sensitivity, such as LEGEND-1000, nEXO, JUNO 50 tons, and CUPID-1T. This framework therefore provides clear targets for future searches.
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All authors Xiao-Gang He, Zhong-Lv Huang, Raymond R. Volkas, Yu-Qi Xiao

High Energy Physics (Phenomenology)

DIS Dijet Production: An operator basis bridging eikonal and TMD regimes

We propose an operator basis for the unpolarized deep-inelastic scattering (DIS) quark-antiquark dijet production process smoothly connecting the all-twist eikonal regime to the back-to-back leading-twist TMD regime at arbitrary Bjorken x. Starting from the background-field quark propagator we construct an operator basis that organizes the eikonal and twist expansions within a unified formulation. Utilizing this operator basis we derive the dijet production amplitudes retaining all contributions required by either the leading-eikonal or the leading-twist description. In the eikonal limit the resulting amplitudes reproduce the all-twist Color Glass Condensate result, while in the back-to-back limit they reduce to the leading-twist gluon TMD-based result at arbitrary x. The operator basis can be systematically extended to include sub-eikonal and higher-twist corrections. Further, by examining the relationship of this operator basis to the improved TMD (iTMD) factorization we recover the iTMD structure in the eikonal limit. However, we find at non-zero x the transverse resummation generates longitudinal phases that prevent factorization in terms of a conventional TMD operator.
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All authors Tiyasa Kar, Swagato Mukherjee, Vladimir Skokov, Shaswat Tiwari, Fei Yao

High Energy Physics (Phenomenology)

Spin-independent scattering of pseudoscalar-mediated dark matter

Dark matter with pseudoscalar couplings provides a well-motivated scenario in which direct-detection signals are suppressed at tree level, since the scattering off nuclei is both spin-dependent and momentum suppressed. While spin-independent scattering is absent at tree level, it arises at one loop and can provide the leading direct-detection signal. We revisit this scenario in a general sub-electroweak effective field theory with a light pseudoscalar mediator, including interactions through to mass-dimension-six. We compute the matching onto the quark and gluon operators relevant for direct detection to determine whether this scenario could be detectable at future experiments, while also requiring consistency with the observed dark matter relic-abundance and indirect-detection limits. We find that while models with a pseudoscalar mediator can generate spin-independent cross sections above the neutrino floor, this generally requires additional new physics below the TeV scale.
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All authors Nicole F. Bell, Giorgio Busoni, Peter Cox, Laura W. Fang, John Gargalionis, Jayden L. Newstead, Ewan N. V. Wallace, Martin J. White, Anthony G. Williams

High Energy Physics (Phenomenology)

Tensor-polarized twist-3 distribution function $f_{LT}$ of spin-1 deuteron

We investigate the twist-2 and twist-3 tensor-polarized partonic structures of the spin-1 deuteron. Using the operator product expansion with local operators, we derive a Wandzura-Wilczek (WW)-like twist-2 relation between the tensor-polarized twist-2 quark distribution $f_{1LL}$ and the twist-3 distribution $f_{LT}$, together with a Burkhardt-Cottingham (BC)-like sum rule. The local-operator formalism makes the Lorentz structure and rotational invariance manifest and provides useful constraints on the twist-3 sector. We then use a phenomenological parametrization of the twist-2 distribution $f_{1LL}(x)$, constrained by HERMES data on the deuteron structure function $b_1$ at $Q^2=2.5~\text{GeV}^2$, to quantitatively estimate the twist-3 distribution $f_{LT}(x)$ within the WW approximation. The resulting $f_{LT}(x)$ has a shape and magnitude comparable to those of $f_{1LL}(x)$, indicating that subleading-twist effects may be relevant for future experiments at relatively low $Q^2$. In this contribution, we summarize the theoretical derivation of the WW-like relation and BC-like sum rule and present a phenomenological estimate of the tensor-polarized twist-3 quark distribution $f_{LT}$ in the deuteron.
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High Energy Physics (Phenomenology)

Simple Modular $S_3$ Models for Lepton Masses and Mixing

We perform a systematic study of an economical class of modular $S_3$ lepton-flavor models without enlarging the continuous gauge symmetry or introducing right-handed neutrinos or additional flavon fields. We provide a complete classification of all inequivalent realizations allowed by the $S_3$ singlet–doublet representation structure and the admissible modular-weight assignments. Their phenomenological viability is investigated for both normal ordering (NO) and inverted ordering (IO) using Bayesian model comparison and parameter-correlation analysis based on current neutrino-oscillation data. We identify 18 viable models for NO and 19 for IO, with 14 satisfying the experimental constraints in both orderings. The viable models successfully accommodate current neutrino-oscillation data while yielding nontrivial predictions for leptonic CP violation, Majorana phases, and observables probing the absolute neutrino-mass scale. Among these predictions, the absolute-mass observables provide the clearest separation between the two orderings. At the best-fit points, the predicted ranges of the effective electron-neutrino mass ($m_\beta$) are completely disjoint between NO and IO, whereas those of the sum of neutrino masses ($\sum_i m_i$) and the effective Majorana mass ($m_{\beta\beta}$) show only partial separation. The IO models generally predict a higher absolute neutrino-mass scale and are consequently more strongly constrained by cosmological observations and more accessible to neutrinoless double-beta-decay searches. Our results show that, despite its economical field content, the modular $S_3$ framework accommodates a diverse set of phenomenologically viable lepton-flavor realizations with experimentally testable predictions.
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Thursday 10 September

High Energy Physics (Phenomenology) · Cross-listed from quant-ph

Comment on arXiv:2510.21705 "Fundamental Impossibility of a Superradiant Neutrino Laser" and comment on arXiv:2510.21692 "Can Bose-Einstein Condensates Enhance Radioactive Decay?"

We show that the small value of the neutrino cross-section rules out superradiance in the laboratory.

High Energy Physics (Phenomenology)

Dark-State Interference in an Effective Confined Three-Level Color System

In this work, a QCD-inspired effective model describes dark-state interference in a confined three-state system with two low-energy $Q\overline{Q}$ states, $|1\rangle$ and $|2\rangle$, and a gluon-excited hybrid state, $|H\rangle$. A stationary chromoelectric flux-tube background enters the unperturbed Hamiltonian, while a time-dependent chromoelectric perturbation couples $|1\rangle$ and $|2\rangle$ to $|H\rangle$ in a $\Lambda$-type configuration. Under two-photon\footnote{We retain standard terms like “two-photon” from the EIT literature only by mathematical analogy, but they do not refer to electromagnetic photons but to the effective frequencies and energy mismatches of chromoelectric perturbations and gluonic excitations that connect confined states.} resonance and within a Markovian Gorini-Kossakowski-Sudarshan-Lindblad master equation, the system forms a coherent superposition that decouples from $|H\rangle$, strongly suppressing the steady-state probe susceptibility $\operatorname{Im}\chi_{\text{CE}}$ as lower-state decoherence vanishes. A phenomenological non-Abelian correction to the hybrid energy mainly shifts and reshapes the transparency window rather than creating the interference itself. The model is not a first-principles QCD calculation of medium opacity but a controlled effective link between dark-state interference in quantum optics and reduced confined color dynamics.
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High Energy Physics (Phenomenology)

M1 Radiative Transitions in the $B_c$ System after the $B_c^\ast(1S)$ Observation: Radial-Node Cancellation and Quark-Line Filtering

The recent ATLAS observation of the $B_c^*(1S)$ meson fixes the ground-state hyperfine splitting and thereby determines the phase space for $B_c^*(1S)\to B_c(1S)\gamma$. We study four $1S$ and $2S$ M1 radiative transitions using relativistic Salpeter wave functions calibrated to the measured ground-state masses, obtaining $\Gamma[B_c^*(1S)\to B_c(1S)\gamma]=5.24\times10^{-2}$~keV. The allowed transitions show no radial cancellation, whereas the hindered $2S\to1S$ amplitudes are residuals of an approximately twenty-fold cancellation across the radial node. A quark-line-resolved analysis shows a strong asymmetry in the crossed hindered channel: the $b$-emission contribution undergoes an $\mathcal O(10^2)$ internal cancellation while the $\bar c$ contribution remains at $\mathcal O(20)$. The corresponding unsigned line strengths show that the small $b$-current is generated by enhanced cancellation rather than by a smaller unsigned contribution. The unmeasured $B_c^*(2S)$ mass remains the main limitation on the $2S\to2S$ radiative width.
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High Energy Physics (Phenomenology)

Radiative corrections to weak interaction processes

The search for physics beyond the Standard Model in low-energy weak interaction processes requires a precise knowledge of the Standard Model background at tree- and loop-level. In many such cases, radiative corrections represent one of the major sources of theory uncertainty due to the non-perturbative structures of nucleon or nuclei. In this review, I discuss several modern strategies based on dispersion relation, lattice gauge theory and nuclear many-body calculations to pin down the hadronic and nuclear uncertainties in the radiative corrections to low-energy weak interaction processes such as beta decays and parity-violating electron-nucleus scattering.
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High Energy Physics (Phenomenology) · Cross-listed from astro-ph.HE

Probing Lorentz Invariance Violation in Cosmogenic Neutrino Propagation with KM3-230213A

We investigate superluminal Lorentz invariance violation (LIV) in the neutrino sector using cosmogenic neutrino fluxes generated with ultrahigh-energy cosmic-ray propagation models. Standard fluxes are calculated with CRPropa 3.2 and subsequently modified using a prescription based on LIV-induced neutrino splitting. Superluminal LIV suppresses the flux at the highest energies while producing an enhancement at PeV - EeV energies. We use the KM3-230213A event as a benchmark to evaluate the sensitivity of current observations to these spectral modifications. Although the available statistics do not allow a formal constraint, the predicted fluxes are particularly sensitive to coefficients in the range $10^{-24} \mathrm{eV}^{-1} \lesssim \delta_{\nu,1} \lesssim 10^{-22}\,\mathrm{eV}^{-1}$, with the results strongly depending on the assumed cosmic-ray source properties. Intermediate coefficients can enhance the expected event rate within the reconstructed energy range of KM3-230213A, whereas larger coefficients may overproduce neutrinos in energy intervals constrained by IceCube and the Pierre Auger Observatory. These results identify a region of observational sensitivity to LIV and provide testable predictions for future neutrino telescopes.
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High Energy Physics (Phenomenology)

The devil in the transition: NLO nucleation and the particle physics behind the PTA signal

We quantify how the treatment of a strongly supercooled phase transition affects the particle-physics interpretation of a nanohertz gravitational-wave signal. For the classically conformal Abelian Higgs model, we calculate the nucleation rate at NLO in the dimensionally reduced theory and test the gradient expansion against explicit fluctuation determinants. A calibrated correction reproduces the determinant exponent with a mean absolute relative difference of $0.8\%$ and allows this information to be included throughout the parameter scan. We propagate the corrected rate through percolation, reheating and gravitational-wave production, and confront the resulting spectra with the NANOGrav 15-year and IPTA DR2 data. The corrected NLO calculation shifts the preferred gauge coupling by $9\%$ and $13\%$, respectively, and the input scale by $18\%$ for NANOGrav. After the determinant calibration, the largest theoretical uncertainties arise from uncertainties in the gravitational-wave spectra and the relation between $R_\star$ and $\beta/H$.
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High Energy Physics (Phenomenology)

Driver and damping of the directed-flow response in heavy-ion collisions

The initial-state geometry plays a crucial role in driving directed flow, while the dissipative response of the medium dampens it. Both of these factors influence how the directed-flow slope varies with system size. We developed a method to differentiate between these driving and damping effects on charged-hadron directed flow in O+O, Cu+Cu, Ru+Ru, Au+Au, and U+U collisions at $\sqrt{s_{\mathrm{NN}}} = 200$~GeV using an improved version of the string-melting AMPT model. We formulated three scaling observables based on the entropy density, the number of participants, and the mass number. A dimensionless ratio was constructed, revealing the threshold mass number $A \approx 35$ in central collisions from the entropy and participant scaling, indicating the onset of collective behavior. We constructed a kinetic-theory Knudsen-number ($\mathrm{Kn}$) map to analyze the contributions of the initial-state driver, which grows as $\mathrm{Kn}^{\kappa}$ with $\kappa \approx 2$, and a final-state viscous damping of the hydrodynamic response with characteristic scale $\mathrm{Kn}_0 \approx 0.27$ for the directed flow slope. This damping scale is found to be about a factor of 2.5 smaller than the $\mathrm{Kn}_0 \approx 0.7$ extracted from the elliptic flow. Furthermore, we determined the ratio of shear viscosity to entropy density, $\eta/s$, to be between 0.10 and 0.20, using an alternative method that does not rely on fitting flow harmonics.
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High Energy Physics (Phenomenology) · Cross-listed from hep-th

Emergent Conformal Symmetry on Superfluid Vortices in Two-Color QCD and Pseudoreal Gauge Theories

Two-color QCD provides a unique first-principles laboratory for strongly interacting matter at finite baryon density, where a diquark condensate realizes a baryonic superfluid. We investigate the internal physics of its quantized superfluid vortices in the chiral limit. We find that a vortex localizes an exact and normalizable $S^3\simeq SU(2)$ family of pion modes. Remarkably, the bulk Wess–Zumino–Witten (WZW) term induces a quantized WZW term for these modes, driving the vortex theory in the infrared to the $SU(2)_1$ WZW conformal field theory with central charge $c=1$. Thus a strongly coupled conformal theory emerges on a vortex in a nonconformal bulk theory. The mechanism extends to pseudoreal $Sp(2N)$ gauge theories, where the corresponding minimal vortex theory flows to $SU(2)_N$, with the level directly encoding the microscopic anomaly coefficient.
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High Energy Physics (Phenomenology) · Cross-listed from astro-ph.CO

The Role of Big Bang Nucleosynthesis in Joint Cosmological Analyses

We perform joint Baryon Acoustic Oscillation (BAO) + Big Bang Nucleosynthesis (BBN) and BAO+BBN+Cosmic Microwave Background (CMB) analyses with Planck CMB and DESI DR2 BAO data, explicitly marginalizing over BBN nuisance parameters for the first time with these data combinations and paying particular attention to the impact of BBN on these results. We find in our fiducial analyses $h=0.6833^{+0.0048}_{-0.0053}$ ($\Lambda$CDM, BAO+BBN), $h=0.6823^{+0.0027}_{-0.0026}$ ($\Lambda$CDM, BAO+BBN+CMB), as well as $h=0.6791^{+0.0069}_{-0.0075},N_{\rm{eff}}=2.974^{+0.098}_{-0.099}$ ($\Lambda$CDM+$N_{\rm{eff}}$, BAO+BBN), and $h=0.6838^{+0.0052}_{-0.0054},N_{\rm{eff}}=3.065^{+0.078}_{-0.076}$ ($\Lambda$CDM+$N_{\rm{eff}}$, BAO+BBN+CMB). We demonstrate how investigator choices can impact results of joint analyses involving BBN. We provide recommendations for the treatment of BBN in light of recent work, and demonstrate a pipeline that accurately accounts for prediction uncertainties in BBN.
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All authors Mehmet Akharman, Nicholas DePorzio, Cara Giovanetti, Hongwan Liu

High Energy Physics (Phenomenology)

One-point charge correlator as a probe for the odderon

We propose the one-point charge correlator (OPCC) in transversely polarized deep inelastic scattering as a new probe of the spin-dependent odderon. The OPCC is an infrared and collinear safe observable constructed solely from the charge and angular information of final-state charged particles. Because the charge weight is odd under charge conjugation, the contribution of the C-even pomeron to the OPCC vanishes identically in the small-$x$ eikonal limit, whereas the contribution of the C-odd spin-dependent odderon survives. We define a transverse single-spin asymmetry by normalizing the spin-dependent OPCC to the unpolarized charged-hadron one-point energy correlator. At small $x$, this asymmetry reduces to a ratio of spin-dependent odderon and pomeron contributions. We provide illustrative estimates of this asymmetry for Electron-Ion Collider kinematics within the small-$x$ dipole framework with Balitsky–Kovchegov evolution to guide experimental studies. Dedicated measurements of the OPCC asymmetry with a transversely polarized proton beam would provide new quantitative constraints on the currently unconstrained spin-dependent odderon.
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All authors Haotian Cao, Zhong-Bo Kang, Diego Padilla, Jani Penttala

High Energy Physics (Phenomenology) · Cross-listed from gr-qc

Constraining Ultralight Scalars with Black Hole Binary Mergers in Galactic Nuclei

Ultralight scalars can form long-lived, macroscopic bound states around spinning black holes, known as superradiance clouds. These clouds provide an additional channel for energy dissipation during close encounters, enhancing the black hole binary formation and merger rates in dense environments such as galactic nuclei. We show that the rate of mergers with mass ratio below $3/10$ in the LIGO-Virgo-KAGRA GWTC-5 catalog can probe ultralight scalars in the mass range $[4\times 10^{-14},10^{-13}]$ eV, complementing existing strategies based on black hole spin measurements.
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All authors Majed Khalaf, Eric Kuflik, Alessandro Lenoci, Nicholas Chamberlain Stone, Ofri Telem

High Energy Physics (Phenomenology)

Muon decay across scales: from LEFT to SMEFT

We revisit precision muon decay in the framework of the LEFT by considering how the LEFT perturbs the total rate as well as the standard and polarization-dependent Michel parameters. We derive the dependence of these observables on the dimension-five and -six LEFT operators, including lepton number violating operators, allowing for arbitrary neutrino flavor assignments. We consider fits of the LEFT to the muon decay data, in particular an approach to neutrino flavor general fits that does not respect the LEFT power counting and assuming new physics couples to all flavors equally and therefore allows for a consistent fit. We then consider how new physics imprints on the SMEFT and subsequently the LEFT in order to constrain specific scenarios of single-field extensions as well as two motivated two-field extensions. While we infer associated mass scales for these scenarios in the hundreds of GeV to multi-TeV range we also find that for the specific cases of lepton number violation, neutrino mass constraints from operator mixing are more restrictive than muon decay.
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