In this work, we present a systematic study of the event characteristics and underlying physics relevant to neutrino-antineutrino discrimination in atmospheric neutrino charged-current interactions in large liquid scintillator detectors. This study encompasses the primary neutrino interactions, the subsequent secondary interactions of final-state particles, and the ensuing neutron captures. We investigate in detail the properties of final-state charged leptons and hadrons, deriving distinct distributions of inelasticity and neutron-capture multiplicity for both neutrino and antineutrino interactions. These distributions are used to quantify the performance of neutrino-antineutrino discrimination. Our findings lay the groundwork for atmospheric neutrino oscillation studies in large liquid scintillator detectors, particularly for determining the neutrino mass ordering.

China

Xinhai He

Gao-song Li

Yu-Feng Li

Wuming Luo

Liang-jian Wen

Atmospheric neutrino charged-current interactions at large liquid- scintillator detectors: I. physics of neutrino-antineutrino discrimination * Supported in part by the National Natural Science Foundation of China (12125506, 12075255), and the CAS Project for Young Scientists in Basic Research (YSBR-099)

In this study, we develop a framework for producing exotic muonic kaon atoms ( $ K\mu $ ) in semileptonic $ D^{0} $ decays using an effective weak Hamiltonian, a helicity-based treatment of leptonic current, and a nonrelativistic bound-state projection. The resulting branching ratio $ BR(D^{0} \to(K\mu )\nu_{\mu})=2.29\times10^{-10} $ is implemented in a ROOT-based code to estimate yields at a relativistic heavy-ion collider (RHIC), large hadron collider (LHC), and super tau-charm facility (STCF). We demonstrate quantitatively that $ K\mu $ atoms, which are also produced through coalescence in the quark–gluon plasma (QGP), offer a sensitive probe of low-momentum primordial muons and early-time electromagnetic radiation, acting as complementary constraints in an otherwise unexplored phase space for thermal dilepton and photon emission. Newly estimated dissociation cross-sections in detector material indicate that secondary-vertex reconstruction should be experimentally feasible, enabling the clean experimental identification of atoms. Projected yields from QGP coalescence in LHC and RHIC heavy-ion collisions and from $ D^{0} $ decays in LHC high-luminosity $ p+p $ collisions indicate that the first observation of $ K\mu $ atoms is within reach.

Xiaofeng Wang

Zebo Tang

United States

Zhangbu Xu

Chi Yang

Wangmei Zha

Yifei Zhang

Production of muonic kaon atoms at high-energy colliders * This work was supported in part by the National Natural Science Foundation of China (12361141827, 12422510), and by the Office of Nuclear Physics within the U.S. Department of Energy Office of Science (DE-FG02-89ER40531). The National Key Research and Development Program of China (2022YFA1604900). W. Zha acknowledges support from the Anhui Provincial Natural Science Foundation (2508085JX002), the Youth Innovation Promotion Association of the Chinese Academy of Sciences, and the Chinese Academy of Sciences (YSBR088)

Multimessenger astroparticle physics provides a new approach to probe new physics beyond the Standard Model. We propose to probe the light dark matter which can interact via the electromagnetic force. To be concrete, we derive the new constraint on the millicharged dark matter from the multimessenger observations of GW170817. In the neutron star merger event GW170817, the first detection of a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi></math>-ray burst delayed by approximately 1.7 seconds relative to the gravitational wave emission was observed. Utilizing this delay, we constrain the parameter space of the millicharged dark matter within the large-scale structure of the Universe. For dark matter mass below <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mrow><mo>−</mo><mn>17</mn></mrow></msup><mtext> </mtext><mtext> </mtext><mi>eV</mi></math>, the parameter <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ε</mi></math> is constrained to be less than <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mn>10</mn><mrow><mo>−</mo><mn>14</mn></mrow></msup></math>, representing the most stringent limits achieved to date.

Wenxing Zhang

Junle Pei

Xin Zhang

Tianjun Li

Multimessenger astroparticle physics: The first constraint on light millicharged dark matter via time-delay analysis of GRB GW170817A

We present a precise and systematic analysis of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mo stretchy="false">→</mo><mi>V</mi><mi>V</mi></math> decays within the factorization-assisted topological-amplitude approach, where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi></math> denotes the set <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">{</mo><msup><mi>D</mi><mn>0</mn></msup><mo>,</mo><msup><mi>D</mi><mo>+</mo></msup><mo>,</mo><msubsup><mi>D</mi><mi>s</mi><mo>+</mo></msubsup><mo stretchy="false">}</mo></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>V</mi></math> represents the vector mesons <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ρ</mi></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>K</mi><mo>*</mo></msup></math>, <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ω</mi></math>, and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>ϕ</mi></math>. Given the limited current experimental data, the factorization-assisted topological-amplitude approach serves as a available phenomenological framework for predicting charmed meson decays to both vector mesons. In this framework, incorporating flavor SU(3) symmetry-breaking effects, we can express nonfactorizable contributions of different modes as a minimal set of universal parameters globally fitted to experimental data. Utilizing 36 experimental data points for <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mo stretchy="false">→</mo><mi>V</mi><mi>V</mi></math> decays, we precisely extract ten nonfactorizable parameters associated with the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi></math> and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>E</mi></math> topological diagrams with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msup><mi>χ</mi><mn>2</mn></msup><mo>/</mo><mrow><mi mathvariant="normal">d</mi><mo>.</mo><mi mathvariant="normal">o</mi><mo>.</mo><mi mathvariant="normal">f</mi><mo>.</mo></mrow><mo>=</mo><mn>8.43</mn></math>. We find that a large strong phase in the longitude <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>E</mi></math> amplitude causes strong destructive interference with the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi></math> longitudinal component, yielding <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mo stretchy="false">∥</mo></msub><mo>&gt;</mo><msub><mi>f</mi><mi>L</mi></msub></math>, contrary to the naive factorization predictions. Additionally, for modes processing exclusively by the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>E</mi></math> diagram, the amplitude hierarchy <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo stretchy="false">|</mo><mi>S</mi><mo stretchy="false">|</mo><mo>&lt;</mo><mo stretchy="false">|</mo><mi>D</mi><mo stretchy="false">|</mo></math> leads to a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi></math>-wave branching fraction larger than that of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi></math> wave. This explains recent observations that contradict <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>S</mi></math>-wave dominance predictions. The predicted branching fractions and polarizations for 28 decay modes are consistent with existing experimental data. Unobserved modes, especially those with branching fractions of the order of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup><mi>–</mi><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>2</mn></mrow></msup></mrow></math>, the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi></math>-wave-dominated modes, and modes exhibiting <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mo stretchy="false">∥</mo></msub><mo>&gt;</mo><msub><mi>f</mi><mi>L</mi></msub></math>, await measurement by BESIII, STCF, Belle II, and LHCb.

Jing Ou-Yang

Hui Zheng

Run-Hui Li

Si-Hong Zhou

Precise theoretical prediction on branching fractions and polarizations of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>D</mi><mo stretchy="false">→</mo><mi>V</mi><mi>V</mi></math> decays

We develop a framework for testing quantum gravity through the stochastic gravitational-wave background produced by evaporating near-Planck-mass primordial black holes. Because gravitons freestream from the emission region without rescattering, they preserve a direct spectral record of the black-hole temperature–mass relation <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>T</mi><mo stretchy="false">(</mo><mi>M</mi><mo stretchy="false">)</mo></math>, a relation that is erased for all other Hawking-radiated species by rapid thermalization. We translate six representative phenomenological beyond-semiclassical frameworks (the generalized uncertainty principle, loop quantum gravity, noncommutative geometry, asymptotic safety, string/Hagedorn physics, and tunneling backreaction) into distinct <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>T</mi><mo stretchy="false">(</mo><mi>M</mi><mo stretchy="false">)</mo></math> parameterizations and compute the resulting gravitational-wave spectra numerically within a hybrid semiclassical-phenomenological framework. Modifications that suppress <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>T</mi><mo stretchy="false">(</mo><mi>M</mi><mo stretchy="false">)</mo></mrow></math> shift the spectral peak by up to 10 decades in frequency, in some cases into the sensitivity bands of next-generation interferometers or resonant-cavity detectors, while models imposing a hard evaporation cutoff produce distinctive peak morphologies that distinguish between phenomenological classes of modified evaporation. We further discuss the impact of different choices for post-inflationary conditions in the very early Universe and note that breaking the remaining cosmological degeneracies and connecting these signatures to specific quantum-gravity theories requires complementary observables. We find that the relative spectral displacement between the standard Hawking prediction and any modified model is cosmology-independent, and hence spectral shape rather than absolute peak frequency provides the cleanest probe of Planck-scale physics.

Stefano Profumo

Probing Planck-scale physics with high-frequency gravitational waves

We examine the origin of the cosmological collider signal using the framework of open effective field theories. Focusing on the single exchange of a massive scalar field, we demonstrate that the trispectrum splits cleanly into its local and non-local components once the heavy-field propagators are decomposed in the Keldysh basis. Integrating out the massive degree of freedom yields a single-field effective field theory for the light scalar that necessarily contains both unitary operators and non-unitary contributions associated with dissipation and stochastic noise. We show that the leading local signal in parity-preserving theories arises from the unitary part of this effective field theory, whereas the non-local signal is intrinsically associated with its stochastic sector. The effective field theory coefficients themselves are a priori non-analytic in the external kinematics; however, this non-analyticity can be softened when a scale hierarchy — such as the heavy-mass expansion — is imposed, up to spurious contributions that ultimately cancel in observables. Finally, we establish a connection between the cosmological collider signal and entropy production, linking the observable non-local signal to intrinsic properties of the quantum state, including its degree of mixedness.

United Kingdom

Thomas Colas

Zhehan Qin

Xi Tong

Open effective field theory and the physics of cosmological collider signals

We present a discovery-era strategy for intensity frontier experiments based on “didecay” events, in which feebly interacting particles (FIPs) are produced in pairs and then both decay inside the detector. This signature may exist in broad classes of models with FIPs decaying in the same way as minimal “portal” particles. The two displaced vertices may allow reconstruction of the pair invariant mass and hence reveal the production channel, information normally inaccessible at these facilities. This, in turn, lets one discriminate between FIP models that share identical decay signatures. As a case study, we consider the model of Higgs-like scalars and show that SHiP, Belle II, and the Downstream@LHCb can each cover wide domains of viable parameter space using didecays.

Germany

Giovani Dalla Valle Garcia

CERN

Maksym Ovchynnikov

Didecay signature of new physics particles at intensity frontier experiments

We study classical background electric fields and the Schwinger effect in de Sitter space. We show that a constant electric field in de Sitter requires the photon to have a tachyonic mass proportional to the Hubble scale. This has physical implications for the induced Schwinger current that affect its IR behaviour. To study this, we recompute the Schwinger current in de Sitter space for charged fermions and minimally coupled scalars, imposing a physically consistent renormalization condition. We find a $\textit{finite and positive}$ Schwinger current even in the massless limit. This is in contrast to previous calculations in the literature, which found a negative IR divergence. We also obtain the first result for the Schwinger current of a non-minimally coupled scalar, including the conformally coupled case, which we find exhibits behaviour very similar to that of the fermion current. Our results may have physical implications for both magnetogenesis and inflationary dark matter production.

Spain

Mar Bastero-Gil

Portugal

Paulo B. Ferraz

António Torres Manso

Slovenia

Italy

Lorenzo Ubaldi

Roberto Vega-Morales

Schwinger current in de Sitter space * This work has been partially supported by Junta de Andalucía Projects P21-00199 and A-FQM-472-UGR20 (FEDER funds); SRA (10.13039/501100011033) and ERDF (PID2022-139466NB-C21) (R.V.M.); PID2022-140831NB-I00, funded by MICIU/AEI/10.13039/501100011033 and FEDER, UE (M.B.G., A.T.M.); by FCT CERN (10.54499/2024.00252.CERN) (M.B.G., A.T.M., P.F.); FCT Grant No. SFRH/BD/151475/2021 and 10.54499/SFRH/BD/151475/2021 (P.F.). LU is supported by the Slovenian Research Agency under research core funding No. P1-0035 and by research grants J1-60026 and J1-4389. This article is based upon work from COST Action COSMIC WISPers CA21106, supported by COST (European Cooperation in Science and Technology). R.V.M. thanks the Mainz Institute for Theoretical Physics (MITP) of the Cluster of Excellence PRISMA$^{+}$ (Project ID 390831469) for its hospitality and partial support during the completion of this work

We present a comprehensive phenomenological study of a class of six vector-like lepton models with seesaw-like mass contributions and strong modifications to Higgs and lepton phenomenology. We focus on lepton flavour conserving and violating observables across all lepton generations and collider observables like $\textit{Z}$ and Higgs decays. In light of the recent progress at the LHC and precision measurements such as muon $\textit{g}$ – 2, as well as in anticipation of upcoming experiments like MEGII, Mu2e/COMET, Mu3e, Belle II and at the HL-LHC, we systematically survey the viable parameter space and identify patterns and correlations. The considered class of models gives rise to a rich and testable phenomenology with robust and complementary probes that allow to distinguish between models in the coming experimental era.

Gregor Daberstiel

Kilian Möhling

Dominik Stöckinger

Hyejung Stöckinger-Kim

From Higgs physics to lepton flavour violation: current bounds and future prospects for vector-like lepton models

The NUCLEUS experiment aims to measure coherent elastic neutrino–nucleus scattering (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>CE</mi><mi>ν</mi><mi>NS</mi></mrow></math>) at unprecedentedly low nuclear recoil energies using gram-scale cryogenic calorimeters operated at the Chooz nuclear power plant in France. Access to recoil energies at the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="script">O</mi><mo stretchy="false">(</mo><mn>10</mn><mtext> </mtext><mtext> </mtext><mi>eV</mi><mo stretchy="false">)</mo></math> scale enables <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>CE</mi><mi>ν</mi><mi>NS</mi></mrow></math> studies at extremely low momentum transfer and provides enhanced sensitivity to new physics. In this work, we present sensitivity projections for the upcoming NUCLEUS technical and physics runs, incorporating a data-driven treatment of the low-energy excess (LEE) observed during commissioning. We develop a likelihood framework that exploits reactor-power variation to disentangle signal and background in a low signal-to-background regime and to assess the impact of the dominant systematic uncertainties. For the Technical Run with a 7 g <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>CaWO</mi><mn>4</mn></msub></math> target, we find competitive sensitivity to several scenarios beyond the Standard Model, which do not require a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>CE</mi><mi>ν</mi><mi>NS</mi></mrow></math> observation. For the Physics Run, assuming complete suppression of the LEE, we project a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>4.7</mn><mi>σ</mi></math> observation of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>CE</mi><mi>ν</mi><mi>NS</mi></mrow></math> with a statistical precision of about 20% in 1 year, enabling a determination of the weak mixing angle at the lowest momentum transfer probed to date with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>CE</mi><mi>ν</mi><mi>NS</mi></mrow></math> and leading <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>CE</mi><mi>ν</mi><mi>NS</mi></mrow></math>-based constraints on the neutrino charge radius and new mediator models.

Austria

H. Abele

G. Angloher

B. Arnold

M. Atzori Corona

A. Bento

France

E. Bossio

F. Buchsteiner

J. Burkhart

F. Cappella

M. Cappelli

N. Casali

R. Cerulli

A. Cruciani

G. Del Castello

M. del Gallo Roccagiovine

S. Dorer

A. Erhart

M. Friedl

S. Fichtinger

V.M. Ghete

M. Giammei

C. Goupy

J. Hakenmüller

D. Hauff

F. Jeanneau

E. Jericha

M. Kaznacheeva

H. Kluck

A. Langenkämper

T. Lasserre

D. Lhuillier

M. Mancuso

R. Martin

B. Mauri

A. Mazzolari

L. McCallin

H. Neyrial

C. Nones

L. Oberauer

L. Peters

F. Petricca

W. Potzel

F. Pröbst

F. Pucci

F. Reindl

M. Romagnoni

J. Rothe

N. Schermer

J. Schieck

S. Schönert

C. Schwertner

L. Scola

G. Soum-Sidikov

L. Stodolsky

A. Schröder

R. Strauss

R. Thalmeier

C. Tomei

L. Valla

M. Vignati

M. Vivier

A. Wallach

P. Wasser

A. Wex

L. Wienke

Prospect of the NUCLEUS experiment at Chooz for coherent elastic neutrino-nucleus scattering and new physics searches