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.

United States

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

China

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

We propose Bell-type inequalities by constructing flavor operators associated with mass identification, flavor change, and charged-current weak mixing which arise from fundamental interactions in the Standard Model. We treat these interactions as measurement settings in a gedanken experiment. For entangled two-particle states, the measurement outcomes of these flavor operators exhibit correlations that violate a Bell-type inequality under the stated assumptions, showing that our result probes contextuality and incompatibility of interaction-defined observables. We discuss how the predicted correlation patterns may be probed with experimental data, clarifying the scope and limitations of Bell-type reasoning in particle physics.

Corbin Pacheco

Nausheen R. Shah

Gedanken experiments of entanglement in particle physics: Interactions, operators and Bell-type inequalities in flavor space

We employ a geometric framework to compute the leading high-energy behaviour of tree-level scattering amplitudes in theories containing $\textit{N}$ Nambu-Goldstone bosons and a single Higgs-like scalar with an arbitrary potential $\textit{V}$. Using these methods, we obtain closed-form expressions for the leading contribution to the full infinite set of tree amplitudes involving any number of Goldstone and Higgs-like external states. These results are then used to derive total cross sections, decay rates, and perturbative unitarity bounds. We then apply our general formalism to the Standard Model scalar sector using the equivalence theorem, working in the regime of small field-space curvature, and use it to characterise the relation between Higgs Effective Field Theory (HEFT) and the Standard Model Effective Field Theory (SMEFT). We analyse three representative classes of models. Two reproduce previously known behaviours, while the third, based on a dilaton effective theory, exhibits a noteworthy feature within the HEFT framework: a smooth decoupling limit that connects HEFT directly to the Standard Model without passing through a SMEFT regime, providing a possible backdoor to the Standard Model.

Rodrigo Alonso

India

Susobhan Chattopadhyay

James Ingoldby

The potential of HEFT and the scale of new physics

Underground laboratories provide the ultra-low background and low-vibration environments essential for rare-event searches, gravitational-wave detection, and quantum-sensing technologies. We report a comprehensive environmental characterisation of the Bedretto tunnel in Ticino, Switzerland, a site offering horizontal access, excellent infrastructure, and the potential to be Europe’s second-deepest and quietest underground laboratory. At the prospective physics site, located beneath a granite overburden exceeding 1400 m, we measure fluxes of: cosmic-muon $$(2.54~\pm ~0.97)~\times 10^{-8}~\upmu /\textrm{s} \,\, /\textrm{cm}^2$$ , $$\gamma $$ -ray $$5.67\pm 0.37\, \gamma /\text {cm}^2/$$ $$\text {sec}$$ , and neutron fluxes $$(5.56 \pm 0.26)\times 10^{-5}~\textrm{neutrons}/\textrm{cm}^2/$$ $$\textrm{sec}$$ , as well as the radon concentration, magnetic-field power spectrum, and seismic backgrounds. The muon flux is suppressed by six orders of magnitude relative to the surface, consistent with an effective depth of about 4000 m water equivalent. Gamma-ray and neutron measurements reflect the local geology and guide shielding requirements for future particle and nuclear physics experiments. Magnetic and seismic noise levels are found to be exceptionally low, meeting or exceeding the criteria for next-generation atom-interferometric gravitational-wave detectors. These results establish the site as a highly competitive, accessible deep-underground location for fundamental-physics experiments.

Switzerland

Björn Penning

Nicolas Angelides

Laura Baudis

Harvey Birch

Abigail Flowers

Florian Jörg

Alexander Kavner

Marcelle Soares-Santos

Aravind Sreekala

Johannes Wüthrich

Guandi Zhao

Chiara Capelli

John Clinton

Jose García

Paolo Crivelli

Domenico Giardini

Evangelos-Leonidas Gkougkousis

Yacine Haddad

Marian Hertrich

Rebecca Hochreutener

Luisa Hötzsch

Philippe Jetzer

Ben Kilminster

Boris Korzh

Frédérick Massin

Knut Morå

Margherita Noia

Francesco Piastra

Christian Regenfus

Federico Sanchez

Steven Schramm

Francesco Riva

Serhan Tufanli

Michele Weber

Stefan Wiemer

Mathilde Wimez

Characterisation of the Bedretto underground site for fundamental physics experiments

The next generation of circular electron-positron colliders, such as the Circular Electron Positron Collider and the Future Circular Collider, will provide an unprecedented level of precision in probing the properties of the Higgs boson. In this study, we examine the flavor-changing neutral Higgs decay $\textit{h}$ → $\textit{bs}$ produced via the Higgs-strahlung process within the framework of the Two-Higgs-Doublet Model Type III. We identify regions of the parameter space that remain viable after applying stringent constraints from current experimental data. By employing a multivariate analysis based on Boosted Decision Trees, we project that a signal significance of 5$\textit{σ}$ can be achieved, even after accounting for irreducible backgrounds and systematic uncertainties. Our findings show that these future colliders could offer a unique avenue for discovering signatures of physics beyond the standard model.

Mexico

M. Arroyo-Ureña

D. Carreño-Diaz

A. García-Gutierrez

T. Valencia-Pérez

M. Villanueva-Utrilla

Beyond the Standard Model Higgs physics: hunting $\textit{h}$ → $\textit{bs}$ with Higgs-strahlung at CEPC and FCC-ee