A Monte Carlo generator of high energy cosmic ray interactions, relying on a very basic and transparent theoretical formalism, in the framework of the Reggeon field theory, is presented. The main motivation for our work is to provide a new cosmic ray interaction model characterized by relatively transparent physics, sufficient parameter freedom, and a high computational efficiency, which can be easily managed by external users, including a retuning of the model parameters. Such a model can be used for studying potential modifications of the interaction treatment, necessary for describing particular sets of data on extensive air showers initiated by high energy cosmic rays, at a microscopic level, thereby keeping a consistency with general restrictions, like the unitarity, energy-momentum and charge conservation, and Lorentz and isospin invariance. Importantly, this should allow one to study a compatibility of such modifications with relevant accelerator data. The model results for particle production and for basic extensive air shower characteristics are presented and discussed.

Sergey Ostapchenko

Tanguy Pierog

Günter Sigl

Basic model for high energy cosmic ray interactions

Since 2019, the Extreme Energy Events (EEE) Project has installed three muon detection stations at the Svalbard Islands ( $$78.9^{\circ } \hbox {N}$$ latitude), employing scintillator-based detectors. This initiative represents the first systematic effort to monitor cosmic-muons rates at high geomagnetic latitudes beyond the Arctic Circle, with the objective of improving our understanding of cosmic-ray propagation and modulation in polar regions. The present study analyses temporal variations in the muon detection rates over a six-year period (2019–2025), including the study of periodic modulations and underlying trends in the observed rates.

Italy

M. Abbrescia

C. Avanzini

L. Baldini

R. Baldini Ferroli

G. Batignani

M. Battaglieri

E. Bossini

F. Carnesecchi

D. Cavazza

C. Cicalò

L. Cifarelli

F. Coccetti

E. Coccia

A. Corvaglia

A. Caro

D. Gruttola

S. Pasquale

L. Galante

M. Garbini

L. Ghezzer

I. Gnesi

F. Gramegna

Norway

E. Gramstad

S. Grazzi

E. Haland

Switzerland

D. Hatzifotiadou

P. Rocca

R. Liotino

G. Mandaglio

A. Margotti

G. Maron

M. Mazziotta

A. Mulliri

R. Nania

F. Noferini

F. Nozzoli

F. Ould-Saada

F. Palmonari

M. Panareo

M. Panetta

R. Paoletti

C. Pellegrino

L. Perasso

O. Pinazza

C. Pinto

S. Pisano

K. Piscicchia

L. Quaglia

M. Rasà

F. Riggi

G. Righini

C. Ripoli

M. Rizzi

B. Sabiu

G. Sartorelli

E. Scapparone

M. Schioppa

G. Scioli

A. Scribano

M. Selvi

A. Shtimermann

M. Taiuti

A. Trifirò

M. Trimarchi

C. Vistoli

L. Votano

M. Williams

A. Zichichi

R. Zuyeuski

Measurement of the cosmic-ray rate over the period 2019–2025 at very high latitude (78.9°N)

We propose and evaluate a source-equals-detector search for the deexcitation of the long-lived isomer <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi>Ta</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>180</mn><mi mathvariant="normal">m</mi></mrow></mmultiscripts></mrow></math> in natural tantalum (Ta), using a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi></math>-ray transition-edge-sensor (TES) array. Two capabilities absent in conventional high-purity germanium (HPGe) searches are exploited: (i) near-unity containment of low-energy secondaries [internal-conversion (IC) electrons and characteristic x-rays] and of the nuclear recoil, enabling a calorimetric, event-by-event measurement of the total deposited energy in the absorber; and (ii) a delayed-coincidence tag using the subsequent <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi>Ta</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>180</mn></mrow></mmultiscripts></mrow></math> electron-capture (EC) decay to <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi>Hf</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>180</mn></mrow></mmultiscripts></mrow></math>. We evaluate the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mn>3</mn><mi>σ</mi></math> discovery reach for IC and for dark-matter (DM)-induced deexcitation in two benchmark scenarios: a strongly interacting DM subcomponent and inelastic DM with off diagonal couplings. Using a background model based on intrinsic radioactivity in the Ta absorber and realistic detector performance, we show that arrays with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi>N</mi></mrow><mrow><mi>TES</mi></mrow></msub><mo>=</mo><mn>256</mn></mrow></math> and 1,000 pixels can reach the theoretically expected IC half-life within 2.6 yr and 0.66 yr, respectively. For an array with <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>N</mi><mi>TES</mi></msub><mo>=</mo><msup><mn>10</mn><mn>4</mn></msup></math> and a five-year exposure, the projected sensitivity to DM-induced de-excitation surpasses limits inferred from HPGe nonobservations of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi>Ta</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>180</mn><mi mathvariant="normal">m</mi></mrow></mmultiscripts></mrow></math> and probes regions of parameter space not covered by current direct-detection experiments.

Japan

A. Gando

K. Ichimura

K. Ishidoshiro

T. Kikuchi

T. Kishimoto

A. Takeuchi

R. Sato

R. Smith

Probing internal conversion and dark-matter-induced deexcitation of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mmultiscripts><mrow><mi>Ta</mi></mrow><mprescripts></mprescripts><none></none><mrow><mn>180</mn><mi mathvariant="normal">m</mi></mrow></mmultiscripts></mrow></math> with a <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi></math>-ray TES array

We study the detectability of GeV-band gamma-ray polarization with the AMS-02 experiment and its proposed successor AMS-100, from Galactic and extragalactic sources. Characterizing gamma-ray polarization in this energy range could shed light on gamma-ray emission mechanisms in the sources; physics beyond the Standard Model, such as the presence of axionlike particles (ALPs), could also induce a distinctive energy-dependent polarization signal due to propagation effects in magnetic fields. We present estimates for the minimum detectable polarization from bright sources and the forecast reach for ALPs. We show that AMS-02 will have sensitivity to gamma-ray polarization only for the brightest steady-state Galactic sources, such as the Vela and Geminga pulsars; it is not expected to be capable of detecting polarization in Galactic or extragalactic sources that have been previously proposed as good targets for ALP searches with gamma-ray intensity measurements. However, AMS-100 observing the extragalactic source NGC1275 would be expected to probe new parameter space even for unfavorable <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>B</mi></math>-field models, with prospects to measure the energy-dependence of such a signal. For Galactic sources, polarization measurements could provide a unique test of scenarios where ALPs induce energy-dependent features in the photon intensity. However, in the absence of a bright transient source (such as a Galactic supernova), the parameter space that would be probed by this approach with ten years of AMS-100 data is already nominally excluded by other experiments, although this conflict may be avoided in specific ALP models.

United States

Xiuyuan Zhang

Yi Jia

Tracy R. Slatyer

Searching for GeV gamma-ray polarization and axionlike particles with AMS-02

Sub-GeV dark matter (DM) with $\textit{s}$-channel resonant self-scattering provides a promising framework for addressing small-scale structure problems. However, models that also account for the observed relic abundance through the same resonance are strongly constrained by current $\textit{γ}$-ray observations, since the associated signals are significantly enhanced. To overcome this limitation, we propose a framework in which the relic abundance and self-scattering are governed independently by two distinct mediators. As a concrete realization, we present a singlet scalar DM model in which self-scattering is mediated by a vector boson associated with a gauged baryon number, while the relic density is determined by forbidden annihilation into dark Higgs bosons that generate the gauge boson mass. By imposing cosmological, experimental, and theoretical constraints, We identify viable parameter regions that reproduce the observed relic density, alleviate small-scale problems, and remain consistent with current bounds. Notably, the model predicts multiple distinctive MeV $\textit{γ}$-ray signals, a significant fraction of which will be testable with next-generation MeV $\textit{γ}$-ray telescopes, including the Compton Spectrometer and Imager (COSI).

Yu Watanabe

Self-interacting sub-GeV dark matter with strong MeV gamma-ray

Recent analyses of Fermi–LAT data have identified a nearly spherical, halo-like excess of gamma rays peaking at <italic>E<inf>&#947;</inf></italic>&#8239;&#8764;&#8239;20&#8201;GeV. If interpreted as dark matter annihilation, the excess directly probes the thermal freeze-out epoch, and therefore any non-standard corrections to the early-Universe expansion rate. In this work we examine the implications of this tentative signal for CET &#937;, an informational and modular extension of relativistic quantum field theory and cosmology. CET &#937; predicts a universal, state-dependent modification to the radiation energy density, <display><formula id='ueq0001'><math altimg='si4.svg'><mrow><msub><mi>&#961;</mi><mstyle mathvariant='normal'><mi>&#937;</mi></mstyle></msub><mrow><mo>(</mo><mi>a</mi><mo>)</mo></mrow><mo linebreak='goodbreak'>=</mo><msub><mi>&#961;</mi><mi>r</mi></msub><mrow><mo>(</mo><mi>a</mi><mo>)</mo></mrow><mrow><mo stretchy='true'>[</mo><mn>1</mn><mo linebreak='badbreak'>+</mo><msub><mi>&#945;</mi><mi>log</mi></msub><mi>log</mi><mspace width='-0.16em' /><mi>log</mi><mrow><mo>(</mo><mi>a</mi><mo linebreak='badbreak'>/</mo><msub><mi>a</mi><mi>i</mi></msub><mo>)</mo></mrow><mo stretchy='true'>]</mo></mrow><mo>,</mo></mrow></math></formula></display>originating from renormalized modular fluctuations in the spectral triple of the theory. The correction is negligible during BBN and CMB epochs, but becomes relevant during thermal WIMP freeze-out. We provide: (i) a derivation of the doubly logarithmic correction from the modular two-point function; (ii) the physical justification of the onset scale <italic>a<inf>i</inf></italic> and its relation to the informational sector; (iii) the full quantitative impact on freeze-out, including numerical solutions; (iv) the evolution of the informational field <math altimg='si5.svg'><mrow><msub><mstyle mathvariant='normal'><mi>&#934;</mi></mstyle><mstyle mathvariant='normal'><mi>&#937;</mi></mstyle></msub><mrow><mo>(</mo><mi>x</mi><mo>)</mo></mrow></mrow></math>, demonstrating that it freezes in at <italic>a</italic> <inf>dec</inf>&#8239;&lt;&#8239; <italic>a<inf>f</inf></italic> and survives to <math altimg='si6.svg'><mrow><mi>z</mi><mo linebreak='goodbreak'>=</mo><mn>0</mn></mrow></math> under gravitational advection; (v) the resulting sub-percent morphological modifications to the annihilation flux; (vi) a comparison with Early Dark Energy, kination, and varying- <italic>N</italic> <inf>eff</inf> models. We show that the range <math altimg='si7.svg'><mrow><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>4</mn></mrow></msup><mspace width='-0.16em' /><mo>&#8818;</mo><mspace width='-0.16em' /><msub><mi>&#945;</mi><mi>log</mi></msub><mspace width='-0.16em' /><mo>&#8818;</mo><mspace width='-0.16em' /><msup><mn>10</mn><mrow><mo>&#8722;</mo><mn>2</mn></mrow></msup></mrow></math> is naturally selected by the theory, remains consistent with Planck, BBN, and BAO constraints, and induces percent-level shifts in the relic abundance while predicting potentially constrainable deviations in the gamma-ray morphology accessible to next-generation MeV&#8211;GeV missions.

Argentina

Christian Balfagón

Informational corrections to the early-Universe radiation sector: CET Ω, WIMP freeze-out, and implications for a possible 20 GeV gamma-ray excess

We argue that collider observables such as hadron number flux can be matched onto a linear combination of detectors/light-ray operators in perturbative QCD. The spectrum of detectors in QCD is subtle, due to recombination between the DGLAP and BFKL trajectories. We explain how to define and renormalize these trajectories at one-loop, systematically incorporating their recombination. The leading and subleading soft gluon theorems play an important role, and our analysis suggests the presence of an infinite series of further subleading soft theorems for squared-amplitudes/form factors. Combined with our light-ray matching hypothesis, the anomalous dimensions of recombined DGLAP/BFKL detectors yield a prediction for the energy dependence of the number of particles in a jet, as well as other predictions for more general energy-weighted hadron measurements. We compare these predictions to Monte-Carlo simulations, finding good agreement.

Cyuan-Han Chang

Hao Chen

David Simmons-Duffin

China

Hua Zhu

Seeing through the confinement screen: DGLAP/BFKL mixing and light-ray matching in QCD

Three black-hole low-mass x-ray binaries (LMXBs) in the Milky Way show rates of period decay which cannot be easily explained by standard mechanisms. Recently, it has been claimed that the anomalous period decays in two of these systems may be explained by dynamical friction due to very high dark matter (DM) densities around the black holes. We critically assess these claims by performing <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>N</mi></math>-body simulations of binaries embedded in dense DM “spikes.” We simulate the previously studied systems XTE <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">J</mi><mn>1118</mn><mo>+</mo><mn>480</mn></mrow></math> and A0620–00, as well as studying the third binary Nova Muscae 1991 for the first time in this context. These simulations show that feedback on the DM distribution plays a crucial role and we rule out previously claimed shallow DM spikes. We set lower limits on the steepness <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi></math> of DM density profiles required to explain the period decay in these LMXBs, requiring <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>γ</mi><mo>≳</mo><mn>2.15</mn><mi>–</mi><mn>2.20</mn></mrow></math> in XTE <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">J</mi><mn>1118</mn><mo>+</mo><mn>480</mn></mrow></math> and A0620–00 and <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>γ</mi><mo>≳</mo><mn>2.3</mn></math> in Nova Muscae 1991. Improved modeling of the long-term evolution of binaries embedded in DM spikes may allow us to exclude even larger densities in future.

Spain

Francesca Scarcella

Bradley J. Kavanagh

Hints of dark matter spikes in low-mass x-ray binaries: A critical assessment

We explore whether the unprecedented energy resolution of upcoming gamma-ray telescopes can uncover relativistic effects in photon spectra resulting from dark matter (DM) annihilation or decay near the supermassive black hole (SMBH) at the Galactic Center (GC), specifically, gravitational redshift, Doppler broadening due to Lorentz boosts, and kinetic energy enhancements arising from high DM velocities. By modeling DM density and velocity profiles under various SMBH formation scenarios and DM properties, we calculate the corresponding gamma-ray spectra and identify the conditions under which SMBH-induced spectral distortions become observable. We find that, in favorable cases, the observed spectra encode the DM velocity distribution near the SMBH, enabling potential discrimination among annihilation mechanisms with different velocity dependencies. Even when SMBH-induced effects are modest, the upcoming COSI mission, with sub-percent energy resolution surpassing the typical DM velocity dispersion at the GC, $$ \mathcal{O}\left({10}^{-3}\right) $$ , may still be able to detect subtle Doppler broadening. These results highlight a promising pathway for determining the origin of gamma-ray signals and probing DM properties through high-resolution spectral measurements.

Alexander Kusenko

Shigeki Matsumoto

Indirect detection of dark matter around a supermassive black hole with high energy-resolution gamma-ray telescopes

Fission fragment spectroscopic measurement has been carried out for the system, 232Th( 9Be, <italic>f</italic>) at E <inf><italic>lab</italic></inf> = 46 MeV. The prompt gamma rays decaying from the excited states of the fission fragments were detected using the INGA (Indian National Gamma Array) spectrometer. The dynamical aspects of the fissioning reaction has been investigated by measuring the contributions from the complete as well as incomplete fusion-fission channels. The relative cumulative isotopic yield distribution profiles of the even-even fission fragments have been measured by using the prompt <italic>&#947;</italic>-ray coincidence analysis technique. From the pair wise measured yields of the fission fragments, the contributions of the competing complete ( 9Be + 232Th &#8239;&#8594;&#8239; 241Pu*) and incomplete (n + 232Th &#8239;&#8594;&#8239; 233Th* and 4,5He + 232Th &#8239;&#8594;&#8239; 236,237U*) fusion-fission channels have been extracted, and the respective values are found to be (66 &#8239;&#177;&#8239; 6)% and (34 &#8239;&#177;&#8239; 4)%. The individual contributions from the two accompanying incomplete fusion-fission channels are also independently measured, and both the channels seem to contribute almost in equal proportions. The measured yields are found to be in good agreement with the GEF (GEneral description of Fission) model predicted results obtained by incorporating the measured contributing factors from the competing fissioning channels. The observed findings are also validated by performing the analysis based on the Bayesian inference method.

India

Krishna Debnath

Aniruddha Dey

P.K. Nayak

A.K. Mondal

R. Shil

A. Kundu

Biswajit Das

K. Mandal

S. Biswas

P. Dey

A. Bairagya

Vishal Malik

A. Sindhu

B. Mukherjee

D.C. Biswas

R. Palit

K. Banerjee

S. Mukhopadhyay

A. Chakraborty

Exploring fission dynamics of 232Th( 9Be, <italic>f</italic>) following prompt <italic>&#947;</italic>-ray spectroscopy