If sub-GeV dark matter (DM) annihilates into charged particles such as $$e^+ e^-$$ , $$\mu ^+ \mu ^-$$ , or $$\pi ^+ \pi ^-$$ , it generates an additional source of electrons and positrons in the cosmic ray (CR) population within our Milky Way. During propagation, these secondary electrons and positrons undergo reacceleration processes, boosting their energies to the GeV scale. Observatories like AMS-02 can detect these high-energy particles, enabling constraints on the properties of sub-GeV DM. By analyzing AMS-02 electron and positron data, the 95% upper limits on the DM annihilation cross-section have been established in the range of $$10^{-28}$$ to $$10^{-27}$$ cm $$^3\,$$ s $$^{-1}$$ , corresponding to DM masses ranging from 100 MeV to 1 GeV. Meanwhile, MeV telescopes will provide complementary constraints on DM properties by detecting photon emissions from such annihilation processes. Notably, the sensitivity of future MeV gamma-ray observatories is projected to approach or match the constraints derived from CR data.

China

Guan-Sen Wang

Bing-Yu Su

Poland

Lei Zu

Lei Feng

Exploring sub-GeV dark matter physics with cosmic ray and future telescopes

High-resolution in-beam <math altimg='si5.svg'><mi>&#947;</mi></math>-ray spectroscopy of the neutron-rich <math altimg='si1.svg'><msup><mrow /><mn>110</mn></msup></math>Mo <math altimg='si19.svg'><msub><mrow /><mn>68</mn></msub></math> and <math altimg='si6.svg'><msup><mrow /><mn>112</mn></msup></math>Mo <math altimg='si61.svg'><msub><mrow /><mn>70</mn></msub></math> isotopes was performed for the first time at relativistic energies. This experiment was conducted at the Radioactive Isotope Beam Factory (RIBF), RIKEN. The <math altimg='si1.svg'><msup><mrow /><mn>110</mn></msup></math>Mo and <math altimg='si6.svg'><msup><mrow /><mn>112</mn></msup></math>Mo isotopes were produced via nucleon removal reactions of radioactive Mo and Tc ions, and the <math altimg='si5.svg'><mi>&#947;</mi></math> rays emitted following these reactions were measured using the High-resolution Cluster Array at RIBF (HiCARI). Doppler-corrected energy spectra enabled the precise determination of transition energies and half-lives through the line-shape method. In addition to providing new lifetime information, the level scheme of <math altimg='si6.svg'><msup><mrow /><mn>112</mn></msup></math>Mo was extended, including the <math altimg='si5.svg'><mi>&#947;</mi></math>-band structure, and the precision of existing level energies was significantly improved. Using the lifetime data, reduced transition probabilities were deduced. The <math altimg='si88.svg'><mrow><mi>B</mi><mo>(</mo><mi>E</mi><mn>2</mn><mo>;</mo><msubsup><mn>2</mn><mn>1</mn><mo>+</mo></msubsup><mo>&#8594;</mo><msubsup><mn>0</mn><mn>1</mn><mo>+</mo></msubsup><mo>)</mo></mrow></math> values indicate large collectivity and deformation, while the properties of the <math altimg='si9.svg'><msubsup><mn>2</mn><mn>2</mn><mo>+</mo></msubsup></math> states and their decay to the ground-state band point to an increase in triaxial deformation from mid-shell toward <math altimg='si89.svg'><mrow><mi>N</mi><mo linebreak='goodbreak'>=</mo><mn>70</mn></mrow></math>. To interpret these findings, two theoretical models were applied and compared with the experimental results highlighting the importance of triaxial deformation.

South Korea

Japan

B. Moon

France

W. Korten

Germany

Spain

K. Wimmer

P. Doornenbal

T.R. Rodríguez

K. Yanase

T. Otsuka

N. Aoi

H. Baba

F. Browne

United States

C. Campbell

United Kingdom

Hong Kong

S. Chen

Z. Chen

H. Crawford

Belgium

H. De Witte

C. Fransen

H. Hess

E. Ideguchi

S. Iwazaki

J. Kim

N. Kitamura

A. Kohda

T. Koiwai

B. Mauss

R. Mizuno

M. Niikura

T. Parry

P. Reiter

H. Sakurai

D. Suzuki

R. Taniuchi

S. Thiel

Y. Yamamoto

First high-resolution in-beam <math altimg='si5.svg'><mi>&#947;</mi></math>-ray spectroscopy of neutron-rich Mo isotopes at relativistic energy

Sub-GeV dark matter (DM) has been attracting more attention due to the negative results searching for traditional weakly interacting massive particles (WIMPs). Such particles are expected to produce gamma rays from annihilation in the MeV energy region. Advancements in technology have opened up possibilities to precisely detect MeV gamma rays, leading to the upcoming space-based mission of the Compton Spectrometer and Imager (COSI). We comprehensively and quantitatively study the phenomenology of sub-GeV DM to determine if the COSI observations will probe their viable model parameter regions. We first construct models to describe sub-GeV DM based on the minimality and renormalizability of quantum field theory. Next, we impose various constraints on the models obtained from cosmological observations (CMB, BBN) and DM searches (accelerator, underground, astrophysical experiments, etc.). Finally, we identify viable parameter regions in each model and discuss whether or not COSI will be sensitive to the parameter regions. We find that a velocity-dependent annihilation cross-section is predicted in some regions, enabling COSI to detect the DM signal while avoiding severe constraints from cosmological observations.

Yu Watanabe

Shigeki Matsumoto

Christopher Karwin

Tom Melia

Michela Negro

Thomas Siegert

Yuki Watanabe

Hiroki Yoneda

Tadayuki Takahashi

Sub-GeV dark matter and MeV gamma-ray detection with COSI

This study investigates ray geodesics and wave propagation on the Beltrami surface, with particular emphasis on the effective potentials governing photon dynamics. We derive the geodesic equations and analyze the Helmholtz equation within this curved geometry, revealing that the resulting potentials are purely repulsive. For ray trajectories, the potential is determined by wormhole parameters such as the throat radius $$\ell ,$$ radial optical distance $\textit{u}$, scale parameter $\textit{R}$, and the angular momentum of the test field. Near the wormhole throat, the potential remains constant, preventing inward motion below a critical energy threshold, whereas at larger radial distances, it decays exponentially, allowing free propagation. In the context of wave propagation, the potential exhibits a centrifugal barrier along with a constant repulsive term at large $\textit{u}$. The Beltrami surface, characterized by constant negative Gaussian curvature, serves as a model for graphene sheets and optical wormholes in condensed matter systems. These results allow us to determine the space- and frequency-dependent refractive index $$n(u,\omega )$$ of the optical medium, and we report quantitative values of the refractive index for different radial optical distances $$u = 10, 20, 30, 40, 50~\text {nm},$$ considering both the visible light and X-ray frequency domains. Our findings provide a coherent framework for understanding photon behavior in such systems, with promising implications for material applications.

Türkiye

Semra Gurtas Dogan

Abdullah Guvendi

Omar Mustafa

Ray geodesics and wave propagation on the Beltrami surface: optics of an optical wormhole

<p>The axionlike particle (ALP) and primordial black hole (PBH) are two representative dark matter (DM) candidates as light bosonic DM and macroscopic objects, respectively. In this work, we investigate the gamma-ray production mechanisms induced by PBH evaporation and ALP-photon coupling <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>g</mi><mrow><mi>a</mi><mi>γ</mi><mi>γ</mi></mrow></msub></math>. The detection of gamma rays is also explored in future satellite telescopes, including AMEGO, e-ASTROGAM, and MAST. We first propose the evaporation-conversion scenario in which light ALPs are emitted by PBHs and are converted into photons in the presence of magnetic field in the Universe. The second scenario assumes ALPs as a dominant DM component in the Milky Way and considers the relativistic electron production from PBH evaporation. The emitted electrons scatter off nonrelativistic ALP in DM halo and produce gamma rays through the ALP-photon coupling. Using the Fisher forecasting method, we calculate the gamma-ray energy spectra from these two scenarios and derive projected sensitivity for the fraction of DM composed of PBHs <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>f</mi><mrow><mi>PBH</mi></mrow></msub></math> and ALP-photon coupling <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>g</mi><mrow><mi>a</mi><mi>γ</mi><mi>γ</mi></mrow></msub></math>.</p>

Tong Li

Rui-Jia Zhang

Probing light axionlike particle via primordial black hole evaporation with gamma-ray observations

In this study, we investigate the gravitational collapses of rotating stellar systems accounting for gamma-ray burst jet progenitors. Based on the virial theorem of hadron collisional relaxations and Newtonian slow-rotating approximation, we analyze the conversion of gravitational binding energy into kinetic energy of hadrons, whose collisions produce photons and electron-positron pairs forming fireballs. Our qualitative analysis implies that rotation effects collimated and spinning fireballs with nontrivial angular momenta along the propagating direction, thus making ultra-relativistic jets. Results reveal the possible trends that the fireball becomes more collimated and the jet angle decreases as the total angular momentum and mass ratio $\textit{J}$/$\textit{M}$ of the slow-rotating collapsing core increases. Discussing the extrapolation of these trends to fast-rotating collapsing systems, we speculate that the ratio $\textit{J}$/$\textit{M}$ should be a key quantity for differentiating long bursts (massive core collapses) from short bursts (binary coalescence). We derive the intrinsic correlations of collimated fireball quantities that should be imprinted on a large sample of observed GRB data as empirical correlations.

Italy

She-Sheng Xue

Collimated and spinning fireballs for ultra-relativistic jets: long vs short gamma-ray bursts by angular momentum and mass ratio

In this paper, we investigate a <math altimg='si1.svg'><mo stretchy='false'>(</mo><mn>1</mn><mo linebreak='badbreak' linebreakstyle='after'>+</mo><mn>3</mn><mo stretchy='false'>)</mo></math>-dimensional static Friedmann-Robertson-Walker (FRW) space-time, pierced by a cosmic string. Our analysis begins with a detail study of the geodesic motion of photon rays in this curved background, focusing on the behavior of the associated effective potential. This allows us to understand how the cosmic string and curvature of space-time influence the trajectories of light rays. Moving beyond ray optics, we explore wave optics by solving the covariant Helmholtz equation in this gravitational setting. By transforming the resulting radial equation into a Schr&#246;dinger-like form, we extract an effective potential and derive a frequency-dependent refractive index. This refractive index shows the combined effects of the cosmic string and the curvature parameter, showing their influence on the wave propagation. Furthermore, we extend our study to a <math altimg='si2.svg'><mo stretchy='false'>(</mo><mn>1</mn><mo linebreak='badbreak' linebreakstyle='after'>+</mo><mn>2</mn><mo stretchy='false'>)</mo></math>-dimensional space-time with disclinations, where we analyze the wave optics phenomena. Through the Helmholtz equation in this lower-dimensional case, we determine the refractive index and discuss how it is affected by the geometric parameters of this lower-dimensional space-time. Through both geometric and wave optics approaches, our work provides a comprehensive understanding of how topological defects and curvature impact geometric and physical optics in curved space-time of three- and four-dimensions.

India

Faizuddin Ahmed

Algeria

Abdelmalek Bouzenada

Ray and wave dynamics in a static FRW spacetime with conical singularity

Detection of sub-GeV dark matter (DM) particles in direct detection experiments is inherently difficult, as their low kinetic energies in the galactic halo are insufficient to produce observable recoils of the heavy nuclei in the detectors. On the other hand, whenever DM particles interact with nucleons, they can be accelerated by scattering with galactic cosmic rays. These cosmic-ray-boosted DM particles can then interact not only through coherent elastic scattering with nuclei, but also through scattering with individual nucleons in the detectors and produce outgoing particles at MeV to GeV kinetic energies. The resulting signal spectrum overlaps with the detection capabilities of modern neutrino experiments. One future experiment is the Deep Underground Neutrino Experiment (DUNE) at the Sanford Underground Research Facility. Our study shows that DUNE has a unique ability to search for cosmic-ray boosted DM with sensitivity comparable to dedicated direct detection experiments in the case of spin-independent interactions. Importantly, DUNE’s sensitivity reaches similar values of DM-nucleon cross sections also in the case of spin-dependent interactions, offering a key advantage over traditional direct detection experiments.

Switzerland

Richard Diurba

Norway

Helena Kolešová

Prospects of detecting cosmic ray up-scattered dark matter with DUNE

<p>Dark photons that are sufficiently light and/or weakly interacting represent a compelling vision of dark matter. Dark photon decay into three photons, which we call the dark photon trident, can be the dominant channel when the dark photon mass falls below the electron pair threshold and can produce a significant flux of x rays. We use 16 years of data from Interrnational Gamma-Ray Astro Physics Laboratory (INTEGRAL)/Spectrometer of INTEGRAL (SPI) to constrain sub-MeV dark photon decay, producing new worlds-best constraints on the kinetic mixing parameter for dark photon masses between 90 and 1022 keV, and comment on the potential for future x-ray observatories to discover the trident decay process.</p>

Sweden

Tim Linden

Thong T.Q. Nguyen

Tim M.P. Tait

X-ray constraints on dark photon tridents

We analyze the impact of higher-twist three-particle $\textit{B}$ -meson light-cone distribution amplitudes (LCDAs) on the non-local form factors for the $$ {B}_s\to \phi \overline{\ell}\ell $$ transition focusing on the ‘charm-loop’ contribution within the light-cone sum rule (LCSR) framework. To analytically continue these charm-loop contributions into the kinematically allowed region of the decay, we employ a hadronic dispersion relation that incorporates intermediate resonant states such as the $\textit{ϕ}$, $\textit{J}$/Ψ and $\textit{ψ}$(2$\textit{S}$) mesons. Here, the LCSR predictions serve as inputs, supplemented by experimental data from two-body decays $\textit{B}$ → $\textit{ϕ}$ + resonance states. Our results indicate that the inclusion of twist-5 and twist-6 LCDAs enhances the non-local form factors — by approximately an order of magnitude — compared to previous estimates, due to partial disruption of cancellation among different twist contributions. This leads to a dilepton invariant mass-squared ($\textit{q}$ )-dependent correction to the Wilson coefficient $\textit{C}$ , which is higher than, but still consistent with the Standard Model prediction without the non-factorizable charm-loop corrections within uncertainties. Additionally, we update the local form factors to include contributions from higher-twist three-particle $\textit{B}$ -meson LCDAs. The phenomenological implications, particularly for the differential branching fraction and angular observables, are also discussed.

M. Khan

Rusa Mandal

Praveen Patil

Canada

Ipsita Ray

Investigating non-local contributions in $$ {B}_s\to \phi \overline{\ell}\ell $$ including higher-twist effects