We show that stars in the inner parsec of the Milky Way can be significantly affected by dark matter annihilation, producing population-level effects that are visible in a Hertzsprung-Russell (HR) diagram. We establish the dark HR diagram, where stars lie on a new stable dark main sequence with similar luminosities, but lower temperatures, than the standard main sequence. The dark matter density in these stars continuously replenishes, granting these stars immortality and solving multiple stellar anomalies. Upcoming telescopes could detect the dark main sequence, offering a new dark matter discovery avenue.

The height of the Milky Way diffusion halo, above which cosmic-rays can freely escape the galaxy, is among the most critical, yet poorly known, parameters in cosmic-ray physics. Measurements of radioactive secondaries, such as 10Be or 26Al, which decay equivalently throughout the diffusive volume, are expected to provide the strongest constraints. This has motivated significant observational work to constrain their isotopic ratios, along with theoretical work to constrain the cross-section uncertainties that are thought to dominate radioactive secondary fluxes. In this work, we show that the imprecise modelling of the Milky Way spiral arms significantly affects our ability to translate 10Be and 26Al fluxes into constraints on the diffusive halo height, biasing our current results. Utilizing state-of-the-art spiral arms models we produce new predictions for the 10Be and 26Al fluxes that motivate upcoming measurements by AMS-02 and HELIX.

The extreme energy of the KM3-230213A event could transform our understanding of the most energetic sources in the Universe. However, it also reveals an inconsistency between the KM3NeT detection and strong IceCube constraints on the ultra-high energy neutrino flux. The most congruous explanation for the KM3NeT and IceCube data requires KM3-230213A to be produced by a (potentially transient) source fortuitously located in a region where the KM3NeT acceptance is maximized. In hadronic models of ultra-high-energy neutrino production, such a source would also produce a bright γ-ray signal, which would cascade to GeV-TeV energies due to interactions with extragalactic background light. We utilize theγ-Cascadepackage to model the spectrum, spatial extension, and time-delay of such a source, and scan a region surrounding the KM3NeT event to search for a consistent γ-ray signal. We find no convincing evidence for a comparableFermi-LAT source and place constraints on a combination of the source redshift and the intergalactic magnetic field strength between the source and Earth.

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.

Early studies of the AMS-02 antiproton ratio identified a possible excess over the expected astrophysical background that could be fit by the annihilation of a weakly interacting massive particle (WIMP). However, recent efforts have shown that uncertainties in cosmic-ray propagation, the antiproton production cross-section, and correlated systematic uncertainties in the AMS-02 data, may combine to decrease or eliminate the significance of this feature. We produce an advanced analysis using the DRAGON2 code which, for the first time, simultaneously fits the antiproton ratio along with multiple secondary cosmic-ray flux measurements to constrain astrophysical and nuclear uncertainties. Compared to previous work, our analysis benefits from a combination of: (1) recently released AMS-02 antiproton data, (2) updated nuclear fragmentation cross-section fits, (3) a rigorous Bayesian parameter space scan that constrains cosmic-ray propagation parameters.

We find no statistically significant preference for a dark matter signal and set strong constraints on WIMP annihilation to bb̅, ruling out annihilation at the thermal cross-section for dark matter masses below ∼ 200 GeV. We do find a positive residual that is consistent with previous work, and can be explained by a ∼ 70 GeV WIMP annihilating below the thermal cross-section. However, our default analysis finds this excess to have a local significance of only 2.8σ, which is decreased to 1.8σ when the look-elsewhere effect is taken into account.

Stellar winds from massive stars may be significant sources of cosmic rays (CRs). To investigate this connection, we report a detailed study of gamma-ray emission near the young Milky Way star cluster (≈0.5 Myr old) in the star-forming region RCW 38 and compare this emission to its stellar wind properties and diffuse X-ray emission. Using 15 yr of Fermi-LAT data in the 0.2–300 GeV band, we find a significant (σ > 22) detection coincident with the star cluster, producing a total gamma-ray luminosity (extrapolated over 0.1–500 GeV) of L_γ =(2.66 ± 0.92) × 10³⁴ erg s⁻¹ adopting a power-law spectral model (Γ = 2.34 ± 0.04). Using an empirical relationship and STARBURST99, we estimate the total wind power to be 8 × 10³⁶ erg s⁻¹, corresponding to a CR acceleration efficiency of η_CR ≃ 0.4 for an assumed diffusion coefficient consistent with D = 10²⁸ cm² s⁻¹. Alternatively, a lower acceleration efficiency of 0.1 can produce this L_γ if the diffusion coefficient is smaller, D ≃ 2.5 × 10²⁷ cm² s⁻¹. Additionally, we analyze Chandra X-ray data from the region and compare the hot-gas pressure to the CR pressure. We find the former is 4 orders of magnitude greater, suggesting that the CR pressure is not dynamically important relative to stellar winds. As RCW 38 is too young for supernovae to have occurred, the high CR acceleration efficiency in RCW 38 demonstrates that stellar winds may be an important source of Galactic CRs.

Tentative observations of cosmic-ray antihelium by the AMS-02 collaboration have re-energized the quest to use antinuclei to search for physics beyond the standard model. However, our transition to a data-driven era requires more accurate models of the expected astrophysical antinuclei fluxes. We use a state-of-the-art cosmic-ray propagation model, fit to high-precision antiproton and cosmic-ray nuclei (B, Be, Li) data, to constrain the antinuclei flux from both astrophysical and dark matter annihilation models. We show that astrophysical sources are capable of producing (1) antideuteron events and (0.1) antihelium-3 events over 15 years of AMS-02 observations. Standard dark matter models could potentially produce higher levels of these antinuclei, but showing a different energy-dependence. Given the uncertainties in these models, dark matter annihilation is still the most promising candidate to explain preliminary AMS-02 results. Meanwhile, any robust detection of antihelium-4 events would require more novel dark matter model building or a new astrophysical production mechanism.

High-resolution infrared data have revealed several young stars in close proximity to Sgr A*. These stars may encounter extremely high dark matter densities. We examine scenarios where dark matter scatters on stellar gas, accumulates in stellar cores, and then annihilates. We study the stars S2, S62, S4711, and S4714 and find three observable effects. First, dark matter interactions can inhibit in situ star formation close to Sgr A*, favoring scenarios where these stars migrate into the Galactic Center. Second, dark matter interactions can delay main sequence evolution, making stars older than they appear. Third, very high dark matter densities can inject enough energy to disrupt main sequence stars, allowing S-star observations to constrain the dark matter density near Sgr A*.

Recent studies indicate that thermally produced dark matter will form highly concentrated, low-mass cusps in the early universe that often survive until the present. While these cusps contain a small fraction of the dark matter, their high density significantly increases the expected 𝛾-ray flux from dark matter annihilation, particularly in searches of large angular regions. We utilize 14 years of Fermi-LAT data to set strong constraints on dark matter annihilation through a detailed study of the isotropic 𝛾-ray background, excluding with 95% confidence dark matter annihilation to 𝑏⁢¯𝑏 final states for dark matter masses below 120 GeV.

High-energy cosmic-ray electrons and positrons cool rapidly as they propagate through the Galaxy, due to synchrotron interactions with magnetic fields and inverse-Compton scattering interactions with photons of the interstellar radiation field. Typically, these energy losses have been modelled as a continuous process. However, inverse-Compton scattering is a stochastic process, characterised by interactions that are rare and catastrophic. In this work, we take the stochasticity of inverse-Compton scattering into account and calculate the contributions to the local electron and positron fluxes from different sources. Compared to the continuous approximation, we find significant changes: for pulsars, which produce electron-positron pairs as they spin down, the spectrum becomes significantly smoother. For TeV-scale dark matter particles, which annihilate into electrons and positrons, the signal becomes strongly enhanced around the energy corresponding to the dark matter mass. Combined, these effects significantly improve our ability to use spectral signatures in the local electron and positron spectra to search for particle dark matter at TeV energies.