• Expert ANR

• Direction/codirection de laboratoire
• Direction d'équipe

• Physique/Astrophysique/Phénomènes cosmiques de haute energie
  
• Physique/Astrophysique/Cosmologie et astrophysique extra-galactique
  
• Physique/Physique des Hautes Energies - Phénoménologie
  
• Physique/Astrophysique/Astrophysique galactique
  
• Physique/Astrophysique
  
• Planète et Univers/Astrophysique/Cosmologie et astrophysique extra-galactique
  
• Planète et Univers/Astrophysique/Astrophysique galactique
  
• Planète et Univers/Astrophysique/Phénomènes cosmiques de haute energie
  
• Physique/Physique des Hautes Energies - Expérience
  
• Planète et Univers/Astrophysique
  

Cold dark matter subhalos are expected to populate galaxies in numbers. If dark matter self-annihilates, these objects turn into prime targets for indirect searches, in particular with gamma-ray telescopes. Incidentally, the Fermi-LAT catalog already contains many unidentified sources that might be associated with subhalos. In this paper, we infer the statistics of those subhalos which could be identified as gamma-ray point-like sources from their predicted distribution properties. We use a semi-analytical model for the Galactic subhalo population, which, in contrast to cosmological simulations, can be made fully consistent with current kinematic constraints in the Milky Way and has no resolution limit. The model incorporates tidal stripping, predicted from a realistic distribution of baryons in the Milky Way. The same baryonic distribution contributes a diffuse gamma-ray foreground, which adds up to that, often neglected, induced by the smooth dark matter and the unresolved subhalos. This idealized configuration, as viewed by an idealized telescope \`a la Fermi-LAT, implies a correlation between point-like subhalo signals and diffuse background. Based on this modeling, we compute the full statistics semi-analytically, and accurately determine the distribution properties of the most luminous subhalos in the sky (relative to background). We find a number of visible subhalos of order ${\cal O}(0-1)$ for optimistic model parameters and a WIMP mass of 100~GeV, maximized for a cored host halo. This barely provides support to the current interpretation of several Fermi unidentified sources as subhalos. We also find that it is more likely to detect the smooth Galactic halo itself before subhalos, should dark matter in the GeV-TeV mass range self-annihilate through $s$-wave processes.

Reducing theoretical uncertainties in Galactic dark matter (DM) searches is an important challenge as several experiments are now delving into the parameter space relevant to popular (particle or not) candidates. Since many DM signal predictions rely on the knowledge of the DM velocity distribution---direct searches, capture by stars, $p$-wave-suppressed or Sommerfeld-enhanced annihilation rate, microlensing of primordial black holes, \etc---it is necessary to assess the accuracy of our current theoretical handle. Beyond Maxwellian approximations or ad-hoc extrapolations of fits on cosmological simulations, approaches have been proposed to self-consistently derive the DM phase-space distribution only from the detailed mass content of the Galaxy and some symmetry assumptions (\eg~the Eddington inversion and its anisotropic extensions). Although theoretically sound, these methods are still based on simplifying assumptions and their relevance to real galaxies can be questioned. In this paper, we use zoomed-in cosmological simulations to quantify the associated uncertainties. Assuming isotropy, we predict the speed distribution and its moments from the DM and baryonic content measured in simulations, and compare them with the true ones. We reach a predictivity down to $\sim 10$\% for some observables, significantly better than some Maxwellian models. This moderate theoretical error is particularly encouraging at a time when stellar surveys like the \textit{Gaia} mission should allow us to improve constraints on Galactic mass models.

Context. The vertical diffusive halo size of the Galaxy, $L$, is a key parameter for dark matter indirect searches. It can be better determined thanks to recent AMS-02 data. Aims. We set constraints on $L$ from Be/B and $^{10}$Be/Be data, and we performed a consistency check with positron data. We detail the dependence of Be/B and $^{10}$Be/Be on $L$ and forecast on which energy range better data would be helpful for future $L$ improvements. Methods. We used USINE V3.5 for the propagation of nuclei, and e+ were calculated with the pinching method. Results. The current AMS-02 Be/B (∼3% precision) and ACE-CRIS $^(10)$Be/Be (∼10% precision) data bring similar and consistent constraints on $L$. The AMS-02 Be/B data alone constrain $L = 5_{−2}^{+3}$ kpc at a 68% confidence level (spanning different benchmark transport configurations), a range for which most models do not overproduce positrons. Future experiments need to deliver percent-level accuracy on 10Be/9Be anywhere below 10 GV to further constrain $L$. Conclusions. Forthcoming AMS-02, HELIX, and PAMELA $^{10}Be/$^{9}$Be results will further test and possibly tighten the limits derived here. Elemental ratios involving radioactive species with different lifetimes (e.g. Al/Mg and Cl/Ar) are also awaited to provide complementary and robuster constraints.