(26) Production(s) de LAVALLE J.
Robust cosmic-ray constraints on $p$-wave annihilating MeV dark matter Auteur(s): Boudaud Mathieu, Lacroix T., Stref M., Lavalle J. (Document sans référence bibliographique) 2018-10-02 Ref HAL: hal-01885830_v1 Exporter : BibTex | endNote Résumé: We recently proposed a method to constrain $s$-wave annihilating MeV dark matter from a combination of the Voyager 1 and the AMS-02 data on cosmic-ray electrons and positrons. Voyager 1 actually provides an unprecedented probe of dark matter annihilation to cosmic rays down to $\sim 10$ MeV, in an energy range where the signal is mostly immune to uncertainties in cosmic-ray propagation. In this letter, we derive for the first time new constraints on $p$-wave annihilation down to the MeV mass range using cosmic-ray data. To proceed, we derive a self-consistent velocity distribution for the dark matter across the Milky Way by means of the Eddington inversion technique and its extension to anisotropic systems. As inputs, we consider state-of-the-art Galactic mass models including baryons and constrained on recent kinematic data, allowing for both a cored or a cuspy halo. We then calculate the flux of cosmic-ray electrons and positrons induced by $p$-wave annihilating dark matter and obtain very stringent limits in the MeV mass range, robustly excluding cross sections greater than $\sim 10^{-22}{\rm cm^3/s}$ (including theoretical uncertainties), about 5 orders of magnitude better than current CMB constraints. This limit assumes that dark matter annihilation is the sole source of cosmic rays, and could therefore be made even more stringent when reliable models of astrophysical backgrounds are included. --------- |
Anatomy of Eddington-like inversion methods in the context of dark matter searches Auteur(s): Lacroix T., Stref M., Lavalle J. (Document sans référence bibliographique) 2018-05-04 Résumé: Irrespective of the dark matter (DM) candidate, several potentially observable signatures derive from the velocity distribution of DM in halos, in particular in the Milky Way (MW) halo. Examples include direct searches for weakly-interacting massive particles (WIMPs), $p$-wave suppressed or Sommerfeld-enhanced annihilation signals, microlensing events of primordial black holes (PBHs), {\em etc}. Most current predictions are based on the Maxwellian approximation which is not only theoretically inconsistent in bounded systems, but also not supported by cosmological simulations. A more consistent method sometimes used in calculations for direct WIMP searches relies on the so-called Eddington inversion method, which relates the DM phase-space distribution function (DF) to its mass density profile and the total gravitational potential of the system. Originally built upon the isotropy assumption, this method can be extended to anisotropic systems. We investigate these inversion methods in the context of Galactic DM searches, motivated by the fact that the MW is a strongly constrained system, and should be even more so with the ongoing Gaia survey. We still draw conclusions that apply to the general case. In particular, we illustrate how neglecting the radial boundary of the DM halo leads to theoretical inconsistencies. We also show that several realistic configurations of the DM halo and the MW baryonic content entail ill-defined DFs, significantly restricting the configuration space over which these inversion methods can apply. We propose consistent solutions to these issues. Finally, we compute several observables inferred from constrained Galactic mass models relevant to DM searches (WIMPs or PBHs), {\em e.g.} moments and inverse moments of the DM speed and relative speed distributions. --------- |
Dynamically constrained model of galactic subhalos and impact on dark on dark matter searches Auteur(s): Stref M., Lavalle J.
Conference: 52nd Rencontres de Moriond on Very High Energy Phenomena in the Universe (La Thuile, IT, 2017-03-18) Ref HAL: hal-01758060_v1 Exporter : BibTex | endNote Résumé: The interaction properties of cold dark matter particles candidates are known tolead to the structuring of dark matter on scales much smaller than typicalgalaxies. This translates into a large population of dark matter subhalos insideour Galaxy, which impacts the predictions for direct and indirect searches. Wepresent a model for this subhalo population that accounts for the gravitationaleffects experienced by those structures (tidal stripping and disk shocking)while remaining consistent with dynamical constraints. The subhalos mass densityand annihilation profiles are derived. The impact of subhalos on indirectsearches with cosmic rays antiprotons is evaluated using the latest data fromthe AMS-02 experiment. |
Indications for a high-rigidity break in the cosmic-ray diffusion coefficient Auteur(s): Genolini Yoann, Serpico Pasquale dario, Boudaud Mathieu, Caroff Sami, Poulin Vivian, Lavalle J., Maurin David, Poireau Vincent, Salati Pierre, Vecchi Manuela (Document sans référence bibliographique) 2017-06-28 Résumé: Using cosmic-ray boron to carbon ratio (B/C) data recently released by the \AMS\ experiment, we find tantalizing indications ({\it decisive evidence}, in Bayesian terms) in favor of a diffusive origin for the broken power-law spectra found in protons ($p$) and helium nuclei (He). The result is robust with respect to currently estimated uncertainties in the cross sections, and in the presence of a small component of primary boron, expected because of spallation at the acceleration site. Reduced errors at high energy as well as further cosmic ray nuclei data (as absolute spectra of C,N, O, Li, Be) may definitively confirm this scenario. |
Novel cosmic-ray electron and positron constraints on MeV dark matter particles Auteur(s): Lavalle J., Boudaud Mathieu, Salati Pierre (Document sans référence bibliographique) 2016-12-22 Résumé: MeV dark matter (DM) particles annihilating or decaying to electron-positron pairs cannot, in principle, be observed via local cosmic-ray (CR) measurements because of the shielding solar magnetic field. In this Letter, we take advantage of the fact that the Voyager I spacecraft, which does measure CRs, has crossed the heliopause in 2012 and can actually, since then, detect interstellar CRs. This opens up a new avenue to probe DM in the sub-GeV energy/mass range that we first exploit here. From a complete description of the transport of electrons and positrons at low energy, we derive predictions for both the secondary astrophysical background and the pair production mechanisms relevant to DM annihilation or decay down to the MeV mass range. Interestingly, we show that reacceleration may push positrons up to energies larger than the DM particle mass. We combine the constraints from the Voyager and AMS-02 data to get novel limits covering a very extended DM particle mass range, from MeV to TeV. In the MeV mass range, our limits reach annihilation cross sections of order $\langle \sigma v\rangle \sim 10^{-28}{\rm cm^3/s}$. Though extracted from a completely different and new probe, these bounds have a strength similar to those obtained with the cosmic microwave background (CMB) --- they are even more stringent for p-wave annihilation. |
Modeling dark matter subhalos in a constrained galaxy: Global mass and boosted annihilation profiles Auteur(s): Stref M., Lavalle J. (Document sans référence bibliographique) 2016-10-07 Ref HAL: hal-01377666_v1 Exporter : BibTex | endNote Résumé: The interaction properties of cold dark matter (CDM) particle candidates, such as those of weakly interacting massive particles (WIMPs), generically lead to the structuring of dark matter on scales much smaller than typical galaxies, potentially down to ∼ 10 −10 M. This clustering translates into a very large population of subhalos in galaxies and affects the predictions for direct and indirect dark matter searches (gamma rays and antimatter cosmic rays). In this paper, we elaborate on previous analytic works to model the Galactic subhalo population, while consistently with current observational dynamical constraints on the Milky Way. In particular, we propose a self-consistent method to account for tidal effects induced by both dark matter and baryons. Our model does not strongly rely on cosmological simulations as they can hardly be fully matched to the real Milky Way, but for setting the initial subhalo mass fraction. Still, it allows to recover the main qualitative features of simulated systems. It can further be easily adapted to any change in the dynamical constraints, and be used to make predictions or derive constraints on dark matter candidates from indirect or direct searches. We compute the annihilation boost factor, including the subhalo-halo cross-product. We confirm that tidal effects induced by the baryonic components of the Galaxy play a very important role, resulting in a local average subhalo mass density 1% of the total local dark matter mass density, while selecting in the most concentrated objects and leading to interesting features in the overall annihilation profile in the case of a sharp subhalo mass function. Values of global annihilation boost factors range from ~ 2 to ~ 20, while the local annihilation rate is about twice less boosted. --------- |
Making sense of the local Galactic escape speed estimates in direct dark matter searches Auteur(s): Lavalle J., Magni S. (Document sans référence bibliographique) 2014-09-30 Résumé: Direct detection (DD) of dark matter (DM) candidates in the $\lesssim$10 GeV mass range is very sensitive to the tail of their velocity distribution. The important quantity is the maximum WIMP speed in the observer's rest frame, i.e. in average the sum of the local Galactic escape speed $v_{\rm esc}$ and of the circular velocity of the Sun $v_c$. While the latter has been receiving continuous attention, the former is more difficult to constrain. The RAVE Collaboration has just released a new estimate of $v_{\rm esc}$ (Piffl {\em et al.}, 2014 --- P14) that supersedes the previous one (Smith {\em et al.}, 2007), which is of interest in the perspective of reducing the astrophysical uncertainties in DD. Nevertheless, these new estimates cannot be used blindly as they rely on assumptions in the dark halo modeling which induce tight correlations between the escape speed and other local astrophysical parameters. We make a self-consistent study of the implications of the RAVE results on DD assuming isotropic DM velocity distributions, both Maxwellian and ergodic. Taking as references the experimental sensitivities currently achieved by LUX, CRESST-II, and SuperCDMS, we show that: (i) the exclusion curves associated with the best-fit points of P14 may be more constraining by up to $\sim 40$\% with respect to standard limits, because the underlying astrophysical correlations induce a larger local DM density; (ii) the corresponding relative uncertainties inferred in the low WIMP mass region may be moderate, down to 10-15\% below 10 GeV. We finally discuss the level of consistency of these results with other independent astrophysical constraints. This analysis is complementary to others based on rotation curves. --------- |