Mathieu Boudaud

Novel cosmic-ray electron and positron constraints on MeV dark matter particles

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 spacecraft Voyager 1s capacity for detecting interstellar CRs since it crossed the heliopause in 2012. This opens up a new avenue to probe DM in the sub-GeV energy/mass range that we exploit here for the first time. 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 ⟨σv⟩∼10^{-28}  cm^{3}/s. An interesting aspect is that these limits barely depend on the details of cosmic-ray propagation in the weak reacceleration case, a configuration which seems to be favored by the most recent B/C data. Though extracted from a completely different and new probe, these bounds have a strength similar to those obtained with the cosmic microwave background-they are even more stringent for p-wave annihilation.

A fussy revisitation of antiprotons as a tool for Dark Matter searches

Antiprotons are regarded as a powerful probe for Dark Matter (DM) indirect detection and indeed current data from PAMELA have been shown to lead to stringent constraints. However, in order to exploit their constraining/discovery power properly, great attention must be put into effects (linked to their propagation in the Galaxy) which may be perceived as subleading but actually prove to be quite relevant. We revisit the computation of the astrophysical background and of the DM antiproton fluxes fully including the effects of: diffusive reacceleration, energy losses including tertiary component and solar modulation (in a force field approximation). Using the updated proton and helium fluxes just released by the AMS-02 experiment we reevaluate the secondary astrophysical antiproton to proton ratio and its uncertainties, and compare it with the ratio preliminarly reported by AMS-02. We find no unambiguous evidence for a significant excess with respect to expectations. Yet, some preference for a flatter energy dependence of the diffusion coefficient (with respect to the MED benchmark often used in the literature) starts to emerge. Finally, we provide a first assessment of the room left for exotic components such as Galactic Dark Matter annihilation, deriving new stringent constraints.

USINE: A code for the propagation of Galactic cosmic rays

USINE is a C++ toolbox for the propagation of Galactic cosmic rays (GCRs). Starting from CR properties (list of nuclei and their properties, interaction cross-sections) and Galactic ingre- dients (source spectra, interstellar medium, radiation field, etc.), several semi-analytical propa- gation models are available (1D and 2D). Non-public versions of USINE were used during the last decade to determine the transport parameters, to study radioactive nuclei, and to test a pos- sible dark matter contribution in antinuclei. This poster illustrates USINE usefulness both as a pedagogic and as a research tool. While preparing for an overdue public release, we are also im- plementing the recently developed ‘pinching method’ to have electrons and positrons in USINE.

What do Galactic electrons and positrons tell us about dark matter

We devise a new semi-analytical method dedicated to the propagation of Galactic electrons and positrons from MeV to TeV energies: the pinching method. It is essentially based on the pinching of inverse Compton and synchrotron energy losses from the magnetic halo, where they take place, inside the Galactic disc. This new tool is fast and allows to carry out extensive scans over parameters. We strongly constrain the cosmic ray propagation parameters by requiring that the secondary component of positrons does not overshoot the AMS-02 measurements. We find that only models with a large diffusion coefficient and a large magnetic halo size are selected by this test. Therefore, we find that the positron excess appears from 1 GeV. We then explore the possibility to explain the positron excess with a component coming from the annihilation of dark matter particles. We show that the pure dark matter interpretation of the AMS-02 positron data is strongly disfavoured. This conclusion is based solely on the positron data, and no other observation, such as the antiproton and gamma ray fluxes or the CMB anisotropies, needs to be invoked. MeV dark matter particles annihilating or decaying to electron-positron pairs cannot, in principle, be observed via local cosmic ray measurements because of the shielding solar magnetic field. We take advantage of spacecraft Voyager-Is capacity for detecting interstellar cosmic rays since it crossed the heliopause in 2012. This opens up a new avenue to probe dark matter particles in the sub-GeV energy/mass range that we exploit here for the first time.

Indications for a high-rigidity break in the cosmic-ray diffusion coefficient

Using cosmic-ray boron to carbon ratio (B/C) data recently released by the AMS-02 experiment, we find tantalizing indications (decisive evidence, in Bayesian terms) in favor of a diffusive origin for the broken power-law spectra found in protons (

A new look at the cosmic ray positron fraction

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Uncertainties on propagation parameters: impact on the interpretation of the positron fraction

) 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.

Robust cosmic-ray constraints on

Mathieu Boudaud∗a, Sandy Aupetita, Sami Caroffb, Antje Putzea, Geneviève Bélangera, Yoann Genolinia, Corrine Goyb, Vincent Poireaub, Vivian Poulina, Sylvie Rosierb, Pierre Salatia, Li Taob, and Manuela Vecchic aLAPTh, Université Savoie Mont Blanc & CNRS, 9 Chemin de Bellevue, B.P.110 Annecy-le-Vieux, F-74941, France bLAPP, Université Savoie Mont Blanc & CNRS, 9 Chemin de Bellevue, B.P.110 Annecy-le-Vieux, F-74941, France cInstituto de Fisica de Saõ Carlos Av. Trabalhador saõ-carlense, 400 CEP: 13566-590 Saõ Carlos (SP), Brazil

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Mathieu Boudauda, Sandy Aupetita, Sami Caroffb, Antje Putzea, Genevieve Belangera, Yoann Genolini∗a, Corine Goyb, Vincent Poireaub, Vivian Poulina, Sylvie Rosierb, Pierre Salatia, Li Taob, and Manuela Vecchic aLAPTh, Universite Savoie Mont Blanc & CNRS, 9 Chemin de Bellevue, B.P.110 Annecy-le-Vieux, F-74941, France bLAPP, Universite Savoie Mont Blanc & CNRS, 9 Chemin de Bellevue, B.P.110 Annecy-le-Vieux, F-74941, France cInstituto de Fisica de Sao Carlos Av. Trabalhador sao-carlense, 400 CEP: 13566-590 Sao Carlos (SP), Brazil