Antiprotons from dark matter annihilation in the Galaxy: Astrophysical uncertainties

Abstract

The latest years have seen steady progresses in WIMP dark matter (DM) searches, with hints of possible signals suggested both in direct and indirect detection. Antiprotons play a key role in this context, since WIMP annihilations can be a copious source of antiprotons, and the antiproton flux from conventional astrophysical sources is predicted with fair accuracy and matches the measured cosmic ray (CR) spectrum very well. Using the publicly available numerical DRAGON code, we reconsider antiprotons as a tool to set constraints on DM models; we compare against the most upto-datep measurements, taking also into account the latest spectral information on the p and He CR fluxes. In particular, we probe carefully the uncertainties associated to both standard astrophysical and DM originated antiprotons, by using a variety of distinctively different assumptions for the propagation of CRs and for the DM distribution in the Galaxy. We find that the impact of the astrophysical uncertainties on constraining the DM properties of a wide class of annihilating DM models can be much stronger, up to a factor of ∼ 50, than the one due to uncertainties on the DM distribution (∼ 2 − 6). Remarkably, even reducing the uncertainties on the propagation parameters derived by local observables, non-local effects can change our predictions for the constraints even by 50%. Nevertheless, currentp data can place tight constraints on DM models, excluding some of those suggested in connection with indirect and direct searches. Finally we discuss the impact of upcoming CR spectral data from the AMS-02 instrument on DM model constraints.

Robustness of dark matter constraints and interplay with collider searches for New Physics

“…The total uncertainty for the secondary antiproton component was assessed in [54,55] to be up to a factor 3 at ∼ 100 GeV. Moreover, the total uncertainty for the DM signal was shown to be as large as a factor of about 20 in [50] and 50 in [51]. These results show how the constraints on the DM particle annihilation cross sections are sensitive to astrophysical and nuclear uncertainties.…”

“…On the one hand, the astrophysical background of secondary antiprotons is affected by the lack of knowledge of the antiproton production cross section from proton-proton and proton-helium interactions, leading to an uncertainty for the flux at the Earth of ∼ 50% (see for example [48,49]). On the other hand, the antiproton flux produced by DM is very sensitive to the DM profile, altering the primary antiproton flux at the Earth by up to a factor of 2-6 [50,51]. In addition, both secondary and primary antiprotons are sensitive to uncertainties related to their propagation throughout the Galaxy [52,53].…”

Annihilation signals from asymmetric dark matter

“…Limits on symmetric DM annihilation cross section to bb from (blue, red, yellow) PAMELA cosmic ray antiproton measurements [51], under different assumptions with respect to propagation of charged particles through the galaxy, and (green) FERMI gamma-ray observations [37]. (Note that the PAMELA bounds correspond to assuming that the DM halo has an Einasto density profile, while the FERMI bounds assume a NFW profile; however, the difference will be minor [52].) the population of which has been measured by the PAMELA experiment (and will also be measured by AMS-02) [51].…”

“…Since antiprotons are charged particles, whose trajectories are affected by galactic magnetic fields, their direction of arrival is not simply related to the location of their source, and very little can be inferred about the galactic DM distribution from such measurements. In addition, there is a considerable degree of uncertainty as to exactly how this propagation through the galaxy occurs, and different models result in significantly different derived constraints on DM annihilation rates [52]. Figure 5 illustrates how the antiproton limits compare to those from gamma-ray observations, under three different propagation scenarios (MIN/MED/MAX) that are standard in the literature, see e.g.…”

AMS-02 antiprotons, at last! Secondary astrophysical component and immediate implications for Dark Matter

“…Until now, the so-called secondary antiprotons (originating from collisions of CR primaries with the interstellar material) have been shown to account for the bulk of the measured flux [18], thus allowing to derive constraints on the DM parameter space and to compute expected sensitivities, respectively based on updated Pamela data [19] and projected Ams-02 data (see e.g. [20,21,22,23,24,25,26,27]). The Ams-02 Collaboration has now presented its preliminary measurements of thep/p ratio [29], with an improved statistical precision and energy range extending to 450 GeV.…”