Cosmic positron and electron excesses: is the dark matter solution a good bet?

by Julien Lavalle (Turin University)

Thursday 19 Mar 2009, 11:00 → 12:00 Europe/Zurich

LAPTH Auditorium, Annecy-le-Vieux (LAPTH Auditorium, Annecy-le-Vieux)

The PAMELA collaboration has recently released its measurements of the cosmic ray positron fraction over an unprecedented energy range, seemingly indicating an excess with respect to the current predictions of the secondary positron background between 10 GeV up to the last data point around 100 GeV . In the same time ATIC has unveiled a less prominent feature in the cosmic electron + positron spectrum, but at higher energy. It is well known for a long time that standard astrophysical sources, like pulsars and supernova remnants could explain both these features, but there could also be contributions from dark matter annihilation. We will discuss this issue in the light of our recent (and ongoing) theoretical works on positrons, both on the secondary background and on primary signatures (standard as well as exotic). We will emphasize the impact of the theoretical uncertainties affecting the propagation modelling. More specifically on the dark matter hypothesis, we will discuss the potential role of cosmological dark matter subhalos in the Galaxy (so-called clumps), showing that they are unlikely to significantly boost the cosmic rays induced by conventional dark matter annihilation, even in optimistic scenarios. We will finally comment on the constraints obtained from other astrophysical messengers, like antiprotons and gamma-rays, underlying the still potential hints of DM manifestations.