Dark radiation constrains on mixed axion/neutralino dark matter

by Andre Lessa (University Sao Paulo)

Friday 1 Mar 2013, 11:00 → 12:00 Europe/Paris

Room 149, Batiment 1

Recent analyses of CMB data combined with the measurement of BAO and H0 show that dark radiation– parametrized by the apparent number of additional neutrinos ∆Neff contributing to the cosmic expansion– is bounded from above by about ∆Neff < 1.6 at 95% CL. We consider the mixed axion/neutralino cold dark matter scenario which arises in R-parity conserving supersymmetric (SUSY) models wherein the strong CP problem is solved by hadronic axions with a concommitant axion(a)/saxion(s)/axino(˜a) supermultiplet. Our new results include improved calculations of thermal axion and saxion production and include effects of saxion decay to axinos and axions. We show that the above bound on ∆Neff is easily satisfied if saxions are mainly thermally produced and mLSP < maxino < ms. However, if the dominant mechanism of saxion production is through coherent oscillations, the CMB data provides a strong bound on saxion production followed by saxion decays to axions. Furthermore we show that scenarios with mixed neutralino/axion dark matter are highly constrained by combined CMB, BBN and Xe-100 constraints. In particular, supersymmetric models with a standard overabundance of neutralino dark matter are excluded for all values of the Peccei-Quinn breaking scale. Next generation WIMP direct detection experiments may be able to discover or exclude mixed axion-neutralino CDM scenarios where s → aa is the dominant saxion decay mode.