Constraining the universal lepton asymmetry
Abstract
The relic cosmic background neutrinos accompanying the cosmic microwave background (CMB) photons may hide a universal lepton asymmetry orders of magnitude larger than the universal baryon asymmetry. At present, the only direct way to probe such an asymmetry is through its effect on the abundances of the light elements produced during primordial nucleosynthesis. The relic light element abundances also depend on the baryon asymmetry, parameterized by the baryon density parameter (\eta_{\mathrm {B}} \equiv n_{\mathrm {B}}/n_{\gamma
} ) and on the earlyuniverse expansion rate, parameterized by the expansion rate factor (S
\equiv H'/H ) or, equivalently, by the effective number of neutrinos (N_{\nu } \equiv 3+43(S^2
1)/7 ). We use data from the CMB (and large scale structure: LSS) along with the observationally inferred relic abundances of deuterium and helium4 to provide new bounds on the universal lepton asymmetry, finding for η_{L}, the analog of η_{B},0.072 ± 0.053 if it is assumed that N_{ν} = 3 and, 0.115 ± 0.095 along with N_{ν} = 3.3_{0.6}^{+0.7}, if N_{ν} is free to vary.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 August 2008
 DOI:
 10.1088/14757516/2008/08/011
 arXiv:
 arXiv:0806.0179
 Bibcode:
 2008JCAP...08..011S
 Keywords:

 High Energy Physics  Phenomenology;
 Astrophysics;
 Nuclear Theory
 EPrint:
 JCAP0808:011,2008