2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/177554Recent data from from the Wilkinson Microwave Anisotropy Probe (WMAP) place important bounds on the neutrino sector. The precise determination of the baryon number in the universe puts a strong constraint on the number of relativistic species during Big-Bang Nucleosynthesis. WMAP data, when combined with the 2dF Galaxy Redshift Survey (2dFGRS), also directly constrain the absolute mass scale of neutrinos. These results impinge upon a neutrino oscillation interpretation of the result from the Liquid Scintillator Neutrino Detector (LSND). We also note that the Heidelberg--Moscow evidence for neutrinoless double beta decay is only consistent with the WMAP+2dFGRS data for the largest values of the nuclear matrix element.5 pages, 2 figures. v2:Streamlined discussion of thermalization; improved discussion of large lepton asymmetry. v3: Added References. v4: More conservative treatment of biasHigh Energy Physics - PhenomenologyAstrophysicstext