We reanalyze the cosmological constraints on the existence of a net universal lepton asymmetry and neutrino degeneracy based upon the latest high resolution CMB sky maps from BOOMERANG , DASI , and MAXIMA-1 .
We generate likelihood functions by marginalizing over ( \hbox { $ { \sl \Omega } _ { b } $ } h ^ { 2 } , \hbox { $ \xi _ { \nu _ { \mu, \tau } } $ } , \hbox { $ \xi _ { % \nu _ { e } } $ } , \Omega _ { \Lambda } ,h,n ) plus the calibaration uncertainties .
We consider flat \Omega _ { M } + \Omega _ { \Lambda } = 1 cosmological models with two identical degenerate neutrino species , \hbox { $ \xi _ { \nu _ { \mu, \tau } } $ } \equiv| \hbox { $ \xi _ { \nu _ { \mu } } $ } | = | \hbox { $ \xi _ { \nu% _ { \tau } } $ } | and a small \xi _ { \nu _ { e } } .
We assign weak top-hat priors on the electron-neutrino degeneracy parameter \xi _ { \nu _ { e } } and \Omega _ { b } h ^ { 2 } based upon allowed values consistent with the nucleosynthesis constraints as a function of \xi _ { \nu _ { \mu, \tau } } .
The change in the background neutrino temperature with degeneracy is also explicitly included , and Gaussian priors for h = 0.72 \pm 0.08 and the experimental calibration uncertainties are adopted .
The marginalized likelihood functions show a slight ( 0.5 \sigma ) preference for neutrino degeneracy .
Optimum values with two equally degenerate \mu and \tau neutrinos imply \hbox { $ \xi _ { \nu _ { \mu, \tau } } $ } = 1.0 ^ { +0.8 ( 1 \sigma ) } _ { -1.0 ( 0.5 \sigma ) } , from which we deduce \xi _ { \nu _ { e } } = 0.09 ^ { +0.15 } _ { -0.09 } , and \Omega _ { b } h ^ { 2 } = 0.021 ^ { +0.06 } _ { -0.002 } .
The 2 \sigma upper limit becomes \hbox { $ \xi _ { \nu _ { \mu, \tau } } $ } \leq 2.1 , which implies \xi _ { \nu _ { e } } \leq 0.30 , and \Omega _ { b } h ^ { 2 } \leq 0.030 .
For only a single large-degeneracy species the optimal value is | \hbox { $ \xi _ { \nu _ { \mu } } $ } | or | \hbox { $ \xi _ { \nu _ { \tau } } $ } | = 1.4 with a 2 \sigma upper limit of | \hbox { $ \xi _ { \nu _ { \mu } } $ } | or | \hbox { $ \xi _ { \nu _ { \tau } } $ } | \leq 2.5