Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Big Bang Nucleosynthesis and Active-Sterile Neutrino Mixing: Evidence
  for Maximal Mu Neutrino <-> Tau Neutrino Mixing in Super Kamiokande?   We discuss Big Bang Nucleosynthesis constraints on maximal
$\nu_\mu\leftrightarrow\nu_s$ mixing. Vacuum $\nu_\mu\leftrightarrow\nu_s$
oscillation has been proposed as one possible explanation of the Super
Kamiokande atmospheric neutrino data. Based on the most recent primordial
abundance measurements, we find that the effective number of neutrino species
for Big Bang Nucleosynthesis (BBN) is $N_\nu\la 3.3$. Assuming that all three
active neutrinos are light (with masses $\ll 1$ MeV), we examine BBN
constraints on $\nu_\mu\leftrightarrow\nu_s$ mixing in two scenarios: (1) a
negligible lepton asymmetry (the standard picture); (2) the presence of a large
lepton asymmetry which has resulted from an amplification by
$\nu_\tau\leftrightarrow\nu_{s'}$ mixing ($\nu_{s'}$ being $\nu_s$ or another
sterile neutrino species). The latter scenario has been proposed recently to
reconcile the BBN constraints and large-angle $\nu_\mu\leftrightarrow\nu_s$
mixing. We find that the large-angle $\nu_\mu\leftrightarrow\nu_s$ mixing in
the first scenario, which would yield $N_\nu\approx 4$, is ruled out as an
explanation of the Super Kamiokande data. It is conceivably possible for the
$\nu_\mu\leftrightarrow\nu_s$ solution to evade BBN bounds in the second
scenario, but only if 200 eV$^2\la m^2_{\nu_\tau}-m^2_{\nu_{s'}}\la 10^4$
eV$^2$ is satisfied, and if $\nu_\tau$ decays non-radiatively with a lifetime
$\la 10^3$ years. This mass-squared difference implies 15 eV$\la
m_{\nu_\tau}\la 100$ eV if $\nu_{s'}$ is much lighter than $\nu_\tau$. We
conclude that maximal (or near maximal) $\nu_\mu\leftrightarrow\nu_\tau$ mixing
is a more likely explanation of the Super Kamiokande data.

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The categories of this paper are: math
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ex
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The categories of this paper are: cond-mat
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The categories of this paper are: q-alg
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The categories of this paper are: funct-an
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The categories of this paper are: solv-int
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The categories of this paper are: math-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: supr-con
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The categories of this paper are: econ
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The categories of this paper are: mtrl-th
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The categories of this paper are: eess
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The categories of this paper are: chao-dyn
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The categories of this paper are: nucl-th
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The categories of this paper are: nlin