$\bf{
<0.19}$

OUR EVALUATION

$<0.17$ 
90 
^{ 1} 

SPEC 
• • • We do not use the following data for averages, fits, limits, etc. • • • 
$<0.15$ 

^{ 2} 

COSM 
$<0.48$ 

^{ 3} 

COSM 
$<0.3$ 

^{ 4} 

COSM 
$<0.42$ 

^{ 4} 

COSM 
$<0.50$ 
90 
^{ 5} 

SPEC 
$<0.65$ 
90 


ASPK 
^{1}
ASSAMAGAN 1996 measurement of ${{\mathit p}_{{\mu}}}$ from ${{\mathit \pi}^{+}}$ $\rightarrow$ ${{\mathit \mu}^{+}}{{\mathit \nu}}$ at rest combined with JECKELMANN 1994 Solution$~$B pion mass yields ${{\mathit m}^{2}}_{{{\mathit \nu}}}$ = $0.016$ $\pm0.023$ with corresponding Bayesian limit listed above. If Solution$~$A is used, ${{\mathit m}^{2}}_{{{\mathit \nu}}}$ = $0.143$ $\pm0.024$ MeV${}^{2}$. Replaces ASSAMAGAN 1994 .

^{2}
DOLGOV 1995 removes earlier assumptions (DOLGOV 1993 ) about thermal equilibrium below $\mathit T_{{\mathrm {QCD}}}$ for wronghelicity Dirac neutrinos (ENQVIST 1993 , FULLER 1991 ) to set more stringent limits.

^{3}
ENQVIST 1993 bases limit on the fact that thermalized wronghelicity Dirac neutrinos would speed up expansion of early universe, thus reducing the primordial abundance. FULLER 1991 exploits the same mechanism but in the older calculation obtains a larger production rate for these states, and hence a lower limit. Neutrino lifetime assumed to exceed nucleosynthesis time, $\sim{}1~$s.

^{4}
Assumes neutrino lifetime $>1~$s. For Dirac neutrinos only. See also ENQVIST 1993 .

^{5}
ANDERHUB 1982 kinematics is insensitive to the pion mass.
