introduction-weak-interaction-volume-one

K(36) = (1/Y) (T/108 ) 8 (4 .4 .41 )
where Y is the reciprocal of the mean number of electrons per nucleon in the
star . We note that (4 .4 .37) is even more temperature-dependent than (4 .4 .36) .
The last method of
neutrino pair production which we shall discuss is that o f
'plasmon' decay . A 'plasmon' is a quantum of excitation of stellar plasma whic h
resonance accelerate s5
wave number k has an energy E given by
electrons, which radiate neutrino pairs . A plasmon with
= 3 rP 2 k (4 .4 .42)
The expression (4 .4 .42) implies that the plasmon is a particle of finite res t
mass G decaying into a neutrino pair . In fact, plasmons are boson s 6 , and decay
P
via the electromagnetic current (4 .4 .3), which, in turn, interacts with th e
weak current (4 .4 .23) . At temperatures of higher than 5 x 1 08 K, the plamon
decay process is thought to dominate neutrino pair production .
We have discussed the possible cause and nature of stellar neutrin o
pair emission above, and we now consider its results and hence the evidence i n
favour of it . For stars of about 1000 solar luminosities, and with radii o f
about 1/10 of the solar radius, it is thought that their central density i s
about 1 0 5 g cm-3 and their temperature is about 3 .5 x 10 8 K . At this temperature
and pressure, the plasmon decay process (4 .4 .38) should have a significan t
effect on the evolution of a star, provided that the self-current term (4 .4 .23 )
is present in the weak P,am,ltonian . The star will, at this point, tend t o
contract, finally becoming a white dwarf . At the stage when its luminosity i s
about 100 solar luminosities, the star should remain at the same radius fo r
10 4 yr if neutrino pair emission does not occur, and 4 x 10 yr if it noes happen .
When the star is at 10 solar luminosities, its lifetime would be 3 x 1 0 5 yr
without neutrino emission, and 4 x 1 0 3 with neutrino emission . Similarly, when
the star has reduced its magnitude to 1 solar luminosity, it should remain i n
this stage for 2 x 106 yr if neutrino emission does not occur, and 2 x 1 0 5 yr
if it does occur . When the star evolves finally into a white dwarf, its interna l
temperature will be too low for neutrino emission to occur . Thus, neutrino
emission would reduce the number of stars with a luminosity of between 100 an d
1 solar luminosity by a factor of about 10 . A search for these so-called 'gap '
stars has set an upper limit on their lifetime of 6 x 1 0 5
yr, tending to favou r
the existence of neutrino emission from stars and hence the self- current terms .