Stars as Laboratories for Fundamental Physics - MPP Theory Group

What Have We Learned from SN 1987A 523
can be produced in pairs by their coupling to the electromagnetic field.
Obvious production processes are the plasmon decay γ pl → ν R ν R and
pair annihilation e + e − → ν R ν R with an intermediate photon. An intermediate
photon can also be coupled to hadronic components of the
medium. Mohapatra and Rothstein (1990) considered nucleon-nucleon
bremsstrahlung, and notably an amplitude where the electromagnetic
field is coupled to an intermediate charged pion. One may well wonder,
however, if this sort of naive perturbative bremsstrahlung calculation
is adequate in a nuclear medium.
A simple estimate of the plasmon decay process begins with the
energy-loss rate Eq. (6.94). Because the electrons in a SN core are
highly relativistic the plasma frequency is given by Eq. (6.43) as ωP 2 =
(4α/3π) (µ 2 e + 1 3 π2 T 2 ) where µ e is the electron chemical potential. For
a SN core ω P ≈ 10 MeV is a reasonable estimate while the relevant
temperature is about T = 30 MeV. Taking approximately Q 1 = 1 in
Eq. (6.94) and applying the approximate criterion Eq. (13.8) one finds
e ν ∼ < 10 −9 e. (13.21)
This is similar to Mohapatra and Rothstein’s (1990) result. Including
the e + e − annihilation process would slightly improve this limit and
extend it to somewhat larger masses.
The bound Eq. (13.21) would apply to any millicharged particle
which is not trapped in the SN core. Mohapatra and Rothstein (1990)
estimated that for a charge in excess of about 10 −7 e the particles would
be sufficiently trapped by scatterings off electrons to leave the SN cooling
time scale essentially unaffected. If they are Dirac neutrinos with a
mass in excess of a few MeV trapping by spin-flip scattering would become
important. Again, it is not obvious how strong the impact of such
trapped particles would be during the infall phase of SN collapse, i.e.
one should not infer that millicharged particles in the trapping regime
would not have a strong impact on SN physics just because their impact
on the Kelvin-Helmholtz cooling phase is small.
13.8.5 Charge Radius
If r.h. neutrinos existed and had an effective electromagnetic interaction
by virtue of a charge radius, they would be produced in a SN core by
the same processes as above where they were assumed to have a charge.
On the basis of the e + e − annihilation process Grifols and Massó (1989)
found a limit of about 3×10 −17 cm on a r.h. charge radius.