Résumé
Phys.Rev. D55 (1997) 4582-4590 We give an improved estimate of primordial magnetic fields generated during
cosmological first order phase transitions. We examine the charge distribution
at the nucleated bubble wall and its dynamics. We consider instabilities on the
bubble walls developing during the phase transition. It is found that damping
of these instabilities due to viscosity and heat conductivity caused by
particle diffusion can be important in the QCD phase transition, but is
probably negligible in the electroweak transition. We show how such
instabilities together with the surface charge densities on bubble walls excite
magnetic fields within a certain range of wavelengths. We discuss how these
magnetic seed fields may be amplified by MHD effects in the turbulent fluid.
The strength and spectrum of the primordial magnetic field at the present time
for the cases where this mechanism was operative during the electroweak or the
QCD phase transition are estimated. On a 10 Mpc comoving scale, field strengths
of the order 10**(-29) G for electroweak and 10**(-20) G for QCD, could be
attained for reasonable phase transition parameters.