Electron neutrino opacity in magnetised media

We study the effects of strong magnetic fields ($B>{10}^{13}$~G) in the cross section for ${\nu }_{e}n\to pe$ scattering in the presence of a degenerate electron background. This can be relevant for the ${\nu }_e$ propagation in the proto-neutron star stage after supernovae collapse. We find that for field strengths $B>{10}^{16}$~G$(E_{\nu }\mathrm{/}10$ MeV${)}^2$ the ${\nu }_e$ opacity is sizeably affected by the magnetic field and can lead to a shift in the location of the electron neutrino sphere towards lower densities. We discuss the implications that this may have for scenarios proposed to explain the observed pulsar velocities.