Rates of neutrino conversion and decay in hot QED plasma

Using a real-time formalism of thermal field theory, we derive the reaction-rate formula for neutrino-conversion (ν → ν ) process and νν̄ ′ annihilation process, which take place in an ultrarelativistic QED plasma consisting of electrons, positrons, and photons. Also derived is the formula for the inverse processes to the above ones. On the basis of the hard-thermal-loop resummation scheme, we include the contribution from the coherent processes. For the case of isotropic neutrino distribution, numerical computation is carried out for the parameter region of type-II super-nova explosion. Defferential reaction rate exhibits characteristic peak structure, which comes from the coherent processes. The contribution from the above processes to the decay or damping rate of a parent massive neutrino ν is also studied. e-mail: [email protected] e-mail: [email protected] Electronic address: e-mail: [email protected]