High-energy neutrino conversion into electron-W pair in magnetic field and its contribution to neutrino absorption

We calculate the conversion rate of high-energy neutrinos propagating in constant magnetic field into an electron-W pair (nu -> W + e) from the imaginary part of the neutrino self-energy. Using the exact propagators in constant magnetic field, the neutrino self-energy has been calculated to all order in the field within the Weinberg-Salam model. We obtain a compact formula in the limit of B << Bcr = m^2/e. We find that above the process threshold Eth \~ 2.2 10^16 (Bcr / B) eV this contribution to the absorption of neutrinos yields an asymptotic absorption length ~ 1.1 (Bcr / B)^2 (10^{16} eV / E) meters.