Positron impact excitations of hydrogen atom under Lorentzian astrophysical plasmas

The excitations of hydrogen atom from its ground state due to positron impact under Lorentzian astrophysical plasma environments have been studied by applying a second order distorted wave theory which takes into account the effect of dipole polarization. Excitation cross sections are calculated as functions of the spectral index and plasma parameters for incident positron energies ranging from 20eV to 300eV. It is shown that the nonthermal effect of plasma significantly modifies the excitation cross sections