CP asymmetry factor in decays at finite temperature

Abstract We present in the conventional equilibrium approach to leptogenesis the complete leading order prediction for the CP asymmetry factor in finite-temperature decays involving Majorana neutrinos. As thermal effects are generally not negligible, the knowledge of the high temperature behavior of the underlying particle physics model, in particular that of mass generation, is required for reliable estimates of matter–antimatter asymmetry through the mechanism of leptogenesis. We present all necessary information needed to obtain the full one-loop evaluation for the thermal CP asymmetry factors for the processes $$N_i\rightarrow \phi + L$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>N</mml:mi> <mml:mi>i</mml:mi> </mml:msub> <mml:mo>→</mml:mo> <mml:mi>ϕ</mml:mi> <mml:mo>+</mml:mo> <mml:mi>L</mml:mi> </mml:mrow> </mml:math> and $$\phi \rightarrow N_i+L$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>ϕ</mml:mi> <mml:mo>→</mml:mo> <mml:msub> <mml:mi>N</mml:mi> <mml:mi>i</mml:mi> </mml:msub> <mml:mo>+</mml:mo> <mml:mi>L</mml:mi> </mml:mrow> </mml:math> at temperatures where they are kinematically allowed. We present a numerical comparison with previous formulae given in the literature.