An effective field theory for non-relativistic Majorana neutrinos

Understand

Heavy Majorana neutrinos enter in many scenarios of physics beyond the Standard Model: in the original seesaw mechanism they provide a natural explanation for the small masses of the Standard Model neutrinos and in the simplest leptogenesis framework they are at the origin of the baryonic matter of the universe.

• In this paper, we develop an effective field theory for non-relativistic Majorana particles, which is analogous to the heavy-quark effective theory.
• Then, we apply it to the case of a heavy Majorana neutrino decaying in a hot and dense plasma of Standard Model particles, whose temperature is much smaller than the mass of the Majorana neutrino but still much larger than the electroweak scale.
• The neutrino width gets zero-temperature contributions that can be computed from in-vacuum matrix elements, and thermal corrections.