Effective Field Theory for a Heavy Majorana Fermion

TL;DR

This paper develops an effective field theory for heavy Majorana fermions, revealing unique symmetry properties and providing a framework for analyzing systems like long-lived gluinos.

Contribution

It formulates a Majorana version of Heavy Quark Effective Theory (HQET), highlighting emergent symmetries and differences from Dirac HQET.

Findings

Majorana HQET has the same degrees of freedom as Dirac HQET.

Emergent U(1) symmetry in Majorana HQET despite the fermion's Majorana nature.

Charge conjugation symmetry emerges in all Majorana HQETs.

Abstract

We formulate an effective theory for systems containing a heavy Majorana fermion, such as bound states of a long-lived gluino. This "Majorana HQET" has the same degrees of freedom as the well-studied Dirac HQET. It respects an emergent U(1) symmetry despite the fundamental absence of a U(1) for Majorana fermions. Reparameterization invariance works identically in the two HQETs. Remarkably, while a Dirac HQET may or may not be charge conjugation symmetric, a charge conjugation symmetry emerges in all Majorana HQETs, potentially offering low energy probes to distinguish the two theories.