Neutrino Masses from the Top Down

TL;DR

This paper surveys various mechanisms for generating small neutrino masses from a string theory perspective, including higher-dimensional operators, instantons, and extra-dimensional effects, highlighting their differences from traditional GUT models.

Contribution

It provides a comprehensive top-down analysis of neutrino mass generation mechanisms inspired by string theory, exploring novel possibilities beyond conventional models.

Findings

String constructions motivate new neutrino mass mechanisms.

Multiple pathways for small Dirac and Majorana masses are identified.

Mixing scenarios between active and sterile neutrinos are explored.

Abstract

General classes of mechanisms for generating small neutrino masses are surveyed from a top-down (superstring) perspective. In particular, string constructions have motivated various possibilities involving higher-dimensional operators, string instantons, and wave function overlaps in large or warped extra dimensions. These may yield small Dirac masses, Majorana masses via the Weinberg operator, or Majorana masses from a seesaw mechanism, though the latter typically differ in detail from the more conventional GUT models. Possibilities for mixing between light active and sterile neutrinos are surveyed.