Neutrino Masses and Mixings from String Theory Instantons

TL;DR

This paper explores how string theory instantons can generate neutrino masses and mixings, leading to natural hierarchies and mixing patterns consistent with experimental data, including tri-bimaximal mixing.

Contribution

It demonstrates that string instantons can produce realistic neutrino mass hierarchies and mixing patterns, including tri-bimaximal mixing, through specific amplitude configurations.

Findings

Hierarchical neutrino masses emerge from instanton contributions.

String amplitudes can produce mixing patterns consistent with experiments.

Tri-bimaximal mixing arises from symmetric correlator values.

Abstract

We study possible patterns of neutrino masses and mixings in string models in which Majorana neutrino masses are generated by a certain class of string theory instantons recently considered in the literature. These instantons may generate either directly the dim=5 Weinberg operator or right-handed neutrino Majorana masses, both with a certain flavour-factorised form. A hierarchy of neutrino masses naturally appears from the exponentially suppressed contributions of different instantons. The flavour structure is controlled by string amplitudes involving neutrino fields and charged instanton zero modes. For some simple choices for these amplitudes one finds neutrino mixing patterns consistent with experimental results. In particular, we find that a tri-bimaximal mixing pattern is obtained for simple symmetric values of the string correlators.