Dark Radiation in LARGE Volume Models

TL;DR

This paper investigates dark radiation production during reheating in LARGE Volume Scenario models, showing that axion decays lead to observable effects on the effective number of neutrino species, with constraints from experiments.

Contribution

It provides a detailed analysis of dark radiation generation in LARGE Volume models, linking decay processes to cosmological observations and constraints.

Findings

Reheating via volume modulus decays produces measurable dark radiation.

The model predicts 1.56 < N_{eff} - N_{eff,SM} < 1.74 in a simple case.

Experimental bounds on N_{eff} constrain model parameters and matter content.

Abstract

We consider reheating driven by volume modulus decays in the LARGE Volume Scenario. Such reheating always generates non-zero dark radiation through the decays to the axion partner, while the only competitive visible sector decays are Higgs pairs via the Giudice-Masiero term. In the framework of sequestered models where the cosmological moduli problem is absent, the simplest model with a shift-symmetric Higgs sector generates 1.56 < N_{eff} - N_{eff,SM} < 1.74. For more general cases, the known experimental bounds on N_{eff} strongly constrain the parameters and matter content of the models.