Loop corrections to Delta N_eff in large volume models

TL;DR

This paper examines how loop corrections affect dark radiation predictions in large volume models, finding that minimal assumptions lead to an overestimation of dark radiation, thus challenging the model's viability.

Contribution

It provides a detailed analysis of loop effects on decay channels in large volume models, refining predictions for dark radiation and testing the model against observational data.

Findings

Loop corrections increase the predicted dark radiation fraction.

The minimal model's predictions are incompatible with current observational constraints.

Radiative effects on the Higgs decay channel are significant for model accuracy.

Abstract

In large volume models reheating is driven by the decays of the volume modulus to the visible sector, while the decays to its axion partners result in dark radiation. In this article we discuss the impact of loop corrections on the only model-independent visible decay channel: the decay into Higgs pairs via a Giudice-Masiero term. Including such radiative effects leads to a more precise determination of the relative fraction of dark radiation, since by contrast all loop corrections to the volume axion decay mode are Planck suppressed. Assuming an MSSM spectrum and that the Giudice-Masiero coupling is fixed at the string scale by a shift symmetry in the Higgs sector, we arrive at a prediction for the effective number of neutrinos. The result turns out to be too large to be consistent with data, highly disfavouring the minimal model.