The Axiverse induced Dark Radiation Problem

Abstract

The string/$M$ theory Axiverse -- a plethora of very light Axion Like Particles (ALPs) with a vast range of masses -- is arguably a generic prediction of string/$M$ theory. String/$M$ theory also tends to predict that the early Universe is dominated by moduli fields. When the heavy moduli decay, before nucleosynthesis, they produce dark radiation in the form of relativistic ALPs. Generically one estimates that the number of relativistic species grows with the number of axions in the Axiverse, in contradiction to the observations that $N_{eff}\le 4$. We explain this problem in detail and suggest some possible solutions to it. The simplest solution requires that the lightest modulus decays only into its own axion superpartner plus Standard Model particles and this severely constrains the moduli Kahler potential and mass matrix.

17 pages, 4 figures

References in corpus (5)

• Non-thermal Dark Matter and the Moduli Problem in String Frameworks
• An M Theory Solution to the Strong CP Problem and Constraints on the Axiverse
• A 3.55 keV Photon Line and its Morphology from a 3.55 keV ALP Line
• Dark Radiation predictions from general Large Volume Scenarios
• Dark Radiation in Anisotropic LARGE Volume Compactifications

Cited by in corpus (12)

• Constraining the mass of dark photons and axion-like particles through black-hole superradiance
• Cosmological window onto the string axiverse and the supersymmetry breaking scale
• The Spectrum of the Axion Dark Sector
• Reheating and Dark Radiation after Fibre Inflation
• The Fate of Dense Scalar Stars
• Cosmology in the presence of multiple light moduli
• Fibre inflation and precision CMB data
• Massive vector field perturbations on extremal and near-extremal static black holes
• Dark Radiation and the Hagedorn Phase
• Non-thermal Axion Dark Radiation and Constraints
• Dark Matter and Dark Energy from a Kaluza-Klein inspired Brans-Dicke Gravity with Barotropic Fluid
• On the dark radiation problem in the axiverse