Relaxing Isocurvature Bounds on String Axion Dark Matter

Abstract

If inflation scale is high, light scalars acquire large quantum fluctuations during inflation.If sufficiently long-lived, they will give rise to CDM isocurvature perturbations, which are highly constrained by the Planck data. Focusing on string axions as such light scalars, we show that thermal inflation can provide a sufficiently large entropy production to dilute the CDM isocurvature perturbations. Importantly, efficient dilution is possible for the string axions, because effectively no secondary coherent oscillations are induced at the end of thermal inflation, in contrast to the moduli fields. We also study the viability of the axion dark matter with mass of about 7 keV as the origin of the 3.5 keV X-ray line excess, in the presence of large entropy production.

18 pages, 2 figures

References in corpus (6)

• Four-dimensional String Compactifications with D-Branes, Orientifolds and Fluxes
• Flux Compactification
• Dark Radiation in LARGE Volume Models
• Update of axion CDM energy density
• The 7 keV axion dark matter and the X-ray line signal
• Multi-Natural Inflation in Supergravity

Cited by in corpus (6)

• Unifying inflation and dark matter with the Peccei-Quinn field: observable axions and observable tensors
• Axions and Axion-Like Particles
• A 3.55 keV line from $\text{DM}\to a\to \gamma$: predictions for cool-core and non-cool-core clusters
• Hidden axion dark matter decaying through mixing with QCD axion and the 3.5 keV X-ray line
• X-ray Line from the Dark Transition Electric Dipole
• Observational consistency and future predictions for a 3.5 keV ALP to photon line