Vector Dark Matter from Inflationary Fluctuations

TL;DR

This paper proposes a new mechanism for vector dark matter production during inflation via quantum fluctuations, resulting in a distinctive peaked power spectrum that links dark matter properties to the inflationary scale.

Contribution

It introduces a novel inflationary production process for vector dark matter with a unique peaked spectrum, differing from scalar and tensor cases, and connects dark matter abundance to inflation parameters.

Findings

Vector dark matter can be produced with a peaked power spectrum during inflation.

The predicted dark matter mass is around 10^-5 eV for high-scale inflation.

Detection of such dark matter could reveal the inflationary scale and history.

Abstract

We calculate the production of a massive vector boson by quantum fluctuations during inflation. This gives a novel dark-matter production mechanism quite distinct from misalignment or thermal production. While scalars and tensors are typically produced with a nearly scale-invariant spectrum, surprisingly the vector is produced with a power spectrum peaked at intermediate wavelengths. Thus dangerous, long-wavelength, isocurvature perturbations are suppressed. Further, at long wavelengths the vector inherits the usual adiabatic, nearly scale-invariant perturbations of the inflaton, allowing it to be a good dark matter candidate. The final abundance can be calculated precisely from the mass and the Hubble scale of inflation, H_I. Saturating the dark matter abundance we find a prediction for the mass m = 10^-5 eV (10^14 GeV/H_I)^4. High-scale inflation, potentially observable in the CMB, motivates an exciting mass range for recently proposed direct detection experiments for hidden photon dark matter. Such experiments may be able to reconstruct the distinctive, peaked power spectrum, verifying that the dark matter was produced by quantum fluctuations during inflation and providing a direct measurement of the scale of inflation. Thus a detection would not only be the discovery of dark matter, it would also provide an unexpected probe of inflation itself.