Off-shell dark matter: A cosmological relic of quantum gravity

Abstract

We study a novel proposal for the origin of cosmological cold dark matter (CDM) which is rooted in the quantum nature of spacetime. In this model, off-shell modes of quantum fields can exist in asymptotic states as a result of spacetime nonlocality (expected in generic theories of quantum gravity) and play the role of CDM, which we dub off-shell dark matter ($\mathrm{O}f\mathrm{DM}$). However, their rate of production is suppressed by the scale of nonlocality (e.g. Planck length). As a result, we show that $\mathrm{O}f\mathrm{DM}$ is only produced in the first moments of big bang, and then effectively decouples (except through its gravitational interactions). We examine the observational predictions of this model: In the context of cosmic inflation, we show that this proposal relates the reheating temperature to the inflaton mass, which narrows down the uncertainty in the number of $e$-foldings of specific inflationary scenarios. We also demonstrate that $\mathrm{O}f\mathrm{DM}$ is indeed cold, and discuss potentially observable signatures on small scale matter power spectrum.