Abstract
One contribution to any dark sector’s abundance comes from its gravitational production during inflation. If the dark sector is weakly coupled to the inflaton and the Standard Model, this can be its only production mechanism. For non-interacting dark sectors, such as a free massive fermion or a free massive vector field, this mechanism has been studied extensively. In this paper we show, via the example of dark massive QED, that the presence of interactions can result in a vastly different mass for the dark matter (DM) particle, which may well coincide with the range probed by upcoming experiments.In the context of dark QED we study the evolution of the energy density in the dark sector after inflation. Inflation produces a cold vector condensate consisting of an enormous number of bosons, which via interesting processes — Schwinger pair production, strong field electromagnetic cascades, and plasma dynamics — transfers its energy to a small number of “dark electrons” and triggers thermalization of the dark sector. The resulting dark electron DM mass range is from 50 MeV to 30 TeV, far different from both the 10−5 eV mass of the massive photon dark matter in the absence of dark electrons, and from the 109 GeV dark electron mass in the absence of dark photons. This can significantly impact the search strategies for dark QED and, more generally, theories with a self-interacting DM sector. In the presence of kinetic mixing, a dark electron in this mass range can be searched for with upcoming direct detection experiments, such as SENSEI-100g and OSCURA.
Highlights
The presence of Dark Matter (DM) is the most convincing evidence we have for Beyond the Standard Model (BSM) physics
We review constraints on the mechanism of ref. [10], where the dark photon is the Dark Matter and there are no dark fermions in the theory
Particle production in a time-varying gravitational background has been an active topic of research for many years, and it is well-appreciated that this is a minimal mechanism to produce the totality of dark matter
Summary
The presence of Dark Matter (DM) is the most convincing evidence we have for Beyond the Standard Model (BSM) physics. Particle production in a time-dependent gravitational background can only occur when there is breaking of scale invariance Taking this into account for inflation, the energy density of particles produced in a momentum mode k, as measured at horizon exit, is captured by this general formula: dρ d ln k. The dynamics of the Higgs/radial mode are decoupled from our considerations In this case, inflation produces the longitudinal component of the massive dark photon, as it maximally breaks scale invariance. Depending on the gauge coupling, strong field QED (SFQED) processes like electromagnetic cascades [14,15,16,17] become cosmologically relevant and important for producing the fermions in the theory This primordial “soup” of longitudinal gauge modes with large occupation numbers and far fewer fermions can eventually thermalize.
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