Lightish but clumpy: scalar dark matter from inflationary fluctuations

Abstract

It is well known that light scalar fields present during inflation are coherently excited. We show that if the field couples to gravity in a non-minimal way, the fluctuations at large scales are suppressed with respect to the small scales ones. This fact allows for the field excitations to make a sizeable contribution to the energy density of the universe without generating too large isocurvature fluctuations at observable scales. We show that this mechanism could generate all the observed dark matter and study the main cosmological implications of this setup.

Dark Matter from Scalar Field Fluctuations

“…Similar ideas have recently been studied in the literature, including e.g. self-interacting [8][9][10][11][12] or non-minimally coupled DM [13][14][15], DM coupled to the inflaton [16], or * ttenkan1@jhu.edu axion DM [17][18][19][20]. In this paper we show that even in the simplest possible case the scalar field can successfully constitute all DM without being in conflict with the CMB data.…”

Misalignment & Co.: (pseudo-)scalar and vector dark matter with curvature couplings

“…The effective mass is then typically of the order of the Hubble scale, leading to a non-trivial evolution of both the field and the fluctuations during inflation. This evolution during inflation impacts all three possible non-thermal scenarios for the production of the dark matter density: misalignment [1][2][3][5][6][7], stochastic [38][39][40][41] and fluctuation [42][43][44][45][46][47] production. After inflation, the Ricci scalar vanishes during radiation domination and the evolution proceeds in the standard way.…”

“…In the discussion above we have focused on the production of non-minimally coupled scalar dark matter through the misalignment mechanism. However, as was discussed in [47], inflationary fluctuations of a non-minimally coupled scalar field can also carry a significant energy density. We now briefly review this alternative production mechanism in order to understand the interplay between the misalignment and the fluctuation-based contribution to the dark matter density.…”

“…which is identical to the expression in the scalar case (cf. [47]) with (1 − κ)/6 ↔ ξ. We can therefore directly translate the results of Sect.…”

“…More recently, increasing attention has been payed to the possibility that the dark matter may also enjoy such couplings. The focus of the studies has been on the generation of dark matter during inflation [42][43][44][45][46][47] or at preheating and reheating [64][65][66][67][68][69][70][71][72]. Graviton-mediated thermal production has also been explored [70][71][72][73][74][75][76].…”