Stochastic dark energy from inflationary quantum fluctuations

Abstract

We study the quantum backreaction from inflationary fluctuations of a very light, non-minimally coupled spectator scalar and show that it is a viable candidate for dark energy. The problem is solved by suitably adapting the formalism of stochastic inflation. This allows us to selfconsistently account for the backreaction on the background expansion rate of the Universe where its effects are large. This framework is equivalent to that of semiclassical gravity in which matter vacuum fluctuations are included at the one loop level, but purely quantum gravitational fluctuations are neglected. Our results show that dark energy in our model can be characterized by a distinct effective equation of state parameter (as a function of redshift) which allows for testing of the model at the level of the background.

Scalar correlation functions for a double-well potential in de Sitter space

“…For other techniques, see Refs. [17][18][19][20][21][22][23][24][25][26][27][28][29] The stochastic approach has become increasingly popular in recent years, likely due to its great efficacy, and in this vein we note the recent works [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46]. Often the focus is on the local probability distribution of the field or on local expectation values, even though the correlation of fluctutations over space is arguably the more relevant object physically.…”

Multiple spectator condensates from inflation

“…trilinear couplings (as in the case of the Higgs [26]) and couplings of multiple fields to the inflationary sector (as in 'M-flation' [27] or the newly proposed model of 'Horizon Feedback Inflation' [28]). The abundance of post-inflationary condensates can also be known to affect various models of dark energy [29], dark matter [30], and the reheating decay efficiency of the inflaton through Higgs thermal blocking [31]. Even from these few examples, it is clear that precise numerical predictions provide an important component in providing the initial conditions to model building in the early Universe.…”

Renormalisation group improvement in the stochastic formalism

“…In specific examples it has been shown to correctly reproduce the leading-log order IR results derived by other means [23][24][25][26][27][28][29]. Recent works addressing foundations of the stochastic approach include references [30][31][32][33][34][35][36][37][38]. During inflation light energetically subdominant scalars probe field values from the vacuum parametrically up to the Hubble scale H. Quantum corrections may induce significant running of couplings over this window and must be accounted in studying the dynamics.…”