Abstract
We study the backreaction of superhorizon fluctuations of a light quantum scalar field on a classical de Sitter geometry by means of the Wilsonian renormalization group. This allows us to treat the gravitationally amplified fluctuations in a nonperturbative manner and to analytically follow the induced renormalization flow of the spacetime curvature as long wavelength modes are progressively integrated out. Unbounded loop corrections in the deep infrared are eventually screened by nonperturbative effects which stabilize the geometry.
Highlights
Despite more than half a century of effort, the extreme smallness of the measured cosmological constant in Planck units remains a major open issue in physics, which directly questions our fundamental understanding of gravity [1,2,3]
It has been long suggested that the classical de Sitter geometry may be unstable against quantum fluctuations [4,5,6,8,9,10,11], a possibility which has received a renewed interest in the past two decades [13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30]
The strong particle production from the de Sitter gravitational field results in dramatically amplified quantum fluctuations and, in turn, in infrared divergent loop contributions [37,38]
Summary
Despite more than half a century of effort (and substantial progress), the extreme smallness of the measured cosmological constant in Planck units remains a major open issue in physics, which directly questions our fundamental understanding of gravity [1,2,3]. A semiclassical description, with quantum fluctuations self-consistently coupled to a (dynamical) classical gravitational field through Einstein’s equations, already provides a framework for a possible solution. Leave alone the hard task of properly computing graviton loop corrections in a de Sitter geometry [31,32,33], even the case of a simple scalar quantum field is far from trivial.
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