Seminarium Teorii Oddziaływań Elementarnych

Quantum fluctuations generated in the early Universe inflationary periodhave an energy-momentum tensor associated to them. This, in principle,represents an aditional source - quantum backreaction - to the (semiclassical) Einstein's equation, on top of the classical background fluids driving the expansion. There are models in which the backreaction from quantum fluctuations eventually, during the expansion of the Universe, becomes comparable to the background fluids driving the expansion, in which case one expects considerable deviations from the classical GR dynamics. I will present some scalar field models in which quantum fluctuations exhibit this behaviour. For certain ranges of model parameters backreaction remains small throughout the history of the expansion (inflationary era and radiation era) and becomes comparable to the background fluid only in late-time matter era. When it becomes important, the backreaction constitutes a cosmological constant type contribution, making it a possible dark energy candidate.