Back-reaction effect in power-law inflation

We revisit an extension of the well-known formalism for gauge-invariant scalar metric fluctuations, to study the spectrums for both, the inflaton and gauge invariant (scalar) metric fluctuations in the framework of a single field inflationary model where the quasi-exponential expansion is driven by an inflation which is minimally coupled to gravity. The proposal here examined is valid also for fluctuations with large amplitude, but for cosmological scales, where vector and te...

We investigate the backreaction of the quantum fluctuations of a very light ($m \!\lesssim\! H_{\text{today}}$) nonminimally coupled spectator scalar field on the expansion dynamics of the Universe. The one-loop expectation value of the energy momentum tensor of these fluctuations, as a measure of the backreaction, is computed throughout the expansion history from the early inflationary universe until the onset of recent acceleration today. We show that, when the nonminimal c...

We demonstrate the existence of a secular back-reaction on inflation using a simple scalar model. The model consists of a massless, minimally coupled scalar with a quartic self-interaction which is a spectator to $\Lambda$-driven inflation. To avoid problems with coincident propagators, and to make the scalars interact more like gravitons, we impose a covariant normal ordering prescription which has the effect of removing tadpole graphs. This version of the theory exhibits a ...

A geometrodynamical quantization of an inflationary universe is considered in order to estimate quantum-gravity effects for the primordial perturbations. Contrary to previous studies in the literature, the back-reaction produced by all the modes of the system is included in our computations. Even if at a classical level the assumption that every mode evolves independently provides a good estimate for the dynamics, our results explicitly show that this is not the case when con...

In this work we present an inflationary mechanism based on fluid dynamics. Starting with the action for a single barotropic perfect fluid, we outline the procedure to calculate the power spectrum and the bispectrum of the curvature perturbation. It is shown that a perfect barotropic fluid naturally gives rise to a non-attractor inflationary universe in which the curvature perturbation is not frozen on super-horizon scales. We show that a scale-invariant power spectrum can be ...

We describe a new mechanism that gives rise to dissipation during cosmic inflation. In the simplest implementation, the mechanism requires the presence of a massive scalar field with a softly-broken global $U(1)$ symmetry, along with the inflaton field. Particle production in this scenario takes place on parametrically sub-horizon scales, at variance with the case of dissipation into gauge fields. Consequently, the backreaction of the produced particles on the inflationary dy...

We examine the spectrum of inflaton fluctuations resulting from any given long period of exponential inflation. Infrared and ultraviolet divergences in the inflaton dispersion summed over all modes do not appear in our approach. We show how the scale-invariance of the perturbation spectrum arises. We also examine the spectrum of scalar perturbations of the metric that are created by the inflaton fluctuations that have left the Hubble sphere during inflation and the spectrum o...

It is shown that the inflationary era in early universe is realized due to the effect of backreaction of quantized matter fields. In fact we start by quantizing a free scalar field in the Friedmann-Robertson-Walker space-time, and the field is fluctuating quantum mechanically around the bottom of the mass potential. We then obtain the vacuum expectation value of the energy density of the scalar field as a functional of the scale factor $a(t)$ of the universe. By plugging it i...

We study the backreaction problem in a mechanism of magnetogenesis from inflation. In usual analysis, it has been assumed that the backreaction due to electromagnetic fields spoils inflation once it becomes important. However, there exists no justification for this assumption. Hence, we analyze magnetogenesis from inflation by taking into account the backreaction. On the contrary to the naive expectation, we show that inflation still continues even after the backreaction begi...

In this paper we propose a new inflation model named (p,q) inflation model in which the inflaton potential contains both positive and negative powers of inflaton field in the polynomial form. We will show that such a simple model can easily generate a large amplitude of tensor perturbation and a negative running of spectral index with large absolute value.