MG12 - Talk detail
 

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 Participant 

Institution

Session

Talk

Abstract

Dark spinor driven inflation

Cosmological inflation is currently considered to be the best paradigm for describing the early stages of the universe. However, it is still unclear what is the nature of the field which drives inflation. In this talk, we will discuss the possibility of spinor field driving inflation. Spinflaton -- a scalar condensate of the dark spinor field -- has a single scalar degree of freedom and leads to the identical acceleration equation as the canonical scalar field. We will discuss the advantages of this model compared to the scalar field driven inflation and discuss its observational relevance.

Ambiguities in second-order cosmological perturbations for non-canonical scalar fields

Over the last few years, it has been realised that non-canonical scalar fields can lead to the accelerated expansion in the early universe. The primordial spectrum in these scenarios not only shows near scale-invariance consistent with CMB observations, but also large primordial non-Gaussianity. Second-order perturbation theory is the primary theoretical tool to investigate such non-Gaussanity. However, it is still unclear which quantities are gauge-invariant in second-order and hence, physical understanding of the various second-order physical quantities is not transparent. As an attempt to understand these quantities, we consider a general non-canonical scalar field, minimally coupled to gravity, on the unperturbed FRW background, where metric fluctuations are neglected a priori. In this simplified set-up, we show that there arise ambiguities in the expressions of physically relevant quantities, such as the effective speed of the perturbations. Further, the stress tensor and energy density display a potential instability which is not present at linear order.

Entanglement and subleading corrections to Bekenstein-Hawking entropy

We consider the entanglement between quantum field degrees of freedom inside and outside the horizon as a plausible source of black-hole entropy. We examine possible deviations of black hole entropy from area proportionality. We show that while the area law holds when the field is in its ground state, a correction term proportional to a fractional power of area results when the field is in a superposition of ground and excited states. We compare our results with the other approaches in the literature.

Ambiguities in second-order cosmological perturbations for non-canonical scalar fields

The problem of propagation of cosmological perturbations can be treated in linear theory as a first approximation, although the exact problem is fundamentally nonlinear. The linear perturbations, due to the general non-canonical scalar fields, in the early and late universe can effect the background geometry and energy density in which they propagate which is known as non-linear feed back or back-reaction effect. However, it is still unclear which quantities are gauge-invariant in second-order and hence, physical understanding of the various second-order physical quantities is not transparent. As an attempt to understand these quantities, we consider a general non-canonical scalar field, minimally coupled to gravity, on the unperturbed FRW background, where metric fluctuations are neglected a priori. In this simplified set-up, we show that there arise ambiguities in the expressions of physically relevant quantities, such as the effective speed of the perturbations. Further, the stress tensor and energy density display a potential instability which is not present at linear order.

Quantum gravitational corrections to the propagator in spacetimes with constant curvature

The existence of a minimal and fundamental length scale, say, the Planck length, is a characteristic feature of almost all the models of quantum gravity. The presence of the fundamental length often leads to the improved ultra-violet behavior of the semi-classical propagators. The hypothesis of path integral duality provides a prescription to evaluate the modified propagator of a free, quantum scalar field in a given spacetime, taking into account the existence of the fundamental length in a locally Lorentz invariant manner. We use this prescription to compute the quantum gravitational modifications to the propagators in spacetimes with constant curvature, and show that: (i) the modified propagators are ultra-violet finite, and (ii) the modifications are non-perturbative in the Planck length. We discuss the implications of our results.

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