Related papers: Massive cosmological scalar perturbations
This research is an extension of the author's article \cite{zar}, in which conformally invariant generalization of string theory was suggested to higher-dimensional objects. Special cases of the proposed theory are Einstein's theory of…
In this essay we offer a comprehensible overview of the gravitational aether scenario. This is a possible extension of Einstein's theory of relativity to the quantum regime via an effective approach. Quantization of gravity usually faces…
A new approach to solving two of the cosmological problems (CCPs) is proposed by introducing the Abbott-Deser (AD) method for defining Killing charges in asymptotic de Sitter space as the only consistent means for defining the ground-state…
Instead of Lorentz invariance, gravitational degrees of freedom may obey Lifshitz scaling at high energies, as it happens in Ho\v{r}ava's proposal for quantum gravity. We study consequences of this proposal for the spectra of primordial…
Structure formation models with a cosmological constant are successful in explaining large-scale structure data, but are threatened by the magnitude-redshift relation for Type Ia supernovae. This has led to discussion of models where the…
In this paper, we present the cosmological perturbation formalism for theories within the framework of affine gravity. These theories are distinguished by their connection, devoid of any metric. Our approach involves segregating…
We show how the primordial bispectrum of density perturbations from inflation may be characterised in terms of manifestly gauge-invariant cosmological perturbations at second order. The primordial metric perturbation, zeta, describing the…
In this paper we study gravitational wave perturbations in a cosmological setting of bigravity which can reproduce the {\Lambda}CDM background and large scale structure. We show that in general gravitational wave perturbations are unstable…
We explore the homogeneous background dynamics and the evolution of generated perturbations of cosmological inflation that is driven by multiple scalar fields interacting with a perfect fluid.Then we apply the method to warm inflation…
The cosmological constant and its phenomenology remain among the greatest puzzles in theoretical physics. We review how modifications of Einstein's general relativity could alleviate the different problems associated with it that result…
The BICEP2 collaboration has recently reported a large tensor fluctuation in the cosmic microwave background, which suggests chaotic inflation models. In this letter, we reconsider the chaotic inflation model in the supergravity. We…
We initiate the study of multi-field inflation using holography. Bulk light scalar fields correspond to nearly marginal operators in the boundary theory and the dual quantum field theory is a deformation of a CFT by such operators. We…
The mimetic gravity theory is one of the interesting modified gravity theories, which aims to unify the matter component of our universe within the power of gravity. The mimetic-like theory can also be responsible for primordial…
This paper represents an in-depth treatment of the chain inflation scenario. We fully determine the evolution of the universe in the model, the necessary conditions in order to have a successful inflationary period, and the matching with…
A new class of modified theories of gravity, consisting of the superposition of the metric Einstein-Hilbert Lagrangian with an $f(\cal R)$ term constructed \`{a} la Palatini was proposed recently. The dynamically equivalent scalar-tensor…
We compute the second-order matching conditions for tensor metric perturbations at an abrupt change in the equation of state. For adiabatic perturbations on large scales the matching hypersurface coincides with a uniform-density…
We show that the field equations for cosmological perturbations in Newtonian gauge always have an adiabatic solution, for which a quantity ${\cal R}$ is non-zero and constant in all eras in the limit of large wavelength, so that it can be…
We asses the contribution to the observed large scale anisotropy of the cosmic microwave background radiation, arising from both gravity waves as well as adiabatic density perturbations, generated by a common inflationary mechanism in the…
Adiabatic perturbations in the cosmology of a quintessential scalar field with exponential potential gravitationally coupled to radiation/matter are investigated in a gauge invariant formalism. The main question addressed in this paper is…
We investigate the scalar sector of linear cosmological perturbations in quadratic gravity. Working in the Einstein frame, we derive the equations of motion in a gauge-independent manner and express them in terms of three sets of…