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We consider the coupled evolution of density, (scalar) metric and dilaton perturbations in the transition from a ``stringy" phase of growing curvature and gravitational coupling to the standard radiation-dominated cosmology. We show that…
We consider an inflationary scenario in the holographic braneworld with a cosmological fluid occupying the 3+1 dimensional brane located at the holographic boundary of an asymptotic ADS$_5$ bulk. The contribution of the boundary conformal…
We report on a large scale numerical study of networks of semilocal cosmic strings in flat space in the parameter regime in which they are perturbatively stable. We find a population of segments with an exponential length distribution and…
We propose a variation of spacetime noncommutative field theory to realize the stringy spacetime uncertainty relation without breaking any of the global symmetries of the homogeneous isotropic universe. We study the spectrum of metric…
The scalar modes of the geometry induced by dimensional decoupling are investigated. In the context of the low energy string effective action, solutions can be found where the spatial part of the background geometry is the direct product of…
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…
Pre--big bang models of inflation based on string cosmology produce a stochastic gravitational wave background whose spectrum grows with decreasing wavelength, and which may be detectable using interferometers such as LIGO. We point out…
We analyze all individual cosmic strings of various lengths in a large ensemble of the global cosmic string networks in the post-inflationary scenario, obtained from numerical simulations on a discrete lattice with $N^3 = 4096^3$. A strong…
After introducing gauge-invariant cosmological perturbation theory we give an improved set of governing equations for multiple fluids including energy transfer. Having defined adiabatic and entropic perturbations we derive the…
Certain features in the primordial scalar power spectrum are known to improve the fit to the cosmological data. We examine whether bouncing scenarios can remain viable if future data confirm the presence of such features. In inflation, the…
It is widely believed that quantum field fluctuation in an inflating background creates the primeval seed perturbation which through subsequent evolution leads to the observed large scale structure of the universe. The standard inflationary…
In the context of the pre-Big Bang scenario of string cosmology, we propose a modified equation for the evolution of the tensor perturbations, which includes the full contribution of possible higher-order curvature and coupling corrections…
We propose that cosmological density perturbation may originate from passive fluctuations of the inflaton, which are induced by colored quantum noise due to the coupling of the inflaton to the quantum environment. At small scales, the…
We study linear cosmological perturbations in a previously introduced family of deformations of general relativity characterized by the absence of new degrees of freedom. The homogeneous and isotropic background in this class of theories is…
We consider the dynamics of a contracting universe ruled by two minimally coupled scalar fields with general exponential potentials. This model describes string-inspired scenarios in the Einstein frame. Both background and perturbations can…
Inflationary models within string theory exhibit unusual scalar field dynamics involving non-minimal kinetic terms and generically referred to as k-inflation. In this situation, the standard slow-roll approach used to determine the behavior…
The inflationary scenarios suggested by the duality properties of string cosmology in the Brans-Dicke (or String) frame are shown to correspond to accelerated contraction (deflation) when Weyl-transformed to the Einstein frame. We point out…
Cosmic strings, a hot subject in the 1980's and early 1990's, lost its appeal when it was found that it leads to inconsistencies in the power spectrum of the measured cosmic microwave background temperature anisotropies. However,…
We show how two simple modifications to the standard cosmic string scenario for structure formation compare to the recently released Boomerang data set. Namely we consider pure string closed models and mixed models where both inflation and…
We investigate the cosmological perturbations in generalized gravity, where the Ricci scalar and a scalar field are non-minimally coupled via an arbitrary function. In the Friedmann-Lemaitre-Robertson-Walker background, by studying the…