Related papers: Chameleonic dilaton, nonequivalent frames, and the…
I briefly review the cosmological constant problem and the issue of dark energy (or quintessence). Within the framework of quantum field theory, the vacuum expectation value of the energy momentum tensor formally diverges as $k^4$. A cutoff…
We consider tachyon condensation in unstable ten-dimensional heterotic string theory with gauge group E8. In the background of a lightlike linear dilaton rolling to weak coupling, we find an exact solution in which the theory decays to a…
We present a wholly self-consistent, complete cyclic bouncing cosmology based on components drawn from string theory and constructed in a way that is under perturbative control throughout (e.g., with temperature much less than the string…
Accelerating universe or the existence of a small and positive cosmological constant is probably the most pressing obstacle as well as opportunity to significantly improving the models of four-dimensional cosmology from fundamental theories…
We consider a universe with a positive effective cosmological constant and a nonminimally coupled scalar field. When the coupling constant is negative, the scalar field exhibits linear growth at asymptotically late times, resulting in a…
I discuss cosmological models either derived from, or inspired by, string theory or M-theory. In particular I discuss solutions in the low-energy effective theory and the role of the dilaton, moduli and antisymmetric form fields in the…
We discuss time - dependent solutions of the leading order string effective equations for a non-zero central charge deficit and curved maximally symmetric space. Some regular solutions are found for the case of non-trivial antisymmetric…
We study a scenario with a transient phase of cosmological acceleration that could potentially be realized in asymptotic corners of String Theory moduli space. A very steep scalar potential is temporarily stabilized by the effect of a…
The cosmological constant problem is the principal obstacle in the attempt to interpret dark energy as the quantum vacuum energy. We suggest that the obstacle can be removed, i.e. that the cosmological constant problem can be resolved by…
There are at least two serious moduli problems in string cosmology. The first is the possibility that moduli dominate the energy density at the time of nucleosynthesis. The second is that they may not find their minima all together. After…
We motivate a relation between dark energy and the scale of new physics in weakly coupled string theory. This mixing between infrared and ultraviolet physics leads to a unique corner for real-world phenomenology: barring fine-tunings, we…
This paper makes the simple observation that a fundamental length, or cutoff, in the context of Friedmann-Lema\^itre-Robertson-Walker (FRW) cosmology implies very different things than for a static universe. It is argued that it is…
The typical scalar field theory has a cosmological constant problem. We propose a generic mechanism by which this problem is avoided at tree level by embedding the theory into a larger theory. The metric and the scalar field coupling…
We propose quantum dynamics for the dipole moving in cosmic string background and show that the classical scale symmetry of a particle moving in cosmic string background is still restored even in the presence of dipole moment of the…
We present exact inhomogeneous and anisotropic cosmological solutions of low-energy string theory containing dilaton and axion fields. The spacetime metric possesses cylindrical symmetry. The solutions describe ever-expanding universes with…
In this article we discuss some aspects of double field theory cosmology with an emphasis on the role played by the dilaton. The cosmological solutions of double field theory equations of motion after coupling a shifted dilaton to them are…
It has recently been conjectured that string theory does not admit de Sitter vacua, and that quintessence explains the current epoch of accelerated cosmic expansion. A proposed, key prediction of this scenario is time-varying couplings in…
To study quantum effects on the bulk tachyon dynamics, we replace $R$ with $f(R)$ in the low-energy effective action that couples gravity, the dilaton, and the bulk closed string tachyon of bosonic closed string theory and study properties…
We review a few off-the-beaten-track ideas in cosmology. They solve a variety of fundamental problems; also they are fun. We start with a description of non-singular dilaton cosmology. In these scenarios gravity is modified so that the…
We compute fermion quantum corrections to the energy of cosmic strings. A number of rather technical tools is needed to formulate this correction and we employ isospin and gauge invariance to verify consistency of these tools. These…