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We consider braneworld scenarios including the leading correction to the Einstein-Hilbert action suggested by superstring theory, the Gauss-Bonnet term. We obtain and study the complete set of equations governing the cosmological dynamics.…
We discuss the cosmological evolution of cosmic strings with time-dependent tension. We show that, in the case that the tension changes as a power of time, the cosmic string network obeys the scaling solution: the characteristic scale of…
In this paper we model the transition from the non-geometric holographic cosmology regime, to the usual radiation dominated (RD) cosmology, known as reheating in the case of (perturbative) inflation. We find that we can easily transition…
We study cosmologies based on low-energy effective string theory with higher-order string corrections to a tree-level action and with a modulus scalar field (dilaton or compactification modulus). In the presence of such corrections it is…
String Gas Cosmology is a model of the evolution of the very early universe based on fundamental principles and key new degrees of freedom of string theory which are different from those of point particle field theories. In String Gas…
During the past two decades, cosmologists turned to particle physics in order to explore the physics of the very early Universe. The main link between the physics of the smallest and largest structures in the Universe is the idea of…
Cosmic (super)strings offer promising ways to test ideas about the early universe and physics at high energies. While in field theory constructions their tension is usually assumed to be constant (or at most slowly-varying), this is often…
We use the Matrix formalism to investigate what happens to strings above the Hagedorn temperaure. We show that it is not a limiting temperature but a temperature at which the continuum string picture breaks down. We study a collection of…
We present several features of a cosmological model based on the Brans-Dicke-Jordan-Thirry action which is scale invariant with a quartic potential for the Jordan scalar field. We show that the radiation dominated era starts with a closed…
Strings at T ~ T_c are known to be subject to the so-called Hagedorn phenomenon, in which a string's entropy (times T) and energy cancel each other and result in the evolution of the string into highly excited states, or "string balls".…
We develop the finite temperature theory of p-adic string models. We find that the thermal properties of these non-local field theories can be interpreted either as contributions of standard thermal modes with energies proportional to the…
Previously developed analytic models for the evolution of cosmic string and monopole networks are applied to networks of monopoles attached to two or more strings; the former case is usually known as cosmic necklaces. These networks are a…
In these notes we present a summary of existing ideas about phase transitions of black hole spacetimes in semiclassical gravity and offer some thoughts on three possible scenarios by which these transitions could take place. Our first theme…
We discuss early cosmology in theories where the fundamental Planck mass is close to the TeV scale. In such theories the standard model fields are localized to a (3+1)-dimensional wall with n new transverse sub-millimeter sized spatial…
We calculate the thermal partition function in the canonical ensemble for type IIB superstrings in the plane wave background with constant null R-R 5-form. The Hagedorn temperature is found to be higher than the corresponding value for…
We present a detailed analysis of {\it excited} cosmic string solutions which possess superconducting currents. These currents can be excited inside the string core, and - if the condensate is large enough - can lead to the excitations of…
Superstring theory predicts the existence of relic metastable particles whose average lifetime is longer than the age of the universe and which could, in principle, be good dark matter candidates. At the same time, these states would be…
In the context of brane world scenario, cosmic superstrings can be formed in D-brane annihilation at the end of the brane inflationary era. The cosmic superstring network has a scaling solution and the characteristic scale of the network is…
We develop a possible cosmology for a Universe with n additional spatial dimensions of variable scale, and an associated scalar field, the radion, which is distinct from the field responsible for inflation, the inflaton. Based on a…
In the context of a homogeneous universe, we note that the appearance of aggressively expanding advanced life is geometrically similar to the process of nucleation and bubble growth in a first-order cosmological phase transition. We exploit…