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- Niayesh Afshordi, Robert Brandenberger
- 2001

We show that the non-linear evolution of long wavelength perturbations may be important in a wide class of inflationary scenarios. We develop a solution for the evolution of such nonlinear perturbations which is exact to first order in a gradient expansion. As a first application, we demonstrate that in single field models of inflation there can be no… (More)

- Tirthabir Biswas, Robert Brandenberger, Anupam Mazumdar, Warren Siegel
- 1992

In [1] it was shown how non-perturbative corrections to gravity can resolve the big bang singularity, leading to a bouncing universe. Depending on the scale of the non-perturbative corrections, the temperature at the bounce may be close to or higher than the Hagedorn temperature. If matter is made up of strings, then massive string states will be excited… (More)

- Robert Brandenberger, Damien A Easson, Dagny Kimberly
- 2008

Brane Gas Cosmology (BGC) is an approach to M-theory cosmology in which the initial state of the Universe is taken to be small, dense and hot, with all fundamental degrees of freedom near thermal equilibrium. Such a starting point is in close analogy with the Standard Big Bang (SBB) model. The topology of the Universe is assumed to be toroidal in all nine… (More)

- Robert Brandenberger, Damien A Easson
- 2004

We investigate a new way of realizing a period of cosmological inflation in the context of brane gas cosmology. It is argued that a gas of codimension one branes, out of thermal equilibrium with the rest of the matter, has an equation of state which can—after stabilization of the dilaton—lead to power-law inflation of the bulk. The most promising… (More)

- Robert Brandenberger, Hassan Firouzjahi, Johanna Karouby
- 2007

The metric around straight arbitrarily-oriented cosmic strings forming a stationary junction is obtained at the linearized level. It is shown that the geometry is flat. The sum rules for lensing by this configuration and the anisotropies of the CMB are obtained.

- Robert Brandenberger, Brandon Carter, Anne-Christine Davis, Mark Trodden
- 1996

We investigate the cosmological consequences of particle physics theories that admit stable loops of superconducting cosmic string-vortons. General symmetry breaking schemes are considered, in which strings are formed at one energy scale and subsequently become superconducting in a secondary phase transition at what may be a considerably lower energy scale.… (More)

- Yi-Fu Cai, Taotao Qiu, Robert Brandenberger, Yun-Song Piao, Xinmin Zhang
- 2008

A Quintom universe with an equation-of-state crossing the cosmological constant boundary can provide a bouncing solution dubbed the Quintom Bounce and thus resolve the Big Bang singularity. In this paper, we investigate the cosmological perturbations of the Quintom Bounce both analytically and numerically. We find that the fluctuations in the dominant mode… (More)

- Tirthabir Biswas, Robert Brandenberger, Damien A Easson, Anupam Mazumdar
- 2005

We study an effective four-dimensional theory with an action with two scalar fields minimally coupled to gravity, and with a matter action which couples to the two scalar fields via an overall field-dependent coefficient in the action. Such a theory could arise from a dimensional reduction of supergravity coupled to a gas of branes winding the compactified… (More)

We motivate inflationary scenarios with many scalar fields, and give a complete formulation of adiabatic and entropy perturbations. We find that if the potential is very flat, or if the theory has a SO(N) symmetry, the calculation of the fluctuation spectrum can be carried out in terms of merely two variables without any further assumption. We do not have… (More)

- Bin Chen, Yi Wang, Wei Xue, Robert Brandenberger
- 2008

Recently it has been shown that string gas cosmology, an alternative model of the very early universe which does not involve a period of cosmological inflation , can give rise to an almost scale invariant spectrum of metric perturbations. Here we calculate the non-Gaussianities of the spectrum of cosmological fluctuations in string gas cosmology, and find… (More)