Title: Ekpyrotic Reheating and Fate of Inflaton Authors: HoSeong La

It is shown that perturbative reheating can reach a sufficiently high temperature with small or negligible inflaton decay rate provided that the inflaton potential becomes negative after inflation. In our model, inflaton and dark energy particle are two independent scalar fields, and, depending on the mass of the inflaton and its coupling to matter fields, there is a possibility that the remaining inflaton after reheating can become a dark matter candidate.

Title: Ekpyrotic universes in F(R) Horava-Lifshďtz gravity Authors: A. J. López-Revelles, Ratbay Myrzakulov, Diego Sáez-Gómez

The Ekpyrotic scenario is studied in the context of some extensions of Horava-Lifshďtz gravity. Some particular solutions that lead to cyclic Hubble parameters are analysed, where the corresponding gravitational actions are reconstructed by using several techniques and auxiliary fields. Its comparison with standard F(R) gravity is performed. In addition, the so-called Little Rip, a stage of the universe evolution when some bounded systems may be dissolute, is also studied in this frame of theories.

Title: Quantum origin of pre-big bang collapse from Induced Matter theory of gravity Authors: Mauricio Bellini (IFIMAR - Mar del Plata University and CONICET)

We revisit a collapsing pre-big bang model of the universe to study with detail the non-perturbative quantum dynamics of the dispersal scalar field whose dynamics becomes from the dynamical foliation of test massless scalar field \phi on a 5D Riemann-flat metric, such that the extra space-like coordinate is noncompact. The important result here obtained is that the evolution of the system, which is described thorough the equation of state has the unique origin in the quantum contributions of the quantum contributions of the effective 4D scalar field.

Title: Pre-Big-Bang Cosmology and Circles in the Cosmic Microwave Background Authors: William Nelson, Edward Wilson-Ewing

We examine the possibility that circles in the cosmic microwave background could be formed by the interaction of a gravitational wave pulse emitted in some pre-big-bang phase of the universe with the last scattering surface. We derive the expected size distribution of such circles, as well as their typical width and (for concentric circles) angular separation. We apply these results in particular to conformal cyclic cosmology, ekpyrotic cosmology as well as loop quantum cosmology with and without inflation in order to determine how the predicted geometric properties of these circles would vary from one model to the other, and thus, if detected, could allow us to differentiate between various pre-big-bang cosmological models. We also show that the angular width and the sine of the angular radius of such circles are inversely proportional. This relation can be used in order to determine whether or not circles observed in the cosmic microwave background are due to energetic pre-big-bang events.

String and loop quantum gravity theories produce fundamentally different views of the universe's origins. The existing theory about the big bang (and about black holes) involves singularities - points of collapse where standard physical measures like density become infinite, causing the equations to break down. String theory offers mechanisms to get around the singularity problem of the big bang: Physicists Paul Steinhardt and Neil Turok have proposed an "ekpyrotic" model, where two universes floating in multidimensional space collide to produce a new beginning for the universe. But string theory can still produce unmanageable infinities. The biggest benefit of loop quantum gravity is that it doesn't involve these singularities and infinities. It predicts a quantum effect where the gravitational force becomes repulsive in the conditions around the big bang, producing a "big bounce" before a singularity can form. If this were the case, it would be possible in principle for some information to pass through this bounce from a previous incarnation of the universe. Loop quantum gravity offers the tantalizing possibility of a prehistory of everything. Read more

Is our universe a recycled version of an earlier cosmos? The idea, which replaces the big bang with a "big bounce", has received a boost: this vision of the birth of the universe can explain why a subsequent process, called inflation, occurred.

"The result puts the idea of inflation on firmer ground, and at the same time makes the bounce scenario much more credible" - Carlo Rovelli, who was not involved in the work but studies quantum gravity at the University of Marseille in France.

Title: Ekpyrotic and Cyclic Cosmology Authors: Jean-Luc Lehners (Version v2)

Ekpyrotic and cyclic cosmologies provide theories of the very early and of the very late universe. In these models, the big bang is described as a collision of branes - and thus the big bang is not the beginning of time. Before the big bang, there is an ekpyrotic phase with equation of state w=P/rho >> 1 (where P is the average pressure and rho the average energy density) during which the universe slowly contracts. This phase resolves the standard cosmological puzzles and generates a nearly scale-invariant spectrum of cosmological perturbations containing a significant non-gaussian component. At the same time it produces small-amplitude gravitational waves with a blue spectrum. The dark energy dominating the present-day cosmological evolution is reinterpreted as a small attractive force between our brane and a parallel one. This force eventually induces a new ekpyrotic phase and a new brane collision, leading to the idea of a cyclic universe. This review discusses the detailed properties of these models, their embedding in M-theory and their viability, with an emphasis on open issues and observational signatures.