We derive a new soft theorem that corresponds to the spontaneous breaking of Lorentz boosts. This is motivated by dynamics inflation in sub-horizon (flat-space) limit, where spacetime becomes flat but boosts are still broken. In this scattering amplitudes become sensible observables. relate emission Goldstone boson (non-relativistic) boost hard amplitudes. on-shell avatar boosts, analogous Adle...

We discuss the existence of de Sitter inflationary solutions for the string-inspired fourth-derivative gravity theories with dilaton field. We consider a space-time of arbitrary dimension D and an arbitrary parametrization of the target space metric. The specific features of the theory in dimension D = 4 and those of the special ghost-free parametrization of the metric are found. We also consid...

After a pedagogical review of elementary cosmology, I go on to discuss some obstacles to obtaining inflationary or accelerating universes in M/string theory. In particular, I give an account of an old ‘no-go theorem’ to this effect. I then describe some recent ideas about the possible role of the tachyon in cosmology. I stress that there are many objections to a naive inflationary model based o...

In this review I briefly describe the evolution of the inflationary theory from the scenario based on the idea of supercooling and expansion in the false vacuum toward the theory of eternally expanding self-reproducing inflationary universe. I describe recent development of inflationary cosmology with Ω 6= 1, and then discuss some issues related to the possibility to verify inflation by compari...

Kaluza-Klein higher derivative induced gravity is studied for its application in the inflationary universe. The stability of an inflationary solution in aD+4-dimensional anisotropic space is analyzed carefully. We show that there is two nontrivial constraints derived from the static assumptions on the D-dimensional scale factor d and scalar field ψ. We find that a physical inflationary solution...

We present a new type of brane inflation motivated by multikink solitonic solutions of a scalar field in five dimensions. In the thin brane limit, we analyze a nonstatic configuration in which the distance between two parallel domain walls decreases. We show that the ensuing spacetime is inflationary, both on the branes, and, for certain potentials, in the bulk. We argue that this inflationary ...

We consider a broad class of inflationary models of two unconstrained chiral superfields, the stabilizer S and the inflaton Φ, which can describe inflationary models with nearly arbitrary potentials. These models include, in particular, the recently introduced theories of cosmological attractors, which provide an excellent fit to the latest Planck data. We show that by adding to the superpotent...

The thermodynamics of inflationary expansion can be either isentropic or non-isentropic. Representing the early universe by a two fluid mixture of radiation energy density ρr and vacuum energy density ρv, the inflationary regime, when the scale factor accelerates R̈ > 0, is for ρv > ρr. From the point of view of two fluid Friedmann cosmology, isentropic inflationary expansion appears as a limiti...