Graviton production due to collapsing extra dimensions is studied. The momenta lying in the extra dimensions are taken into account. A D-dimensional background is matched to an effectively four-dimensional standard radiation dominated universe. Using observational constraints on the present gravitational wave spectrum, a bound on the maximal temperature at the beginning of the radiation era is ...

We provide a completely quantum-mechanical derivation of the spectrum of gravitational waves produced in any inflationary cosmology. The gravitational waves result from a sequence of Bogoliubov transformations between creation and annihilation operators defined in de Sitter space and in radiation-and matter-dominated Robertson-Walker spacetimes. We discuss how the results depend on the initial ...

Two new formulas which express n-graviton MHV tree amplitudes in terms of sums of squares of n-gluon amplitudes are discussed. The first formula is derived from recursion relations. The second formula, simpler because it involves fewer permutations, is obtained from the variant of the Berends, Giele, Kuijf formula given in arXiv:0707.1035.

We compute some components of the graviton propagator in loop quantum gravity, using the spinfoam formalism, up to some second order terms in the expansion parameter.

The non-linear realisation based on $A_1^{+++}$ is known to describe gravity in terms of both the graviton and dual graviton. We extend this analysis at linearised level find equations motion for first higher description that it contains. also give a systematic method finding additional fields beyond those are required construct actions all possible descriptions realisation. show these closely ...

The complete result for the effective potential for two graviton exchange at two loops in M(atrix) theory can be expressed in terms of a generalized hypergeometric function.