Quantum Gravity

We use the example of inflationary physics to discuss the possibility that short distance physics might be imprinted on long-distance observables. In particular, we focus on issues involving decoupling in field theory.

If string theory is the correct theory which unifies gravity with the other forces of nature at a quantum level, it should determine the evolution of the earliest stages of the universe. I will discuss how stringy signatures of this early phase may be visible in current cosmological observations.

I will discuss possible tests of the grainularity of space including modified dispersion relations in the formation of white dwarfs and neutron stars and constraints on a stochastic direction field from atomic system tests.

I will describe work aimed at understanding the dynamics of gravitational collapse in a fully quantum setting. Its emphasis is on the role played by fundamental discreteness. The approach used suggests modifications of a black hole\'s mass loss rate and thermodynamical properties. Numerical simulations of collapse with quantum gravity corrections indicate that black holes form with a mass gap.

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If large extra dimensions exist, microscopic black holes may be created in TeV particle colliders and in Earth\'s atmosphere by the collisions of ultrahigh-energy cosmic rays with atmospheric nuclei. The decay of these black holes could soon be observed at the Large Hadron Collider or the Pierre Auger Observatory. Monte Carlo codes have been developed to simulate these events. In this talk I will introduce two of these codes (CATFISH for the LHC and GROKE for the PAO), and discuss how mini black holes can be distinguished from standard model or susy events.

This talk will review proposed tests of ideas about quantum gravity, including searches for quantum decoherence, probes of the possible energy-dependence of the velocity of light, and the nature of vacuum energy. Motivations will be drawn from a non-critical string theory framework.

I\'ll give a broad review of various ways of looking for large, small, and warped extra dimensions and will give only a brief review of the black-hole business, particularly an introduction based on the original paper we wrote and recent work on Randall-Sundrum black holes.

Observables in (quantum) General Relativity can be constructed from (quantum) reference frame -- a physical observable is then a relation between a system of interest and the reference frame. A possible interpretation of DSR can be derived from the notion of deformed reference frame (cf Liberati-Sonego-Visser). We present a toy model and study an example of such quantum relational observables. We show how the intrinsic quantum nature of the reference frame naturally leads to a deformation of the symmetries, comforting DSR to be a good candidate to describe the QG semi-classical regime.

The talk gives a brief overview over different versions of doubly or deformed special relativity (DSR) and its motivation, which comes from the occurrence of a fundamental invariant length in quantum gravity (QG). Despite its QG origin, DSR is a modification of flat space geometry without explicit notion of gravity. In the literature there is a considerable amount of work done to probe deformations of special relativity in classical and quantum mechanics and quantum field theory without taking into account intermediate steps between QG and flat space, like general relativity or quantum field theory in curved space. The more special part of this contribution makes one step into this gap by comparing the DSR modifications of simple quantum scattering of a particle in flat space with the modifications caused by a weak classical gravitational field.