The Quest for Quantum gravity : Testing times for theories?

por Dr. N. Mavromatos (King's College, London)

jueves 9 mar. 2000 11:30 → 12:30 Europe/Madrid

Sala Seminarios (Dpto. de Física Teórica (UVEG))

A satisfactory model for quantum gravity may necessitate a completely new perception for space time at sub-Planckian (length) scales, which may even have a cellular (foamy) structure. After a brief introduction to some theoretical models (including string and brane theories) I discuss physical consequences of such cellular (foamy) structures for the propagation of low-energy matter. In particular I argue that there may be non-trivial `optical' properties of the quantum-gravity `medium'resulting in a non-trivial index of refraction and other stochastic effects as far as propagation of, say, massless particles is concerned. The phenomenon is analogous to light dispersion by atoms in the air, but the crucial difference is that the phenomenon becomes stronger the higher the energy of the probe is, which may be qualitatively understood by the fact that high energy probes cause a bigger `distortion' of the space time fluid. Given that such effects build up the further the particle probe travels thorugh the foam, it becomes apparent that the most sensitive probes of such potential quantum-gravity effects should be astrophysical. I detail one such example, light from Gamma-Ray-Bursters (GRB) the majority of which are known to date to be at cosmological distances from earth. I discuss how quantum-gravity phenomenology can be done using such probes. Some discussion on other tests of quantum gravity foam (both terrestrial and astrophysical (such as high-energy neutrinos from cosmic rays) can be given if time allows.