Some recent developments in the study of quantum gravity and its semiclassical limit are reviewed. The discussion includes the role of constraint equations in quantization, the definition of 'time' in the semiclassical limit, the various forms of 'backreaction' in semiclassical gravity and the role of vacuum fluctuations in quantum gravity.
Many approaches to quantum gravity consider the revision of the space-time geometry and the structure of elementary particles. One of the main candidates is string theory. It is possible that this theory will be able to describe the problem of hierarchy, provided that there is an appropriate Calabi-Yau geometry. In this paper we will proceed from the traditional view on the structure of elementary particles in the usual four-dimensional space-time. The only condition is that quarks and leptons should have a common emerging structure. When a new formula for the mass of the hierarchy is obtained, this structure arises from topological quantum theory and a suitable choice of dimensional units.
Quantum fields in curved spacetime, semiclassical gravity, quantum gravity phenomenology, and analogue models: parallel session D4
