MG11 
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Abstract

Multivalued Lagrangians and non-singular Cosmologies

In high energy physics renormalization group techniques suggest the possibility that Lagrangians could be multi-valued functions of scalars built from the fields. In a simplified model we investigate the consequences of an analogous formulation in the context of gravitational theories. In this case the curvature can naturally acquire an upper bound. We then suggest that it could be interesting to use this property to address the singularity problem in cosmological models.

Ultraviolet regularization of divergences and child universe production

We shortly review a recent classical model which suggests the idea that the child universe formation process could be an effective process to regulate ultraviolet divergences in quantum theories of gravity. We then present evidence that some essential properties of this classical model do survive semiclassical quantization. Finally, we analyze again the fundamental features of this idea from the point of view of the extended, semiclassical, framework.

Quantum gravity signatures in MAGIC observations of a very high energy source?

For decades the efforts toward a better understanding of the interplay between theories of gravity and quantum principles have faced a formidable obstacle: this obstacle is the difficulty of obtaining models in which the evidence of this interplay could appear at an energy scale accessible for present day experiments/observations. In the last years this perspective has changed, and one of the possibilities that has been considered is that quantum gravity effects could manifest themselves in the propagation of light that is coming from astrophysical sources. In this talk we will review in this perspective observations of a very high energy distance source by the MAGIC telescope.