Search Talks

Recent data from the PAMELA, Fermi/LAT and INTEGRAL/SPI experiments, among others, give evidence of excess electrons and positrons in the galaxy, which might be due to annihilation of dark matter. Models in which the dark matter transforms under a hidden nonabelian gauge symmetry can naturally account for the unusual features needed to fit these data. I will discuss generic features of such models, some of their distinctive consequences for cosmology, and new results for reconciling their predictions with the anomalous observations. Special attention will be given to the 511 keV gamma ray excess observed by INTEGRAL, and to the possibility that high energy lepton excesses get significant contributions from dark matter annihilation in subhalos rather than the main halo of our galaxy.

I will discuss the qualitative differences between the single-field and multifield cyclic universes, in particular the resulting global "phoenix" structure and its relation to dark energy. The multifield cyclic universe arises naturally from embedding the cyclic universe in supergravity and leads to distinct observational predictions regarding non-gaussian signatures in the CMB. I will present a simplified derivation of these predictions.

After implementing an effective minimal length, we will present a new class of spacetimes, describing both neutral and charged black holes. As a result, we will improve the conventional Schwarzschild and Reisner-Nordstroem spacetimes, smearing out their singularities at the origin. On the thermodynamic side, we will show how the new black holes admit a maximum temperature, followed by the ``SCRAM phase'', a thermodynamic stable shut down, characterized by a positive black hole heat capacity. As a consequence, also for the neutral solution, in place of the runaway behavior of the temperature, one finds that the evaporation ends up with a zero temperature extremal black hole, i.e. a final configuration entirely governed by the minimal length. For the charged case, both the Hawking and Schwinger pair creation will be discussed in this new scenario. We will also analyze the above solutions in the presence of extra dimensions and the connections with the production of mini black holes, which is foreseen in the extreme energy hadron collisions at the LHC in the next few months. Finally we will discuss further developments and possible connections with other approaches in this field.

The relation between loop quantum gravity (LQG) and ordinary quantum field theory (QFT) on a fixed background spacetime still bears many obstacles. When looking at LQG and ordinary QFT from a mathematical perspective it turns out that the two frameworks are rather different: Although LQG is a true continuum theory its Hilbert space is defined in terms of certain embedded graphs which are labeled by irreducible representations of SU(2). The natural arena for ordinary QFT, on the other hand, is a Fock space which strongly uses the metric properties of the underlying continuum spacetime. In this talk I will review this issue and show how one can use Born--Oppenheimer methods to further progress towards an understanding of (matter) quantum field theories from first principles.

Of all four forces only the weak interaction has experimentally exhibited parity violation. At the same time observations suggest that general relativity may require modification to account for dark matter and dark energy. Could it be that this modification involves gravitational parity violation? Many of the dominant approaches to quantum gravity, such as string theory and loop quantum gravity, point to an effective parity violating extension to general relativity known as Chern-Simons General Relativity (CSGR). In this colloquium I will discuss the uniqueness and phenomenological implications of parity violation in CSGR. In particular, I will discuss how CSGR can work together with inflation to generate the cosmic baryon asymmetry in a most economical fashion, through gravitational waves; and its predictions for upcoming CMB polarization experiments. I will also discuss current predictions of CSGR on binary pulsars, neutron stars and prospects for the LISA/LIGO gravitational wave detectors. While we focus on a specific theory for concreteness, some of the results presented in this colloquium can be seen as model independent.