¨     Cosmology

 

*      Determining the nature of DARK ENERGY

 

The accelerated expansion of our universe, and consequently that it apparently contains a substantial amount of dark energy are still unexplained. Interpreting and understanding the accelerating universe is arguably one of the major scientific challenges of our times. The challenge can be approached on several levels, from the most practical level: how to interpret the data, through an intermediate level: penomenological models that can be embedded into theories of fundamental physics, to the most profound level: the cosmological constant problem.                                                    

 

¨     String Theory

 

*      Particle physics & Cosmology in flux compactifications

                                                                                                

A novel view of the space of solutions of string theory is starting to emerge, "the stringy landscape" in which there is a very large number of candidate vacuua in the discretuum - perhaps on the order of 10500. Only a very small fraction of these (less than 10-120) would  have an acceptably small cosmological constant and live long enough to be acceptable, and when additional conditions such as cosmological viability and particle physics constraints are added, this number will no doubt be substantially reduced, however, it is still likely to be extremely large.

 

¨     Black holes & other Space-times with causal boundaries

 

*      Quantum Entanglement, thermodynamics & area

         

Interpreting the thermodynamic properties of black holes and other space-times with horizons and uncovering their underlying statistical mechanics remains a challenge in spite of the intense efforts and the progress that has been achieved over the last 30 years. What does the black hole entropy measure, the degeneracy of microstates, entanglement entropy between the inside and outside of the horizon, or some intrinsic gravitational entropy? Is the quantum mechanics of space-times with causal boundaries unitary? If so, why do some of them look thermal and non-unitary in some approximation?

 

Aiming to understand the physics of space-times with causal boundaries, we pursue the entanglement point of view:  that their statistical properties arise because classical observers access only a part of the whole quantum state and hence describe physics by the density matrix which results from tracing over the inaccessible degrees of freedom.