¨ 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.