This series consists of talks in the area of Quantum Gravity.
Causal
Dynamical Triangulations” (CDT) is a lattice theory where aspects of quantum
gravity can be studied. Two-dimensional CDT can be solved analytically and the
continuum (quantum) Hamiltonian obtained.
In this talk I will show that this continuum Hamiltonian is the one obtained by
quantizing two-dimensional projectable Horava-Lifshitz gravity.
We construct a
self-consistent model which describes a black hole from formation to
evaporation including the back reaction from the Hawking radiation. In the case
where a null shell collapses, at the beginning the evaporation occurs, but it
stops eventually, and a horizon and singularity appear. On the other hand, in
the generic collapse process of a continuously distributed null matter, the
black hole evaporates completely without forming a macroscopically large
Both AdS/CFT duality and more general reasoning from quantum gravity point to a rich collection of boundary observables that always evolve unitarily. The physical quantum gravity states described by these observables must be solutions of the spatial diffeomorphism and Wheeler-deWitt constraints, which implies that the state space does not factorize into a tensor product of localized degrees of freedom.
I will review some problems of the black hole paradigm and explore other
possibilities for the final state of stellar collapse other than an evaporating
black hole. In particular I will use the so-called transplanckian problem as a
guide in this search for a compelling scenario for the evaporation of
ultracompact objects.
I will recall the
main motivations for considering spin foam models in their Group Field Theory
(GFT) versions, which are quantum field theories defined on group manifolds. As
for any other quantum field theory, a fully consistent definition of the latter
must involve renormalization. I will briefly review a specific class of GFTs,
called tensorial, for which progress in this direction has recently been possible.
A new just-renormalizable model, in three dimensions and on the SU(2) group,
Tensor models are
generalization of matrix models, and are studied as discrete models for quantum gravity for more than two-dimensions. Among them, the rank-three tensor models can be interpreted as theories of dynamical fuzzy spaces, and they generally have the feature of
We describe of the evaporation
process as driven by the dynamical evolution of the quantum gravitational
degrees of freedom resident at the horizon, as identified by the Loop Quantum
Gravity kinematics. Using a parallel with the Brownian motion, we interpret the
first law of quantum dynamical horizon in terms of a fluctuation-dissipation
relation applied to this fundamental discrete structure. In this way, the
horizon evolution is described in terms of relaxation to an equilibrium state
It is known that the entanglement entropy of quantum
fields on the black hole
background contributes to the Bekenstein-Hawking entropy,and that its
divergences can be absorbed into the renormalization of gravitational
couplings. By introducing a Wilsonian cutoff scale and the concepts of
the renormalization group, we can expand this observation
into a broader framework for understanding black hole entropy. At a
given RG scale, two contributions to the black hole entropy can be
The
combinatorial problems associated with the counting of black hole states in
loop quantum gravity can be analyzed by using suitable generating functions.
These not only provide very useful tools for exact computations, but can also
be used to perform an statistical analysis of the black hole degeneracy
spectrum, study the interesting substructure found in the entropy of
microscopic black holes and its asymptotic behavior for large horizon areas.
The methods that will be described are relevant for the discussion of the
There are several
fundamental predictions of quantum field theory, such as Hawking radiation (i.e., black hole evaporation) or the Sauter-Schwinger effect (i.e., electron-positron pair creation out of the quantum vacuum by a strong electric field), which have so far eluded direct experimental verification.
However, it should be possible to gain some experimental access to these effects via suitable condensed matter analogues. In this talk, some possibilities for reproducing such fundamental
quantum effects in the laboratory are discussed.