Scientific Activity

Topics :

1) Quantum fields in curved space and black hole evaporation

2) Acoustic black holes

3) Black holes and cosmology in braneworlds

1) One of the most atonishing results of last century
theoretical physics is with no doubts the prediction
 made by Hawking that black holes are not completely
black but radiate thermally. This surprising result has
been derived by Hawking using the framework of quantum
field theory in curved spacetimes, where matter fields
are quantized with the use of standard quantum field
theory methods whereas gravity is treated classically
according to Einstein General Relativity theory.

A detailed and pedagogical presentation of the Hawking effect
and its physical implications, as well as a discussion on backreaction
effects in black hole spacetimes has been presented in the
book "Modeling black hole evaporation", published by Imperial College
Press/World Scientific in January 2005.

We have determined the leading order quantum correction
to the Schwarzschild metric and to the Newtonian potential via a
numerical calculation of the stress energy tensor for conformal fields
in a zero temperature (Boulware) vacuum state. The results are in
agreement with those obtained in the weak-field approximation using
Feynman diagrams.

Finally, we have shown that the regularity conditions for the stress tensor
in the extreme Reissner-Nordstrom black hole are fulfilled irrespective
of the type of collapse and of the model used.

2) In 1981 a remarkable paper by Unruh showed that a quantum
emission similar to the one predicted by Hawking for black
holes is expected in a seemingly completely different
context, namely fluids undergoing hypersonic motion. This
far reaching result opened a continuously developing field
of research (the so called black hole analogue models) in
condensed matter physics where, unlike gravity, the hope to
perform experimental tests on these theoretical predictions
does not seem so remote.

In this context we have studied for the first time, using
theoretical methods borrowed from quantum field theory in
curved spacetimes, the backreaction this emitted radiation
has on the fluid. In particular we have shown that the quantum
effects slow down the fluid and that, in analogy with the evaporation
of charged black holes, the temperature of the emitted phonons

3) A new scenario where one can in principle attack the
backreaction problem in black hole spacetimes concerns the use
of the Randall-Sundrum (RS) braneworlds, where our
universe is seen as a hypersurface (the brane) immersed in
five dimensional anti-de Sitter spacetime (the bulk),
and of Maldacena's AdS/CFT correspondence. In this context
we have verified that the classical bulk computation concerning
the correction to the newtonian potential on the brane is in agreement
with the semiclassical one described above (see point 1).

Aside from this, we have also studied brane cosmological solutions
resulting from anisotropic bulk configurations.

Research Program:

For the future we intend to perform the following investigations:
- Search for analytical approximations of the stress energy tensor
in Boulware state in Schwarzschild spacetime to match the results
found numerically.
- Numerical study of vacuum polarization in static black holes;
- Numerical and analytical studies of analog models of black holes, 
  in particular those constructed from Bose-Einstein condensates;
- Numerical and analytical studies of classical bulk solutions in RS
  models corresponding to time dependent (gravitational collapse)
  configurations in the brane and connection to black hole evaporation.