Vitor Cardoso

BLACK HOLES AND STRINGS AT THE WATER TAP?

Black strings are very important fundamental objects in string theory, and are basically stretched black holes. Black strings are often unstable, suffering from a localization or Gregory-Laflamme instability: a black string, perturbed along the extra dimension develops crests and troughs, eventually leading to the disruption of the string.
Together with Óscar Dias we have shown that many black branes behave as a usual membrane endowed with surface tension - the force that holds soap bubbles and water together. With this analogy the Gregory-Laflamme instability is to be expected: black branes break into smaller fragments, just as water dripping from a faucet breaks into small drops. This is also the reason why rain comes in droplets and not as thin cylinders! Together with Leonardo Gualtieri, we are trying to understand how well the analogs can model other features of their general relativistic cousins with horizons. This will hopefully allow one to understand how well soap bubbles and water can mimic event horizons...

BLACK HOLES AT THE LHC

Tests of Newtonian gravity have excluded new forces comparable in strength to gravity for ranges from 200 micrometers to nearly one light-year, but it is hard to make any judgment for very small distances. During the last years there has been a renewal of interest in testing Newtonian gravity at microscopic scales, based on many specific theoretical predictions of modifications to gravity in this regime. The most popular among these theories assume that our universe is in fact (n+4)-dimensional, with the n extra dimensions compactified in a very small length scale, which explains why we haven't detected them yet. Since Newton's law has not been tested for small distances, extra dimensions are theoretically and experimentally allowed.
In these scenarios, gravity gets stronger at small distances, thus new phenomena is possible once we admit the existence of large (``large'' here means less than a milimeter) extra dimensions. The most generic and spectacular result of such a framework would be the production of black holes at particle accelerators and cosmic rays. Experimental clues to the physics of black hole decay would not only prove once and for all the validity of General Relativity in the strong field regime, but could also provide experimental hints to a quantum gravity theory. In the work with Marco and Leonardo, we completely describe the evaporation of a n+4-dimensional non-rotating black hole. It turns out that for large n, most of the Hawking radiation escapes to the extra dimensions, and is therefore "missing energy" in the experiments.