378 research outputs found
Fermion Tunneling from Dynamical Horizons
The instability against emission of fermionic particles by the trapping
horizon of an evolving black hole is analyzed using the Hamilton-Jacobi
tunneling method. This method automatically selects one special expression for
the surface gravity of a changing horizon. The results also apply to point
masses embedded in an expanding universe. As a bonus of the tunneling method,
we gain the insight that the surface gravity still defines a temperature
parameter as long as the evolution is sufficiently slow that the black hole
pass through a sequence of quasi-equilibrium states, and that black holes
should be semi-classically unstable even in a hypothetical world without
bosonic fields.Comment: 8 pages, standard Latex document, few references adde
On the Unruh effect in de Sitter space
We give an interpretation of the temperature in de Sitter universe in terms
of a dynamical Unruh effect associated with the Hubble sphere. As with the
quantum noise perceived by a uniformly accelerated observer in static
space-times, observers endowed with a proper motion can in principle detect the
effect. In particular, we study a "Kodama observer" as a two-field Unruh
detector for which we show the effect is approximately thermal. We also
estimate the back-reaction of the emitted radiation and find trajectories
associated with the Kodama vector fields are stable.Comment: 8 pages; corrected typos; sections structure revise
Hamilton-Jacobi Method and Gravitation
Studying the behaviour of a quantum field in a classical, curved, spacetime
is an extraordinary task which nobody is able to take on at present time.
Independently by the fact that such problem is not likely to be solved soon,
still we possess the instruments to perform exact predictions in special,
highly symmetric, conditions. Aim of the present contribution is to show how it
is possible to extract quantitative information about a variety of physical
phenomena in very general situations by virtue of the so-called Hamilton-Jacobi
method. In particular, we shall prove the agreement of such semi-classical
method with exact results of quantum field theoretic calculations.Comment: To appear in the proceedings of "Cosmology, the Quantum Vacuum, and
Zeta Functions": A workshop with a celebration of Emilio Elizalde's Sixtieth
birthday, Bellaterra, Barcelona, Spain, 8-10 Mar 201
On tunneling across horizons
The tunneling method for stationary black holes in the Hamilton-Jacobi
variant is reconsidered in the light of various critiques that have been moved
against. It is shown that once the tunneling trajectories have been correctly
identified the method isfree from internal inconsistencies, it is manifestly
covariant, it allows for the extension to spinning particles and it can even be
used without solving the Hamilton-Jacobi equation. These conclusions borrow
support on a simple analytic continuation of the classical action of a
pointlike particle, made possible by the unique assumption that it should be
analytic in complexified Schwarzschild or Kerr-Newman spacetimes. A more
general version of the Parikh-Wilczek method will also be proposed along these
lines.Comment: Latex Document, 5 pages, 2 figures, title changed, abstract changed,
added references, results unchange
Predicted properties of Galactic and Magellanic Classical Cepheids in the SDSS filters
We present the first extensive and detailed theoretical scenario for the
interpretation of Cepheid properties observed in the SDSS filters. Three sets
of nonlinear convective pulsation models, corresponding to the chemical
compositions of Cepheids in the Milky Way, the Large Magellanic Cloud and the
Small Magellanic Cloud respectively, are transformed into the SDSS bands by
relying on updated model atmospheres. The resulting observables, namely the
instability strip boundaries and the light curves, as well as the
Period-Luminosity, the Wesenheit and the Period-Luminosity-Colour relations,
are discussed as a function of the metal content, for both the fundamental and
the first overtone mode. The fundamental PL relations are found to deviate from
linear relations when computed over the whole observed Cepheid period range,
especially at the shorter wavelenghts, confirming previous findings in the
Johnson-Cousins bands. The obtained slopes are found to be mildly steeper than
the ones of the semiempirical and the empirical relations available in the
literature and covering roughly the same period range, with the discrepancy
ranging from about 13% in u-band to about 3% in z.Comment: Accepted for publication in MNRA
On Tunnelling Through the Black Hole Horizon
It is shown here that there is no way for particle creation to occur by
quantum tunneling through an infinitesimal neighborhood of the black hole
horizon. This result is a trivial consequence of the regularity of the horizon,
the equivalence principle and the general covariance of the relativistic theory
of gravity. Moreover, we also confirm the less trivial statement that no
particle creation by quantum tunneling through the black hole horizon is
possible independent of the size of the presupposed tunneling domain.Comment: 21 pages, new section is adde
- …