36 research outputs found
Quantum superradiance on static black hole space-times
We study the quantum analogue of the classical process of superradiance for a massless charged scalar field on a static charged black hole space-time. We show that an “in” vacuum state, which is devoid of particles at past null infinity, contains an outgoing flux of particles at future null infinity. This radiation is emitted in the superradiant modes only, and is nonthermal in nature
Addendum to “Absorption of a massive scalar field by a charged black hole”
In [1] we studied the absorption cross section of a scalar field of mass m impinging on a static black hole of mass M and charge Q. We presented numerical results using the partial-wave method, and analytical results in the high- and low-frequency limit. Our low-frequency approximation was only valid if the (dimensionless) field velocity v exceeds vc=2πMm. In this addendum we give the complementary result for v≲vc, and we consider the possible physical relevance of this regime
On-axis scalar absorption cross section of Kerr–Newman black holes: Geodesic analysis, sinc and low-frequency approximations
We investigate null geodesics impinging parallel to the rotation axis of a Kerr–Newman black hole, and show that the absorption cross section for a massless scalar field in the eikonal limit can be described in terms of the photon orbit parameters. We compare our sinc and low-frequency approximations with numerical results, showing that they are in excellent agreement
Spectral lines of extreme compact objects
We study the absorption of scalar fields by extreme/exotic compact objects (ECOs)—horizonless alternatives to black holes—via a simple model in which dissipative mechanisms are encapsulated in a single parameter. Trapped modes, localized between the ECO core and the potential barrier at the photonsphere, generate Breit-Wigner-type spectral lines in the absorption cross section. Absorption is enhanced whenever the wave frequency resonates with a trapped mode, leading to a spectral profile which differs qualitatively from that of a black hole. We introduce a model based on Nariai spacetime, in which properties of the spectral lines are calculated in closed form. We present numerically calculated absorption cross sections and transmission factors for example scenarios and show how the Nariai model captures the essential features. We argue that, in principle, ECOs can be distinguished from black holes through their absorption spectra
Do static sources respond to massive scalar particles from the Hawking radiation as uniformly accelerated ones do in the inertial vacuum?
We revisit the recently found equivalence for the response of a static scalar
source interacting with a {\em massless} Klein-Gordon field when the source is
(i) static in Schwarzschild spacetime, in the Unruh vacuum associated with the
Hawking radiation and (ii) uniformly accelerated in Minkowski spacetime, in the
inertial vacuum, provided that the source's proper acceleration is the same in
both cases. It is shown that this equivalence is broken when the massless
Klein-Gordon field is replaced by a {\em massive} one.Comment: 4 pages, 2 figure
Interaction of Hawking radiation with static sources in deSitter and Schwarzschild-deSitter spacetimes
We study and look for similarities between the response rates and of a static scalar source
with constant proper acceleration interacting with a massless,
conformally coupled Klein-Gordon field in (i) deSitter spacetime, in the
Euclidean vacuum, which describes a thermal flux of radiation emanating from
the deSitter cosmological horizon, and in (ii) Schwarzschild-deSitter
spacetime, in the Gibbons-Hawking vacuum, which describes thermal fluxes of
radiation emanating from both the hole and the cosmological horizons,
respectively, where is the cosmological constant and is the black
hole mass. After performing the field quantization in each of the above
spacetimes, we obtain the response rates at the tree level in terms of an
infinite sum of zero-energy field modes possessing all possible angular
momentum quantum numbers. In the case of deSitter spacetime, this formula is
worked out and a closed, analytical form is obtained. In the case of
Schwarzschild-deSitter spacetime such a closed formula could not be obtained,
and a numerical analysis is performed. We conclude, in particular, that and do not coincide in
general, but tend to each other when or . Our
results are also contrasted and shown to agree (in the proper limits) with
related ones in the literature.Comment: ReVTeX4 file, 9 pages, 5 figure
Quantum mechanics emerges from information theory applied to causal horizons
It is suggested that quantum mechanics is not fundamental but emerges from
classical information theory applied to causal horizons. The path integral
quantization and quantum randomness can be derived by considering information
loss of fields or particles crossing Rindler horizons for accelerating
observers. This implies that information is one of the fundamental roots of all
physical phenomena. The connection between this theory and Verlinde's entropic
gravity theory is also investigated.Comment: REvtex4-1, 6pages, 2 figures, final versio
Black holes and Hawking radiation in spacetime and its analogues
These notes introduce the fundamentals of black hole geometry, the thermality
of the vacuum, and the Hawking effect, in spacetime and its analogues.
Stimulated emission of Hawking radiation, the trans-Planckian question, short
wavelength dispersion, and white hole radiation in the setting of analogue
models are also discussed. No prior knowledge of differential geometry, general
relativity, or quantum field theory in curved spacetime is assumed.Comment: 31 pages, 9 figures; to appear in the proceedings of the IX SIGRAV
School on 'Analogue Gravity', Como (Italy), May 2011, eds. D. Faccio et. al.
(Springer
Quantum Inequalities for the Electromagnetic Field
A quantum inequality for the quantized electromagnetic field is developed for
observers in static curved spacetimes. The quantum inequality derived is a
generalized expression given by a mode function expansion of the four-vector
potential, and the sampling function used to weight the energy integrals is
left arbitrary up to the constraints that it be a positive, continuous function
of unit area and that it decays at infinity. Examples of the quantum inequality
are developed for Minkowski spacetime, Rindler spacetime and the Einstein
closed universe.Comment: 19 pages, 1 table and 1 figure. RevTex styl