89 research outputs found
Quantum properties of the Dirac field on BTZ black hole backgrounds
We consider a Dirac field on a -dimensional uncharged BTZ black hole
background. We first find out the Dirac Hamiltonian, and study its
self-adjointness properties. We find that, in analogy to the Kerr-Newman-AdS
Dirac Hamiltonian in dimensions, essential self-adjointness on
of the reduced (radial) Hamiltonian is implemented
only if a suitable relation between the mass of the Dirac field and the
cosmological radius holds true. The very presence of a boundary-like
behaviour of is at the root of this problem. Also, we determine in a
complete way qualitative spectral properties for the non-extremal case, for
which we can infer the absence of quantum bound states for the Dirac field.
Next, we investigate the possibility of a quantum loss of angular momentum for
the -dimensional uncharged BTZ black hole. Unlike the corresponding
stationary four-dimensional solutions, the formal treatment of the level
crossing mechanism is much simpler. We find that, even in the extremal case, no
level crossing takes place. Therefore, no quantum loss of angular momentum via
particle pair production is allowed.Comment: 19 pages; IOP styl
Experimental quantum cosmology in time-dependent optical media
It is possible to construct artificial spacetime geometries for light by
using intense laser pulses that modify the spatiotemporal properties of an
optical medium. Here we theoretically investigate experimental possibilities
for studying spacetime metrics of the form
. By tailoring the laser
pulse shape and medium properties, it is possible to create a refractive index
variation that can be identified with . Starting from a
perturbative solution to a generalised Hopfield model for the medium described
by an we provide estimates for the number of photons generated by the
time-dependent spacetime. The simplest example is that of a uniformly varying
that therefore describes the Robertson-Walker metric, i.e. a
cosmological expansion. The number of photon pairs generated in experimentally
feasible conditions appears to be extremely small. However, large photon
production can be obtained by periodically modulating the medium and thus
resorting to a resonant enhancement similar to that observed in the dynamical
Casimir effect. Curiously, the spacetime metric in this case closely resembles
that of a gravitational wave. Motivated by this analogy we show that a periodic
gravitational wave can indeed act as an amplifier for photons. The emission for
an actual gravitational wave will be very weak but should be readily observable
in the laboratory analogue.Comment: Version accepted fro publication in New Journal of Physic
Quantum instability for charged scalar particles on charged Nariai and ultracold black hole manifolds
We analyze in detail the quantum instability which characterizes charged
scalar field on three special de Sitter charged black hole backgrounds. In
particular, we compute exactly the imaginary part of the effective action for
scalar charged fields on the ultracold I, ultracold II and Nariai charged black
hole backgrounds. Both the transmission coefficient approach and the
-function approach are exploited. Thermal effects on this quantum
instability are also taken into account in presence of a non-zero black hole
temperature (ultracold I and Nariai).Comment: 20 pages, IOP styl
Quantum Effects for the Dirac Field in Reissner-Nordstrom-AdS Black Hole Background
The behavior of a charged massive Dirac field on a Reissner-Nordstrom-AdS
black hole background is investigated. The essential self-adjointness of the
Dirac Hamiltonian is studied. Then, an analysis of the discharge problem is
carried out in analogy with the standard Reissner-Nordstrom black hole case.Comment: 18 pages, 5 figures, Iop styl
Absence of Normalizable Time-periodic Solutions for The Dirac Equation in Kerr-Newman-dS Black Hole Background
We consider the Dirac equation on the background of a Kerr-Newman-de Sitter
black hole. By performing variable separation, we show that there exists no
time-periodic and normalizable solution of the Dirac equation. This conclusion
holds true even in the extremal case. With respect to previously considered
cases, the novelty is represented by the presence, together with a black hole
event horizon, of a cosmological (non degenerate) event horizon, which is at
the root of the possibility to draw a conclusion on the aforementioned topic in
a straightforward way even in the extremal case.Comment: 12 pages. AMS styl
Removal of contaminants of emerging concern from real wastewater by an innovative hybrid membrane process - UltraSound, Adsorption, and Membrane ultrafiltration (USAMe®).
Abstract The low-level presence of emerging contaminants (ECs) in the environment has raised a great concern due to their persistence, chronic toxicological, and endocrine disrupting effects on terrestrial and aquatic organisms. Wastewater treatment plants (WWTPs) have become hotspots for the spread of these contaminants to the environment as conventional processes are not efficient in removing them. Thus, the integration of advanced treatment methods within the chain of WWTPs is very essential. In this study, the innovative hybrid process USAMe® which integrates ultrasound irradiation (US), adsorption (A) and membrane filtration (Me) was investigated for the removal of ECs from secondary effluents. Diclofenac, carbamazepine, and amoxicillin were selected due to their large consumption and frequent presence in the aquatic environment. All three ECs were spiked into real secondary wastewater effluent at two concentrations of 10 ppm and 100 ppb. Membrane ultrafiltration and its combination with US (USMe) or adsorption (AMe) were also studied as control tests. The hybrid combination of all the three methods in the USAMe® processes elevated the EC removals to above 99% as compared to only around 90% in the AMe process. All effluents of the hybrid USAMe® processes gave "No Effect" to D. magna, with immobilization of ≤20%. Therefore, results showed that the USAMe® process was efficient in not only removing ECs, but also in generating safe and less toxic treated effluents; thereby displaying its potential as an advanced method for wastewater treatment
Blackbody emission from light interacting with an effective moving dispersive medium
Intense laser pulses excite a nonlinear polarisation response that may create
an effective flowing medium and, under appropriate conditions, a blocking
horizon for light. Here we analyse in detail the interaction of light with such
laser-induced flowing media, fully accounting for the medium dispersion
properties. An analytical model based on a first Born-approximation is found to
be in excellent agreement with numerical simulations based on Maxwell's
equations and shows that when a blocking horizon is formed, the stimulated
medium scatters light with a blackbody emission spectrum. Based on these
results, diamond is proposed as a promising candidate medium for future studies
of Hawking emission from artificial, dispersive horizons
Divergences problem in black hole brick-wall model
In this work we review, in the framework of the so-called brick wall model,
the divergence problem arising in the one loop calculations of various
thermodynamical quantities, like entropy, internal energy and heat capacity.
Particularly we find that, if one imposes that entanglement entropy is equal to
the Bekenstein-Hawking one, the model gives problematic results. Then a
proposal of solution to the divergence problem is made following the zeroth law
of black hole mechanics.Comment: 19 pages, reviseted-extended version accepted by Phys. Rev.
Hawking Radiation Entropy and Horizon Divergences
We review the problem of divergences in one--loop thermodynamical quantities
for matter fields in thermal equilibrium on a black hole background. We discuss
a number of results obtained for various thermodynamical quantities. Then we
discuss the ansatz called ``literal interpretation" of zeroth law of black hole
mechanics and try to explain the diseases of the conical defect procedure in
light of this ansatz. Finally, an analysis of the consequences implied by our
ansatz on the calculation of the partition function is made.Comment: 32 pages, uses Phyzz
Quantum entropy of the Kerr black hole arising from gravitational perturbation
The quantum entropy of the Kerr black hole arising from gravitational
perturbation is investigated by using Null tetrad and \'t Hooft\'s brick-wall
model. It is shown that effect of the graviton\'s spins on the subleading
correction is dependent of the square of the spins and the angular momentum per
unit mass of the black hole, and contribution of the logarithmic term to the
entropy will be positive, zero, and negative for different value of .Comment: 8 pages, 1 figure, Latex. to appear in Phys. Rev.
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