5,877 research outputs found
The Cardy-Verlinde formula and entropy of Topological Reissner-Nordstr\"om black holes in de Sitter spaces
In this paper we discuss the question of whether the entropy of cosmological
horizon in Topological Reissner-Nordstr\"om- de Sitter spaces can be described
by the Cardy-Verlinde formula, which is supposed to be an entropy formula of
conformal field theory in any dimension. Furthermore, we find that the entropy
of black hole horizon can also be rewritten in terms of the Cardy-Verlinde
formula for these black holes in de Sitter spaces, if we use the definition due
to Abbott and Deser for conserved charges in asymptotically de Sitter spaces.
Our result is in favour of the dS/CFT correspondence.Comment: 6 pages, accepted for publication in IJMP
Macroscopic detection of the strong stochasticity threshold in Fermi-Pasta-Ulam chains of oscillators
The largest Lyapunov exponent of a system composed by a heavy impurity
embedded in a chain of anharmonic nearest-neighbor Fermi-Pasta-Ulam oscillators
is numerically computed for various values of the impurity mass . A
crossover between weak and strong chaos is obtained at the same value
of the energy density (energy per degree of freedom)
for all the considered values of the impurity mass . The threshold \epsi
lon_{_T} coincides with the value of the energy density at which a
change of scaling of the relaxation time of the momentum autocorrelation
function of the impurity ocurrs and that was obtained in a previous work ~[M.
Romero-Bastida and E. Braun, Phys. Rev. E {\bf65}, 036228 (2002)]. The complete
Lyapunov spectrum does not depend significantly on the impurity mass . These
results suggest that the impurity does not contribute significantly to the
dynamical instability (chaos) of the chain and can be considered as a probe for
the dynamics of the system to which the impurity is coupled. Finally, it is
shown that the Kolmogorov-Sinai entropy of the chain has a crossover from weak
to strong chaos at the same value of the energy density that the crossover
value of largest Lyapunov exponent. Implications of this result
are discussed.Comment: 6 pages, 5 figures, revtex4 styl
Quantitative FDG-PET/CT predicts local recurrence and survival for squamous cell carcinoma of the anus
Molecular-beam epitaxy of CrSi_2 on Si(111)
Chromium disilicide layers have been grown on Si(111) in a commercial molecular‐beam epitaxy machine. Thin layers (10 nm) exhibit two epitaxial relationships, which have been identified as CrSi_2(0001)//Si(111) with CrSi_2[1010]//Si[101], and CrSi_2(0001)//Si(111) with CrSi_2[1120]//Si[101]. The latter case represents a 30° rotation of the CrSi_2 layer about the Si surface normal relative to the former case. Thick (210 nm) layers were grown by four different techniques, and the best‐quality layer was obtained by codeposition of Cr and Si at an elevated temperature. These layers are not single crystal; the largest grains are observed in a layer grown at 825 °C and are 1–2 μm across
BRST quantization of the massless minimally coupled scalar field in de Sitter space (zero modes, euclideanization and quantization)
We consider the massless scalar field on the four-dimensional sphere .
Its classical action is degenerate
under the global invariance . We then quantize
the massless scalar field as a gauge theory by constructing a BRST-invariant
quantum action. The corresponding gauge-breaking term is a non-local one of the
form where
is a gauge parameter and is the volume of . It allows us to
correctly treat the zero mode problem. The quantum theory is invariant under
SO(5), the symmetry group of , and the associated two-point functions have
no infrared divergence. The well-known infrared divergence which appears by
taking the massless limit of the massive scalar field propagator is therefore a
gauge artifact. By contrast, the massless scalar field theory on de Sitter
space - the lorentzian version of - is not invariant under the
symmetry group of that spacetime SO(1,4). Here, the infrared divergence is
real. Therefore, the massless scalar quantum field theories on and
cannot be linked by analytic continuation. In this case, because of zero modes,
the euclidean approach to quantum field theory does not work. Similar
considerations also apply to massive scalar field theories for exceptional
values of the mass parameter (corresponding to the discrete series of the de
Sitter group).Comment: This paper has been published under the title "Zero modes,
euclideanization and quantization" [Phys. Rev. D46, 2553 (1992)
Quantum Diffeomorphisms and Conformal Symmetry
We analyze the constraints of general coordinate invariance for quantum
theories possessing conformal symmetry in four dimensions. The character of
these constraints simplifies enormously on the Einstein universe . The global conformal symmetry algebra of this space determines
uniquely a finite shift in the Hamiltonian constraint from its classical value.
In other words, the global Wheeler-De Witt equation is {\it modified} at the
quantum level in a well-defined way in this case. We argue that the higher
moments of should not be imposed on the physical states {\it a priori}
either, but only the weaker condition . We
present an explicit example of the quantization and diffeomorphism constraints
on for a free conformal scalar field.Comment: PlainTeX File, 37 page
Osmotic pressure of matter and vacuum energy
The walls of the box which contains matter represent a membrane that allows
the relativistic quantum vacuum to pass but not matter. That is why the
pressure of matter in the box may be considered as the analog of the osmotic
pressure. However, we demonstrate that the osmotic pressure of matter is
modified due to interaction of matter with vacuum. This interaction induces the
nonzero negative vacuum pressure inside the box, as a result the measured
osmotic pressure becomes smaller than the matter pressure. As distinct from the
Casimir effect, this induced vacuum pressure is the bulk effect and does not
depend on the size of the box. This effect dominates in the thermodynamic limit
of the infinite volume of the box. Analog of this effect has been observed in
the dilute solution of 3He in liquid 4He, where the superfluid 4He plays the
role of the non-relativistic quantum vacuum, and 3He atoms play the role of
matter.Comment: 5 pages, 1 figure, JETP Lett. style, version accepted in JETP Letter
Stationary Einstein-Maxwell fields in arbitrary dimensions
The Einstein-Maxwell equations in D-dimensions admitting (D-3) commuting
Killing vector fields have been investigated. The existence of the electric,
magnetic and twist potentials have been proved. The system is formulated as the
harmonic map coupled to gravity on three-dimensional base space generalizing
the Ernst system in the four-dimensional stationary Einstein-Maxwell theory.
Some classes of the new exact solutions have been provided, which include the
electro-magnetic generalization of the Myers-Perry solution, which describes
the rotating black hole immersed in a magnetic universe, and the static charged
black ring solution.Comment: 26 page
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