3,104 research outputs found
Instability of a two-dimensional extremal black hole
We consider the perturbation of tachyon about the extremal ground state of a
two-dimensional (2D) electrically charged black hole. It is found that the
presenting potential to on-coming tachyonic wave takes a double-humped barrier
well. This allows an exponentially growing mode with respect to time. This
extremal ground state is classically unstable. We conclude that the 2D extremal
electrically charged black hole cannot be a candidate for the stable endpoint
of the Hawking evaporation.Comment: 9 pages 2 figures, RevTeX, to be published in Phys. Rev D, to obtain
gifures contact Author ([email protected]
The Fisher-Rao metric for projective transformations of the line
A conditional probability density function is defined for measurements arising from a projective transformation of the line. The conditional density is a member of a parameterised family of densities in which the parameter takes values in the three dimensional manifold of projective transformations of the line. The Fisher information of the family defines on the manifold a Riemannian metric known as the Fisher-Rao metric. The Fisher-Rao metric has an approximation which is accurate if the variance of the measurement errors is small. It is shown that the manifold of parameter values has a finite volume under the approximating metric.
These results are the basis of a simple algorithm for detecting those projective transformations of the line which are compatible with a given set of measurements. The algorithm searches a finite list of representative parameter values for those values compatible with the measurements. Experiments with the algorithm suggest that it can detect a projective transformation of the line even when the correspondences between the components of the measurements in the domain and the range of the projective transformation are unknown
Cosmic holographic bounds with UV and IR cutoffs
We introduce the cosmic holographic bounds with two UV and IR cutoff scales,
to deal with both the inflationary universe in the past and dark energy in the
future. To describe quantum fluctuations of inflation on sub-horizon scales, we
use the Bekenstein-Hawking energy bound. However, it is not justified that the
D-bound is satisfied with the coarse-grained entropy. The Hubble bounds are
introduced for classical fluctuations of inflation on super-horizon scales. It
turns out that the Hubble entropy bound is satisfied with the entanglement
entropy and the Hubble temperature bound leads to a condition for the slow-roll
inflation. In order to describe the dark energy, we introduce the holographic
energy density which is the one saturating the Bekenstein-Hawking energy bound
for a weakly gravitating system. Here the UV (IR) cutoff is given by the Planck
scale (future event horizon), respectively. As a result, we find the close
connection between quantum and classical fluctuations of inflation, and dark
energy.Comment: 15page
BTZ black hole and quantum Hall effect in the bulk/boundary dynamics
We point out an interesting analogy between the BTZ black hole and QHE
(Quantum Hall effect) in the (2+1)-dimensional bulk/boundary theories. It is
shown that the Chern-Simons/Liouville(Chern-Simons/chiral boson) is an
effective description for the BTZ black hole (QHE). Also the
IR(bulk)-UV(boundary) connection for a black hole information bound is realized
as the UV(low-lying excitations on bulk)-IR(long-range excitations on boundary)
connection in the QHE. An inflow of conformal anomaly( central charge)
onto the timelike boundary of AdS by the Noether current corresponds to an
inflow of chiral anomaly onto the edge of disk by the Hall current.Comment: 8 pages, this version to appear in Phys. Rev.
Unitarity issue in BTZ black holes
We study the wave equation for a massive scalar in three-dimensional
AdS-black hole spacetimes to understand the unitarity issues in a semiclassical
way. Here we introduce four interesting spacetimes: the non-rotating BTZ black
hole (NBTZ), pure AdS spacetime (PADS), massless BTZ black hole (MBTZ), and
extremal BTZ black hole (EBTZ). Our method is based on the potential analysis
and solving the wave equation to find the condition for the frequency
exactly. In the NBTZ case, one finds the quasinormal (complex and discrete)
modes which signals for a non-unitary evolution. Real and discrete modes are
found for the PADS case, which means that it is unitary obviously. On the other
hand, we find real and continuous modes for the two extremal black holes of
MBTZ and EBTZ. It suggests that these could be candidates for the unitary
system.Comment: 14 pages, contracted version to appear in MPL
Nonpropagation of massive mode on AdS2 in topologically massive gravity
Making use of Achucarro-Ortiz (AO) type of dimensional reduction, we study
the topologically massive gravity with a negative cosmological constant on AdS2
spacetimes. For a constant dilaton, this two-dimensional model also admits
three AdS2 vacuum solutions, which are related to two AdS3 and warped AdS3
backgrounds with an identification upon uplifting three dimensions. We carry
out the perturbation analysis around these backgrounds to find what is a
physically propagating field. However, it turns out that there is no
propagating massive mode on AdS2 background, in contrast to the Kaluza-Klein
(KK) type of dimensional reduction. We note that two dimensionally reduced
actions are different and thus, the non-equivalence of their on-shell
amplitudes is obtained.Comment: 19 pages, version to appear in EPJ
Phase transitions for the Lifshitz black holes
We study possibility of phase transitions between Lifshitz black holes and
other configurations by using free energies explicitly. A phase transition
between Lifshitz soliton and Lifshitz black hole might not occur in three
dimensions. We find that a phase transition between Lifshitz and BTZ black
holes unlikely occurs because they have different asymptotes. Similarly, we
point out that any phase transition between Lifshitz and black branes unlikely
occurs in four dimensions since they have different asymptotes. This is
consistent with a necessary condition for taking a phase transition in the
gravitational system, which requires the same asymptote.Comment: 19 pages, 7 figures, a revised version to appear in EPJ
Slowly rotating black holes in the Horava-Lifshitz gravity
We investigate slowly rotating black holes in the Ho\v{r}ava-Lifshitz (HL)
gravity. For and , we find a slowly rotating black
hole of the Kehagias-Sfetsos solution in asymptotically flat spacetimes. We
discuss their thermodynamic properties by computing mass, temperature, angular
momentum, and angular velocity on the horizon.Comment: 12 pages, no figures, version to appear in EPJ
Concurrent Magnetic and Metal-Insulator Transitions in (Eu,Sm)B_6 Single Crystals
The effects of magnetic doping on a EuB_6 single crystal were investigated
based on magnetic and transport measurements. A modest 5% Sm substitution for
Eu changes the magnetic and transport properties dramatically and gives rise to
concurrent antiferromagnetic and metal-insulator transitions (MIT) from
ferromagnetic MIT for EuB6. Magnetic doping simultaneously changes the
itinerant carrier density and the magnetic interactions. We discuss the origin
of the concurrent magnetic MIT in (Eu,Sm)B_6.Comment: 13 pages, 3 figures, final version to appear in Appl. Phys. Lett
- …