445 research outputs found
The Entropy Function for the Black Holes of Nariai Class
Based on the fact that the near horizon geometry of the extremal
Schwarzschild-de Sitter black holes is Nariai geometry, we define the black
holes of Nariai class as the configuration whose near-horizon geometry is
factorized as two dimensional de Sitter space-time and some compact topology,
that is Nariai geometry. We extend the entropy function formalism to the case
of the black holes of Nariai class. The conventional entropy function (for the
extremal black holes) is defined as Legendre transformation of Lagrangian
density, thus the `Routhian density', over two dimensional anti-de Sitter. As
for the black holes of Nariai class, it is defined as {\em minus} `Routhian
density' over two dimensional de Sitter space-time. We found an exact agreement
of the result with Bekenstein-Hawking entropy. The higher order corrections are
nontrivial only when the space-time dimension is over four, that is, .
There is a subtlety as regards the temperature of the black holes of Nariai
class. We show that in order to be consistent with the near horizon geometry,
the temperature should be non-vanishing despite the extremality of the black
holes.Comment: references added, compatible with the published versio
Noncommutativity, generalized uncertainty principle and FRW cosmology
We consider the effects of noncommutativity and the generalized uncertainty
principle on the FRW cosmology with a scalar field. We show that, the
cosmological constant problem and removability of initial curvature singularity
find natural solutions in this scenarios.Comment: 8 pages, to appear in IJT
Ricci-flat deformation of orbifolds and localized tachyonic modes
We study Ricci-flat deformations of orbifolds in type II theory. We obtain a
simple formula for mass corrections to the twisted modes due to the
deformations, and apply it to originally tachyonic and massless states in
several examples. In the case of supersymmetric orbifolds, we find that
tachyonic states appear when the deformation breaks all the supersymmetries. We
also study nonsupersymmetric orbifolds C^2/Z_{2N(2N+1)}, which is T-dual to N
type 0 NS5-branes. For N>=2, we compute mass corrections for states, which have
string scale tachyonic masses. We find that the corrected masses coincide to
ones obtained by solving the wave equation for the tachyon field in the smeared
type 0 NS5-brane background geometry. For N=1, we show that the unstable mode
representing the bubble creation is the unique tachyonic mode.Comment: 20 pages, minor collection
Development of KAISTSAT-4 Expanding the Role of Small Satellite for Scientific Research
The fourth Korean small satellite, KAISTSAT-4, is under development by Satellite Technology Research Center (SaTReC) of the Korea Advanced Institute of Science and Technology (KAIST). The KAISTSAT-4 program was commenced on October 1998 with multiple mission objectives, which include exploring space science, deploying satellite-based data collection system and development of precision star sensor. Despite severe constraints on mass and size, these advanced science and engineering payloads are expected to deliver various useful results and exhibit the unique role of small satellite. We present an overview of the KAISTSAT-4 mission and describe its current status. Finally the prospect of future small satellite programs is briefly introduced
Effective Finite Temperature Partition Function for Fields on Non-Commutative Flat Manifolds
The first quantum correction to the finite temperature partition function for
a self-interacting massless scalar field on a dimensional flat manifold
with non-commutative extra dimensions is evaluated by means of dimensional
regularization, suplemented with zeta-function techniques. It is found that the
zeta function associated with the effective one-loop operator may be nonregular
at the origin. The important issue of the determination of the regularized
vacuum energy, namely the first quantum correction to the energy in such case
is discussed.Comment: amslatex, 14 pages, to appear in Phys. Rev.
Phenomenology of Particle Production and Propagation in String-Motivated Canonical Noncommutative Spacetime
We outline a phenomenological programme for the search of effects induced by
(string-motivated) canonical noncommutative spacetime. The tests we propose are
based, in analogy with a corresponding programme developed over the last few
years for the study of Lie-algebra noncommutative spacetimes, on the role of
the noncommutativity parameters in the dispersion relation. We focus on
the role of deformed dispersion relations in particle-production collision
processes, where the noncommutativity parameters would affect the threshold
equation, and in the dispersion of gamma rays observed from distant
astrophysical sources. We emphasize that the studies here proposed have the
advantage of involving particles of relatively high energies, and may therefore
be less sensitive to "contamination" (through IR/UV mixing) from the UV sector
of the theory. We also explore the possibility that the relevant deformation of
the dispersion relations could be responsible for the experimentally-observed
violations of the GZK cutoff for cosmic rays and could have a role in the
observation of hard photons from distant astrophysical sources.Comment: With respect to the experimental information available at the time of
writing version 1 of this manuscript (hep-th/0109191v1) the situation has
evolved significantly. Our remarks on the benefits of high-energy
observations found additional encouragement from the results reported in
hep-th/020925
Open Strings in Exactly Solvable Model of Curved Spacetime and PP-Wave Limit
In this paper we study the superstring version of the exactly solvable string
model constructed by Russo and Tseytlin. This model represents superstring
theory in a curved spacetime and can be seen as a generalization of the Melvin
background. We investigate D-branes in this model as probes of the background
geometry by constructing the boundary states. We find that spacetime
singularities in the model become smooth at high energy from the viewpoint of
open string. We show that there always exist bulk (movable) D-branes by the
effect of electric flux. The model also includes Nappi-Witten model as the
Penrose limit and supersymmetry is enhanced in the limit. We examine this
phenomenon in the open string spectrum. We also find the similar enhancement of
supersymmetry can be occurred in several coset models.Comment: Latex, 32 pages, typos corrected, references added, to appear in
JHEP, eq.(2.22) correcte
Transversely-intersecting D-branes at finite temperature and chiral phase transition
We consider Sakai-Sugimoto like models consisting of Dq-Dp-anti-Dp-branes
where flavor Dp and anti-Dp-branes transversely intersect color Dq-branes along
two (r+1)-dimensional subspaces. For some values of p and q, the theory of
intersections dynamically breaks non-Abelian chiral symmetry which is
holographically realized as a smooth connection of the flavor branes at some
point in the bulk of the geometry created by Dq-branes. We analyze the system
at finite temperature and map out different phases of the theory representing
chiral symmetry breaking and restoration. For q<5 we find that, unlike the
zero-temperature case, there exist two branches of smoothly-connected solutions
for the flavor branes, one getting very close to the horizon of the background
and the other staying farther away from it. At low temperatures, the solution
which stays farther away from the horizon determines the vacuum. For background
D5 and D6-branes we find that the flavor branes, like the zero temperature
case, show subtle behavior whose dual gauge theory interpretation is not clear.
We conclude with some comments on how chiral phase transition in these models
can be seen from their open string tachyon dynamics.Comment: 35 pages, 7 figures, minor changes, published versio
Observation of a Narrow Resonance of Mass 2.46 GeV/c^2 Decaying to D_s^*+ pi^0 and Confirmation of the D_sJ^* (2317) State
Using 13.5 inverse fb of e+e- annihilation data collected with the CLEO II
detector we have observed a narrow resonance in the Ds*+pi0 final state, with a
mass near 2.46 GeV. The search for such a state was motivated by the recent
discovery by the BaBar Collaboration of a narrow state at 2.32 GeV, the
DsJ*(2317)+ that decays to Ds+pi0. Reconstructing the Ds+pi0 and Ds*+pi0 final
states in CLEO data, we observe peaks in both of the corresponding
reconstructed mass difference distributions, dM(Dspi0)=M(Dspi0)-M(Ds) and
dM(Ds*pi0)=M(Ds*pi0)-M(Ds*), both of them at values near 350 MeV. We interpret
these peaks as signatures of two distinct states, the DsJ*(2317)+ plus a new
state, designated as the DsJ(2463)+. Because of the similar dM values, each of
these states represents a source of background for the other if photons are
lost, ignored or added. A quantitative accounting of these reflections confirms
that both states exist. We have measured the mean mass differences
= 350.0 +/- 1.2 [stat] +/- 1.0 [syst] MeV for the DsJ*(2317) state, and
= 351.2 +/- 1.7 [stat] +/- 1.0 [syst] MeV for the new DsJ(2463)+
state. We have also searched, but find no evidence, for decays of the two
states via the channels Ds*+gamma, Ds+gamma, and Ds+pi+pi-. The observations of
the two states at 2.32 and 2.46 GeV, in the Ds+pi0 and Ds*+pi0 decay channels
respectively, are consistent with their interpretations as (c anti-strange)
mesons with orbital angular momentum L=1, and spin-parities of 0+ and 1+.Comment: 16 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLNS, version to be published in Physical
Review D; minor modifications and fixes to typographical errors, plus an
added section on production properties. The main results are unchanged; they
supersede those reported in hep-ex/030501
Measurement of the Charge Asymmetry in
We report on a search for a CP-violating asymmetry in the charmless hadronic
decay B -> K*(892)+- pi-+, using 9.12 fb^-1 of integrated luminosity produced
at \sqrt{s}=10.58 GeV and collected with the CLEO detector. We find A_{CP}(B ->
K*(892)+- pi-+) = 0.26+0.33-0.34(stat.)+0.10-0.08(syst.), giving an allowed
interval of [-0.31,0.78] at the 90% confidence level.Comment: 7 pages postscript, also available through
http://w4.lns.cornell.edu/public/CLNS, submitted to PR
- …