299 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
Single Event Effects in the Pixel readout chip for BTeV
In future experiments the readout electronics for pixel detectors is required
to be resistant to a very high radiation level. In this paper we report on
irradiation tests performed on several preFPIX2 prototype pixel readout chips
for the BTeV experiment exposed to a 200 MeV proton beam. The prototype chips
have been implemented in commercial 0.25 um CMOS processes following radiation
tolerant design rules. The results show that this ASIC design tolerates a large
total radiation dose, and that radiation induced Single Event Effects occur at
a manageable level.Comment: 15 pages, 6 Postscript figure
Non-supersymmetric Attractors in Born-Infeld Black Holes with a Cosmological Constant
We investigate the attractor mechanism for spherically symmetric extremal
black holes in Einstein-Born-Infeld-dilaton theory of gravity in
four-dimensions, in the presence of a cosmological constant. We look for
solutions analytic near the horizon by using perturbation method. It is shown
that the values of the scalar fields at the horizon are only dependent on the
charges carried by the black hole and are irrelevant in their asymptotic
values. This analysis supports the validity of non-supersymmetric attractors in
the presence of higher derivative interactions in the gauge fields part and in
non-asymptotically flat spacetime.Comment: 18 pages, no figu
Comments on Heterotic Flux Compactifications
In heterotic flux compactification with supersymmetry, three different
connections with torsion appear naturally, all in the form .
Supersymmetry condition carries , the Dirac operator has , and
higher order term in the effective action involves . With a view toward
the gauge sector, we explore the geometry with such torsions. After reviewing
the supersymmetry constraints and finding a relation between the scalar
curvature and the flux, we derive the squared form of the zero mode equations
for gauge fermions. With \d H=0, the operator has a positive potential term,
and the mass of the unbroken gauge sector appears formally positive definite.
However, this apparent contradiction is avoided by a no-go theorem that the
compactification with and \d H=0 is necessarily singular, and the
formal positivity is invalid. With \d H\neq 0, smooth compactification
becomes possible. We show that, at least near smooth supersymmetric solution,
the size of should be comparable to that of \d H and the consistent
truncation of action has to keep term. A warp factor equation of
motion is rewritten with contribution included precisely, and
some limits are considered.Comment: 31 pages, a numerical factor correcte
Entropy Function for Non-extremal D1D5 and D2D6NS5-branes
We apply the entropy function formalism to non-extremal D1D5 and
D2D6NS5-branes whose throat approximation is given by the Schwarzschild black
hole in AdS_3\times S^3\times T^4 and AdS_3\times S^2\times S^1\times T^4,
respectively. We find the Bekenstein-Hawking entropy and the (alpha')^3R^4
corrections from the value of the entropy function at its saddle point. While
the higher derivative terms have no effect on the temperature, they decrease
the value of the entropy.Comment: 17 Pages, Latex file; Minor additions, version published in JHE
Non-extremal black holes from the generalised r-map
We review the timelike dimensional reduction of a class of five-dimensional
theories that generalises 5D, N = 2 supergravity coupled to vector multiplets.
As an application we construct instanton solutions to the four-dimensional
Euclidean theory, and investigate the criteria for solutions to lift to static
non-extremal black holes in five dimensions.
We focus specifically on two classes of models: STU-like models, and models
with a block diagonal target space metric. For STU-like models the second order
equations of motion of the four-dimensional theory can be solved explicitly,
and we obtain the general solution. For block diagonal models we find a
restricted class of solutions, where the number of independent scalar fields
depends on the number of blocks. When lifting these solutions to five
dimensions we show, by explicit calculation, that one obtains static
non-extremal black holes with scalar fields that take finite values on the
horizon only if the number of integration constants reduces by exactly half.Comment: 22 pages. Based on talk by OV at "Black Objects in Supergravity
School" (BOSS2011), INFN, Frascati, Italy, 9-13 May, 201
Fundamental Superstrings as Holograms
The worldsheet of a macroscopic fundamental superstring in the Green-Schwarz
light-cone gauge is viewed as a possible boundary hologram of the near horizon
region of a small black string. For toroidally compactified strings, the
hologram has global symmetries of AdS_3 \times S^{d-1} \times T^{8-d}, (d
=3,..,8), only some of which extend to local conformal symmetries. We construct
the bulk string theory in detail for the particular case of d=3. The symmetries
of the hologram are correctly reproduced from this exact worldsheet description
in the bulk. Moreover, the central charge of the boundary Virasoro algebra
obtained from the bulk agrees with the Wald entropy of the associated small
black holes. This construction provides an exact CFT description of the near
horizon region of small black holes both in Type-II and heterotic string theory
arising from multiply wound fundamental superstrings.Comment: 46 pages, JHEP style. v2: Comments, references adde
Approximate solution of the Duffin-Kemmer-Petiau equation for a vector Yukawa potential with arbitrary total angular momenta
The usual approximation scheme is used to study the solution of the
Duffin-Kemmer-Petiau (DKP) equation for a vector Yukawa potential in the
framework of the parametric Nikiforov-Uvarov (NU) method. The approximate
energy eigenvalue equation and the corresponding wave function spinor
components are calculated for arbitrary total angular momentum in closed form.
Further, the approximate energy equation and wave function spinor components
are also given for case. A set of parameter values is used to obtain the
numerical values for the energy states with various values of quantum levelsComment: 17 pages; Communications in Theoretical Physics (2012). arXiv admin
note: substantial text overlap with arXiv:1205.0938, and with
arXiv:quant-ph/0410159 by other author
D-branes in Nongeometric Backgrounds
"T-fold" backgrounds are generically-nongeometric compactifications of string
theory, described by T^n fibrations over a base N with transition functions in
the perturbative T-duality group. We review Hull's doubled torus formalism,
which geometrizes these backgrounds, and use the formalism to constrain the
D-brane spectrum (to leading order in g_s and alpha') on T^n fibrations over
S^1 with O(n,n;Z) monodromy. We also discuss the (approximate) moduli space of
such branes and argue that it is always geometric. For a D-brane located at a
point on the base N, the classical ``D-geometry'' is a T^n fibration over a
multiple cover of N.Comment: 29 pages; uses harvmac.tex; v2: substantial revision throughou
Compactifications of Heterotic Theory on Non-Kahler Complex Manifolds: I
We study new compactifications of the SO(32) heterotic string theory on
compact complex non-Kahler manifolds. These manifolds have many interesting
features like fewer moduli, torsional constraints, vanishing Euler character
and vanishing first Chern class, which make the four-dimensional theory
phenomenologically attractive. We take a particular compact example studied
earlier and determine various geometrical properties of it. In particular we
calculate the warp factor and study the sigma model description of strings
propagating on these backgrounds. The anomaly cancellation condition and
enhanced gauge symmetry are shown to arise naturally in this framework, if one
considers the effect of singularities carefully.
We then give a detailed mathematical analysis of these manifolds and
construct a large class of them. The existence of a holomorphic (3,0) form is
important for the construction. We clarify some of the topological properties
of these manifolds and evaluate the Betti numbers. We also determine the
superpotential and argue that the radial modulus of these manifolds can
actually be stabilized.Comment: 75 pages, Harvmac, no figures; v2: Some new results added, typos
corrected and references updated. Final version to appear in JHE
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