437 research outputs found
Kerr/CFT Correspondence in the Low Energy Limit of Heterotic String Theory
We investigate the recently proposed Kerr/CFT correspondence in the context
of heterotic string theory. The Kerr/CFT correspondence states that the
near-horizon states of an extremal four (or higher) dimensional black hole
could be identified with a certain chiral conformal field theory under the
conjecture that the central charges from the non-gravitational fields vanish.
The corresponding Virasoro algebra is generated by a class of diffeomorphisms
which preserves the appropriate boundary conditions on the near-horizon
geometry. To understand the chiral conformal field theory, we consider the
class of extremal Kerr-Sen black hole (that contains three non-gravitational
fields) as a class of solutions in the low energy limit (effective field
theory) of heterotic string theory. We derive the expression of the conserved
charges for the extremal Kerr-Sen solutions that contain dilaton, abelian gauge
filed and antisymmetric tensor filed. We confirm and extend the validity of the
conjecture (that the central charges from the non-gravitational fields vanish)
for theories including antisymmetric tensor fields. We combine the calculated
central charges with the expected form of the temperature using the Cardy
formula to obtain the entropy of the extremal black hole microscopically; in
agreement with the macroscopic Bekenstein-Hawking entropy of the extremal black
hole.Comment: 14 pages, a few sentences added to the introduction, version to
appear in JHE
Yet Another Realization of Kerr/CFT Correspondence
The correspondence between the Kerr black hole and a boundary CFT has been
conjectured recently. The conjecture has been proposed first only for the half
of the CFT, namely for left movers. For right movers, the correspondence has
been also found out through the suitable asymptotic boundary condition.
However, the boundary conditions for these two studies are exclusive to each
other. The boundary condition for left movers does not allow the symmetry of
right movers, and vice versa. We propose new boundary condition which allows
both of left and right movers.Comment: 6 pages, references adde
SNAP-8 corrosion program Quarterly progress report, period ending 31 May 1965
Differences in corrosion and mass transfer rates in corrosion loops for SNAP-8 system and effectiveness of cold trapping in reducing hydrogen concentratio
Snap-8 corrosion program quarterly progress report, period ending 28 feb. 1965
SNAP-8 corrosion program - hydrogen solubility in sodium-potassium, permeability of hydrogen and deuterum through stainless steel, and phase equilibri
CFT Duals for Extreme Black Holes
It is argued that the general four-dimensional extremal Kerr-Newman-AdS-dS
black hole is holographically dual to a (chiral half of a) two-dimensional CFT,
generalizing an argument given recently for the special case of extremal Kerr.
Specifically, the asymptotic symmetries of the near-horizon region of the
general extremal black hole are shown to be generated by a Virasoro algebra.
Semiclassical formulae are derived for the central charge and temperature of
the dual CFT as functions of the cosmological constant, Newton's constant and
the black hole charges and spin. We then show, assuming the Cardy formula, that
the microscopic entropy of the dual CFT precisely reproduces the macroscopic
Bekenstein-Hawking area law. This CFT description becomes singular in the
extreme Reissner-Nordstrom limit where the black hole has no spin. At this
point a second dual CFT description is proposed in which the global part of the
U(1) gauge symmetry is promoted to a Virasoro algebra. This second description
is also found to reproduce the area law. Various further generalizations
including higher dimensions are discussed.Comment: 18 pages; v2 minor change
The Central Charge of the Warped AdS^3 Black Hole
The AdS/CFT conjecture offers the possibility of a quantum description for a
black hole in terms of a CFT. This has led to the study of general AdS^3 type
black holes with a view to constructing an explicit toy quantum black hole
model. Such a CFT description would be characterized by its central charge and
the dimensions of its primary fields. Recently the expression for the central
charges (C_L, C_R) of the CFT dual to the warped AdS^3 have been determined
using asymptotic symmetry arguments. The central charges depend, as expected,
on the warping factor. We show that topological arguments, used by Witten to
constrain central charges for the BTZ black hole, can be generalized to deal
with the warped AdS^3 case. Topology constrains the warped factor to be
rational numbers while quasinormal modes are conjectured to give the dimensions
of primary fields. We find that in the limit when warping is large or when it
takes special rational values the system tends to Witten's conjectured unique
CFT's with central charges that are multiples of 24.Comment: 6 pages, Latex fil
Constructing near-horizon geometries in supergravities with hidden symmetry
We consider the classification of near-horizon geometries in a general
two-derivative theory of gravity coupled to abelian gauge fields and uncharged
scalars in four and five dimensions, with one and two commuting rotational
symmetries respectively. Assuming that the theory of gravity reduces to a 3d
non-linear sigma model (as is typically the case for ungauged supergravities),
we show that the functional form of any such near-horizon geometry may be
determined. As an example we apply this to five dimensional minimal
supergravity. We also construct an example of a five parameter near-horizon
geometry solution to this theory with S^1 X S^2 horizon topology. We discuss
its relation to the near-horizon geometries of the yet to be constructed
extremal black rings with both electric and dipole charges.Comment: Latex, 30 pages. v2: discussion in section 5 modified and improved,
other minor changes, references adde
String Theory on Warped AdS_3 and Virasoro Resonances
We investigate aspects of holographic duals to time-like warped AdS_3
space-times--which include G\"odel's universe--in string theory. Using
worldsheet techniques similar to those that have been applied to AdS_3
backgrounds, we are able to identify space-time symmetry algebras that act on
the dual boundary theory. In particular, we always find at least one Virasoro
algebra with computable central charge. Interestingly, there exists a dense set
of points in the moduli space of these models in which there is actually a
second commuting Virasoro algebra, typically with different central charge than
the first. We analyze the supersymmetry of the backgrounds, finding related
enhancements, and comment on possible interpretations of these results. We also
perform an asymptotic symmetry analysis at the level of supergravity, providing
additional support for the worldsheet analysis.Comment: 24 pages + appendice
Low-cost Sensors on Unmanned Aerial Vehicles: an Advancement in Air Quality Measurement
With the rapid industrialization and the current status of climate change, air pollution has become a global concern. However, detecting atmospheric pollutants is costly, time-consuming, and cumbersome. Currently, the Environmental Protection Agency (US EPA) utilizes filter-based techniques in their federal reference and federal equivalent methods (FRM and FEM, respectively) to measure ground-based particulate matter (PM) levels in the atmosphere. Recently, the development of low-cost sensors has helped in combatting the high cost associated with acquiring these measurements. These sensors allow for PM concentrations to be measured at high resolutions. Due to their surface mounted nature, the EPA’s methods are limited in measuring the concentrations of PM at the ground-level. Hence, they lack the ability of determining the concentrations at various altitudes, which is important in characterizing the origin and the formation pathway of such pollutants. To address these shortcomings, we propose placing multiple low-cost sensors on Unmanned Aerial Vehicles (UAVs) to measure the concentrations of PM in Daytona Beach, FL. Sampling will be conducted seasonally, and the PM concentrations will be compared to their counterpart observations obtained using the EPA’s methods. The findings of this study should aid in the development of low-cost air pollution sensors that can be hosted on UAVs. This work promises to be advantageous in detecting air pollutants in both congested and remote areas
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