371 research outputs found
Typicality versus thermality: An analytic distinction
In systems with a large degeneracy of states such as black holes, one expects
that the average value of probe correlation functions will be well approximated
by the thermal ensemble. To understand how correlation functions in individual
microstates differ from the canonical ensemble average and from each other, we
study the variances in correlators. Using general statistical considerations,
we show that the variance between microstates will be exponentially suppressed
in the entropy. However, by exploiting the analytic properties of correlation
functions we argue that these variances are amplified in imaginary time,
thereby distinguishing pure states from the thermal density matrix. We
demonstrate our general results in specific examples and argue that our results
apply to the microstates of black holes.Comment: 22 pages + appendices, 3 eps figure
Very high quality factor measured in annealed fused silica
We present the results of quality factor measurements for rod samples made of
fused silica. To decrease the dissipation we annealed our samples. The highest
quality factor that we observed was for a mode at
384 Hz. This is the highest published value of in fused silica measured to
date.Comment: 8 pages, 2 figure
An Exact Fluctuating 1/2-BPS Configuration
This work explores the role of thermodynamic fluctuations in the two
parameter giant and superstar configurations characterized by an ensemble of
arbitrary liquid droplets or irregular shaped fuzzballs. Our analysis
illustrates that the chemical and state-space geometric descriptions exhibit an
intriguing set of exact pair correction functions and the global correlation
lengths. The first principle of statistical mechanics shows that the possible
canonical fluctuations may precisely be ascertained without any approximation.
Interestingly, our intrinsic geometric study exemplifies that there exist exact
fluctuating 1/2-BPS statistical configurations which involve an ensemble of
microstates describing the liquid droplets or fuzzballs. The Gaussian
fluctuations over an equilibrium chemical and state-space configurations
accomplish a well-defined, non-degenerate, curved and regular intrinsic
Riemannian manifolds for all physically admissible domains of black hole
parameters. An explicit computation demonstrates that the underlying chemical
correlations involve ordinary summations, whilst the state-space correlations
may simply be depicted by standard polygamma functions. Our construction
ascribes definite stability character to the canonical energy fluctuations and
to the counting entropy associated with an arbitrary choice of excited boxes
from an ensemble of ample boxes constituting a variety of Young tableaux.Comment: Minor changes, added references, 30 pages, 4 figures, PACS numbers:
04.70.-s: Physics of black holes; 04.70.-Bw: Classical black holes; 04.50.Gh
Higher-dimensional black holes, black strings, and related objects; 04.60.Cf
Gravitational aspects of string theory, accepted for publication in JHE
Superconductivity, Electron Paramagnetic Resonance, and Raman Scattering Studies of Heterofullerides with Cs and Mg
In the present study, the results of investigation of physical properties of heterofullerides A3−xMxC60 (A=K, Rb, Cs, M=Be, Mg, Ca, Al, Fe, Tl, x=1,2); as well as RbCsTlC60, KCsTlC60, and KMg2C60 are described. All of the fullerides were synthesized by the exchange reactions of alkaline fullerides with anhydrous metal halides. Superconductivity was found in RbCsTlC60 and KCsTlC60
Optical and transport properties of short period InAs/GaAs superlattices near quantum dot formation
We have investigated the optical and transport properties of MBE grown
short-period superlattices of InAs/GaAs with different numbers of periods (3 <=
N <= 24) and a total thickness 14 nm. Bandstructure calculations show that
these superlattices represent a quantum well with average composition
In_0.16Ga_0.84As. The electron wave functions are only slightly modulated by
the superlattice potential as compared to a single quantum well with the same
composition, which was grown as a reference sample. The photoluminescence, the
resistance, the Shubnikov-de Haas effect and the Hall effect have been measured
as a function of the InAs layer thickness Q in the range 0.33 <= Q <= 2.7
monolayers (ML). The electron densities range from 6.8 to 11.5x10^11 cm^-2 for
Q <= 2.0 ML. The photoluminescence and magnetotransport data show that only one
subband is occupied. When Q >= 2.7 ML quantum dots are formed and the metallic
type of conductivity changes to variable range hopping conductivity.Comment: 15 pages (incl.7 figures); pdf file; submitted to Semicond. Sci.
Techno
Electron transport and optical properties of shallow GaAs/InGaAs/GaAs quantum wells with a thin central AlAs barrier
Shallow GaAs/InGaAs/GaAs quantum well structures with and without a three
monolayer thick AlAs central barrier have been investigated for different well
widths and Si doping levels. The transport parameters are determined by
resistivity measurements in the temperature range 4-300 K and magnetotransport
in magnetic fields up to 12 T. The (subband) carrier concentrations and
mobilities are extracted from the Hall data and Shubnikov-de Haas oscillations.
We find that the transport parameters are strongly affected by the insertion of
the AlAs central barrier. Photoluminescence spectra, measured at 77 K, show an
increase of the transition energies upon insertion of the barrier. The
transport and optical data are analyzed with help of self-consistent
calculations of the subband structure and envelope wave functions. Insertion of
the AlAs central barrier changes the spatial distribution of the electron wave
functions and leads to the formation of hybrid states, i.e. states which extend
over the InGaAs and the delta-doped layer quantum wells.Comment: 14 pages, pdf fil
Emission from the D1D5 CFT: Higher Twists
We study a certain class of nonextremal D1D5 geometries and their ergoregion
emission. Using a detailed CFT computation and the formalism developed in
arXiv:0906.2015 [hep-th], we compute the full spectrum and rate of emission
from the geometries and find exact agreement with the gravity answer.
Previously, only part of the spectrum had been reproduced using a CFT
description. We close with a discussion of the context and significance of the
calculation.Comment: 39 pages, 6 figures, late
On the existence of supergravity duals to D1--D5 CFT states
We define a metric operator in the 1/2-BPS sector of the D1-D5 CFT, the
eigenstates of which have a good semi-classical supergravity dual; the
non-eigenstates cannot be mapped to semi-classical gravity duals. We also
analyse how the data defining a CFT state manifests itself in the gravity side,
and show that it is arranged into a set of multipoles. Interestingly, we find
that quantum mechanical interference in the CFT can have observable
manifestations in the semi-classical gravity dual. We also point out that the
multipoles associated to the normal statistical ensemble fluctuate wildly,
indicating that the mixed thermal state should not be associated to a
semi-classical geometry.Comment: 22 pages, 2 figures. v2 : references added, typos correcte
Excitations in the deformed D1D5 CFT
We perform some simple computations for the first order deformation of the
D1D5 CFT off its orbifold point. It had been shown earlier that under this
deformation the vacuum state changes to a squeezed state (with the further
action of a supercharge). We now start with states containing one or two
initial quanta and write down the corresponding states obtained under the
action of deformation operator. The result is relevant to the evolution of an
initial excitation in the CFT dual to the near extremal D1D5 black hole: when a
left and a right moving excitation collide in the CFT, the deformation operator
spreads their energy over a larger number of quanta, thus evolving the state
towards the infrared.Comment: 26 pages, Latex, 4 figure
Deforming the D1D5 CFT away from the orbifold point
The D1D5 brane bound state is believed to have an `orbifold point' in its
moduli space which is the analogue of the free Yang Mills theory for the D3
brane bound state. The supergravity geometry generated by D1 and D5 branes is
described by a different point in moduli space, and in moving towards this
point we have to deform the CFT by a marginal operator: the `twist' which links
together two copies of the CFT. In this paper we find the effect of this
deformation operator on the simplest physical state of the CFT -- the Ramond
vacuum. The twist deformation leads to a final state that is populated by pairs
of excitations like those in a squeezed state. We find the coefficients
characterizing the distribution of these particle pairs (for both bosons and
fermions) and thus write this final state in closed form.Comment: 30 pages, 4 figures, Late
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