865 research outputs found
The Foaming Three-Charge Black Hole
We find a very large set of smooth horizonless geometries that have the same
charges and angular momenta as the five-dimensional, maximally-spinning,
three-charge, BPS black hole (J^2 = Q^3). Our solutions are constructed using a
four-dimensional Gibbons-Hawking base space that has a very large number of
two-cycles. The entropy of our solutions is proportional to Q^(1/2). In the
same class of solutions we also find microstates corresponding to zero-entropy
black rings, and these are related to the microstates of the black hole by
continuous deformations.Comment: 14 pages, harvma
Mergers and Typical Black Hole Microstates
We use mergers of microstates to obtain the first smooth horizonless
microstate solutions corresponding to a BPS three-charge black hole with a
classically large horizon area. These microstates have very long throats, that
become infinite in the classical limit; nevertheless, their curvature is
everywhere small. Having a classically-infinite throat makes these microstates
very similar to the typical microstates of this black hole. A rough CFT
analysis confirms this intuition, and indicates a possible class of dual CFT
microstates.
We also analyze the properties and the merging of microstates corresponding
to zero-entropy BPS black holes and black rings. We find that these solutions
have the same size as the horizon size of their classical counterparts, and we
examine the changes of internal structure of these microstates during mergers.Comment: 49 pages, 5 figures. v2 references adde
Resolving the Structure of Black Holes: Philosophizing with a Hammer
We give a broad conceptual review of what we have learned about black holes
and their microstate structure from the study of microstate geometries and
their string theory limits. We draw upon general relativity, supergravity,
string theory and holographic field theory to extract universal ideas and
structural features that we expect to be important in resolving the information
problem and understanding the microstate structure of Schwarzschild and Kerr
black holes. In particular, we emphasize two conceptually and physically
distinct ideas, with different underlying energy scales: a) the transition that
supports the microstate structure and prevents the formation of a horizon and
b) the representation of the detailed microstate structure itself in terms of
fluctuations around the transitioned state. We also show that the supergravity
mechanism that supports microstate geometries becomes, in the string theory
limit, either brane polarization or the excitation of non-Abelian degrees of
freedom. We thus argue that if any mechanism for supporting structure at the
horizon scale is to be given substance within string theory then it must be
some manifestation of microstate geometries.Comment: 32 pages + reference
Bubbles on Manifolds with a U(1) Isometry
We investigate the construction of five-dimensional, three-charge
supergravity solutions that only have a rotational U(1) isometry. We show that
such solutions can be obtained as warped compactifications with a singular
ambi-polar hyper-Kahler base space and singular warp factors. We show that the
complete solution is regular around the critical surface of the ambi-polar
base. We illustrate this by presenting the explicit form of the most general
supersymmetric solutions that can be obtained from an Atiyah-Hitchin base space
and its ambi-polar generalizations. We make a parallel analysis using an
ambi-polar generalization of the Eguchi-Hanson base space metric. We also show
how the bubbling procedure applied to the ambi-polar Eguchi-Hanson metric can
convert it to a global AdS_2xS^3 compactification.Comment: 33 pages, 5 figures, LaTeX; references adde
From Andreev bound states to Majorana fermions in topological wires on superconducting substrates : a story of mutation
We study the proximity effect in a topological nanowire tunnel coupled to an
s-wave superconducting substrate. We use a general Green's function approach
that allows us to study the evolution of the Andreev bound states in the wire
into Majorana fermions. We show that the strength of the tunnel coupling
induces a topological transition in which the Majorana fermionic states can be
destroyed when the coupling is very strong. Moreover, we provide a
phenomenologial study of the effects of disorder in the superconductor on the
formation of Majorana fermions. We note a non-trivial effect of a quasiparticle
broadening term which can take the wire from a topological into a
non-topological phase in certain ranges of parameters. Our results have also
direct consequences for a nanowire coupled to an inhomogenous superconductor
Black Rings in Taub-NUT
We construct the most generic three-charge, three-dipole-charge, BPS
black-ring solutions in a Taub-NUT background. These solutions depend on seven
charges and six moduli, and interpolate between a four-dimensional black hole
and a five-dimensional black ring. They are also instrumental in determining
the correct microscopic description of the five-dimensional BPS black rings.Comment: 16 pages, harvma
Determining the spin-orbit coupling via spin-polarized spectroscopy of magnetic impurities
We study the spin-resolved spectral properties of the impurity states
associated to the presence of magnetic impurities in two-dimensional, as well
as one-dimensional systems with Rashba spin-orbit coupling. We focus on Shiba
bound states in superconducting materials, as well as on impurity states in
metallic systems. Using a combination of a numerical T-matrix approximation and
a direct analytical calculation of the bound state wave function, we compute
the local density of states (LDOS) together with its Fourier transform (FT). We
find that the FT of the spin-polarized LDOS, a quantity accessible via
spin-polarized STM, allows to accurately extract the strength of the spin-orbit
coupling. Also we confirm that the presence of magnetic impurities is strictly
necessary for such measurement, and that non-spin-polarized experiments cannot
have access to the value of the spin-orbit coupling.Comment: 26 pages, 6 figure
Non-extremal Black Hole Microstates: Fuzzballs of Fire or Fuzzballs of Fuzz ?
We construct the first family of microstate geometries of near-extremal black
holes, by placing metastable supertubes inside certain scaling supersymmetric
smooth microstate geometries. These fuzzballs differ from the classical black
hole solution macroscopically at the horizon scale, and for certain probes the
fluctuations between various fuzzballs will be visible as thermal noise far
away from the horizon. We discuss whether these fuzzballs appear to infalling
observers as fuzzballs of fuzz or as fuzzballs of fire. The existence of these
solutions suggests that the singularity of non-extremal black holes is resolved
all the way to the outer horizon and this "backwards in time" singularity
resolution can shed light on the resolution of spacelike cosmological
singularities.Comment: 34 pages, 10 figure
Double-gap superconducting proximity effect in nanotubes
We theoretically explore the possibility of a superconducting proximity
effect in single-walled metallic carbon nanotubes due to the presence of a
superconducting substrate. An unconventional double-gap situation can arise in
the two bands for nanotubes of large radius wherein the tunneling is (almost)
symmetric in the two sublattices. In such a case, a proximity effect can take
place in the symmetric band below a critical experimentally-accessible Coulomb
interaction strength in the nanotube. Furthermore, due to interactions in the
nanotube, the appearance of a BCS gap in this band stabilizes superconductivity
in the other band at lower temperatures. We also discuss the scenario of highly
asymmetric tunneling and show that this case too supports double-gap
superconductivity.Comment: 4 pages, 2 figure
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