25,959 research outputs found
Unlocking the Axion-Dilaton in 5D Supergravity
We revisit supersymmetric solutions to five dimensional ungauged N=1
supergravity with dynamic hypermultiplets. In particular we focus on a
truncation to the axion-dilaton contained in the universal hypermultiplet. The
relevant solutions are fibrations over a four-dimensional Kahler base with a
holomorphic axion-dilaton. We focus on solutions with additional symmetries and
classify Killing vectors which preserve the additional structure imposed by
supersymmetry; in particular we extend the existing classification of solutions
with a space-like U(1) isometry to the case where the Killing vector is
rotational. We elaborate on general geometrical aspects which we illustrate in
some simple examples. We especially discuss solutions describing the
backreaction of M2-branes, which for example play a role in the black hole
deconstruction proposal for microstate geometries.Comment: 48 pages + appendices, 5 figure
Elasticity, fluctuations and vortex pinning in ferromagnetic superconductors: A "columnar elastic glass"
We study the elasticity, fluctuations and pinning of a putative spontaneous
vortex solid in ferromagnetic superconductors. Using a rigorous thermodynamic
argument, we show that in the idealized case of vanishing crystalline pinning
anisotropy the long-wavelength tilt modulus of such a vortex solid vanishes
identically, as guaranteed by the underlying rotational invariance. The
vanishing of the tilt modulus means that, to lowest order, the associated
tension elasticity is replaced by the softer, curvature elasticity. The effect
of this is to make the spontaneous vortex solid qualitatively more susceptible
to the disordering effects of thermal fluctuations and random pinning. We study
these effects, taking into account the nonlinear elasticity, that, in three
dimensions, is important at sufficiently long length scales, and showing that a
``columnar elastic glass'' phase of vortices results. This phase is controlled
by a previously unstudied zero-temperature fixed point and it is characterized
by elastic moduli that have universal strong wave-vector dependence out to
arbitrarily long length scales, leading to non-Hookean elasticity. We argue
that, although translationally disordered for weak disorder, the columnar
elastic glass is stable against the proliferation of dislocations and is
therefore a topologically ordered {\em elastic} glass. As a result, the
phenomenology of the spontaneous vortex state of isotropic magnetic
superconductors differs qualitatively from a conventional,
external-field-induced mixed state. For example, for weak external fields ,
the magnetic induction scales {\em universally} like , with .Comment: Minor editorial changes, version to be published in PRB, 39 pages, 7
figure
Generating asymptotically plane wave spacetimes
In an attempt to study asymptotically plane wave spacetimes which admit an
event horizon, we find solutions to vacuum Einstein's equations in arbitrary
dimension which have a globally null Killing field and rotational symmetry. We
show that while such solutions can be deformed to include ones which are
asymptotically plane wave, they do not posses a regular event horizon. If we
allow for additional matter, such as in supergravity theories, we show that it
is possible to have extremal solutions with globally null Killing field, a
regular horizon, and which, in addition, are asymptotically plane wave. In
particular, we deform the extremal M2-brane solution in 11-dimensional
supergravity so that it behaves asymptotically as a 10-dimensional vacuum plane
wave times a real line.Comment: 23 pages, 1 eps figure; harvmac; v2:refs added; v3:minor comments
adde
On the smoothness of the multi-BMPV black hole spacetime
We demonstrate that, in a multi-BMPV black hole spacetime, the event horizon
is not smooth. We explicitly show that for a simpler configuration comprising a
line of static extremal black holes and a single BMPV black hole, the metric at
the horizon of the BMPV black hole is once, but not twice, continuously
differentiable. We argue that this result is also valid when all the black
holes are rotating. The Maxwell field strength is shown to be continuous, but
not differentiable at the horizon. We also briefly demonstrate that previous
work done to show lack of smoothness of static multi-centre solutions in five
dimensions is not significantly modified by the inclusion of a higher
derivative term in the action for five dimensional supergravity.Comment: 17 pages; reference adde
Tunable transport with broken space-time symmetries
Transport properties of particles and waves in spatially periodic structures
that are driven by external time-dependent forces manifestly depend on the
space-time symmetries of the corresponding equations of motion. A systematic
analysis of these symmetries uncovers the conditions necessary for obtaining
directed transport. In this work we give a unified introduction into the
symmetry analysis and demonstrate its action on the motion in one-dimensional
periodic, both in time and space, potentials. We further generalize the
analysis to quasi-periodic drivings, higher space dimensions, and quantum
dynamics. Recent experimental results on the transport of cold and ultracold
atomic ensembles in ac-driven optical potentials are reviewed as illustrations
of theoretical considerations.Comment: Phys. Rep., in pres
Odd-parity superconductors with two-component order parameters: nematic and chiral, full gap and Majorana node
Motivated by the recent experiment indicating that superconductivity in the
doped topological insulator CuBiSe has an odd-parity pairing
symmetry with rotational symmetry breaking, we study the general class of
odd-parity superconductors with two-component order parameters in trigonal and
hexagonal crystal systems. In the presence of strong spin-orbit interaction, we
find two possible superconducting phases below , a time-reversal-breaking
(i.e., chiral) phase and an anisotropic (i.e., nematic) phase, and determine
their relative energetics from the gap function in momentum space. The nematic
superconductor generally has a full quasi-particle gap, whereas the chiral
superconductor with a three-dimensional (3D) Fermi surface has point nodes with
lifted spin degeneracy, resulting in itinerant Majorana fermions in the bulk
and topological Majorana arcs on the surface.Comment: 4+ pages, 2 figures; 20 pages suppl mat + 4 figures; published
versio
Nonlinear Elasticity, Fluctuations and Heterogeneity of Nematic Elastomers
Liquid crystal elastomers realize a fascinating new form of soft matter that
is a composite of a conventional crosslinked polymer gel (rubber) and a liquid
crystal. These {\em solid} liquid crystal amalgams, quite similarly to their
(conventional, fluid) liquid crystal counterparts, can spontaneously partially
break translational and/or orientational symmetries, accompanied by novel soft
Goldstone modes. As a consequence, these materials can exhibit unconventional
elasticity characterized by symmetry-enforced vanishing of some elastic moduli.
Thus, a proper description of such solids requires an essential modification of
the classical elasticity theory. In this work, we develop a {\em rotationally
invariant}, {\em nonlinear} theory of elasticity for the nematic phase of ideal
liquid crystal elastomers. We show that it is characterized by soft modes,
corresponding to a combination of long wavelength shear deformations of the
solid network and rotations of the nematic director field. We study thermal
fluctuations of these soft modes in the presence of network heterogeneities and
show that they lead to a large variety of anomalous elastic properties, such as
singular length-scale dependent shear elastic moduli, a divergent elastic
constant for splay distortion of the nematic director, long-scale
incompressibility, universal Poisson ratios and a nonlinear stress-strain
relation fo arbitrary small strains. These long-scale elastic properties are
{\em universal}, controlled by a nontrivial zero-temperature fixed point and
constitute a qualitative breakdown of the classical elasticity theory in
nematic elastomers. Thus, nematic elastomers realize a stable ``critical
phase'', characterized by universal power-law correlations, akin to a critical
point of a continuous phase transition, but extending over an entire phase.Comment: 61 pages, 24 eps pages, submitted to Annals of Physic
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