557 research outputs found
The Ground State of the ``Frozen'' Electron Phase in Two-Dimensional Narrow-Band Conductors with a Long-Range Interelectron Repulsion. Stripe Formation and Effective Lowering of Dimension
In narrow-band conductors a weakly screened Coulomb interelectron repulsion
can supress narrow-band electrons' hopping, resulting in formation of a
``frozen'' electron phase which differs principally from any known macroscopic
self-localized electron state including the Wigner crystal. In a zero-bandwidth
limit the ``frozen'' electron phase is a classical lattice system with a
long-range interparticle repulsion. The ground state of such systems has been
considered in the case of two dimensions for an isotropic pair potential of the
mutual particle repulsion. It has been shown that particle ordering into
stripes and effective lowering of dimension universally resides in the ground
state for any physically reasonable pair potential and for any geometry of the
conductor lattice. On the basis of this fact a rigorous general procedure to
fully describe the ground state has been formulated. Arguments have been
adduced that charge ordering in High-T_c superconductors testifies to presence
of a ``frozen'' electron phase in these systems.Comment: 5 pages, LaTeX 2.09, 1 figure in external PostScript files. To appear
in Phys.Rev B Rapid Communication
First search for double-beta decay of 184Os and 192Os
A search for double-beta decay of osmium has been realized for the first time
with the help of an ultra-low background HPGe gamma detector at the underground
Gran Sasso National Laboratories of the INFN (Italy). After 2741 h of data
taking with a 173 g ultra-pure osmium sample limits on double-beta processes in
184Os have been established at the level of T_{1/2} about 10^{14}-10^{17} yr.
Possible resonant double-electron captures in 184Os were searched for with a
sensitivity T_{1/2} about 10^{16} yr. A half-life limit T_{1/2} > 5.3 10^{19}
yr was set for the double-beta decay of 192Os to the first excited level of
192Pt. The radiopurity of the osmium sample has been investigated and
radionuclides 137Cs, 185Os and 207Bi were detected in the sample, while
activities of 40K, 60Co, 226Ra and 232Th were limited at the mBq/kg level.Comment: 12 pages, 7 figures, 2 table
Search for 2\beta\ decays of 96Ru and 104Ru by ultra-low background HPGe gamma spectrometry at LNGS: final results
An experiment to search for double beta decay processes in 96Ru and 104Ru,
which are accompanied by gamma rays, has been realized in the underground Gran
Sasso National Laboratories of the I.N.F.N. (Italy). Ruthenium samples with
masses of about (0.5-0.7) kg were measured with the help of ultra-low
background high purity Ge gamma ray spectrometry. After 2162 h of data taking
the samples were deeply purified to reduce the internal contamination of 40K.
The last part of the data has been accumulated over 5479 h. New improved half
life limits on 2\beta+/\epsilon \beta+/2\epsilon\ processes in 96Ru have been
established on the level of 10^{20} yr, in particular for decays to the ground
state of 96Mo: T1/2(2\nu 2\beta+) > 1.4 10^{20} yr, T1/2(2\nu \epsilon\beta+) >
8.0 10^{19} yr and T1/2(0\nu 2K) > 1.0 10^{21} yr (all limits are at 90% C.L.).
The resonant neutrinoless double electron captures to the 2700.2 keV and 2712.7
keV excited states of 96Mo are restricted as: T1/2(0\nu KL) > 2.0 10^{20} yr
and T1/2(0\nu 2L) > 3.6 10^{20} yr, respectively. Various two neutrino and
neutrinoless 2\beta\ half lives of 96Ru have been estimated in the framework of
the QRPA approach. In addition, the T1/2 limit for 0\nu 2\beta- transitions of
104Ru to the first excited state of 104Pd has been set as > 6.5 10^{20} yr.Comment: 14 pages, 5 figures, 2 tables; version accepted for publication on
Phys. Rev.
Hydrodynamics from the Dp-brane
We complete the computation of viscous transport coefficients in the near
horizon geometries that arise from a stack of black Dp-branes for p=2,...,6 in
the decoupling limit. The main new result is the obtention of the bulk
viscosity which, for all p, is found to be related to the speed of sound by the
simple relation \zeta/\eta = -2(v_s^2-1/p). For completeness the shear
viscosity is rederived from gravitational perturbations in the shear and scalar
channels. We comment on technical issues like the counterterms needed, or the
possible dependence on the conformal frame.Comment: 15 page
Shear viscosity from R-charged AdS black holes
We compute the shear viscosity in the supersymmetric Yang-Mills theory dual
to the STU background. This is a thermal gauge theory with a chemical
potential. The quotient of the shear viscosity over the entropy density
exhibits no deviation from the well known result 1/4\pi.Comment: 9 pages, some references updated, abstract and some typos correcte
Causality and the AdS Dirichlet problem
The (planar) AdS Dirichlet problem has previously been shown to exhibit
superluminal hydrodynamic sound modes. This problem is defined by bulk
gravitational dynamics with Dirichlet boundary conditions imposed on a rigid
timelike cut-off surface. We undertake a careful examination of this set-up and
argue that, in most cases, the propagation of information between points on the
Dirichlet hypersurface is nevertheless causal with respect to the induced light
cones. In particular, the high-frequency dynamics is causal in this sense.
There are however two exceptions and both involve boundary gravitons whose
propagation is not constrained by the Einstein equations. These occur in i)
AdS, where the boundary gravitons generally do not respect the induced
light cones on the boundary, and ii) Rindler space, where they are related to
the infinite speed of sound in incompressible fluids. We discuss implications
for the fluid/gravity correspondence with rigid Dirichlet boundaries and for
the black hole membrane paradigm.Comment: 29 pages, 5 figures. v2: added refs. v3: minor clarification
From Petrov-Einstein to Navier-Stokes in Spatially Curved Spacetime
We generalize the framework in arXiv:1104.5502 to the case that an embedding
may have a nonvanishing intrinsic curvature. Directly employing the Brown-York
stress tensor as the fundamental variables, we study the effect of finite
perturbations of the extrinsic curvature while keeping the intrinsic metric
fixed. We show that imposing a Petrov type I condition on the hypersurface
geometry may reduce to the incompressible Navier-Stokes equation for a fluid
moving in spatially curved spacetime in the near-horizon limit.Comment: 17 pages, references added, generalizing the metric form in part 3,
version published in JHE
Construction of bosonic string theory on infinitely curved Anti-de Sitter space
Free scalar field theory in the sector with a large number of particles can
be interpreted as bosonic string theory on anti-de Sitter space of vanishing
radius. Different ways of writing the field theory Hamiltonian translate to
different ways of reparametrizing the world-sheet sigma coordinate. Adding a
mass term in the field theory corresponds to cutting off the warped AdS
direction, with cut-off inversely proportional to the mass. The string theory
has neither tachyon, nor critical dimension.Comment: 18 pages, latex, using revte
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