821 research outputs found
The Effective Action in Gauged Supergravity on Hyperbolic Background and Induced Cosmological Constant
The one-loop effective action for 4-dimensional gauged supergravity with
negative cosmological constant, is investigated in space-times with compact
hyperbolic spatial section. The explicit expansion of the effective action as a
power series of the curvature on hyperbolic background is derived, making use
of heat-kernel and zeta-regularization techniques. The induced cosmological and
Newton constants are computed.Comment: 9 pages, UTF 23
Motion Correction Using Deep Learning Neural Networks - Effects of Data Representation
An in-silico investigation of the effects of ultrasound data representation on the accuracy of the motion prediction made using deep learning neural networks was carried out. The representations studied include: linear (‘envelope’), log compressed, linear with phase and log compressed with phase. A UNet model was trained to predict non-rigid deformation field using a fixed and a moving image pair as the input. The results illustrate that the choice of the representation plays an important role on the accuracy of motion estimation. Specifically, representations with phase information outperform the representations without phase. Furthermore, log-compressed data yielded predictions with higher accuracy than the linear data
Neotectonics of the Caucasus and Kura valley, Azerbaijan
Analysis of remote sensing, gravity, earthquake, horizontal and vertical motion data in the
broader Azerbaijan region, located between the colliding Arabia and Eurasian Platform, indicates
the overall dextral transpression. The region undergoes deformation by NW-SE striking
transpressional strike-slip faults, pure strike-slip faults and thrusts. It is also deformed by N-S to
NE-SW striking sinistral strike-slip faults. The study area is located to the NE of the main
indentation point. The direction of indentation is roughly parallel to the NW-SE trending
symmetry axis of the fanning horizontal motion vectors, to the NNW-SSE trending axis of the
fanning 1-stress trajectories and to the fastest slowdown direction of horizontal motions in front
of the advancing Arabia, which are all roughly parallel to the Arabian motion vector. The broader
Azerbaijan region is situated in the eastern side of these fan-shaped patterns. It is characterized by
1 trends progressively changing from NNW-SSE to NE-SW and by the seismoactive zone
thickness increasing SE-ward underneath the Kura Valley from 40 to almost 70 km. Its eastern
portion, typical by its small-block mosaic structure, contains some unusual local stress regimes. It
is argued that they are related to the addition of the regional tectonic stress, highly perturbed
along numerous local strike-slip faults, to local stresses generated by interactions of local rotating
blocks. This eastern portion is most prone to block rotations, being most distant from the main
indentation point and being affected by the least transpressive strike-slip faulting
Scaling in a Nonconservative Earthquake Model of Self-Organised Criticality
We numerically investigate the Olami-Feder-Christensen model for earthquakes
in order to characterise its scaling behaviour. We show that ordinary finite
size scaling in the model is violated due to global, system wide events.
Nevertheless we find that subsystems of linear dimension small compared to the
overall system size obey finite (subsystem) size scaling, with universal
critical coefficients, for the earthquake events localised within the
subsystem. We provide evidence, moreover, that large earthquakes responsible
for breaking finite size scaling are initiated predominantly near the boundary.Comment: 6 pages, 6 figures, to be published in Phys. Rev. E; references
sorted correctl
Universality of the Operator Product Expansions of SCFT_4
We study the operator product algebra of the supercurrent J and Konishi
superfield K in four-dimensional supersymmetric gauge theories. The Konishi
superfield appears in the JJ OPE and the algebra is characterized by two
central charges c and c' and an anomalous dimension h for K. In free field
(one-loop) approximation, c~3N_v+N_\chi and c'~N_\chi, where N_v and N_\chi
are, respectively, the number of vector and chiral multiplets in the theory. In
higher order c, c' and h depend on the gauge and Yukawa couplings and we obtain
the two-loop contributions by combining earlier work on c with our own
calculations of c'. The major result is that the radiative corrections to the
central charges cancel when the one-loop beta-functions vanish, suggesting that
c and c' (but not h) are invariant under continuous deformations of
superconformal theories. The behavior of c and c' along renormalization group
flows is studied from the viewpoint of a c-theorem.Comment: LaTeX file, 11 pages, no figur
Analytical approximation of the stress-energy tensor of a quantized scalar field in static spherically symmetric spacetimes
Analytical approximations for and of a
quantized scalar field in static spherically symmetric spacetimes are obtained.
The field is assumed to be both massive and massless, with an arbitrary
coupling to the scalar curvature, and in a zero temperature vacuum state.
The expressions for and are divided into
low- and high-frequency parts. The contributions of the high-frequency modes to
these quantities are calculated for an arbitrary quantum state. As an example,
the low-frequency contributions to and are
calculated in asymptotically flat spacetimes in a quantum state corresponding
to the Minkowski vacuum (Boulware quantum state). The limits of the
applicability of these approximations are discussed.Comment: revtex4, 17 pages; v2: three references adde
Some general properties of the renormalized stress-energy tensor for static quantum states on (n+1)-dimensional spherically symmetric black holes
We study the renormalized stress-energy tensor (RSET) for static quantum
states on (n+1)-dimensional, static, spherically symmetric black holes. By
solving the conservation equations, we are able to write the stress-energy
tensor in terms of a single unknown function of the radial co-ordinate, plus
two arbitrary constants. Conditions for the stress-energy tensor to be regular
at event horizons (including the extremal and ``ultra-extremal'' cases) are
then derived using generalized Kruskal-like co-ordinates. These results should
be useful for future calculations of the RSET for static quantum states on
spherically symmetric black hole geometries in any number of space-time
dimensions.Comment: 9 pages, no figures, RevTeX4, references added, accepted for
publication in General Relativity and Gravitatio
Propagators and WKB-exactness in the plane wave limit of AdSxS
Green functions for the scalar, spinor and vector fields in a plane wave
geometry arising as a Penrose limit of are obtained. The
Schwinger-DeWitt technique directly gives the results in the plane wave
background, which turns out to be WKB-exact. Therefore the structural
similarity with flat space results is unveiled. In addition, based on the local
character of the Penrose limit, it is claimed that for getting the correct
propagators in the limit one can rely on the first terms of the direct geodesic
contribution in the Schwinger-DeWitt expansion of the original propagators .
This is explicitly shown for the Einstein Static Universe, which has the same
Penrose limit as with equal radii, and for a number of other
illustrative cases.Comment: 18 pages, late
Energy-Momentum Tensor of Particles Created in an Expanding Universe
We present a general formulation of the time-dependent initial value problem
for a quantum scalar field of arbitrary mass and curvature coupling in a FRW
cosmological model. We introduce an adiabatic number basis which has the virtue
that the divergent parts of the quantum expectation value of the
energy-momentum tensor are isolated in the vacuum piece of , and
may be removed using adiabatic subtraction. The resulting renormalized
is conserved, independent of the cutoff, and has a physically transparent,
quasiclassical form in terms of the average number of created adiabatic
`particles'. By analyzing the evolution of the adiabatic particle number in de
Sitter spacetime we exhibit the time structure of the particle creation
process, which can be understood in terms of the time at which different
momentum scales enter the horizon. A numerical scheme to compute as a
function of time with arbitrary adiabatic initial states (not necessarily de
Sitter invariant) is described. For minimally coupled, massless fields, at late
times the renormalized goes asymptotically to the de Sitter invariant
state previously found by Allen and Folacci, and not to the zero mass limit of
the Bunch-Davies vacuum. If the mass m and the curvature coupling xi differ
from zero, but satisfy m^2+xi R=0, the energy density and pressure of the
scalar field grow linearly in cosmic time demonstrating that, at least in this
case, backreaction effects become significant and cannot be neglected in de
Sitter spacetime.Comment: 28 pages, Revtex, 11 embedded .ps figure
CoRoT/ESTA-TASK 1 and TASK 3 comparison of the internal structure and seismic properties of representative stellar models: Comparisons between the ASTEC, CESAM, CLES, GARSTEC and STAROX codes
We compare stellar models produced by different stellar evolution codes for
the CoRoT/ESTA project, comparing their global quantities, their physical
structure, and their oscillation properties. We discuss the differences between
models and identify the underlying reasons for these differences. The stellar
models are representative of potential CoRoT targets. Overall we find very good
agreement between the five different codes, but with some significant
deviations. We find noticeable discrepancies (though still at the per cent
level) that result from the handling of the equation of state, of the opacities
and of the convective boundaries. The results of our work will be helpful in
interpreting future asteroseismology results from CoRoT.Comment: 26 pages, 21 figures, accepted for publication in Astrophysics and
Space Science, CoRoT/ESTA Volum
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