106 research outputs found
Artificial Intelligence, Expert Systems and Law
Artificial Intelligence, Expert Systems and La
Correspondence between Minkowski and de Sitter Quantum Field Theory
In this letter we show that the ``preferred'' Klein-Gordon Quantum Field
Theories (QFT's) on a d-dimensional de Sitter spacetime can be obtained from a
Klein-Gordon QFT on a (d+1)-dimensional ``ambient'' Minkowski spacetime
satisfying the spectral condition and, conversely, that a Klein-Gordon QFT on a
(d+1)-dimensional ``ambient'' Minkowski spacetime satisfying the spectral
condition can be obtained as superposition of d-dimensional de Sitter
Klein-Gordon fields in the preferred vacuum. These results establish a
correspondence between QFT's living on manifolds having different dimensions.
The method exposed here can be applied to study other situations and notably
QFT on Anti de Sitter spacetime.Comment: 7 pages, no figures, typos corrected, added one referenc
Validation of AIRS V6 Surface Temperature over Greenland with GCN and NOAA Stations
This work compares the temporal and spatial characteristics of the AIRSAMSU (Atmospheric Infrared Sounder Advanced Microwave Sounding Unit A) Version 6 and MODIS (Moderate resolution Imaging Spectroradiometer) Collection 5 derived surface temperatures over Greenland. To estimate uncertainties in space-based surface temperature measurements, we re-projected the MODIS Ice Surface Temperature (IST) to 0.5 by 0.5 degree spatial resolution. We also re-gridded AIRS Skin Temperature (Ts) into the same grid but classified with different cloud conditions and surface types. These co-located data sets make intercomparison between the two instruments relatively straightforward. Using this approach, the spatial comparison between the monthly mean AIRS Ts and MODIS IST is in good agreement with RMS 2K for May 2012. This approach also allows the detection of any long-term calibration drift and the careful examination of calibration consistency in the MODIS and AIRS temperature data record. The temporal correlations between temperature data are also compared with those from in-situ measurements from GC-Net (GCN) and NOAA stations. The coherent time series of surface temperature evident in the correlation between AIRS Ts and GCN temperatures suggest that at monthly time scales both observations capture the same climate signal over Greenland. It is also suggested that AIRS surface air temperature (Ta) can be used to estimate the boundary layer inversion
SU(2) Flux Distributions on Finite Lattices
We studied SU(2) flux distributions on four dimensional euclidean lattices
with one dimension very large. By choosing the time direction appropriately we
can study physics in two cases: one is finite volume in the zero temperature
limit, another is finite temperature in the the intermediate to large volume
limit. We found that for cases of beta > beta crit there is no intrinsic string
formation. Our lattices with beta > beta crit belong to intermediate volume
region, and the string tension in this region is due to finite volume effects.
In large volumes we found evidence for intrinsic string formation.Comment: 21 pages text, 12 pages of postscript figure
Duality in Scalar Field Theory on Noncommutative Phase Spaces
We describe a novel duality symmetry of Phi(4)-theory defined on
noncommutative Euclidean space and with noncommuting momentum coordinates. This
duality acts on the fields by Fourier transformation and scaling. It is an
extension, to interactions defined with a star-product, of that which arises in
quantum field theories of non-interacting scalar particles coupled to a
constant background electromagnetic field. The dual models are in general of
the same original form but with transformed coupling parameters, while in
certain special cases all parameters are essentially unchanged. Using a
particular regualarization we show, to all orders of perturbation theory, that
that this duality also persists at the quantum level. We also point out various
other properties of this class of noncommutative field theories.Comment: 13 pages LaTeX; Minor corrections, references added, comment about
self-dual models added to section
Brane World Gravity in an AdS Black Hole
We consider a model of brane world gravity in the context of non-conformal
non-SUSY matter. In particular we modify the earlier strong coupling solution
to the glueball spectrum in an Black Hole by introducing a
Randall-Sundrum Planck brane as a UV cut-off. The consequence is a new
normalizable zero mass tensor state, which gives rise to an effective
Einstein-Hilbert theory of gravity, with exponentially small corrections set by
the mass gap to the discrete glueball spectrum. However the simplest
microscopic theory for the Planck brane is found to have a tachyonic
instability in the radion mode.Comment: 25 pages, late
String windings in the early universe
We study string dynamics in the early universe. Our motivation is the
proposal of Brandenberger and Vafa, that string winding modes may play a key
role in decompactifying three spatial dimensions. We model the universe as a
homogeneous but anisotropic 9-torus filled with a gas of excited strings. We
adopt initial conditions which fix the dilaton and the volume of the torus, but
otherwise assume all states are equally likely. We study the evolution of the
system both analytically and numerically to determine the late-time behavior.
We find that, although dynamical evolution can indeed lead to three large
spatial dimensions, such an outcome is not statistically favored.Comment: 26 pages, LaTeX, 4 eps figure
Hamiltonian domain wall fermions at strong coupling
We apply strong-coupling perturbation theory to gauge theories containing
domain-wall fermions in Shamir's surface version. We construct the effective
Hamiltonian for the color-singlet degrees of freedom that constitute the
low-lying spectrum at strong coupling. We show that the effective theory is
identical to that derived from naive, doubled fermions with a mass term, and
hence that domain-wall fermions at strong coupling suffer both doubling and
explicit breaking of chiral symmetry. Since we employ a continuous fifth
dimension whose extent tends to infinity, our result applies to overlap
fermions as well.Comment: Revtex, 21 pp. Some changes in Introduction, dealing with consistency
with previous wor
Open Wilson Lines and Group Theory of Noncommutative Yang-Mills Theory in Two Dimensions
The correlation functions of open Wilson line operators in two-dimensional
Yang-Mills theory on the noncommutative torus are computed exactly. The
correlators are expressed in two equivalent forms. An instanton expansion
involves only topological numbers of Heisenberg modules and enables extraction
of the weak-coupling limit of the gauge theory. A dual algebraic expansion
involves only group theoretic quantities, winding numbers and translational
zero modes, and enables analysis of the strong-coupling limit of the gauge
theory and the high-momentum behaviour of open Wilson lines. The dual
expressions can be interpreted physically as exact sums over contributions from
virtual electric dipole quanta.Comment: 37 pages. References adde
Preheating After Modular Inflation
We study (p)reheating in modular (closed string) inflationary scenarios, with
a special emphasis on Kahler moduli/Roulette models. It is usually assumed that
reheating in such models occurs through perturbative decays. However, we find
that there are very strong non-perturbative preheating decay channels related
to the particular shape of the inflaton potential (which is highly nonlinear
and has a very steep minimum). Preheating after modular inflation, proceeding
through a combination of tachyonic instability and broad-band parametric
resonance, is perhaps the most violent example of preheating after inflation
known in the literature. Further, we consider the subsequent transfer of energy
to the standard model sector in scenarios where the standard model particles
are confined to a D7-brane wrapping the inflationary blow-up cycle of the
compactification manifold or, more interestingly, a non-inflationary blow up
cycle. We explicitly identify the decay channels of the inflaton in these two
scenarios. We also consider the case where the inflationary cycle shrinks to
the string scale at the end of inflation; here a field theoretical treatment of
reheating is insufficient and one must turn instead to a stringy description.
We estimate the decay rate of the inflaton and the reheat temperature for
various scenarios.Comment: 34 pages, 10 figures. Accepted for publication in JCA
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