21,187 research outputs found
Use of satellite data and modeling to asses the influence of stratospheric processes on the troposphere
The research is comprised of the following tasks: use of simple analytical and numerical models of a coupled troposphere-stratosphere system to examine the effects of radiation and ozone on planetary wave dynamics and the tropospheric circulation; use of satellite data obtained from the Nimbus 7 Limb Infrared Monitor of the Stratosphere (LIMS) instrument and Solar Backscattered Ultraviolet (SBUV) experiment, in conjunction with National Meteorological Center (NMC) data, to determine the planetary wave vertical structures, dominant wave spectra, ozone spectra, and time variations in diabatic heating rate; and synthesis of the modeling and observational results to provide a better understanding of the effects that stratospheric processes have on tropospheric dynamics
On higher derivative corrections to Wess-Zumino and Tachyonic actions in type II super string theory
We evaluate in detail the string scattering amplitude to compute different
interactions of two massless scalars, one tachyon and one closed string
Ramond-Ramond field in type II super string theory. In particular we find two
scalar field and two tachyon couplings to all orders of up to
on-shell ambiguity. We then obtain the momentum expansion of this amplitude and
apply this infinite number of couplings to actually check that the infinite
number of tachyon poles of S-matrix element of this amplitude for the
case (where is the spatial dimension of a D-brane and is the rank
of a Ramond-Ramond field strength) to all orders of is precisely
equal to the infinite number of tachyon poles of the field theory. In addition
to confirming the couplings of closed string Ramond-Ramond field to the
world-volume gauge field and scalar fields including commutators, we also
propose an extension of the Wess-Zumino action which naturally reproduces these
new couplings in field theory such that they could be confirmed with direct
S-matrix computations. Finally we show that the infinite number of massless
poles and contact terms of this amplitude for the case can be
reproduced by Chern-Simons, higher derivative corrections of the Wess-Zumino
and symmetrized trace tachyon DBI actions.Comment: 51 pages, some refs and comments added, typos are removed. Almost all
ambiguities in BPS and non-BPS effective actions have been addresse
Free Energies and Probe Actions for Near-horizon D-branes and D1 + D5 System
By working with the free energy for the type II supergravity near-horizon
solution of N coincident non-extremal Dp-branes we study the transitions among
the non-conformal Dp-brane system, the perturbative super Yang-Mills theory and
a certain system associated with M theory. We derive a relation between this
free energy and the action of a Dp-brane probe in the N Dp-brane background.
Constructing the free energy for the five dimensional black hole labeled by the
D1-brane and D5-brane charges we find the similar relation between it and the
action of a D1 or D5 brane probe in the D1 + D5 brane background. These
relations are explained by the massive open strings stretched between the
relevant D-branesComment: 14 pages, LaTeX2e, no figure
Microcausality of spin-induced noncommutative theories
In this brief report, the microcausility of quantum field theory on
spin-induced noncom- mutative spacetime is discussed. It is found that for
spacelike seperation the microcausality is not obeyed by the theory generally.
It means that Lorentz covariance can not guaran- tee microcausality in quantum
field thoery. We also give some comments about quantum field thoeries on such
noncommutative spacetime and the relations between noncommutative spacetime and
causality.Comment: 9 pages, no figur
Hypervelocity runaways from the Large Magellanic Cloud
We explore the possibility that the observed population of Galactic
hypervelocity stars (HVSs) originate as runaway stars from the Large Magellanic
Cloud (LMC). Pairing a binary evolution code with an N-body simulation of the
interaction of the LMC with the Milky Way, we predict the spatial distribution
and kinematics of an LMC runaway population. We find that runaway stars from
the LMC can contribute Galactic HVSs at a rate of . This is composed of stars at different points of
stellar evolution, ranging from the main-sequence to those at the tip of the
asymptotic giant branch. We find that the known B-type HVSs have kinematics
which are consistent with an LMC origin. There is an additional population of
hypervelocity white dwarfs whose progenitors were massive runaway stars.
Runaways which are even more massive will themselves go supernova, producing a
remnant whose velocity will be modulated by a supernova kick. This latter
scenario has some exotic consequences, such as pulsars and supernovae far from
star-forming regions, and a small rate of microlensing from compact sources
around the halo of the LMC.Comment: MNRAS, in pres
5D Yang-Mills instantons from ABJM Monopoles
In the presence of a background supergravity flux, N M2-branes will expand
via the Myers effect into M5-branes wrapped on a fuzzy three-sphere. In
previous work the fluctuations of the M2-branes were shown to be described by
the five-dimensional Yang-Mills gauge theory associated to D4-branes. We show
that the ABJM prescription for eleven-dimensional momentum in terms of magnetic
flux lifts to an instanton flux of the effective five-dimensional Yang-Mills
theory on the sphere, giving an M-theory interpretation for these instantons.Comment: 29 pages, Latex; v2: added references and a comment on the
graviphoton coupling in section 5; v3: typos corrected and references adde
Noncommutative scalar field minimally coupled to gravity
A model for noncommutative scalar fields coupled to gravity based on the
generalization of the Moyal product is proposed. Solutions compatible with
homogeneous and isotropic flat Robertson-Walker spaces to first non-trivial
order in the perturbation of the star-product are presented. It is shown that
in the context of a typical chaotic inflationary scenario, at least in the
slow-roll regime, noncommutativity yields no observable effect.Comment: Talk presented at the Workshop on Quantum Gravity and Noncommutative
Geometry, 20-23 July 2004, Universidade Lus\'ofona, Lisbon, Portugal. To
appear at Int. J. Mod. Phys.
Drinfeld-Manin Instanton and Its Noncommutative Generalization
The Drinfeld-Manin construction of U(N) instanton is reformulated in the ADHM
formulism, which gives explicit general solutions of the ADHM constraints for
U(N) (N>=2k-1) k-instantons. For the N<2k-1 case, implicit results are given
systematically as further constraints, which can be used to the collective
coordinate integral. We find that this formulism can be easily generalized to
the noncommutative case, where the explicit solutions are as well obtained.Comment: 17 pages, LaTeX, references added, mailing address added,
clarifications adde
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