4,333 research outputs found
Supergravity with Self-dual B fields and Instantons in Noncommutative Gauge Theory
We study Type IIB supergravity in the presence of (euclidean) D3 branes and
nonzero self-dual B-fields. We point out that the Einstein frame metric is
identical to the full geometry for D3 branes without B fields turned on.
Furthermore, in a decoupling limit in which the theory is conjectured to be
dual to noncommutative Yang-Mills theory, the entire Einstein metric remains
intact, and in particular, is asymptotically flat. We construct D-instanton
solutions in this geometry. We show that in the decoupling limit the
D-instanton action agrees with the action of the corresponding instanton in the
noncommutative Yang-Mills theory and is expressed in terms of the open string
coupling. Some other aspects of this correspondence, which have unusual
features because the underlying metric is asymptotically flat, are explored.Comment: 25 pages, harvma
Radiative interactions in laminar duct flows
Analyses and numerical procedures are presented for infrared radiative energy transfer in gases when other modes of energy transfer occur simultaneously. Two types of geometries are considered, a parallel plate duct and a circular duct. Fully developed laminar incompressible flows of absorbing-emitting species in black surfaced ducts are considered under the conditions of uniform wall heat flux. The participating species considered are OH, CO, CO2, and H2O. Nongray as well as gray formulations are developed for both geometries. Appropriate limiting solutions of the governing equations are obtained and conduction-radiation interaction parameters are evaluated. Tien and Lowder's wide band model correlation was used in nongray formulation. Numerical procedures are presented to solve the integro-differential equations for both geometries. The range of physical variables considered are 300 to 2000 K for temperature, 0.1 to 100.0 atm for pressure, and 0.1 to 100 cm spacings between plates/radius of the tube. An extensive parametric study based on nongray formulation is presented. Results obtained for different flow conditions indicate that the radiative interactions can be quite significant in fully developed incompressible flows
Antiferromagnetism and phase separation in the t-J model at low doping: a variational study
Using Gutzwiller-projected wave functions, I estimate the ground-state energy
of the t-J model for several variational states relevant for high-temperature
cuprate superconductors. The results indicate antiferromagnetism and phase
separation at low doping both in the superconducting state and in the
staggered-flux normal state proposed for the vortex cores. While phase
separation in the underdoped superconducting state may be relevant for the
stripe formation mechanism, the results for the normal state suggest that
similar charge inhomogeneities may also appear in vortex cores up to relatively
high doping values.Comment: 4 pages, 3 figures, reference adde
Supergravity couplings to Noncommutative Branes, Open Wilson Lines and Generalised Star Products
Noncommutative gauge theories can be constructed from ordinary
gauge theories in lower dimensions. Using this construction we identify the
operators on noncommutative D-branes which couple to linearized supergravity
backgrounds, from a knowledge of such couplings to lower dimensional D-branes
with no field. These operators belong to a class of gauge invariant
observables involving open Wilson lines. Assuming a DBI form of the coupling we
show, to second order in the gauge potential but to all orders of the
noncommutativity parameter, that our proposal agrees with the operator obtained
in terms of ordinary gauge fields by considering brane actions in backgrounds
and then using the Seiberg-Witten map to rewrite this in terms of
noncommutative gauge fields. Our result clarify why a certain {\it commutative}
but {\it non-associative} ``generalized star product'' appears both in the
expansion of the open Wilson line, as well as in string amplitude computations
of open string - closed string couplings. We outline how our procedure can be
used to obtain operators in the noncommutative theory which are holographically
dual to supergravity modes.Comment: 23 pages, no figures, harvmac, typos in equations corrected, some
discussion revised, acknowledgement adde
Magnetic Moments of Branes and Giant Gravitons
We study the magnetic analogue of Myers' Dielectric Effect and, in some
cases, relate it to the blowing up of particles into branes, first investigated
by Greevy, Susskind and Toumbas. We show that branes or gravitons in M
theory, moving in a magnetic four-form field strength background expand into a
non-commutative two sphere. Both examples of constant magnetic field and
non-constant fields in curved backgrounds generated by branes are considered.
We find, in all cases, another solution, consisting of a two-brane wrapping a
classical two-sphere, which has all the quantum numbers of the branes.
Motivated by this, we investigate the blowing up of gravitons into branes in
backgrounds different from . We find the phenomenon is quite
general. In many cases with less or even no supersymmetry we find a brane
configuration which has the same quantum numbers and the same energy as a
massless particle in supergravity.Comment: 30 pages, no figures, harvma
Gaussian Neighborhood-prime Labeling of Graphs Containing Hamiltonian Cycle
In this paper, we examine Gaussian neighborhood-prime labeling of generalized Peterson graph and graphs which contain Hamiltonian cycle
Axions as Quintessence in String Theory
We construct a model of quintessence in string theory based on the idea of
axion monodromy as discussed by McAllister, Silverstein and Westphal
arXiv:0808.0706. In the model, the quintessence field is an axion whose shift
symmetry is broken by the presence of 5-branes which are placed in highly
warped throats. This gives rise to a potential for the axion field which is
slowly varying, even after incorporating the effects of moduli stabilization
and supersymmetry breaking. We find that the resulting time dependence in the
equation of state of Dark Energy is potentially detectable, depending on the
initial conditions. The model has many very light extra particles which live in
the highly warped throats, but these are hard to detect. A signal in the
rotation of the CMB polarization can also possibly arise.Comment: 41 pages, 1 figure, v2: references adde
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Results of an aqueous source term model for a radiological risk assessment of the Drigg LLW Site, U.K.
A radionuclide source term model has been developed which simulates the biogeochemical evolution of the Drigg low level waste (LLW) disposal site. The DRINK (DRIgg Near field Kinetic) model provides data regarding radionuclide concentrations in groundwater over a period of 100,000 years, which are used as input to assessment calculations for a groundwater pathway. The DRINK model also provides input to human intrusion and gaseous assessment calculations through simulation of the solid radionuclide inventory. These calculations are being used to support the Drigg post closure safety case. The DRINK model considers the coupled interaction of the effects of fluid flow, microbiology, corrosion, chemical reaction, sorption and radioactive decay. It represents the first direct use of a mechanistic reaction-transport model in risk assessment calculations
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