6,001 research outputs found
Stationary quantum Markov process for the Wigner function
As a stochastic model for quantum mechanics we present a stationary quantum
Markov process for the time evolution of the Wigner function on a lattice phase
space Z_N x Z_N with N odd. By introducing a phase factor extension to the
phase space, each particle can be treated independently. This is an improvement
on earlier methods that require the whole distribution function to determine
the evolution of a constituent particle. The process has branching and
vanishing points, though a finite time interval can be maintained between the
branchings. The procedure to perform a simulation using the process is
presented.Comment: 12 pages, no figures; replaced with version accepted for publication
in J. Phys. A, title changed, an example adde
The Influence of N14(e-,nu)C14(alpha,gamma)O18 reaction on the He-Ignition in Degenerate Physical Conditions
The importance of NCO chain on the onset of the He-flash in degenerate
physical conditions has been reevaluated. We find that low-mass, metal-rich (Z
0.001) structures climbing the Red Giant Branch do never attain the
physical conditions suitable for the onset of this chain, while at lower
metallicities the energy contribution provided by NCO reaction is too low to
affect the onset of the central He-flash. At the same time, our evolutionary
models suggest that for a Carbon-Oxygen White Dwarf of mass M_{WD}=0.6 M_sun
accreting He-rich matter, directly or as a by-product of an overlying H-burning
shell, at rates suitable for a dynamical He-flash, the NCO energy contribution
is not able to keep hot enough the He-shell and in turn to avoid the occurrence
of a strong electron degeneracy and the ensuing final explosion.Comment: 15 pages, 3 tables, 10 figure, to appear in Ap
Strings between branes
D-brane configurations containing fundamental strings are constructed as
classical solutions of Yang-Mills theory. The fundamental strings in these
systems stretch between D-branes. In the case of D1-branes, this construction
gives smooth (classical) resolutions of string junctions and string networks.
Using a non-abelian Yang-Mills analysis of the string current, the string
charge density is computed and is shown to have support in the region between
the D-brane world-volumes. The 't Hooft-Polyakov monopole is analyzed using
similar methods, and is shown to contain D-strings whose flux has support off
the D-brane world-volume defined by the Higgs scalar field, when this field is
interpreted in terms of a transverse dimension. The constructions presented
here are used to give a qualitative picture of tachyon condensation in the
Yang-Mills limit, where fundamental strings and lower-dimensional D-branes
arise in a volume of space-time where brane-antibrane annihilation has
occurred.Comment: 35 pages, 16 eps figures, JHEP style; v2: a comment adde
Detection of a Far-Infrared Bow-Shock Nebula Around R Hya: the First MIRIAD Results
We present the first results of the MIRIAD (MIPS [Multiband Imaging
Photometer for Spitzer] Infra-Red Imaging of AGB [asymptotic giant branch]
Dustshells) project using the Spitzer Space Telescope. The primary aim of the
project is to probe the material distribution in the extended circumstellar
envelopes (CSE) of evolved stars and recover the fossil record of their mass
loss history. Hence, we must map the whole of the CSEs plus the surrounding sky
for background subtraction, while avoiding the central star that is brighter
than the detector saturation limit. With our unique mapping strategy, we have
achieved better than one MJy/sr sensitivity in three hours of integration and
successfully detected a faint (< 5 MJy/sr), extended (~400 arcsec) far-infrared
nebula around the AGB star R Hya. Based on the parabolic structure of the
nebula, the direction of the space motion of the star with respect to the
nebula shape, and the presence of extended H alpha emission co-spatial to the
nebula, we suggest that the detected far-IR nebula is due to a bow shock at the
interface of the interstellar medium and the AGB wind of this moving star. This
is the first detection of the stellar-wind bow-shock interaction for an AGB
star and exemplifies the potential of Spitzer as a tool to examine the detailed
structure of extended far-IR nebulae around bright central sources. \Comment: 10 pages, 2 figures, accepted for publication in ApJ
Aspects of Puff Field Theory
We describe some features of the recently constructed "Puff Field Theory,"
and present arguments in favor of it being a field theory decoupled from
gravity. We construct its supergravity dual and calculate the entropy of this
theory in the limit of large 't Hooft coupling. We also determine the leading
irrelevant operator that governs its deviation from N=4 super Yang-Mills
theory.Comment: 31 pages, 1 figur
Non-commutative gauge theory on D-branes in Melvin Universes
Non-commutative gauge theory with a non-constant non-commutativity parameter
can be formulated as a decoupling limit of open strings ending on D3-branes
wrapping a Melvin universe. We construct the action explicitly and discuss
various physical features of this theory. The decoupled field theory is not
supersymmetric. Nonetheless, the Coulomb branch appears to remain flat at least
in the large N and large 't Hooft coupling limit. We also find the analogue of
Prasad-Sommerfield monopoles whose size scales with the non-commutativity
parameter and is therefore position dependent.Comment: 15 pages, 1 figure, reference adde
Cluster Structure in Cosmological Simulations I: Correlation to Observables, Mass Estimates, and Evolution
We use Enzo, a hybrid Eulerian AMR/N-body code including non-gravitational
heating and cooling, to explore the morphology of the X-ray gas in clusters of
galaxies and its evolution in current generation cosmological simulations. We
employ and compare two observationally motivated structure measures: power
ratios and centroid shift. Overall, the structure of our simulated clusters
compares remarkably well to low-redshift observations, although some
differences remain that may point to incomplete gas physics. We find no
dependence on cluster structure in the mass-observable scaling relations, T_X-M
and Y_X-M, when using the true cluster masses. However, estimates of the total
mass based on the assumption of hydrostatic equilibrium, as assumed in
observational studies, are systematically low. We show that the hydrostatic
mass bias strongly correlates with cluster structure and, more weakly, with
cluster mass. When the hydrostatic masses are used, the mass-observable scaling
relations and gas mass fractions depend significantly on cluster morphology,
and the true relations are not recovered even if the most relaxed clusters are
used. We show that cluster structure, via the power ratios, can be used to
effectively correct the hydrostatic mass estimates and mass-scaling relations,
suggesting that we can calibrate for this systematic effect in cosmological
studies. Similar to observational studies, we find that cluster structure,
particularly centroid shift, evolves with redshift. This evolution is mild but
will lead to additional errors at high redshift. Projection along the line of
sight leads to significant uncertainty in the structure of individual clusters:
less than 50% of clusters which appear relaxed in projection based on our
structure measures are truly relaxed.Comment: 57 pages, 18 figures, accepted to ApJ, updated definition of T_X and
M_gas but results unchanged, for version with full resolution figures, see
http://www.ociw.edu/~tesla/sims.ps.g
Finite Temperature QCD on Anisotropic Lattices
We present results for mesonic propagators in temporal and spatial direction
and for topological properties at T below and above the deconfining transition
in quenched QCD. We use anisotropic lattices and Wilson fermions.Comment: 6 pages, 7 figures, Talk given at 16th International Symposium on
Lattice Field Theory (LATTICE 98(hightemp)) , Boulder, CO, 13-18 Jul 1998.
(Replaced: Fig.4 corrected, further minor modifications in legends and text.
Monopoles, noncommutative gauge theories in the BPS limit and some simple gauge groups
For three conspicuous gauge groups, namely, SU(2), SU(3) and SO(5), and at
first order in the noncommutative parameter matrix h\theta^{\mu\nu}, we
construct smooth monopole --and, some two-monopole-- fields that solve the
noncommutative Yang-Mills-Higgs equations in the BPS limit and that are formal
power series in h\theta^{\mu\nu}. We show that there exist noncommutative BPS
(multi-)monopole field configurations that are formal power series in
h\theta^{\mu\nu} if, and only if, two a priori free parameters of the
Seiberg-Witten map take very specific values. These parameters, that are not
associated to field redefinitions nor to gauge transformations, have thus
values that give rise to sharp physical effects.Comment: 30 pages, no figure
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