4,964 research outputs found
Path Integral Approach to Residual Gauge Fixing
In this paper we study the question of residual gauge fixing in the path
integral approach for a general class of axial-type gauges including the
light-cone gauge. We show that the two cases -- axial-type gauges and the
light-cone gauge -- lead to very different structures for the explicit forms of
the propagator. In the case of the axial-type gauges, fixing the residual
symmetry determines the propagator of the theory completely. On the other hand,
in the light-cone gauge there is still a prescription dependence even after
fixing the residual gauge symmetry, which is related to the existence of an
underlying global symmetry.Comment: revtex 13pages, slightly expanded discussion, version to be published
in Physical Review
An evolved disk surrounding the massive main sequence star MWC 297?
We present the results of the interferometric observations of the
circumstellar disk surrounding MWC 297 in the continuum at 230 GHz (1.3 mm) and
in the (J=2-1) rotational transitions of CO,CO and CO
using the Submillimeter Array. At a distance of 250 pc, MWC 297 is one of the
closest, young massive stars (M 10 M) to us. Compact
continuum emission is detected towards MWC 297 from which we estimate a disk
mass (gas+dust) of 0.07 M and a disk radius of 80 AU. Our
result demonstrates that circumstellar disks can survive around massive stars
well into their main sequence phase even after they have become optically
visible. Complementing our observations with the data compiled from the
literature, we find the submm dust opacity index to be between 0.1 and
0.3. If the emission is optically thin, the low value of indicates the
presence of relatively large grains in the disk, possibly because of grain
growth. We do not detect any CO emission associated with the continuum source.
We argue that the CO emission from the disk is likely optically thin, in
which case, we derive an upper limit to the gas mass which implies significant
depletion of molecular gas in the disk. The mass of this disk and the
evolutionary trends observed are similar to those found for intermediate mass
Herbig Ae stars and low mass T Tauri stars.Comment: 4 pages, 3 Figures, accepted for publication in ApJ
Non-chiral current algebras for deformed supergroup WZW models
We study deformed WZW models on supergroups with vanishing Killing form. The
deformation is generated by the isotropic current-current perturbation which is
exactly marginal under these assumptions. It breaks half of the global
isometries of the original supergroup. The current corresponding to the
remaining symmetry is conserved but its components are neither holomorphic nor
anti-holomorphic. We obtain the exact two- and three-point functions of this
current and a four-point function in the first two leading orders of a 1/k
expansion but to all orders in the deformation parameter. We further study the
operator product algebra of the currents, the equal time commutators and the
quantum equations of motion. The form of the equations of motion suggests the
existence of non-local charges which generate a Yangian. Possible applications
to string theory on Anti-de Sitter spaces and to condensed matter problems are
briefly discussed.Comment: 43 pages, Latex, one eps figure; v.2: minor corrections, a reference
adde
Structural and nuclear characterizations of defects created by noble gas implantation in silicon oxide
Thermally grown silicon oxide layer was implanted at room temperature with 300keV Xe at fluences ranging from 0.5 to 5x10Xe/cm. Bubbles created after Xe-implantation provided a low-k silicon oxide that has potential use as a dielectric material for interconnects in Si integrated circuits. Transmission Electron Microscopy (TEM), Rutherford Backscattering Spectrometry (RBS) and Positron Annihilation Spectroscopy (PAS) were used to provide a comprehensive characterization of defects (bubbles, vacancy, gas atoms and other types of defects) created by Xe implantation in layer. These measurements suggest that the bubbles observed with TEM for all fluences were a consequence of the interaction between Xe and vacancies (V), with complexes created in the zone where V and Xe profiles overlap. Negatively charged defects such as (, and ) are also created after implantation
Level rearrangement in exotic atoms and quantum dots
A presentation and a generalisation are given of the phenomenon of level
rearrangement, which occurs when an attractive long-range potential is
supplemented by a short-range attractive potential of increasing strength. This
problem has been discovered in condensate-matter physics and has also been
studied in the physics of exotic atoms. A similar phenomenon occurs in a
situation inspired by quantum dots, where a short-range interaction is added to
an harmonic confinement.Comment: 12 pages, 11 figures, RevTeX
Thermal Operator Representation of Finite Temperature Graphs
Using the mixed space representation (t,p) in the context of scalar field
theories, we prove in a simple manner that the Feynman graphs at finite
temperature are related to the corresponding zero temperature diagrams through
a simple thermal operator, both in the imaginary time as well as in the real
time formalisms. This result is generalized to the case when there is a
nontrivial chemical potential present. Several interesting properties of the
thermal operator are also discussed.Comment: 20 pages, seven figure
Quantization in a General Light-front Frame
In this paper, we study the question of quantization of quantum field
theories in a general light-front frame. We quantize scalar, fermion as well as
gauge field theories in a systematic manner carrying out the Hamiltonian
analysis carefully. The decomposition of the fields into positive and negative
frequency terms needs to be done carefully after which we show that the (anti)
commutation relations for the quantum operators become frame independent. The
frame dependence is completely contained in the functions multiplying these
operators in the field decomposition. We derive the propagators from the vacuum
expectation values of the time ordered products of the fields.Comment: 14 pages, revtex, version to be published in Phys. Rev. D with the
discussion of Abelian field quantization replaced by the non-Abelian field
and some comments added on the Mandelstam-Liebbrandt prescriptio
Dark Energy density in models with Split Supersymmetry and degenerate vacua
In N=1 supergravity supersymmetric (SUSY) and non-supersymmetric Minkowski
vacua originating in the hidden sector can be degenerate. In the supersymmetric
phase in flat Minkowski space non-perturbative supersymmetry breakdown may take
place in the observable sector, inducing a non-zero and positive vacuum energy
density. Assuming that such a supersymmetric phase and the phase in which we
live are degenerate, we estimate the value of the cosmological constant. We
argue that the observed value of the dark energy density can be reproduced in
the Split-SUSY scenario of the supersymmetry breaking if the SUSY breaking
scale is of order of 10^{10} GeV.Comment: 20 pages, 1 figure, some minor changes to the text, references adde
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