52,356 research outputs found
BRST extension of the Faddeev model
The Faddeev model is a second class constrained system. Here we construct its
nilpotent BRST operator and derive the ensuing manifestly BRST invariant
Lagrangian. Our construction employs the structure of Stuckelberg fields in a
nontrivial fashion.Comment: 4 pages, new references adde
The Classical and Quantum Theory of Relativistic p-Branes without Constraints
It is shown that a relativistic (i.e. a Poincar{\' e} invariant) theory of
extended objects (called p-branes) is not necessarily invariant under
reparametrizations of corresponding -dimensional worldsheets (including
worldlines for ). Consequnetly, no constraints among the dynamical
variables are necessary and quantization is straightforward. Additional degrees
of freedom so obtained are given a physical interpretation as being related to
membrane's elastic deformations ("wiggleness"). In particular, such a more
general, unconstrained theory implies as solutions also those p-brane states
that are solutions of the conventional theory of the Dirac-Nambu-Goto type.Comment: 21 page
Variational Approach to Hard Sphere Segregation Under Gravity
It is demonstrated that the minimization of the free energy functional for
hard spheres and hard disks yields the result that excited granular materials
under gravity segregate not only in the widely known "Brazil nut" fashion, i.e.
with the larger particles rising to the top, but also in reverse "Brazil nut"
fashion. Specifically, the local density approximation is used to investigate
the crossover between the two types of segregation occurring in the liquid
state, and the results are found to agree qualitatively with previously
published results of simulation and of a simple model based on condensation.Comment: 10 pages, 3 figure
Fluxon analogues and dark solitons in linearly coupled Bose-Einstein condensates
Two effectively one-dimensional parallel coupled Bose-Einstein condensates in
the presence of external potentials are studied. The system is modelled by
linearly coupled Gross-Pitaevskii equations. In particular, grey-soliton-like
solutions representing analogues of superconducting Josephson fluxons as well
as coupled dark solitons are discussed. Theoretical approximations based on
variational formulations are derived. It is found that the presence of a
magnetic trap can destabilize the fluxon analogues. However, stabilization is
possible by controlling the effective linear coupling between the condensates.Comment: 14 pages, 7 figures, The paper is to appear in Journal of Physics
Spectroscopic Follow-up of X-ray Sources in the ChaMPlane Survey: Identification of a New Cataclysmic Variable
We present a multi-object optical spectroscopy follow-up study of X-ray
sources in a field along the Galactic Plane (l=327.42 deg, b=2.26 deg) which is
part of the Chandra Multi-wavelength Plane survey (ChaMPlane). We obtained
spectra for 46 stars, including 15 likely counterparts to X-ray sources, and
sources showing an H-alpha color excess. This has led to the identification of
a new cataclysmic variable (CV), CXOPS J154305.5-522709, also named ChaMPlane
Bright Source 7 (CBS~7), and we identified 8 X-ray sources in the field as
active late-type stars. CBS~7 was previously studied in X-rays and showed a
hard spectrum and two periods: 1.22+/-0.08 h and 2.43+/-0.26 h. We present here
clear evidence that the source is a CV through the detection of H, HeI and HeII
emission lines in its optical spectrum. The hard X-ray spectrum and the
presence of the HeII 4686 in emission with a large equivalent width suggest a
magnetic CV. The near-infrared counterpart is significantly variable, and we
found a period consistent with the longest X-ray period at 2.39+/-0.05 h but
not the shortest X-ray period. If this period is the orbital period, this would
place the system in the CV period gap. The possible orbital period suggests a
dM4+/-1 companion star. The distance is then estimated to be ~1 kpc. The system
could be a relatively hard and X-ray luminous polar or an intermediate polar,
possibly nearly-synchronous.Comment: accepted for publication in ApJ; 6 figures, 5 tables, 8 pages with
emulateapj styl
Strong correlation effects in the doped Hubbard model in infinite dimensions
The density of states and the optical conductivity of the doped Hubbard model
on a Bethe lattice with infinite connectivities have been studied using an
analytic variant of the Lanczos continued fraction method. The spectral weight
of the gap states and the position of the chemical potential upon hole or
electron doping have been studied. We argue that the strong correlation effects
such as gap states and midinfrared band shown in two dimensions also appear in
infinite dimensions.Comment: 9 pages, revtex, 3 figures upon reques
Massless and Massive Three Dimensional Super Yang-Mills Theory and Mini-Twistor String Theory
We propose various ways of adding mass terms to three-dimensional twistor
string theory. We begin with a review of mini-twistor space--the reduction of
D=4 twistor space to D=3. We adapt the two proposals for twistor string theory,
Witten's and Berkovits's, to D=3 super Yang-Mills theory. In Berkovits's model,
we identify the enhanced R-symmetry. We then construct B-model topological
string theories that, we propose, correspond to D=3 Yang-Mills theory with
massive spinors and massive and massless scalars in the adjoint representation
of the gauge group. We also analyze the counterparts of these constructions in
Berkovits's model. Some of our constructions can be lifted to D=4, where
infinitesimal mass terms correspond to VEVs of certain superconformal gravity
fields.Comment: 69 pages; Typos correcte
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