1,392 research outputs found
The mass of X-Ray Nova Scorpii 1994 (=GRO J1655--40)]
We have obtained high and intermediate resolution optical spectra of the
black-hole candidate Nova Sco 1994 in May/June 1998, when the source was in
complete (X-ray) quiescence. We measure the radial velocity curve of the
secondary star and obtain a semi-amplitude of K_2=215.5+/-2.4 km/s, which is 6
per cent lower than the only previously determined value. This new value for
K_2 thus reduces the binary mass function to f(M) = 2.73+/-0.09 Mo. Using only
the high resolution spectra we constrain the rotational broadening of the
secondary star, vsini, to lie in the range 82.9-94.9 km/s (95 per cent
confidence) and thus constrain the binary mass ratio to lie in the range
0.337--0.436 (95 per cent confidence). We can also combine our results with
published limits for the binary inclination to constrain the mass of the
compact object and secondary star to the ranges 5.5 -- 7.9 and 1.7 -- 3.3 Mo
respectively (95 per cent confidence). Finally, we report on the detection of
the Lithium resonance line at 6707.8 A, with an equivalent width of 55+/-8 mA.Comment: 5 pages, 5 figures, accepted by MNRA
A Magnetic Monopole in Pure SU(2) Gauge Theory
The magnetic monopole in euclidean pure SU(2) gauge theory is investigated
using a background field method on the lattice.
With Monte Carlo methods we study the mass of the monopole in the full
quantum theory.
The monopole background under the quantum fluctuations is induced by imposing
fixed monopole boundary conditions on the walls of a finite lattice volume.
By varying the gauge coupling it is possible to study monopoles with scales
from the hadronic scale up to high energies.
The results for the monopole mass are consistent with a conjecture we made
previously in a realization of the dual superconductor hypothesis of
confinement.Comment: 33 pages uufiles-compressed PostScript including (all) 12 figures,
preprint numbers ITFA-93-19 (Amsterdam), OUTP-93-21P (Oxford), DFTUZ/93/23
(Zaragoza
Observation of Goos-H\"{a}nchen shifts in metallic reflection
We report the first observation of the Goos-Hnchen
shift of a light beam incident on a metal surface. This phenomenon is
particularly interesting because the Goos-Hnchen shift
for polarized light in metals is negative and much bigger than the positive
shift for polarized light. The experimental result for the measured shifts
as a function of the angle of incidence is in excellent agreement with
theoretical predictions. In an energy-flux interpretation, our measurement
shows the existence of a backward energy flow at the bare metal surface when
this is excited by a polarized beam of light.Comment: The parer was published on Optics Express. The new version is
modified according to the reviewers suggestion
Four dimensional R^4 superinvariants through gauge completion
We fully compute the N=1 supersymmetrization of the fourth power of the Weyl
tensor in d=4 x-space with the auxiliary fields. In a previous paper, we showed
that their elimination requires an infinite number of terms; we explicitely
compute those terms to order \kappa^4 (three loop). We also write, in
superspace notation, all the possible N=1 actions, in four dimensions, that
contain pure R^4 terms (with coupling constants). We explicitely write these
actions in terms of the \theta components of the chiral density \epsilon and
the supergravity superfields R, G_m, W_{ABC}. Using the method of gauge
completion, we compute the necessary \theta components which allow us to write
these actions in x-space. We discuss under which circumstances can these extra
R^4 correction terms be reabsorbed in the pure supergravity action, and their
relevance to the quantum supergravity/string theory effective actions.Comment: 20 pages, no figures. Sec. 3 clarified; typos correcte
Torons and black hole entropy
We consider a supersymmetric system of D-5-branes compactified on a 5-torus
with a self-dual background field strength on a 4-torus and carrying
left-moving momentum along a circle. The corresponding supergravity solution
describes a 5-dimensional black hole with a regular horizon. The entropy of
this black hole may be explained in terms of the Landau degeneracy for open
strings stretching between different branes. In the gauge theory approximation
this D-5-brane system is described by a super Yang-Mills theory with a t'Hooft
twist. By choosing a supersymmetric branch of the theory we obtain perfect
agreement with the entropy formula. The result relies on the number of massless
torons associated with the gauge field components that obey twisted boundary
conditions.Comment: 31 pages, latex. Some equations corrected. Final version to be
published in Nuclear Physics
Probing spacetime foam with extragalactic sources
Due to quantum fluctuations, spacetime is probably ``foamy'' on very small
scales. We propose to detect this texture of spacetime foam by looking for
core-halo structures in the images of distant quasars. We find that the Very
Large Telescope interferometer will be on the verge of being able to probe the
fabric of spacetime when it reaches its design performance. Our method also
allows us to use spacetime foam physics and physics of computation to infer the
existence of dark energy/matter, independent of the evidence from recent
cosmological observations.Comment: LaTeX, 11 pages, 1 figure; version submitted to PRL; several
references added; very useful comments and suggestions by Eric Perlman
incorporate
NNLO Corrections to the Polarized Drell-Yan Coefficient Function
We present the full next-to-next-to-leading order (NNLO) corrections to the
coefficient function for the polarized cross section of
the Drell-Yan process. We study the effect of these corrections on the process
at an C.M. energy . All QCD partonic
subprocesses have been included provided the lepton pair is created by a
virtual photon, which is a valid approximation for a lepton pair invariant mass
. For this reaction the dominant subprocess is given by and its higher order corrections so that it provides us with an
excellent tool to measure the polarized sea-quark densities.Comment: 5 pages, 5 figures, 7th DESY Workshop on Elementary Particle Theory,
Loops and Legs in Quantum Field Theory, Zinnowitz, Germany, April 25-30, 200
Hard X-ray lags in GRO J1719-24
We have used the Fourier cross spectra of GRO J1719-24, as obtained with
BATSE, to estimate the phase lags between the X-ray flux variations in the
20--50 and 50--100 keV energy bands as a function of Fourier frequency in the
interval 0.002--0.488 Hz. Our analysis covers the entire ~80 day X-ray outburst
of this black-hole candidate, following the first X-ray detection on 1993
September 25. The X-ray variations in the 50--100 keV band lag those in the
20--50 keV energy band by an approximately constant phase difference of 0.072
+/- 0.010 rad in the frequency interval 0.02--0.20 Hz. The peak phase lags in
the interval 0.02--0.20 Hz are about twice those of Cyg X-1 and GRO
J0422+32.These results are consistent with models for Comptonization regions
composed of extended non-uniform clouds around the central source.Comment: 10 pages, including 4 postscript figures, AASTEX. Accepted for
publication by Ap
Probing for Instanton Quarks with epsilon-Cooling
We use epsilon-cooling, adjusting at will the order a^2 corrections to the
lattice action, to study the parameter space of instantons in the background of
non-trivial holonomy and to determine the presence and nature of constituents
with fractional topological charge at finite and zero temperature for SU(2). As
an additional tool, zero temperature configurations were generated from those
at finite temperature with well-separated constituents. This is achieved by
"adiabatically" adjusting the anisotropic coupling used to implement finite
temperature on a symmetric lattice. The action and topological charge density,
as well as the Polyakov loop and chiral zero-modes are used to analyse these
configurations. We also show how cooling histories themselves can reveal the
presence of constituents with fractional topological charge. We comment on the
interpretation of recent fermion zero-mode studies for thermalized ensembles at
small temperatures.Comment: 26 pages, 14 figures in 33 part
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