11,732 research outputs found
Classification of String-like Solutions in Dilaton Gravity
The static string-like solutions of the Abelian Higgs model coupled to
dilaton gravity are analyzed and compared to the non-dilatonic case. Except for
a special coupling between the Higgs Lagrangian and the dilaton, the solutions
are flux tubes that generate a non-asymptotically flat geometry. Any point in
parameter space corresponds to two branches of solutions with two different
asymptotic behaviors. Unlike the non-dilatonic case, where one branch is always
asymptotically conic, in the present case the asymptotic behavior changes
continuously along each branch.Comment: 15 pages, 6 figures. To be published in Phys. Rev.
Second virial coefficient in one dimension, as a function of asymptotic quantities
A result from Dodd and Gibbs[1] for the second virial coefficient of
particles in 1 dimension, subject to delta-function interactions, has been
obtained by direct integration of the wave functions. It is shown that this
result can be obtained from a phase shift formalism, if one includes the
contribution of oscillating terms. The result is important in work to follow,
for the third virial coefficient, for which a similar formalism is being
developed. We examine a number of fine points in the quantum mechanical
formalisms.Comment: 7 pages, no figures, submitted to Molecular Physic
Structure and Mass of a Young Globular Cluster in NGC 6946
Using the Wide Field Planetary Camera 2 on board the Hubble Space Telescope,
we have imaged a luminous young star cluster in the nearby spiral galaxy NGC
6946. The cluster has an absolute visual magnitude M(V)=-13.2, comparable to
the brightest young `super-star clusters' in the Antennae merger galaxy. UBV
colors indicate an age of about 15 Myr. The cluster has a compact core (core
radius = 1.3 pc), surrounded by an extended envelope. We estimate that the
effective radius (Reff) = 13 pc, but this number is uncertain because the outer
parts of the cluster profile gradually merge with the general field. Combined
with population synthesis models, the luminosity and age of the cluster imply a
mass of 8.2x10^5 Msun for a Salpeter IMF extending down to 0.1 Msun, or
5.5x10^5 Msun if the IMF is log-normal below 0.4 Msun. Depending on model
assumptions, the central density of the cluster is between 5300 Msun pc^-3 and
17000 Msun pc^-3, comparable to other high-density star forming regions. We
also estimate a dynamical mass for the cluster, using high-dispersion spectra
from the HIRES spectrograph on the Keck I telescope. The velocity dispersion is
10.0 +/- 2.7 km/s, implying a total cluster mass within 65 pc of (1.7 +/- 0.9)
x 10^6 Msun. Comparing the dynamical mass with the mass estimates based on the
photometry and population synthesis models, the mass-to-light ratio is at least
as high as for a Salpeter IMF extending down to 0.1 Msun, although a turn-over
in the IMF at 0.4 Msun is still possible within the errors. The cluster will
presumably remain bound, evolving into a globular cluster-like object.Comment: 33 pages, including 10 figures and 3 tables. Accepted for publication
in the Astrophysical Journa
Using mixed data in the inverse scattering problem
Consider the fixed- inverse scattering problem. We show that the zeros
of the regular solution of the Schr\"odinger equation, , which are
monotonic functions of the energy, determine a unique potential when the domain
of the energy is such that the range from zero to infinity. This
suggests that the use of the mixed data of phase-shifts
, for which the zeros of the regular solution are monotonic in both domains,
and range from zero to infinity, offers the possibility of determining the
potential in a unique way.Comment: 9 pages, 2 figures. Talk given at the Conference of Inverse Quantum
Scattering Theory, Hungary, August 200
Young Super Star Clusters in the Starburst of M82: The Catalogue
Recent results from Hubble Space Telescope (HST) have resolved starbursts as
collections of compact young stellar clusters. Here we present a photometric
catalogue of the young stellar clusters in the nuclear starburst of M82,
observed with the HST WFPC2 in Halpha (F656N) and in four optical broad-band
filters. We identify 197 young super stellar clusters. The compactness and high
density of the sources led us to develop specific techniques to measure their
sizes. Strong extinction lanes divide the starburst into five different zones
and we provide a catalogue of young super star clusters for each of these. In
the catalogue we include relative coordinates, radii, fluxes, luminosities,
masses, equivalent widths, extinctions, and other parameters. Extinction values
have been derived from the broad-band images. The radii range between 3 and 9
pc, with a mean value of 5.7 +/- 1.4pc, and a stellar mass between 10e4 and
10e6 Mo. The inferred masses and mean separation, comparable to the size of
super star clusters, together with their high volume density, provides strong
evidence for the key ingredients postulated by Tenorio et al. (2003) as
required for the development of a supergalactic wind.Comment: 45 pages, 5 figures, 12 tables. Accepted for publication in ApJ.
Added Erratu
Quantum Coherent String States in AdS_3 and SL(2,R) WZWN Model
In this paper we make the connection between semi-classical string
quantization and exact conformal field theory quantization of strings in 2+1
Anti de Sitter spacetime. More precisely, considering the WZWN model
corresponding to SL(2,R) and its covering group, we construct quantum {\it
coherent} string states, which generalize the ordinary coherent states of
quantum mechanics, and show that in the classical limit they correspond to
oscillating circular strings. After quantization, the spectrum is found to
consist of two parts: A continuous spectrum of low mass states (partly
tachyonic) fulfilling the standard spin-level condition necessary for unitarity
|j|< k/2, and a discrete spectrum of high mass states with asymptotic behaviour
m^2\alpha'\propto N^2 (N positive integer). The quantization condition for the
high mass states arises from the condition of finite positive norm of the
coherent string states, and the result agrees with our previous results
obtained using semi-classical quantization. In the k\to\infty limit, all the
usual properties of coherent or {\it quasi-classical} states are recovered. It
should be stressed that we consider the circular strings only for simplicity
and clarity, and that our construction can easily be used for other string
configurations too. We also compare our results with those obtained in the
recent preprint hep-th/0001053 by Maldacena and Ooguri.Comment: Misprints corrected. Final version to appear in Phys. Rev.
S-matrix poles and the second virial coefficient
For cutoff potentials, a condition which is not a limitation for the
calculation of physical systems, the S-matrix is meromorphic. We can express it
in terms of its poles, and then calculate the quantum mechanical second virial
coefficient of a neutral gas.
Here, we take another look at this approach, and discuss the feasibility,
attraction and problems of the method. Among concerns are the rate of
convergence of the 'pole' expansion and the physical significance of the
'higher' poles.Comment: 20 pages, 8 tables, submitted to J. Mol. Phy
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