1,962,211 research outputs found
Draco -- A Failure of the Tidal Model
We test whether the structural properties of the nearby dwarf spheroidal
(dSph) galaxy Draco, a well-studied Milky Way companion, can be reconciled with
the suggestion that dSphs are unbound tidal remnants with a large depth extent
along the line of sight. In order to apply the observational test of this
hypothesis suggested by Klessen & Zhao, we use public photometric data from the
Sloan Digital Sky Survey (SDSS) to explore the width of Draco's blue horizontal
branch over a range of areas covering 0.06 square degrees to 6.25 square
degrees centered on Draco. The SDSS database is the only currently existing
database with sufficient depth and area coverage to permit a stringent test of
the tidal models. We show that blue horizontal branch stars extend beyond the
previously inferred limiting radii of Draco, consistent with the observed
absence of a truncated stellar surface density profile of this dSph. We
calculate new models for a galaxy without dark matter, using Draco's
morphological properties as constraints. The resulting models are unable to
reproduce the narrow observed horizontal branch width of Draco, which stays
roughly constant regardless of the field of view. We conclude that Draco cannot
be the remnant of a tidally disrupted satellite, but is probably strongly
dark-matter dominated. (ABSTRACT ABBREVIATED)Comment: 26 pages, 9 figures included, accepted for publication in ApJ,
high-resolution version available at
http://www.aip.de./~ralf/Publications/p22.abstract.htm
Asymptotic behaviour of two-point functions in multi-species models
We extract the long-distance asymptotic behaviour of two-point correlation
functions in massless quantum integrable models containing multi-species
excitations. For such a purpose, we extend to these models the method of a
large-distance regime re-summation of the form factor expansion of correlation
functions. The key feature of our analysis is a technical hypothesis on the
large-volume behaviour of the form factors of local operators in such models.
We check the validity of this hypothesis on the example of the
-invariant XXX magnet by means of the determinant representations for
the form factors of local operators in this model. Our approach confirms the
structure of the critical exponents obtained previously for numerous models
solvable by the nested Bethe Ansatz.Comment: 45 pages, 1 figur
Maxwell Superalgebras and Abelian Semigroup Expansion
The Abelian semigroup expansion is a powerful and simple method to derive new
Lie algebras from a given one. Recently it was shown that the -expansion of
leads us to the Maxwell algebra
. In this paper we extend this result to superalgebras, by proving
that different choices of abelian semigroups lead to interesting
Maxwell Superalgebras. In particular, the minimal Maxwell superalgebra
and the -extended Maxwell superalgebra recently found by the Maurer Cartan expansion procedure, are
derived alternatively as an -expansion of . Moreover we show that new minimal Maxwell superalgebras type
and their -extended generalization can be obtained
using the -expansion procedure.Comment: 31 pages, some clarifications in the abstract,introduction and
conclusion, typos corrected, a reference and acknowledgements added, accepted
for publication in Nuclear Physics
N=1 Supergravity and Maxwell superalgebras
We present the construction of the supergravity action from the minimal
Maxwell superalgebra , which can be derived from the
superalgebra by applying the abelian
semigroup expansion procedure. We show that , pure supergravity can
be obtained alternatively as the MacDowell-Mansouri like action built from the
curvatures of the Maxwell superalgebra . We extend this
result to all minimal Maxwell superalgebras type . The
invariance under supersymmetry transformations is also analized.Comment: 22 pages, published versio
Electromagnetic response and effective gauge theory of graphene in a magnetic field
The electromagnetic response of graphene in a magnetic field is studied, with
particular emphasis on the quantum features of its ground state (vacuum). The
graphene vacuum, unlike in conventional quantum Hall systems, is a dielectric
medium and carries an appreciable amount of electric and magnetic
susceptibilities. The dielectric effect grows rapidly with increasing filling
factor nu in such a way that reflects the 'relativistic' Landau-level
characteristics of graphene as well as its valley and spin degeneracy. A close
look into the dielectric function also reveals that the Coulomb interaction is
efficiently screened on the scale of the magnetic length, leading to a
prominent reduction of the exciton spectra in graphene. In addition, an
effective gauge theory of graphene is constructed out of the response. It is
pointed out thereby that the electric susceptibility is generally expressed as
a ratio of the Hall conductance to the Landau gap.Comment: 9 pages, 3 figures, revtex, corrected typo
On the Weakening of Chromospheric Magnetic Field in Active Regions
Simultaneous measurement of line-of-sight (LOS) magnetic and velocity fields
at the photosphere and chromosphere are presented. Fe I line at
and at are used respectively for deriving the
physical parameters at photospheric and chromospheric heights. The LOS magnetic
field obtained through the center-of-gravity method show a linear relation
between photospheric and chromospheric field for field strengths less than 700
G. But in strong field regions, the LOS magnetic field values derived from
are much weaker than what one gets from the linear relationship
and also from those expected from the extrapolation of the photospheric
magnetic field. We discuss in detail the properties of magnetic field observed
in from the point of view of observed velocity gradients. The
bisector analysis of Stokes profiles show larger velocity
gradients in those places where strong photospheric magnetic fields are
observed. These observations may support the view that the stronger fields
diverge faster with height compared to weaker fields.Comment: accepted for publication in Ap
Sklyanin Bracket and Deformation of the Calogero-Moser System
A two-dimensional integrable system being a deformation of the rational
Calogero-Moser system is constructed via the symplectic reduction, performed
with respect to the Sklyanin algebra action. We explicitly resolve the
respective classical equations of motion via the projection method and quantize
the system.Comment: 14 pages, no figure
Conformal Sigma Models with Anomalous Dimensions and Ricci Solitons
We present new non-Ricci-flat Kahler metrics with U(N) and O(N) isometries as
target manifolds of superconformally invariant sigma models with an anomalous
dimension. They are so-called Ricci solitons, special solutions to a Ricci-flow
equation. These metrics explicitly contain the anomalous dimension and reduce
to Ricci-flat Kahler metrics on the canonical line bundles over certain coset
spaces in the limit of vanishing anomalous dimension.Comment: 9 pages, no figure
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