561 research outputs found
A new kind of McKay correspondence from non-Abelian gauge theories
The boundary chiral ring of a 2d gauged linear sigma model on a K\"ahler
manifold classifies the topological D-brane sectors and the massless open
strings between them. While it is determined at small volume by simple group
theory, its continuation to generic volume provides highly non-trivial
information about the -branes on , related to the derived category
. We use this correspondence to elaborate on an extended notion of
McKay correspondence that captures more general than orbifold singularities. As
an illustration, we work out this new notion of McKay correspondence for a
class of non-compact Calabi-Yau singularities related to Grassmannians.Comment: 29 pages, harvmac(b), 2 fig
About the morphology of dwarf spheroidal galaxies and their dark matter content
The morphological properties of the Carina, Sculptor and Fornax dwarfs are
investigated using new wide field data with a total area of 29 square degrees.
The stellar density maps are derived, hinting that Sculptor possesses tidal
tails indicating interaction with the Milky Way. Contrary to previous studies
we cannot find any sign of breaks in the density profiles for the Carina and
Fornax dwarfs. The possible existence of tidal tails in Sculptor and of King
limiting radii in Fornax and Carina are used to derive global M/L ratios,
without using kinematic data. By matching those M/L ratios to kinematically
derived values we are able to constrain the orbital parameters of the three
dwarfs. Fornax cannot have M/L smaller than 3 and must be close to its
perigalacticon now. The other extreme is Sculptor that needs to be on an orbit
with an eccentricity bigger than 0.5 to be able to form tidal tails despite its
kinematic M/L.Comment: 9 pages, 7 figures, accepted by A&
Calculations for Mirror Symmetry with D-branes
We study normal functions capturing D-brane superpotentials on several one-
and two-parameter Calabi-Yau hypersurfaces and complete intersections in
weighted projective space. We calculate in the B-model and interpret the
results using mirror symmetry in the large volume regime, albeit without
identifying the precise A-model geometry in all cases. We identify new classes
of extensions of Picard-Fuchs equations, as well as a novel type of topology
changing phase transition involving quantum D-branes. A 4-d domain wall which
is obtained in one region of closed string moduli space from wrapping a
four-chain interpolating between two Lagrangian submanifolds is, for other
values of the parameters, represented by a disk ending on a single Lagrangian.Comment: 42 page
A method to polarise antiprotons in storage rings and create polarised antineutrons
An intense circularely polarised photon beam interacts with a cooled
antiproton beam in a storage ring. Due to spin dependent absorption cross
sections for the reaction gamma+antiproton > pi- + antineutron a built-up of
polarisation of the stored antiprotons takes place. Figures-of-merit around 0.1
can be reached in principle over a wide range of antiproton energies. In this
process antineutrons with Polarisation > 70% emerge. The method is presented
for the case of 300 MeV/c cooled antiproton beam
D-Branes on K3-Fibrations
B-type D-branes are constructed on two different K3-fibrations over IP_1
using boundary conformal field theory at the rational Gepner points of these
models. The microscopic CFT charges are compared with the Ramond charges of
D-branes wrapped on holomorphic cycles of the corresponding Calabi-Yau
manifold. We study in particular D4-branes and bundles localized on the K3
fibers, and find from CFT that each irreducible component of a bundle on K3
gains one modulus upon fibration over IP_1. This is in agreement with
expectations and so provides a further test of the boundary CFT.Comment: 16p, harvmac, tables.tex; typos corrected, refs added, discussion
about moduli spaces improve
The cosmic evolution of the spatially-resolved star formation rate and stellar mass of the CALIFA survey
We investigate the cosmic evolution of the absolute and specific star
formation rate (SFR, sSFR) of galaxies as derived from a spatially-resolved
study of the stellar populations in a set of 366 nearby galaxies from the
CALIFA survey. The analysis combines GALEX and SDSS images with the 4000 break,
H_beta, and [MgFe] indices measured from the datacubes, to constrain parametric
models for the SFH, which are then used to study the cosmic evolution of the
star formation rate density (SFRD), the sSFR, the main sequence of star
formation (MSSF), and the stellar mass density (SMD). A delayed-tau model,
provides the best results, in good agreement with those obtained from
cosmological surveys. Our main results from this model are: a) The time since
the onset of the star formation is larger in the inner regions than in the
outer ones, while tau is similar or smaller in the inner than in the outer
regions. b) The sSFR declines rapidly as the Universe evolves, and faster for
early than for late type galaxies, and for the inner than for the outer regions
of galaxies. c) SFRD and SMD agree well with results from cosmological surveys.
At z< 0.5, most star formation takes place in the outer regions of late spiral
galaxies, while at z>2 the inner regions of the progenitors of the current E
and S0 are the major contributors to SFRD. d) The inner regions of galaxies are
the major contributor to SMD at z> 0.5, growing their mass faster than the
outer regions, with a lookback time at 50% SMD of 9 and 6 Gyr for the inner and
outer regions. e) The MSSF follows a power-law at high redshift, with the slope
evolving with time, but always being sub-linear. f) In agreement with galaxy
surveys at different redshifts, the average SFH of CALIFA galaxies indicates
that galaxies grow their mass mainly in a mode that is well represented by a
delayed-tau model, with the peak at z~2 and an e-folding time of 3.9 Gyr.Comment: 23 pages, 16 figures, 6 tables, accepted for publication in Astronomy
& Astrophysics. *Abridged abstract
HST/STIS Spectra of Nuclear Star Clusters in Spiral Galaxies: Dependence of Age and Mass On Hubble Type
(Abridged) We study the nuclear star clusters in spiral galaxies of various
Hubble types using spectra obtained with STIS on-board HST. We observed the
nuclear clusters in 40 galaxies, selected from two previous HST/WFPC2 imaging
surveys. The spectra provide a better separation of cluster light from
underlying galaxy light than is possible with ground-based spectra. To infer
the star formation history, metallicity and dust extinction, we fit weighted
superpositions of single-age stellar population templates to the spectra. The
luminosity-weighted age ranges from 10 Myrs to 10 Gyrs. The stellar populations
of NCs are generally best fit as a mixture of populations of different ages.
This indicates that NCs did not form in a single event, but instead they had
additional star formation long after the oldest stars formed. On average, the
sample clusters in late-type spirals have a younger luminosity-weighted mean
age than those in early-type spirals (log(age/yr) = 8.37+/-0.25 vs.
9.23+/-0.21). The average cluster masses are smaller in late-type spirals than
in early-type spirals (log(M/Msun) = 6.25+/-0.21 vs. 7.63+/-0.24), and exceed
the masses typical of globular clusters. The cluster mass correlates strongly
with both the Hubble type of the host galaxy and the luminosity of its bulge.
The latter correlation has the same slope as the well-known correlation between
supermassive black hole mass and bulge luminosity. The properties of both
nuclear clusters and black holes are therefore intimately connected to the
properties of the host galaxy.Comment: AJ submitted (original submission Nov 30, 2005, present version
includes changes based on referee recommendations). 69 pages, 16 figures, 7
table
Stability of Landau-Ginzburg branes
We evaluate the ideas of Pi-stability at the Landau-Ginzburg point in moduli
space of compact Calabi-Yau manifolds, using matrix factorizations to B-model
the topological D-brane category. The standard requirement of unitarity at the
IR fixed point is argued to lead to a notion of "R-stability" for matrix
factorizations of quasi-homogeneous LG potentials. The D0-brane on the quintic
at the Landau-Ginzburg point is not obviously unstable. Aiming to relate
R-stability to a moduli space problem, we then study the action of the gauge
group of similarity transformations on matrix factorizations. We define a naive
moment map-like flow on the gauge orbits and use it to study boundary flows in
several examples. Gauge transformations of non-zero degree play an interesting
role for brane-antibrane annihilation. We also give a careful exposition of the
grading of the Landau-Ginzburg category of B-branes, and prove an index theorem
for matrix factorizations.Comment: 46 pages, LaTeX, summary adde
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