1,206 research outputs found
Dark Matter and The Anthropic Principle
We evaluate the problem of galaxy formation in the landscape approach to
phenomenology of the axion sector. With other parameters of standard LambdaCDM
cosmology held fixed, the density of cold dark matter is bounded below relative
to the density of baryonic matter by the requirement that structure should form
before the era of cosmological constant domination of the universe. Galaxies
comparable to the Milky Way can only form if the ratio also satisfies an upper
bound. The resulting constraint on the density of dark matter is too loose to
select a low axion decay constant or small initial displacement angle on
anthropic grounds.Comment: 17 pages, 1 figur
Polynomial Structure of the (Open) Topological String Partition Function
In this paper we show that the polynomial structure of the topological string
partition function found by Yamaguchi and Yau for the quintic holds for an
arbitrary Calabi-Yau manifold with any number of moduli. Furthermore, we
generalize these results to the open topological string partition function as
discussed recently by Walcher and reproduce his results for the real quintic.Comment: 15 page
Open mirror symmetry for Pfaffian Calabi-Yau 3-folds
We investigate the open mirror symmetry of certain non-complete intersection
Calabi- Yau 3-folds, so called pfaffian Calabi-Yau. We perform the prediction
of the number of disk invariants of several examples by using the direct
integration method proposed recently and the open mirror symmetry. We treat
several pfaffian Calabi-Yau 3-folds in and branes with two
discrete vacua. Some models have the two special points in its moduli space,
around both of which we can consider different A-model mirror partners. We
compute disc invariants for both cases. This study is the first application of
the open mirror symmetry to the compact non-complete intersections in toric
variety.Comment: 64 pages; v2: typos corrected, minor changes, references added; v3:
published version, minor corrections and improvement
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
Status of Nucleon Resonances with Masses
We discuss different interpretations of peaks observed a few years ago by
Tatischeff et al. in missing mass spectra of the reaction , which
were declared as new exited nucleon states with small masses. A study of the
possible production of such states in the process by analyzing the invariant mass spectrum of
is proposed. It is shown that the data, obtained recently at MAMI-B, can allow
to analyze this process and to get information about an existence of exited
nucleon states with small masses.Comment: 4 pages, 2 figures, LaTeX with ws-p8-50x6-00.cls. Talk presented at
the NSTAR2001 Workshop, Mainz, Germany, March 7-10, 200
Nuclear Star Clusters across the Hubble Sequence
Over the last decade, HST imaging studies have revealed that the centers of
most galaxies are occupied by compact, barely resolved sources. Based on their
structural properties, position in the fundamental plane, and spectra, these
sources clearly have a stellar origin. They are therefore called ``nuclear star
clusters'' (NCs) or ``stellar nuclei''. NCs are found in galaxies of all Hubble
types, suggesting that their formation is intricately linked to galaxy
evolution. In this contribution, I briefly review the results from recent
studies of NCs, touch on some ideas for their formation, and mention some open
issues related to the possible connection between NCs and supermassive black
holes.Comment: 6 page conference proceedings, to appear in "The impact of HST on
European Astronomy" (41st ESLAB Symposium), pdflatex file, uses svmult.cls
(included
Extended Holomorphic Anomaly in Gauge Theory
The partition function of an N=2 gauge theory in the Omega-background
satisfies, for generic value of the parameter beta=-eps_1/eps_2, the, in
general extended, but otherwise beta-independent, holomorphic anomaly equation
of special geometry. Modularity together with the (beta-dependent) gap
structure at the various singular loci in the moduli space completely fixes the
holomorphic ambiguity, also when the extension is non-trivial. In some cases,
the theory at the orbifold radius, corresponding to beta=2, can be identified
with an "orientifold" of the theory at beta=1. The various connections give
hints for embedding the structure into the topological string.Comment: 25 page
KMOS view of the Galactic Centre I. Young stars are centrally concentrated
The Galactic centre hosts a crowded, dense nuclear star cluster with a
half-light radius of 4 pc. Most of the stars in the Galactic centre are cool
late-type stars, but there are also >100 hot early-type stars in the central
parsec of the Milky Way. These stars are only 3-8 Myr old. Our knowledge of the
number and distribution of early-type stars in the Galactic centre is
incomplete. Only a few spectroscopic observations have been made beyond a
projected distance of 0.5 pc of the Galactic centre. The distribution and
kinematics of early-type stars are essential to understand the formation and
growth of the nuclear star cluster. We cover the central >4pc^2 of the Galactic
centre using the integral-field spectrograph KMOS. We extracted more than 1,000
spectra from individual stars and identified early-type stars based on their
spectra. Our data set contains 114 bright early-type stars: 6 have narrow
emission lines, 23 are Wolf-Rayet stars, 9 stars have featureless spectra, and
76 are O/B type stars. Our wide-field spectroscopic data confirm that the
distribution of young stars is compact, with 90% of the young stars identified
within 0.5 pc of the nucleus. We identify 24 new O/B stars primarily at large
radii. We estimate photometric masses of the O/B stars and show that the total
mass in the young population is >12,000M_sun. The O/B stars all appear to be
bound to the Milky Way nuclear star cluster, while less than 30% belong to the
clockwise rotating disk. The central concentration of the early-type stars is a
strong argument that they have formed in situ. A large part of the young O/B
stars is not on the disk, which either means that the early-type stars did not
all form on the same disk or that the disk is dissolving rapidly. [abridged]Comment: 27 pages, 17 figures, matches journal version: Corrected typos,
corrected Notes in Table B.
ABCD of Beta Ensembles and Topological Strings
We study beta-ensembles with Bn, Cn, and Dn eigenvalue measure and their
relation with refined topological strings. Our results generalize the familiar
connections between local topological strings and matrix models leading to An
measure, and illustrate that all those classical eigenvalue ensembles, and
their topological string counterparts, are related one to another via various
deformations and specializations, quantum shifts and discrete quotients. We
review the solution of the Gaussian models via Macdonald identities, and
interpret them as conifold theories. The interpolation between the various
models is plainly apparent in this case. For general polynomial potential, we
calculate the partition function in the multi-cut phase in a perturbative
fashion, beyond tree-level in the large-N limit. The relation to refined
topological string orientifolds on the corresponding local geometry is
discussed along the way.Comment: 33 pages, 1 figur
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