2,558 research outputs found
Multi-Caloron solutions
We discuss the construction of multi-caloron solutions with non-trivial
holonomy, both as approximate superpositions and exact self-dual solutions. The
charge k SU(n) moduli space can be described by kn constituent monopoles. Exact
solutions help us to understand how these constituents can be seen as
independent objects, which seems not possible with the approximate
superposition. An "impurity scattering" calculation provides relatively simple
expressions. Like at zero temperature an explicit parametrization requires
solving a quadratic ADHM constraint, achieved here for a class of axially
symmetric solutions. We will discuss the properties of these exact solutions in
detail, but also demonstrate that interesting results can be obtained without
explicitly solving for the constraint.Comment: 31 pages, 7 figures (in 19 parts
On How to Extend the NIR Tully-Fisher Relation to be Truly All-Sky
Dust extinction and stellar confusion by the Milky Way reduce the efficiency
of detecting galaxies at low Galactic latitudes, creating the so-called Zone of
Avoidance. This stands as a stumbling block in charting the distribution of
galaxies and cosmic flow fields, and therewith our understanding of the local
dynamics in the Universe (CMB dipole, convergence radius of bulk flows). For
instance, ZoA galaxies are generally excluded from the whole-sky Tully-Fisher
Surveys () even if catalogued. We show here that by
fine-tuning the near-infrared TF relation, there is no reason not to extend
peculiar velocity surveys deeper into the ZoA. Accurate axial ratios ()
are crucial to both the TF sample selection and the resulting TF distances. We
simulate the effect of dust extinction on the geometrical properties of
galaxies. As expected, galaxies appear rounder with increasing obscuration
level, even affecting existing TF samples. We derive correction models and
demonstrate that we can reliably reproduce the intrinsic axial ratio from the
observed value up to extinction level of about mag (
mag), we also recover a fair fraction of galaxies that otherwise would fall out
of an uncorrected inclination limited galaxy sample. We present a
re-calibration of the 2MTF relation in the NIR , , and -bands for
isophotal rather than total magnitudes, using their same calibration sample.
Both TF relations exhibit similar scatter at high Galactic latitudes. However,
the isophotal TF relation results in a significant improvement in the scatter
for galaxies in the ZoA, and low surface brightness galaxies in general,
because isophotal apertures are more robust in the face of significant stellar
confusion.Comment: 12 pages, 10 figures, 4 tables, accepted for publication in MNRA
Galaxy peculiar velocities in the Zone of Avoidance
Dust extinction and stellar confusion of the Milky Way hinder the detection
of galaxies at low Galactic latitude, creating the so-called Zone of Avoidance
(ZoA). This has hampered our understanding of the local dynamics, cosmic flow
fields and the origin of the Cosmic Microwave Background dipole. The ZoA () is also excluded from the "whole-sky" Two Micron All-Sky Survey
(2MASS) Redshift Survey (2MRS) and 2MASS Tully-Fisher Survey (2MTF). The latter
aims to provide distances and peculiar velocities for all bright inclined 2MASS
galaxies with \leq 11\hbox{.\!\!^{\rm m}}25. Correspondingly,
knowledge about the density distribution in the ZoA remains limited to
statistical interpolations. To improve on this bias we pursued two different
surveys to fill in the southern and northern ZoA. These data will allow a
direct measurement of galaxy peculiar velocities. In this paper we will present
a newly derived optimized Tully-Fisher (TF) relation that allow accurate
measures of galaxy distances and peculiar velocities for dust-obscured
galaxies. We discuss further corrections for magnitudes and biases and present
some preliminary results on flow fields in the southern ZoA.Comment: 6 pages, 3 figures, to appear in Proceedings of SAIP2013, the 58th
Annual Conference of the South African Institute of Physics, edited by Roelf
Botha and Thulani Jili (SAIP and University of Zululand, 2014). ISBN:
978-0-620-62819-
On Nahm's transformation with twisted boundary conditions
Following two different tracks, we arrive at a definition of Nahm's
transformation valid for self-dual fields on the 4-dimensional torus with
non-zero twist tensor.The transform is again a self-dual gauge field defined on
a new torus and with non-zero twist tensor. It preserves the property of being
an involution.Comment: 18 page
HI Bright Galaxies in the Southern Zone of Avoidance
A blind survey for HI bright galaxies in the southern Zone of Avoidance, (212
deg < l < 36 deg; |b| < 5 deg), has been made with the 21 cm multibeam receiver
on the Parkes 64 m radiotelescope. The survey, sensitive to normal spiral
galaxies to a distance of about 40 Mpc and more nearby dwarfs, detected 110
galaxies. Of these, 67 have no counterparts in the NASA/IPAC Extragalactic
Database. In general, the uncataloged galaxies lie behind thicker obscuration
than do the cataloged objects. All of the newly-discovered galaxies have HI
flux integrals more than an order of magnitude lower than the Circinus galaxy.
The survey recovers the Puppis cluster and foreground group (Kraan-Korteweg &
Huchtmeier 1992), and the Local Void remains empty. The HI mass function
derived for the sample is satisfactorily fit by a Schechter function with
parameters alpha = 1.51 +- 0.12, Phi* = 0.006 +- 0.003, and log M* = 9.7 +-
0.10.Comment: To appear in The Astronomical Journa
Constituent monopoles through the eyes of fermion zero-modes
We use the fermion zero-modes in the background of multi-caloron solutions
with non-trivial holonomy as a probe for constituent monopoles. We find in
general indication for an extended structure. However, for well separated
constituents these become point-like. We analyse this in detail for the SU(2)
charge 2 case, where one is able to solve the relevant Nahm equation exactly,
beyond the piecewize constant solutions studied previously. Remarkably the
zero-mode density can be expressed in the high temperature limit as a function
of the conserved quantities that classify the solutions of the Nahm equation.Comment: 35 pages, 9 figures (in 26 parts
Calorons, instantons and constituent monopoles in SU(3) lattice gauge theory
We analyze the zero-modes of the Dirac operator in quenched SU(3) gauge
configurations at non-zero temperature and compare periodic and anti-periodic
temporal boundary conditions for the fermions. It is demonstrated that for the
different boundary conditions often the modes are localized at different
space-time points and have different sizes. Our observations are consistent
with patterns expected for Kraan - van Baal solutions of the classical
Yang-Mills equations. These solutions consist of constituent monopoles and the
zero-modes are localized on different constituents for different boundary
conditions. Our findings indicate that the excitations of the QCD vacuum are
more structured than simple instanton-like lumps.Comment: Remarks added. To appear in Phys. Rev.
Counting Yang-Mills Dyons with Index Theorems
We count the supersymmetric bound states of many distinct BPS monopoles in
N=4 Yang-Mills theories and in pure N=2 Yang-Mills theories. The novelty here
is that we work in generic Coulombic vacua where more than one adjoint Higgs
fields are turned on. The number of purely magnetic bound states is again found
to be consistent with the electromagnetic duality of the N=4 SU(n) theory, as
expected. We also count dyons of generic electric charges, which correspond to
1/4 BPS dyons in N=4 theories and 1/2 BPS dyons in N=2 theories. Surprisingly,
the degeneracy of dyons is typically much larger than would be accounted for by
a single supermultiplet of appropriate angular momentum, implying many
supermutiplets of the same charge and the same mass.Comment: 34 pages, 1 figure, LaTe
Topology and confinement
These lectures contain an introduction to instantons, calorons and dyons of
the Yang--Mills gauge theory. Since we are interested in the mechanism of
confinement and of the deconfinement phase transition at some critical
temperature, the Yang--Mills theory is formulated and studied at nonzero
temperatures. We introduce ``calorons with a nontrivial holonomy'' that are
generalizations of instantons and can be viewed as ``made of'' constituent
dyons. The quantum weight with which these calorons contribute to the
Yang--Mills partition function is considered, and the ensuing statistical
mechanics of the ensemble of interacting dyons is discussed. We argue that a
simple semiclassical picture based on dyons satisfies all known criteria of
confinement and explains the confinement-deconfinement phase transition. This
refers not only to the SU(N) gauge groups where dyons lead to the expected
behaviour of the observables with N, but also to the exceptional G(2) group
whose group center, unlike SU(N), is trivial. Despite being centerless, the
G(2) gauge group possesses confinement at low temperatures, and a 1st order
deconfinement transition, according to several latest lattice simulations,
indicating that confinement-deconfinement is not related to the group center.
Dyons, however, reproduce this behaviour.Comment: Lectures at the ITEP Winter School (February 2009, Moscow) and
Schladming Winter School (March 2009, Schladming, Austria), 42 pages, 16
figure
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