2,207 research outputs found
Global gauge anomalies in coset models of conformal field theory
We study the occurrence of global gauge anomalies in the coset models of
two-dimensional conformal field theory that are based on gauged WZW models. A
complete classification of the non-anomalous theories for a wide family of
gauged rigid adjoint or twisted-adjoint symmetries of WZW models is achieved
with the help of Dynkin's classification of Lie subalgebras of simple Lie
algebras.Comment: 25 page
The effects of violating detailed balance on critical dynamics
We present an overview of the effects of detailed-balance violating
perturbations on the universal static and dynamic scaling behavior near a
critical point. It is demonstrated that the standard critical dynamics
universality classes are generally quite robust: In systems with non-conserved
order parameter, detailed balance is effectively restored at criticality. This
also holds for models with conserved order parameter, and isotropic
non-equilibrium perturbations. Genuinely novel features are found only for
models with conserved order parameter and spatially anisotropic noise
correlations.Comment: 4 pages, revtex, no figure
Analysis of CMB foregrounds using a database for Planck
Within the scope of the Planck IDIS (Integrated Data Information System)
project we have started to develop the data model for time-ordered data and
full-sky maps. The data model is part of the Data Management Component (DMC), a
software system designed according to a three-tier architecture which allows
complete separation between data storage and processing. The DMC is already
being used for simulation activities and the modeling of some foreground
components. We have ingested several Galactic surveys into the database and
used the science data-access interface to process the data. The data structure
for full-sky maps utilises the HEALPix tessellation of the sphere. We have been
able to obtain consistent measures of the angular power spectrum of the
Galactic radio continuum emission between 408 MHz and 2417 MHz.Comment: 7 pages, 6 figures. To appear in the Proceedings of the MPA/ESO/MPE
Joint Astronomy Conference "Mining The Sky
Urincholesterinbestimmung im Rahmen der Früherkennung und Verlaufskontrolle von Harnblasentumoren
The angular power spectrum of radio emission at 2.3 GHz
We have analysed the Rhodes/HartRAO survey at 2326 MHz and derived the global
angular power spectrum of Galactic continuum emission. In order to measure the
angular power spectrum of the diffuse component, point sources were removed
from the map by median filtering. A least-square fit to the angular power
spectrum of the entire survey with a power law spectrum C_l proportional to
l^{-alpha}, gives alpha = 2.43 +/- 0.01 for l = 2-100. The angular power
spectrum of radio emission appears to steepen at high Galactic latitudes and
for observed regions with |b| > 20 deg, the fitted spectral index is alpha =
2.92 +/- 0.07. We have extrapolated this result to 30 GHz (the lowest frequency
channel of Planck) and estimate that no significant contribution to the sky
temperature fluctuation is likely to come from synchrotron at degree-angular
scalesComment: 10 pages, 10 figures, accepted for publication by Astronomy &
Astrophysic
On the relationship between cyclic and hierarchical three-species predator-prey systems and the two-species Lotka-Volterra model
We aim to clarify the relationship between interacting three-species models
and the two-species Lotka-Volterra (LV) model. We utilize mean-field theory and
Monte Carlo simulations on two-dimensional square lattices to explore the
temporal evolution characteristics of two different interacting three-species
predator-prey systems: (1) a cyclic rock-paper-scissors (RPS) model with
conserved total particle number but strongly asymmetric reaction rates that
lets the system evolve towards one corner of configuration space; (2) a
hierarchical food chain where an additional intermediate species is inserted
between the predator and prey in the LV model. For model variant (1), we
demonstrate that the evolutionary properties of both minority species in the
steady state of this stochastic spatial three-species corner RPS model are well
approximated by the LV system, with its emerging characteristic features of
localized population clustering, persistent oscillatory dynamics, correlated
spatio-temporal patterns, and fitness enhancement through quenched spatial
disorder in the predation rates. In contrast, we could not identify any regime
where the hierarchical model (2) would reduce to the two-species LV system. In
the presence of pair exchange processes, the system remains essentially
well-mixed, and we generally find the Monte Carlo simulation results for the
spatially extended model (2) to be consistent with the predictions from the
corresponding mean-field rate equations. If spreading occurs only through
nearest-neighbor hopping, small population clusters emerge; yet the requirement
of an intermediate species cluster obviously disrupts spatio-temporal
correlations between predator and prey, and correspondingly eliminates many of
the intriguing fluctuation phenomena that characterize the stochastic spatial
LV system.Comment: 13 pages, 4 figures; to appear in Eur. Phys. J. B (2012
Stagnation Point Radiative Heating Relations for Venus Entry
Improved analytic expressions for calculating the stagnation point radiative heating during entry into the atmosphere of Venus have been developed. These analytic expressions can be incorporated into entry trajectory simulation codes. Together with analytical expressions for convective heating at the stagnation point, the time-integrated total heat load at the stagnation point is used in determining the thickness of protective material required, and hence the mass of the fore body heatshield of uniform thickness
B polarization of the CMB from Faraday rotation
We study the effect of Faraday rotation due to a homogeneous magnetic field
on the polarization of the cosmic microwave background (CMB). Scalar
fluctuations give rise only to parity-even E-type polarization of the CMB.
However in the presence of a magnetic field, a non-vanishing parity-odd B-type
polarization component is produced through Faraday rotation. We derive the
exact solution for the E and B modes generated by scalar perturbations
including the Faraday rotation effect of a uniform magnetic field, and evaluate
their cross-correlations with temperature anisotropies. We compute the angular
autocorrelation function of the B-modes in the limit that the Faraday rotation
is small. We find that primordial magnetic fields of present strength around
G rotate E-modes into B-modes with amplitude comparable to those
due to the weak gravitational lensing effect at frequencies around
GHz. The strength of B-modes produced by Faraday rotation scales as
. We evaluate also the depolarizing effect of Faraday rotation upon
the cross correlation between temperature anisotropy and E-type polarization.Comment: 11 pages, 4 figures. Minor changes to match the published versio
Towards a model of full-sky Galactic synchrotron intensity and linear polarisation: a re-analysis of the Parkes data
We have analysed the angular power spectra of the Parkes radio continuum and
polarisation survey of the Southern galactic plane at 2.4 GHz. We have found
that in the multipole range l=40-250 the angular power spectrum of the
polarised intensity is well described by a power-law spectrum with fitted
spectral index alpha_L = 2.37 +- 0.21. In the same multipole range the angular
power spectra of the E and B components of the polarised signal are
significantly flatter, with fitted spectral indices respectively of alpha_E =
1.57 +- 0.12 and alpha_B = 1.45 +- 0.12. Temperature fluctuations in the E and
B components are mostly determined by variations in polarisation angle. We have
combined these results with other data from available radio surveys in order to
produce a full-sky toy model of Galactic synchrotron intensity and linear
polarisation at high frequencies (> 10 GHz). This can be used to study the
feasibility of measuring the Cosmic Microwave Background polarisation with
forthcoming experiments and satellite missions.Comment: 17 pages, 11 figures. Accepted for publication in A&A. Paper with
higher quality images available at
ftp://astro.esa.int/pub/synchrotron/paper.ps.g
Construction and properties of a topological index for periodically driven time-reversal invariant 2D crystals
We present mathematical details of the construction of a topological
invariant for periodically driven two-dimensional lattice systems with
time-reversal symmetry and quasienergy gaps, which was proposed recently by
some of us. The invariant is represented by a gap-dependent -valued index that is simply related to the Kane-Mele invariants of
quasienergy bands but contains an extra information. As a byproduct, we prove
new expressions for the two-dimensional Kane-Mele invariant relating the latter
to Wess-Zumino amplitudes and the boundary gauge anomaly.Comment: published version ; 56 pages, 15 figure
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