63 research outputs found
Higher-loop anomalies in chiral gravities
The one-loop anomalies for chiral gravity are derived using the
Fujikawa regularisation method. The expected two-loop anomalies are then
obtained by imposing the Wess-Zumino consistency conditions on the one-loop
results. The anomalies found in this way agree with those already known from
explicit Feynman diagram calculations. We then directly verify that the order
non-local BRST Ward identity anomalies, arising from the ``dressing''
of the one-loop results, satisfy Lam's theorem. It is also shown that in a
rigorous calculation of anomaly for the BRST charge, one recovers both
the non-local as well as the local anomalies. We further verify that, in chiral
gravities, the non-local anomalies in the BRST Ward identity can be obtained by
the application of the anomalous operator , calculated using operator
products, to an appropriately defined gauge fermion. Finally, we give arguments
to show why this relation should hold generally in reparametrisation-invariant
theories.Comment: 21 pages, latex, 12 figures as uuencoded postscript. To appear in
Nucl. Phys.
Effects of cold dark matter decoupling and pair annihilation on cosmological perturbations
Weakly interacting massive particles are part of the lepton-photon plasma in
the early universe until kinetic decoupling, after which time the particles
behave like a collisionless gas with nonzero temperature. The Boltzmann
equation for WIMP-lepton collisions is reduced to a Fokker-Planck equation for
the evolution of the WIMP distribution including scalar density perturbations.
This equation and the Einstein and fluid equations for the plasma are solved
numerically including the acoustic oscillations of the plasma before and during
kinetic decoupling, the frictional damping occurring during kinetic decoupling,
and the free-streaming damping occurring afterwards and throughout the
radiation-dominated era. An excellent approximation reduces the solution to
quadratures for the cold dark matter density and velocity perturbations. The
subsequent evolution is followed through electron pair annihilation and the
radiation-matter transition; analytic solutions are provided for both large and
small scales. For a 100 GeV WIMP with bino-type interactions, kinetic
decoupling occurs at a temperature MeV. The transfer function in the
matter-dominated era leads to an abundance of small cold dark matter halos;
with a smooth window function the Press-Schechter mass distribution is for 10 MeV) M.Comment: 18 pages, 12 figures; corrected error in bino decoupling temperature,
figures update
High redshift radio galaxies and divergence from the CMB dipole
Previous studies have found our velocity in the rest frame of radio galaxies
at high redshift to be substantially larger than that inferred from the CMB
temperature dipole anisotropy. We construct a full sky catalogue NVSUMSS, by
merging the NVSS and SUMSS catalogues and removing local sources by various
means including cross-correlating with the 2MRS catalogue. We take into account
both aberration and Doppler boost to deduce our velocity from the hemispherical
number count asymmetry, as well as via a 3-dimensional linear estimator. Both
the magnitude and direction depend on cuts made to the catalogue, e.g. on the
lowest source flux, however these effects are small. With the hemispheric
number count asymmetry method we obtain a velocity of 1729 187 km/s i.e.
about 4 times larger than that obtained from the CMB dipole, but close in
direction, towards RA=149 2 degree, DEC = -17 12 degree. With the
3-dimensional estimator, the derived velocity is 1355 174 km/s towards
RA=141 11 degree, DEC=-9 10 degree. We assess the statistical
significance of these results by constructing catalogues of random
distributions and show that they are at best significant at the
(99.95% confidence) level.Comment: 13 pages, 12 figures, 10 tables; matches published versio
Gravitational Clustering to All Perturbative Orders
We derive the time evolution of the density contrast to all orders of perturbation theory, by solving the Einstein equation for scale-invariant fluctuations. These fluctuations are represented by an infinite series in inverse powers of the radial parameter. In addition to the standard growing modes, we find infinitely many more new growing modes for open and closed universes
Reconstruction of primordial density fields
The Monge-Ampere-Kantorovich (MAK) reconstruction is tested against
cosmological N-body simulations. Using only the present mass distribution
sampled with particles, and the assumption of homogeneity of the primordial
distribution, MAK recovers for each particle the non-linear displacement field
between its present position and its Lagrangian position on a primordial
uniform grid. To test the method, we examine a standard LCDM N-body simulation
with Gaussian initial conditions and 6 models with non-Gaussian initial
conditions: a chi-squared model, a model with primordial voids and four weakly
non-Gaussian models. Our extensive analyses of the Gaussian simulation show
that the level of accuracy of the reconstruction of the nonlinear displacement
field achieved by MAK is unprecedented, at scales as small as about 3 Mpc. In
particular, it captures in a nontrivial way the nonlinear contribution from
gravitational instability, well beyond the Zel'dovich approximation. This is
also confirmed by our analyses of the non-Gaussian samples. Applying the
spherical collapse model to the probability distribution function of the
divergence of the displacement field, we also show that from a
well-reconstructed displacement field, such as that given by MAK, it is
possible to accurately disentangle dynamical contributions induced by
gravitational clustering from possible initial non-Gaussianities, allowing one
to efficiently test the non-Gaussian nature of the primordial fluctuations. In
addition, a simple application of MAK using the Zel'dovich approximation allows
one to also recover accurately the present-day peculiar velocity field on
scales of about 8 Mpc.Comment: Version to appear in MNRAS, 24 pages, 21 figures appearing (uses 35
figure files), 1 tabl
The Cosmological Mean Density and its Local Variations Probed by Peculiar Velocities
Peculiar velocities thoughout the region of the local supercluster are
reconstructed by two different orbit-retracing methods. The requirement of the
optimal correlation between the radial components of reconstructed velocities
and the observed peculiar velocities derived from our extensive new catalog of
distances puts stringent constraints on the values of the cosmological
parameters. Our constraints intersect those from studies of microwave
background fluctuations and statistical properties of galaxy clustering: the
ensemble of constraints are consistent with Omega_m=0.22\pm 0.02. While motions
throughout the Local Supercluster provide a measure of the mean ratio of mass
to light, there can be large local fluctuations. Our reconstruction of the
infall velocities in the immediate vicinity of the Virgo Cluster shows that
there is a mass-to-light anomaly of a factor of 3 to 6 between groups in the
general field environment and the heavily populated Virgo Cluster.Comment: 4 pages, 2 figures, version to appear in Astrophysical Journal
Letter
Observational biases in Lagrangian reconstructions of cosmic velocity fields
Lagrangian reconstruction of large-scale peculiar velocity fields can be
strongly affected by observational biases. We develop a thorough analysis of
these systematic effects by relying on specially selected mock catalogues. For
the purpose of this paper, we use the MAK reconstruction method, although any
other Lagrangian reconstruction method should be sensitive to the same
problems. We extensively study the uncertainty in the mass-to-light assignment
due to luminosity incompleteness, and the poorly-determined relation between
mass and luminosity. The impact of redshift distortion corrections is analyzed
in the context of MAK and we check the importance of edge and finite-volume
effects on the reconstructed velocities. Using three mock catalogues with
different average densities, we also study the effect of cosmic variance. In
particular, one of them presents the same global features as found in
observational catalogues that extend to 80 Mpc/h scales. We give recipes,
checked using the aforementioned mock catalogues, to handle these particular
observational effects, after having introduced them into the mock catalogues so
as to quantitatively mimic the most densely sampled currently available galaxy
catalogue of the nearby universe. Once biases have been taken care of, the
typical resulting error in reconstructed velocities is typically about a
quarter of the overall velocity dispersion, and without significant bias. We
finally model our reconstruction errors to propose an improved Bayesian
approach to measure Omega_m in an unbiased way by comparing the reconstructed
velocities to the measured ones in distance space, even though they may be
plagued by large errors. We show that, in the context of observational data, a
nearly unbiased estimator of Omega_m may be built using MAK reconstruction.Comment: 29 pages, 21 figures, 6 tables, Accepted by MNRAS on 2007 October 2.
Received 2007 September 30; in original form 2007 July 2
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