201 research outputs found
The 2dF Galaxy Redshift Survey as a Cosmological Laboratory
The 2dF Galaxy Redshift Survey (2dFGRS) of 230,000 redshifts of nearby
(z~0.1) galaxies is now complete. It has allowed the 2dFGRS team and others to
estimate fundamental cosmological parameters and to study galaxy intrinsic
properties. Here we highlight three recent key results from the survey: (i) an
upper limit of about 2eV on the total mass of the three neutrino flavours, and
an intriguing reasonable fitting of the 2dFGRS power spectrum to a Mixed Dark
Matter model without a Cosmological Constant, but with a low Hubble constant;
(ii) the bimodality of the galaxy population in both spectral parameterisation
and in colour; and (iii) the clustering of different galaxy types and evidence
for relative stochastic biasing.Comment: Based on invited talks at RESCEU6 (Tokyo) and 'Tully60' (Sydney); to
appear in Pub. Ast. Soc. of Australia, ed. J. Bland-Hawthorn; 4 pages, 4
figure
Phenomenological construction of a relativistic nucleon-nucleon interaction for the superfluid gap equation in finite density systems
We construct phenomenologically a relativistic particle-particle channel
interaction which suits the gap equation for nuclear matter. This is done by
introducing a density-independent momentum-cutoff parameter to the relativistic
mean field (Hartree and Hartree-Fock) models so as to reproduce the pairing
properties obtained by the Bonn-B potential and not to change the saturation
property. The interaction so obtained can be used for the Relativistic
Hartree-Bogoliubov calculation, but some reservation is necessary for the
Relativistic Hartree-Fock-Bogoliubov calculation.Comment: 30 pages, 18 eps figures, uses elsart. Major revision ---
Hartree-Fock calculations are added. To appear in Nuclear Physics
Superfluid vortices in neutron stars
A microscopic, quantum mechanical model for neutron vortices in the crust of
a neutron star is presented. After a brief introduction to the Bogoliubov- de
Gennes equations, which form the basis for our calculations, we present results
for density distributions, vortex core sizes and vortex energies, both for an
isolated neutron vortex and for the case when the vortex core overlaps with a
cylindrical nucleus. Earlier results on the vortex core size are confirmed,
indicating a much less dramatic variation of the vortex core size with density
than predicted by the BCS formula.Comment: 28 pages, 8 figures. To appear in Astronomy & Astrophysic
Detection of transplanckian effects in the cosmic microwave background
Quantum gravity effects are expected to modify the primordial density
fluctuations produced during inflation and leave their imprint on the cosmic
microwave background observed today. We present a new analysis discussing
whether these effects are detectable, considering both currently available data
and simulated results from an optimal CMB experiment. We find that the WMAP
(Wilkinson Microwave Anisotropy Probe) data show no evidence for the particular
signature considered in this work but give an upper bound on the parameters of
the model. However, a hypothetical experiment shows that with proper data, the
trans-Planckian effects should be detectable through alternate sampling
methods. This fuzzy conclusion is a result of the nature of the oscillations,
since they give rise to a likelihood hypersurface riddled with local maxima. A
simple Bayesian analysis shows no significant evidence for the simulated data
to prefer a trans-Planckian model. Conventional Markov chain Monte Carlo (MCMC)
methods are not suitable for exploring this complicated landscape, but
alternative methods are required to solve the problem. This, however, requires
extremely high-precision data.Comment: 9 pages, 22 figure
Are all perturbations created equal? An analysis of the WMAP 5- and 7-year data without inflationary prejudice
We submit recent claims of a semi-significant detection of primordial tensor
perturbations in the WMAP data to a closer scrutiny. Our conclusion is in brief
that no such mode is present at a detectable level once the analysis is done
more carefully. These claims have their root in a brief debate in the late
1990s about the standard calculation of the scalar and tensor spectra in
standard inflationary theory, where Grishchuk and collaborators claimed that
their amplitudes should be roughly equal. We give a brief summary of the debate
and our own reasons for why the standard calculation is correct.Comment: 12 pages, submitted to Phys. Rev.
Triplet Pairing in Neutron Matter
The separation method developed earlier by us [Nucl. Phys. {\bf A598} 390
(1996)] to calculate and analyze solutions of the BCS gap equation for
S pairing is extended and applied to P--F pairing in
pure neutron matter. The pairing matrix elements are written as a separable
part plus a remainder that vanishes when either momentum variable is on the
Fermi surface. This decomposition effects a separation of the problem of
determining the dependence of the gap components in a spin-angle representation
on the magnitude of the momentum (described by a set of functions independent
of magnetic quantum number) from the problem of determining the dependence of
the gap on angle or magnetic projection. The former problem is solved through a
set of nonsingular, quasilinear integral equations, providing inputs for
solution of the latter problem through a coupled system of algebraic equations
for a set of numerical coefficients. An incisive criterion is given for finding
the upper critical density for closure of the triplet gap. The separation
method and its development for triplet pairing exploit the existence of a small
parameter, given by a gap-amplitude measure divided by the Fermi energy. The
revised BCS equations admit analysis revealing universal properties of the full
set of solutions for P pairing in the absence of tensor coupling,
referring especially to the energy degeneracy and energetic order of these
solutions. The angle-average approximation introduced by Baldo et al. is
illuminated in terms of the separation-transformed BCS problem and the small
parameter expansion..
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