2,152 research outputs found
Constraints on the solid dark universe model
If the dark energy is modelled as a relativistic elastic solid then the
standard CDM and CDM models, as well as lattice configurations of
cosmic strings or domain walls, are points in the two-dimensional parameter
space . We present a detailed analysis of the best fitting
cosmological parameters in this model using data from a range of observations.
We find that the is improved by by including the two
parameters and that the CDM model is only the best fit to the
data when a large number of different datasets are included. Using CMB
observations alone we find that and with the addition of
Large-Scale Structure data and . We conclude that the models based on topological defects provide a good
fit to the current data, although CDM cannot be ruled out.Comment: 10 page
Evidence for massive neutrinos from CMB and lensing observations
We discuss whether massive neutrinos (either active or sterile) can reconcile
some of the tensions within cosmological data that have been brought into focus
by the recently released {\it Planck} data. We point out that a discrepancy is
present when comparing the primary CMB and lensing measurements both from the
CMB and galaxy lensing data using CFHTLenS, similar to that which arises when
comparing CMB measurements and SZ cluster counts. A consistent picture emerges
and including a prior for the cluster constraints and BAOs we find that: for an
active neutrino model with 3 degenerate neutrinos, , whereas for a sterile neutrino, in addition to 3 neutrinos
with a standard hierarchy and , and . In both cases there is a significant detection of modification to
the neutrino sector from the standard model and in the case of the sterile
neutrino it is possible to reconcile the BAO and local measurements.
However, a caveat to our result is some internal tension between the CMB and
lensing/cluster observations, and the masses are in excess of those estimated
from the shape of the matter power spectrum from galaxy surveys.Comment: 5 pages, 3 figures, clarifications added, comparison with WMAP-9 plus
high-l added, version accepted in Physical Review Letter
Tight constraints on F- and D-term hybrid inflation scenarios
We use present cosmological data from the cosmic microwave background,
large-scale structure and deuterium at high redshifts to constrain
supersymmetric F- and D-term hybrid inflation scenarios including possible
contributions to the CMB anisotropies from cosmic strings. Using two different
realizations of the cosmic string spectrum, we find that the minimal version of
the D-term model is ruled out at high significance. F-term models are also in
tension with the data. We also discuss possible non-minimal variants of the
models.Comment: 4 pages, 2 figure
Anisotropic dark energy and CMB anomalies
We investigate the breaking of global statistical isotropy caused by a dark
energy component with an energy-momentum tensor which has point symmetry, that
could represent a cubic or hexagonal crystalline lattice. In such models
Gaussian, adiabatic initial conditions created during inflation can lead to
anisotropies in the cosmic microwave background whose spherical harmonic
coefficients are correlated, contrary to the standard assumption. We develop an
adaptation of the line of sight integration method that can be applied to
models where the background energy-momentum tensor is isotropic, but whose
linearized perturbations are anisotropic. We then show how this can be applied
to the cases of cubic and hexagonal symmetry. We compute quantities which show
that such models are indistinguishable from isotropic models even in the most
extreme parameter choices, in stark contrast to models with anisotropic initial
conditions based on inflation. The reason for this is that the dark energy
based models contribute to the CMB anistropy via the inegrated Sachs-Wolfe
effect, which is only relevent when the dark energy is dominant, that is, on
the very largest scales. For inflationary models, however, the anisotropy is
present on all scales.Comment: 18 pages, 9 figure
Constraints on Supersymmetric Models of Hybrid Inflation
We point out that the inclusion of a string component contributing around 5%
to the CMB power spectrum amplitude on large scales can increase the preferred
value of the spectral index n_s of density fluctuations measured by CMB
experiments. While this finding applies to any cosmological scenario involving
strings, we consider in particular models of supersymmetric hybrid inflation,
which predict n_s >= 0.98, in tension with the CMB data when strings are not
included. Using MCMC analysis we constrain the parameter space allowed for F-
and D-term inflation. For the F-term model, using minimal supergravity
corrections, we find that \log\kappa= -2.34\pm 0.38 and M= (0.518\pm 0.059) *
10^16 GeV. The inclusion of non-minimal supergravity corrections can modify
these values somewhat. In the corresponding analysis for D-term inflation, we
find \log\kappa= -4.24\pm 0.19 and m_FI= (0.245\pm 0.031) * 10^16 GeV. Under
the assumption that these models are correct, these results represent precision
measurements of important parameters of a Grand Unified Theory. We consider the
possible uncertainties in our measurements and additional constraints on the
scenario from the stochastic background of gravitational waves produced by the
strings. The best-fitting model predicts a B-mode polarization signal \approx
0.3 \mu K rms peaking at l \approx 1000. This is of comparable amplitude to the
expected signal due to gravitational lensing of the adiabatic E-mode signal on
these scales.Comment: 21 pages, 16 figure
Elephant cognition in primate perspective
On many of the staple measures of comparative psychology, elephants show no obvious differences from other mammals, such as primates: discrimination learning, memory, spontaneous tool use, etc. However, a range of more naturalistic measures have recently suggested that elephant cognition may be rather different. Wild elephants sub-categorize humans into groups, independently making this classification on the basis of scent or colour. In number discrimination, elephants show no effects of absolute magnitude or relative size disparity in making number judgements. In the social realm, elephants show empathy into the problems faced by others, and give hints of special abilities in cooperation, vocal imitation and perhaps teaching. Field data suggest that the elephant’s vaunted reputation for memory may have a factual basis, in two ways. Elephants’ ability to remember large-scale space over long periods suggests good cognitive mapping skills. Elephants’ skill in keeping track of the current locations of many family members implies that working memory may be unusually developed, consistent with the laboratory finding that their quantity judgements do not show the usual magnitude effects.Publisher PDFPeer reviewe
Beltway: Getting Around Garbage Collection Gridlock
We present the design and implementation of a new garbage collection framework that significantly generalizes existing copying collectors. The Beltway framework exploits and separates object age and incrementality. It groups objects in one or more increments on queues called belts, collects belts independently, and collects increments on a belt in first-in-first-out order. We show that Beltway configurations, selected by command line options, act and perform the same as semi-space, generational, and older-first collectors, and encompass all previous copying collectors of which we are aware. The increasing reliance on garbage collected languages such as Java requires that the collector perform well. We show that the generality of Beltway enables us to design and implement new collectors that are robust to variations in heap size and improve total execution time over the best generational copying collectors of which we are aware by up to 40%, and on average by 5 to 10%, for small to moderate heap sizes. New garbage collection algorithms are rare, and yet we define not just one, but a new family of collectors that subsumes previous work. This generality enables us to explore a larger design space and build better collectors
Tilted Physics: A Cosmologically Dipole-Modulated Sky
Physical constants and cosmological parameters could vary with position. On
the largest scales such variations would manifest themselves as gradients
across our Hubble volume, leading to dipole-modulation of the cosmic microwave
anisotropies. This generically leads to a correlation between adjacent
multipoles in the spherical harmonics expansion of the sky, a distinctive
signal which should be searched for in future data sets.Comment: 4 pages, 3 figure
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