355 research outputs found
Weak Gravitational Lensing by Voids
We consider the prospects for detecting weak gravitational lensing by
underdensities (voids) in the large-scale matter distribution. We derive the
basic expressions for magnification and distortion by spherical voids.
Clustering of the background sources and cosmic variance are the main factors
which limit in principle the detection of lensing by voids. We conclude that
only voids with radii larger than \hm have lensing signal to noise
larger than unity.Comment: 12 pages, 7 figures, uses mn-1_4.sty file, submitted to MNRA
Constraining Dark Energy with Clusters: Complementarity with Other Probes
The Figure of Merit Science Working Group (FoMSWG) recently forecast the
constraints on dark energy that will be achieved prior to the Joint Dark Energy
Mission (JDEM) by ground-based experiments that exploit baryon acoustic
oscillations, type Ia supernovae, and weak gravitational lensing. We show that
cluster counts from on-going and near-future surveys should provide robust,
complementary dark energy constraints. In particular, we find that optimally
combined optical and Sunyaev-Zel'dovich effect cluster surveys should improve
the Dark Energy Task Force (DETF) figure of merit for pre-JDEM projects by a
factor of two even without prior knowledge of the nuisance parameters in the
cluster mass-observable relation. Comparable improvements are achieved in the
forecast precision of parameters specifying the principal component description
of the dark energy equation of state parameter as well as in the growth index
gamma. These results indicate that cluster counts can play an important
complementary role in constraining dark energy and modified gravity even if the
associated systematic errors are not strongly controlled.Comment: 6 pages, 3 figures, accepted to Phys. Rev. D. Discussion section
adde
Cosmic microwave background and large-scale structure constraints on a simple quintessential inflation model
We derive constraints on a simple quintessential inflation model, based on a
spontaneously broken Phi^4 theory, imposed by the Wilkinson Microwave
Anisotropy Probe three-year data (WMAP3) and by galaxy clustering results from
the Sloan Digital Sky Survey(SDSS). We find that the scale of symmetry breaking
must be larger than about 3 Planck masses in order for inflation to generate
acceptable values of the scalar spectral index and of the tensor-to-scalar
ratio. We also show that the resulting quintessence equation-of-state can
evolve rapidly at recent times and hence can potentially be distinguished from
a simple cosmological constant in this parameter regime.Comment: 5 pages, 2 figure
Halo Model Analysis of Cluster Statistics
We use the halo model formalism to provide expressions for cluster abundances
and bias, as well as estimates for the correlation matrix between these
observables. Off-diagonal elements due to scatter in the mass tracer scaling
with mass are included, as are observational effects such as biases/scatter in
the data, detection rates (completeness), and false detections (purity). We
apply the formalism to a hypothetical volume limited optical survey where the
cluster mass tracer is chosen to be the number of member galaxies assigned to a
cluster. Such a survey can strongly constrain
(), the power law index where
(), and perhaps even
the Hubble parameter (). We find cluster abundances and
bias not well suited for constraining or the amplitude . We
also find that without bias information and are degenerate,
implying constraints on the former are strongly dependent on priors used for
the latter and vice-versa. The degeneracy stems from an intrinsic scaling
relation of the halo mass function, and hence it should be present regardless
of the mass tracer used in the survey.Comment: 27 pages, 11 figures, references adde
Cosmological constraints on pseudo-Nambu-Goldstone bosons
Particle physics models with pseudo-Nambu-Goldstone bosons (PNGBs) are characterized by two mass scales: a global spontaneous symmetry breaking scale, f, and a soft (explicit) symmetry breaking scale, Lambda. General model insensitive constraints were studied on this 2-D parameter space arising from the cosmological and astrophysical effects of PNGBs. In particular, constraints were studied arising from vacuum misalignment and thermal production of PNGBs, topological defects, and the cosmological effects of PNGB decay products, as well as astrophysical constraints from stellar PNGB emission. Bounds on the Peccei-Quinn axion scale, 10(exp 10) GeV approx. = or less than f sub pq approx. = or less than 10(exp 10) to 10(exp 12) GeV, emerge as a special case, where the soft breaking scale is fixed at Lambda sub QCD approx. = 100 MeV
Dibaryons in neutron stars
The effects are studied of H-dibaryons on the structure of neutron stars. It was found that H particles could be present in neutron stars for a wide range of dibaryon masses. The appearance of dibaryons softens the equations of state, lowers the maximum neutron star mass, and affects the transport properties of dense matter. The parameter space is constrained for dibaryons by requiring that a 1.44 solar mass neutron star be gravitationally stable
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