302 research outputs found
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
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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
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
Late time cosmological phase transitions 1: Particle physics models and cosmic evolution
We described a natural particle physics basis for late-time phase transitions in the universe. Such a transition can seed the formation of large-scale structure while leaving a minimal imprint upon the microwave background anisotropy. The key ingredient is an ultra-light pseudo-Nambu-Goldstone boson with an astronomically large (O(kpc-Mpc)) Compton wavelength. We analyze the cosmological signatures of and constraints upon a wide class of scenarios which do not involve domain walls. In addition to seeding structure, coherent ultra-light bosons may also provide unclustered dark matter in a spatially flat universe, omega sub phi approx. = 1
The Three-point Function as a Probe of Models for Large-scale Structure
We analyze the consequences of models of structure formation for higher-order
(-point) galaxy correlation functions in the mildly non-linear regime.
Several variations of the standard cold dark matter model with
scale-invariant primordial perturbations have recently been introduced to
obtain more power on large scales, 20 h Mpc, e.g., low-matter-density
(non-zero cosmological constant) models, `tilted' primordial spectra, and
scenarios with a mixture of cold and hot dark matter. They also include models
with an effective scale-dependent bias, such as the cooperative galaxy
formation scenario of Bower, etal. (1993). We show that higher-order galaxy
correlation functions can provide a useful test of such models and can
discriminate between models with true large-scale power in the density field
and those where the galaxy power arises from scale-dependent bias: a bias with
rapid scale-dependence leads to a dramatic decrease of the hierarchical
amplitudes at large scales. Current observational constraints on the
three-point amplitudes and can place limits on the bias
parameter(s) and appear to disfavor, but not yet rule out, the hypothesis that
scale-dependent bias is responsible for the extra power observed on large
scales.Comment: 20 pages (5 figues available on request), LaTeX,
FERMILAB-Pub-93-140-
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