2,115 research outputs found
Baryogenesis after Hyperextended Inflation
We study a baryogenesis mechanism operating in the context of hyperextended
inflation and making use of a coupling between the scalar field and a standard
model global current, such as B or B-L. The method is efficient at temperatures
at which these currents are not conserved due to some higher dimensional
operator. The particle physics and cosmological phenomenology are discussed. We
consider constraints stemming from nucleosynthesis and solar system
experiments.Comment: 7 pages, 1 figure, uses RevTe
Challenges for Superstring Cosmology
We consider whether current notions about superstring theory below the Planck
scale are compatible with cosmology. We find that the anticipated form for the
dilaton interaction creates a serious roadblock for inflation and makes it
unlikely that the universe ever reaches a state with zero cosmological constant
and time-independent gravitational constant.Comment: 14 pages, 2 figures available as eps files on reques
Extended Inflation from Strings
We study the possibility of extended inflation in the effective theory of
gravity from strings compactified to four dimensions and find that it strongly
depends on the mechanism of supersymmetry breaking. We consider a general class
of string--inspired models which are good candidates for successful extended
inflation. In particular, the --problem of ordinary extended inflation
is automatically solved by the production of only very small bubbles until the
end of inflation. We find that the inflaton field could belong either to the
untwisted or to the twisted massless sectors of the string spectrum, depending
on the supersymmetry breaking superpotential.Comment: 18p
Probing deviations from General Relativity with the Euclid spectroscopic survey
We discuss the ability of the planned Euclid mission to detect deviations
from General Relativity using its extensive redshift survey of more than 50
Million galaxies. Constraints on the gravity theory are placed measuring the
growth rate of structure within 14 redshift bins between z=0.7 and z=2. The
growth rate is measured from redshift-space distortions, i.e. the anisotropy of
the clustering pattern induced by coherent peculiar motions. This is performed
in the overall context of the Euclid spectroscopic survey, which will
simultaneously measure the expansion history of the universe, using the power
spectrum and its baryonic features as a standard ruler, accounting for the
relative degeneracies of expansion and growth parameters. The resulting
expected errors on the growth rate in the different redshift bins, expressed
through the quantity f\sigma_8, range between 1.3% and 4.4%. We discuss the
optimisation of the survey configuration and investigate the important
dependence on the growth parameterisation and the assumed cosmological model.
We show how a specific parameterisation could actually drive the design towards
artificially restricted regions of the parameter space. Finally, in the
framework of the popular "\gamma -parameterisation", we show that the Euclid
spectroscopic survey alone will already be able to provide substantial evidence
(in Bayesian terms) if the growth index differs from the GR value \gamma=0.55
by at least \sim 0.13. This will combine with the comparable inference power
provided by the Euclid weak lensing survey, resulting in Euclid's unique
ability to provide a decisive test of modified gravity.Comment: 18 pages, 15 figures, accepted by MNRA
Positive tension 3-branes in an bulk
In this work, we review and extend the so-called consistency conditions for
the existence of a braneworld scenario in arbitrary dimensions in the
Brans-Dicke (BD) gravitational theory. After that, we consider the particular
case of a five-dimensional scenario which seems to have phenomenological
interesting implications. We show that, in the BD framework, it is possible to
achieve necessary conditions pointing to the possibility of accommodating
branes with positive tensions in an AdS bulk by the presence of the additional
BD scalar field, avoiding in this way the necessity of including unstable
objects in the compactification scheme. Furthermore, in the context of time
variable brane tension, it is shown that the brane tension may change its sign,
following the bulk cosmological constant sign.Comment: 15 pages, new version to appear in JHE
Fully-automated bioreactor process control eliminates hands-on time through closed-loop cloud software integration
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Probing the Origins of Voids in the Distribution of Galaxies
If the voids that we see today in the distribution of galaxies existed at
recombination, they will leave an imprint on the cosmic microwave background
(CMB). On the other hand, if these voids formed much later, their effect on the
CMB will be negligible and will not be observed with the current generation of
experiments. In this paper presented at the 2004 Annual Scientific Meeting of
the Astronomical Society of Australia, we discuss our ongoing investigations
into voids of primordial origin. We show that if voids in the cold dark matter
distribution existed at the epoch of decoupling, they could contribute
significantly to the apparent rise in CMB power on small scales detected by the
Cosmic Background Imager (CBI) Deep Field. Here we present our improved method
for predicting the effects of primordial voids on the CMB in which we treat a
void as an external source in the cold dark matter (CDM) distribution employing
a Boltzmann solver. Our improved predictions include the effects of a
cosmological constant (Lambda) and acoustic oscillations generated by voids at
early times. We find that models with relatively large voids on the last
scattering surface predict too much CMB power in an Einstein--de Sitter
background cosmology but could be consistent with the current CMB observations
in a Lambda-CDM universe.Comment: 9 pages, 8 figures, paper presented at the 2004 Annual Scientific
Meeting of the Astronomical Society of Australia, accepted for publication in
PAS
Generalized Brans-Dicke cosmology in the presence of matter and dark energy
We study the Generalized Brans-Dicke cosmology in the presence of matter and
dark energy. Of particular interest for a constant Brans-Dicke parameter, the
de Sitter space has also been investigated.Comment: 9 page
Redshift-weighted constraints on primordial non-Gaussianity from the clustering of the eBOSS DR14 quasars in Fourier space
We present constraints on local primordial non-Gaussianity (PNG),
parametrized through , using the Sloan Digital Sky Survey
IV extended Baryon Oscillation Spectroscopic Survey Data Release 14 quasar
sample. We measure and analyze the anisotropic clustering of the quasars in
Fourier space, testing for the scale-dependent bias introduced by primordial
non-Gaussianity on large scales. We derive and employ a power spectrum
estimator using optimal weights that account for the redshift evolution of the
PNG signal. We find constraints of at 95%
confidence level. These are amont the tightest constraints from Large Scale
Structure (LSS) data. Our redshift weighting improves the error bar by 15% in
comparison to the unweighted case. If quasars have lower response to PNG, the
constraint degrades to , with a 40% improvement
over the standard approach. We forecast that the full eBOSS dataset could reach
using optimal methods and full
range of scales.Comment: 28 pages, 12 figures. Comments welcome
Gravity and the Quantum Vacuum Inertia Hypothesis
In previous work it has been shown that the electromagnetic quantum vacuum,
or electromagnetic zero-point field, makes a contribution to the inertial
reaction force on an accelerated object. We show that the result for inertial
mass can be extended to passive gravitational mass. As a consequence the weak
equivalence principle, which equates inertial to passive gravitational mass,
appears to be explainable. This in turn leads to a straightforward derivation
of the classical Newtonian gravitational force. We call the inertia and
gravitation connection with the vacuum fields the quantum vacuum inertia
hypothesis. To date only the electromagnetic field has been considered. It
remains to extend the hypothesis to the effects of the vacuum fields of the
other interactions. We propose an idealized experiment involving a cavity
resonator which, in principle, would test the hypothesis for the simple case in
which only electromagnetic interactions are involved. This test also suggests a
basis for the free parameter which we have previously defined to
parametrize the interaction between charge and the electromagnetic zero-point
field contributing to the inertial mass of a particle or object.Comment: 18 pages, no figures. Annalen der Physik, 2005, in press. New version
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