123 research outputs found
Italy and COVID-19: the changing patient flow in an orthopedic trauma center emergency department.
'No abstract
Induced-gravity Inflation and the Density Perturbation Spectrum
Recent experimental determinations of the spectral index describing the
scalar mode spectrum of density perturbations encourage comparison with
predictions from models of the very early universe. Unlike extended inflation,
Induced-gravity Inflation predicts a power spectrum with , in close agreement with the experimental measurements.Comment: 11pp, no figures. Plain LaTeX. HUTP-94/A011. Revised edition --
Forthcoming in Physics Letters
COVID-19: not a contraindication for surgery in patients with proximal femur fragility fractures.
'No abstract
Conformal Couplings in Induced Gravity
It is found that the induced gravity with conformal couplings requires the
conformal invariance in both classical and quantum levels for consistency. This
is also true for the induced gravity with an extended conformal coupling
interacting with torsion.Comment: 10 pages, Revtex3.0, to appear in General Relativity and Gravitatio
The Constraint of a General Effective Potential in Vector Torsion Coupled Conformally Induced Gravity
It is found that the deviation of an effective potential from the quartic
form is related to the metric and vector torsion dependencies of the effective
potential in the vector torsion coupled conformally induced gravity.Comment: 3pages Revtex 3.0, no figur
Open Inflationary Universes in the Induced Gravity Theory
The induced gravity theory is a variant of Jordan--Brans--Dicke theory where
the `dilaton' field possesses a potential. It has the unusual feature that in
the presence of a false vacuum there is a {\em stable} static solution with the
dilaton field displaced from the minimum of its potential, giving perfect de
Sitter expansion. We demonstrate how this solution can be used to implement the
open inflationary universe scenario. The necessary second phase of inflation
after false vacuum decay by bubble nucleation is driven by the dilaton rolling
from the static point to the minimum of its potential. Because the static
solution is stable whilst the false vacuum persists, the required evolution
occurs for a wide range of initial conditions. As the exterior of the bubble is
perfect de Sitter space, there is no problem with fields rolling outside the
bubble, as in one of the related models considered by Linde and Mezhlumian, and
the expansion rates before and after tunnelling may be similar which prevents
problematic high-amplitude super-curvature modes from being generated. Once
normalized to the microwave background anisotropies seen by the COBE satellite,
the viable models form a one-parameter family for each possible .Comment: 7 pages RevTeX file with three figures incorporated (uses RevTeX and
epsf). Also available by e-mailing ARL, or by WWW at
http://star-www.maps.susx.ac.uk/papers/early_papers.htm
Scaling solutions in general non-minimal coupling theories
A class of generalized non-minimal coupling theories is investigated, in
search of scaling attractors able to provide an accelerated expansion at the
present time. Solutions are found in the strong coupling regime and when the
coupling function and the potential verify a simple relation. In such cases,
which include power law and exponential functions, the dynamics is independent
of the exact form of the coupling and the potential. The constraint from the
time variability of , however, limits the fraction of energy in the scalar
field to less than 4% of the total energy density, and excludes accelerated
solutions at the present.Comment: 10 pages, 3 figures, accepted for publication in Phys. Rev.
Equation of State of Oscillating Brans-Dicke Scalar and Extra Dimensions
We consider a Brans-Dicke scalar field stabilized by a general power law
potential with power index at a finite equilibrium value. Redshifting
matter induces oscillations of the scalar field around its equilibrium due to
the scalar field coupling to the trace of the energy momentum tensor. If the
stabilizing potential is sufficiently steep these high frequency oscillations
are consistent with observational and experimental constraints for arbitrary
value of the Brans-Dicke parameter . We study analytically and
numerically the equation of state of these high frequency oscillations in terms
of the parameters and and find the corresponding evolution of the
universe scale factor. We find that the equation of state parameter can be
negative and less than -1 but it is not related to the evolution of the scale
factor in the usual way. Nevertheless, accelerating expansion is found for a
certain parameter range. Our analysis applies also to oscillations of the size
of extra dimensions (the radion field) around an equilibrium value. This
duality between self-coupled Brans-Dicke and radion dynamics is applicable for
where D is the number of extra dimensions.Comment: 10 two-column pages, RevTex4, 8 figures. Added clarifying
discussions, new references. Accepted in Phys. Rev. D (to appear
Big bang nucleosynthesis constraints on scalar-tensor theories of gravity
We investigate BBN in scalar-tensor theories of gravity with arbitrary matter
couplings and self-interaction potentials. We first consider the case of a
massless dilaton with a quadratic coupling to matter. We perform a full
numerical integration of the evolution of the scalar field and compute the
resulting light element abundances. We demonstrate in detail the importance of
particle mass thresholds on the evolution of the scalar field in a radiation
dominated universe. We also consider the simplest extension of this model
including a cosmological constant in either the Jordan or Einstein frame.Comment: 19 pages, 30 eps figure
Constraints in the Context of Induced-gravity Inflation
Constraints on the required flatness of the scalar potential for a
cousin-model to extended inflation are studied. It is shown that, unlike
earlier results, Induced-gravity Inflation can lead to successful inflation
with a very simple lagrangian and , rather than
as previously reported. A second order phase transition further
enables this model to escape the \lq big bubble' problem of extended inflation,
while retaining the latter's motivations based on the low-energy effective
lagrangians of supergravity, superstring, and Kaluza-Klein theories.Comment: 19 pp; 3 figures (not included -- available from author). Plain
LaTeX. In press in Physical Review
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