Phys. Rev. D 55, 4603 (1997) We study the phenomenological constraints on a recently proposed model of
open inflation in the context of induced gravity. The main interest of this
model is the ...relatively small number of parameters, which may be constrained by
many different types of observation. We evaluate the complete spectrum of
density perturbations, which contains continuum sub-curvature modes, a discrete
super curvature mode, and a mode associated with fluctuations in the bubble
wall. From these, we compute the angular power spectrum of temperature
fluctuations in the microwave background, and derive bounds on the parameters
of the model so that the predicted spectrum is compatible with the observed
anisotropy of the microwave background and with large-scale structure
observations. We analyze the matter era and the approach of the model to
general relativity. The model passes all existing constraints.
We study the behaviour of inflationary density perturbations in the vicinity of horizon crossing, using numerical evolution of the relevant mode equations. We explore two specific scenarios. In one, ...inflation is temporarily ended because a portion of the potential is too steep to support inflation. We find that perturbations on super-horizon scales can be modified, usually leading to a large amplification, because of entropy perturbations in the scalar field. This leads to a broad feature in the power spectrum, and the slow-roll and Stewart--Lyth approximations, which assume the perturbations reach an asymptotic regime well outside the horizon, can fail by many orders of magnitude in this regime. In the second scenario we consider perturbations generated right at the end of inflation, which re-enter shortly after inflation ends --- such perturbations can be relevant for primordial black hole formation.
We point out that the effect of reionization on the microwave anisotropy power spectrum is not necessarily negligible on the scales probed by COBE. It can lead to an upward shift of the COBE ...normalization by more than the one-sigma error quoted ignoring reionization. We provide a fitting function to incorporate reionization into the normalization of the matter power spectrum.
We estimate the production of gravitinos during and after the end of a period of warm inflation, a model in which radiation is produced continuously as the field rolls down the potential producing ...dissipation. We find that gravitino production is efficient for models in the strong dissipation regime, with the result that standard nucleosynthesis is disrupted unless the magnitude of the inflaton potential is very small. Combining this with the constraint from the thermal production of adiabatic density perturbations we find the dissipation rate must be extraordinarily strong, or that the potential is very flat.
Phys.Rev.D70:041502,2004 We revisit the calculation of the abundance of primordial black holes (PBHs)
formed from primordial density perturbations, using a formation criterion
derived by Shibata and ...Sasaki which refers to a metric perturbation variable
rather than the usual density contrast. We implement a derivation of the PBH
abundance which uses peaks theory, and compare it to the standard calculation
based on a Press--Schechter-like approach. We find that the two are in
reasonable agreement if the Press--Schechter threshold is in the range
$\Delta_{{\rm th}} \simeq 0.3$ to 0.5, but advocate use of the peaks theory
expression which is based on a sounder theoretical footing.
Phys.Rev.D55:609-615,1997 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 $\Omega_0$.
Phys.Rev. D54 (1996) 7191-7198 We use a numerical code for accurate computation of the amplitude of linear
density perturbations and gravitational waves generated by single-field
inflation models to ...study the accuracy of existing analytic results based on
the slow-roll approximation. We use our code to calculate the coefficient of an
expansion about the exact analytic result for power-law inflation; this
generates a fitting function which can be applied to all inflationary models to
obtain extremely accurate results. In the appropriate limit our results confirm
the Stewart--Lyth analytic second-order calculation, and we find that their
results are very accurate for inflationary models favoured by current
observational constraints.
The XMM Cluster Survey (XCS) is a serendipitous search for galaxy clusters using all publicly available data in the XMM-Newton Science Archive. Its main aims are to measure cosmological parameters ...and trace the evolution of X-ray scaling relations. In this paper we present the first data release from the XMM Cluster Survey (XCS-DR1). This consists of 503 optically confirmed, serendipitously detected, X-ray clusters. Of these clusters, 255 are new to the literature and 356 are new X-ray discoveries. We present 464 clusters with a redshift estimate (0.06 < z < 1.46), including 261 clusters with spectroscopic redshifts. In addition, we have measured X-ray temperatures (Tx) for 402 clusters (0.4 < Tx < 14.7 keV). We highlight seven interesting subsamples of XCS-DR1 clusters: (i) 10 clusters at high redshift (z > 1.0, including a new spectroscopically-confirmed cluster at z = 1.01); (ii) 67 clusters with high Tx (> 5 keV); (iii) 131 clusters/groups with low Tx (< 2 keV); (iv) 27 clusters with measured Tx values in the SDSS `Stripe 82' co-add region; (v) 78 clusters with measured Tx values in the Dark Energy Survey region; (vi) 40 clusters detected with sufficient counts to permit mass measurements (under the assumption of hydrostatic equilibrium); (vii) 105 clusters that can be used for applications such as the derivation of cosmological parameters and the measurement of cluster scaling relations. The X-ray analysis methodology used to construct and analyse the XCS-DR1 cluster sample has been presented in a companion paper, Lloyd-Davies et al. (2010).
In hybrid inflation models, typically only a tiny fraction of possible initial conditions give rise to successful inflation, even if one assumes spatial homogeneity. We analyze some possible ...solutions to this initial conditions problem, namely assisted hybrid inflation and hybrid inflation on the brane. While the former is successful in achieving the onset of inflation for a wide range of initial conditions, it lacks sound physical motivation at present. On the other hand, in the context of the presently much discussed brane cosmology, extra friction terms appear in the Friedmann equation which solve this initial conditions problem in a natural way.
Phys.Rev. D54 (1996) 2557-2563 We investigate, in a model-independent way, the conditions required to obtain
a satisfactory model of extended inflation in which inflation is brought to an
end by a ...first-order phase transition. The constraints are that the correct
present strength of the gravitational coupling is obtained, that the present
theory of gravity is satisfactorily close to general relativity, that the
perturbation spectra from inflation are compatible with large scale structure
observations and that the bubble spectrum produced at the phase transition
doesn't conflict with the observed level of microwave background anisotropies.
We demonstrate that these constraints can be summarized in terms of the
behaviour in the conformally related Einstein frame, and can be compactly
illustrated graphically. We confirm the failure of existing models including
the original extended inflation model, and construct models, albeit rather
contrived ones, which satisfy all existing constraints.
