Lambda-inflation and CMB anisotropy

We explore a broad class of three-parameter inflationary models, called the $\Lambda$-inflation, and its observational predictions: high abundance of cosmic gravitational waves consistent with the Harrison-Zel'dovich spectrum of primordial cosmological perturbations, the non-power-law wing-like spectrum of matter density perturbations, high efficiency of these models to meet current observational tests, and others. We show that a parity contribution of the gravitational waves and adiabatic density perturbations into the large-scale temperature anisotropy, T/S $\sim 1$, is a common feature of $\Lambda$-inflation; the maximum values of T/S (basically not larger than 10) are reached in models where (i) the local spectrum shape of density perturbations is flat or slightly red ($n_S{}_\sim^< 1$), and (ii) the residual potential energy of the inflaton is near the GUT scale ($V_0^{{1/4}} \sim 10^{16} GeV$). The conditions to find large T/S in the paradigm of cosmic inflation and the relationship of T/S to the ratio of the power spectra, $r$, and to the inflationary $\gamma$ and Hubble parameters, are discussed. We argue that a simple estimate, T/S$\simeq 3r\simeq 12\gamma \simeq (\frac{H}{6\times 10^{13}{\rm GeV}})^2$, is true for most known inflationary solutions and allows to relate straightforwardly the important parameters of observational and physical cosmology.Comment: 29 pages, 3 figures include

Blue spectra and induced formation of primordial black holes

We investigate the statistical properties of primordial black hole (PBH) formation in the very early Universe. We show that the high level of inhomogeneity of the early Universe leads to the formation of the first generation PBHs. %The existence of these PBHs This causes later the appearance of a dust-like phase of the cosmological expansion. We discuss here a new mechanism for the second generation of PBH formation during the dust-like phase. This mechanism is based on the coagulation process. We demonstrate that the blue power spectrum of initial adiabatic perturbations after inflation leads to overproduction of primordial black holes with $10^9$g$\le M\le10^{15}$g if the power index is $n\ge1.2$.Comment: 16 pages, 2 figure

Chaotic behavior in a Z_2 x Z_2 field theory

We investigate the presence of chaos in a system of two real scalar fields with discrete Z_2 x Z_2 symmetry. The potential that identify the system is defined with a real parameter r and presents distinct features for r>0 and for r<0. For static field configurations, the system supports two topological sectors for r>0, and only one for r<0. Under the assumption of spatially homogeneous fields, the system exhibts chaotic behavior almost everywhere in parameter space. In particular a more complex dynamics appears for r>0; in this case chaos can decrease for increasing energy, a fact that is absent for r<0.Comment: Revtex, 13 pages, no figures. Version with figures in Int. J. Mod. Phys. A14 (1999) 496

Bubble fluctuations in Ω<1\Omega<1 inflation

In the context of the open inflationary universe, we calculate the amplitude of quantum fluctuations which deform the bubble shape. These give rise to scalar field fluctuations in the open Friedman-Robertson-Walker universe which is contained inside the bubble. One can transform to a new gauge in which matter looks perfectly smooth, and then the perturbations behave as tensor modes (gravitational waves of very long wavelength). For $(1-\Omega)<<1$, where $\Omega$ is the density parameter, the microwave temperature anisotropies produced by these modes are of order $\delta T/T\sim H(R_0\mu l)^{-1/2} (1-\Omega)^{l/2}$. Here, $H$ is the expansion rate during inflation, $R_0$ is the intrinsic radius of the bubble at the time of nucleation, $\mu$ is the bubble wall tension and $l$ labels the different multipoles ($l>1$). The gravitational backreaction of the bubble has been ignored. In this approximation, $G\mu R_0<<1$, and the new effect can be much larger than the one due to ordinary gravitational waves generated during inflation (unless, of course, $\Omega$ gets too close to one, in which case the new effect disappears).Comment: 17 pages, 3 figs, LaTeX, epsfig.sty, available at ftp://ftp.ifae.es/preprint/ft/uabft387.p

Complete power spectrum for an induced gravity open inflation model

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.Comment: 12 pages RevTeX file with four 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.html Only change is additional reference

Influence of biological activity on 65Zn and 109Cd removal from tidal water by chronically-polluted mangrove sediments

The biological activity influence on the mangrove sediment capacity to remove 65Zn and 109Cd from tidal water was evaluated in a site chronically polluted. Benthic Activity Indexes (BAI), corresponding to relative estimates of biological impact on radiotracer accumulation, were higher for 109Cd (~ 38%) than for 65Zn (~ 10%) in the top centimetre of sediment. However, BAI exceeded 96% for deeper sediment layers. This apparent decrease in radiotracer diffusion into deep sediments through biological activity inhibition is stronger than reported for much less polluted mangrove nearby, suggesting that benthic organisms tolerant of chronic metal pollution may affect metal sorption mechanisms.info:eu-repo/semantics/publishedVersio

On the Transverse-Traceless Projection in Lattice Simulations of Gravitational Wave Production

It has recently been pointed out that the usual procedure employed in order to obtain the transverse-traceless (TT) part of metric perturbations in lattice simulations was inconsistent with the fact that those fields live in the lattice and not in the continuum. It was claimed that this could lead to a larger amplitude and a wrong shape for the gravitational wave (GW) spectra obtained in numerical simulations of (p)reheating. In order to address this issue, we have defined a consistent prescription in the lattice for extracting the TT part of the metric perturbations. We demonstrate explicitly that the GW spectra obtained with the old continuum-based TT projection only differ marginally in amplitude and shape with respect to the new lattice-based ones. We conclude that one can therefore trust the predictions appearing in the literature on the spectra of GW produced during (p)reheating and similar scenarios simulated on a lattice.Comment: 22 pages, 8 figures, Submitted to JCA

On the Theory of Fermionic Preheating

In inflationary cosmology, the particles constituting the Universe are created after inflation due to their interaction with moving inflaton field(s) in the process of preheating. In the fermionic sector, the leading channel is out-of equilibrium particle production in the non-perturbative regime of parametric excitation, which respects Pauli blocking but differs significantly from the perturbative expectation. We develop theory of fermionic preheating coupling to the inflaton, without and with expansion of the universe, for light and massive fermions, to calculate analytically the occupation number of created fermions, focusing on their spectra and time evolution. In the case of large resonant parameter $q$ we extend for rermions the method of successive parabolic scattering, earlier developed for bosonic preheating. In an expanding universe parametric excitation of fermions is stochastic. Created fermions very quickly, within tens of inflaton oscillations, fill up a sphere of radius $\simeq q^{1/4}$ in monetum space. We extend our formalism to the production of superheavy fermions and to `instant' fermion creation.Comment: 14 pages, latex, 12 figures, submitted for publicatio

Dynamics of Assisted Inflation

We investigate the dynamics of the recently proposed model of assisted inflation. In this model an arbitrary number of scalar fields with exponential potentials evolve towards an inflationary scaling solution, even if each of the individual potentials is too steep to support inflation on its own. By choosing an appropriate rotation in field space we can write down explicitly the potential for the weighted mean field along the scaling solution and for fields orthogonal to it. This demonstrates that the potential has a global minimum along the scaling solution. We show that the potential close to this attractor in the rotated field space is analogous to a hybrid inflation model, but with the vacuum energy having an exponential dependence upon a dilaton field. We present analytic solutions describing homogeneous and inhomogeneous perturbations about the attractor solution without resorting to slow-roll approximations. We discuss the curvature and isocurvature perturbation spectra produced from vacuum fluctuations during assisted inflation.Comment: 9 pages, 2 figures, latex with revtex and eps

Phase-plane analysis of Friedmann-Robertson-Walker cosmologies in Brans-Dicke gravity

We present an autonomous phase-plane describing the evolution of Friedmann-Robertson-Walker models containing a perfect fluid (with barotropic index gamma) in Brans-Dicke gravity (with Brans-Dicke parameter omega). We find self-similar fixed points corresponding to Nariai's power-law solutions for spatially flat models and curvature-scaling solutions for curved models. At infinite values of the phase-plane variables we recover O'Hanlon and Tupper's vacuum solutions for spatially flat models and the Milne universe for negative spatial curvature. We find conditions for the existence and stability of these critical points and describe the qualitative evolution in all regions of the (omega,gamma) parameter space for 0-3/2. We show that the condition for inflation in Brans-Dicke gravity is always stronger than the general relativistic condition, gamma<2/3.Comment: 24 pages, including 9 figures, LaTe