Overproduction Of Black Holes Research Articles

Effect of curvaton decay on the primordial power spectrum

We study the effect of curvaton decay on the primordial power spectrum. Using analytical approximations and also numerical calculations, we find that the power spectrum is enhanced during the radiation dominated era after the curvaton decay. The amplitude of the Bardeen potential is controlled by the fraction of the energy density in the curvaton at the time of curvaton decay. We show that the enhancement in the amplitude of the primordial curvature perturbation is, however, not large enough to lead to primordial black hole overproduction on scales which re-enter the horizon after the time of curvaton decay.

The cyclical reversible transitions of the universe’s evolution

In this work we propose cyclical reversible transitions as the scenario in which the universe evolves, through a series consisting of reversible expansion, temporary stability, and contraction. Our model is based on the comparison between local and global time-dependent densities {ρ0(τ0),ρ(τ)} instead of the critical density ρc, local and global time-dependent Hubble parameters {H0(τ0),H(τ)}, and the variations {Δρ(τ),ΔH(τ)} due to cosmological chaotic fluctuations, which are generally ignored in certain oscillating models. By taking into account all these factors, a rate equation in the form of (H0/H)2∝(ρ0/ρ) has been established, and from it we derive some others, to provide a mechanism that is responsible for the cyclical reversible transitions. Also, the problems of singularities, black hole overproduction, and the second law of thermodynamics arising in oscillating universe models are conceptually resolved.

The phantom bounce: a new oscillating cosmology

An oscillating universe cycles through a series of expansions andcontractions. We propose a model in which ‘phantom’ energy withp<−ρ grows rapidly and dominates the late-time expanding phase. The universe’s energy densityis so large that the effects of quantum gravity are important at both the beginning and theend of each expansion (or contraction). The bounce can be caused by high energymodifications to the Friedmann equation, which make the cosmology non-singular. Theclassic black hole overproduction of oscillating universes is resolved due to their destructionby the phantom energy.

Black hole production in tachyonic preheating

We present fully non-linear simulations of a self-interacting scalar field in the early universeundergoing tachyonic preheating. We find that density perturbations on subhorizon scaleswhich are amplified by tachyonic instability maintain long range correlations evenduring the succeeding parametric resonance, in contrast to the predictions from thestandard models of preheating dominated by parametric resonance. As a resultthe final spectrum exhibits memory and is not universal in shape. We find thatthroughout the subsequent era of parametric resonance the equation of state of theuniverse is almost dust-like; hence the Jeans wavelength is much smaller than thehorizon scale. If our 2D simulations are accurate reflections of the situation in 3D,then there are wide regions of parameter space ruled out by overproduction ofblack holes. It is likely however that realistic parameter values, consistent withCOBE/WMAP normalization, are safely outside this black hole overproduction region.