A new inflationary universe scenario: A possible solution of the horizon, flatness, homogeneity, isotropy and primordial monopole problems

http://risa.stanford.edu/teaching/362/particledarkmatter.pdf

Particle dark matter: Evidence, candidates and constraints

A new inflationary universe scenario is suggested, which is free of the shortcomings of the previous one and provides a possible solution of the horizon, flatness, homogeneity and isotropy problems in cosmology, and also a solution of the primordial monopole problem in grand unified theories.

A New Inflationary Universe Scenario: A Possible Solution of the Horizon, Flatness, Homogeneity, Isotropy and Primordial Monopole Problems

QUANTUM gravitational effects are usually ignored in calculations of the formation and evolution of black holes. The justification for this is that the radius of curvature of space-time outside the event horizon is very large compared to the Planck length (Għ/c3)1/2 ≈ 10−33 cm, the length scale on which quantum fluctuations of the metric are expected to be of order unity. This means that the energy density of particles created by the gravitational field is small compared to the space-time curvature. Even though quantum effects may be small locally, they may still, however, add up to produce a significant effect over the lifetime of the Universe ≈ 1017 s which is very long compared to the Planck time ≈ 10−43 s. The purpose of this letter is to show that this indeed may be the case: it seems that any black hole will create and emit particles such as neutrinos or photons at just the rate that one would expect if the black hole was a body with a temperature of (κ/2π) (ħ/2k) ≈ 10−6 (M/M)K where κ is the surface gravity of the black hole1. As a black hole emits this thermal radiation one would expect it to lose mass. This in turn would increase the surface gravity and so increase the rate of emission. The black hole would therefore have a finite life of the order of 1071 (M/M)−3 s. For a black hole of solar mass this is much longer than the age of the Universe. There might, however, be much smaller black holes which were formed by fluctuations in the early Universe2. Any such black hole of mass less than 1015 g would have evaporated by now. Near the end of its life the rate of emission would be very high and about 1030 erg would be released in the last 0.1 s. This is a fairly small explosion by astronomical standards but it is equivalent to about 1 million 1 Mton hydrogen bombs. It is often said that nothing can escape from a black hole. But in 1974, Stephen Hawking realized that, owing to quantum effects, black holes should emit particles with a thermal distribution of energies — as if the black hole had a temperature inversely proportional to its mass. In addition to putting black-hole thermodynamics on a firmer footing, this discovery led Hawking to postulate 'black hole explosions', as primordial black holes end their lives in an accelerating release of energy.

Black Hole Explosions

Many aspects of the large-scale structure of the Universe can be described successfully using cosmological models in which $27\ifmmode\pm\else\textpm\fi{}1%$ of the critical mass-energy density consists of cold dark matter (CDM). However, few---if any---of the predictions of CDM models have been successful on scales of $\ensuremath{\sim}10\text{ }\text{ }\mathrm{kpc}$ or less. This lack of success is usually explained by the difficulty of modeling baryonic physics (star formation, supernova and black-hole feedback, etc.). An intriguing alternative to CDM is that the dark matter is an extremely light ($m\ensuremath{\sim}{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}$) boson having a de Broglie wavelength $\ensuremath{\lambda}\ensuremath{\sim}1\text{ }\text{ }\mathrm{kpc}$, often called fuzzy dark matter (FDM). We describe the arguments from particle physics that motivate FDM, review previous work on its astrophysical signatures, and analyze several unexplored aspects of its behavior. In particular, (i) FDM halos or subhalos smaller than about $1{0}^{7}(m/{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}{)}^{\ensuremath{-}3/2}$ ${M}_{\ensuremath{\bigodot}}$ do not form, and the abundance of halos smaller than a few times $1{0}^{10}(m/{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}{)}^{\ensuremath{-}4/3}$ ${M}_{\ensuremath{\bigodot}}$ is substantially smaller in FDM than in CDM. (ii) FDM halos are comprised of a central core that is a stationary, minimum-energy solution of the Schr\"odinger-Poisson equation, sometimes called a ``soliton,'' surrounded by an envelope that resembles a CDM halo. The soliton can produce a distinct signature in the rotation curves of FDM-dominated systems. (iii) The transition between soliton and envelope is determined by a relaxation process analogous to two-body relaxation in gravitating N-body systems, which proceeds as if the halo were composed of particles with mass $\ensuremath{\sim}\ensuremath{\rho}{\ensuremath{\lambda}}^{3}$ where $\ensuremath{\rho}$ is the halo density. (iv) Relaxation may have substantial effects on the stellar disk and bulge in the inner parts of disk galaxies, but has negligible effect on disk thickening or globular cluster disruption near the solar radius. (v) Relaxation can produce FDM disks but a FDM disk in the solar neighborhood must have a half-thickness of at least $\ensuremath{\sim}300(m/{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}{)}^{\ensuremath{-}2/3}\text{ }\text{ }\mathrm{pc}$ and a midplane density less than $0.2(m/{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}{)}^{2/3}$ times the baryonic disk density. (vi) Solitonic FDM subhalos evaporate by tunneling through the tidal radius and this limits the minimum subhalo mass inside $\ensuremath{\sim}30\text{ }\text{ }\mathrm{kpc}$ of the Milky Way to a few times $1{0}^{8}(m/{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}{)}^{\ensuremath{-}3/2}$ ${M}_{\ensuremath{\bigodot}}$. (vii) If the dark matter in the Fornax dwarf galaxy is composed of CDM, most of the globular clusters observed in that galaxy should have long ago spiraled to its center, and this problem is resolved if the dark matter is FDM. (viii) FDM delays galaxy formation relative to CDM but its galaxy-formation history is consistent with current observations of high-redshift galaxies and the late reionization observed by Planck. If the dark matter is composed of FDM, most observations favor a particle mass $\ensuremath{\gtrsim}{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}$ and the most significant observational consequences occur if the mass is in the range $1--10\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}$. There is tension with observations of the Lyman-$\ensuremath{\alpha}$ forest, which favor $m\ensuremath{\gtrsim}10--20\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}22}\text{ }\text{ }\mathrm{eV}$ and we discuss whether more sophisticated models of reionization may resolve this tension.

Ultralight scalars as cosmological dark matter

Is it easy to save the gravitino

On considere l'instabilite gravitationnelle d'un etat spatialement uniforme d'un champ scalaire relativiste sur un fond independant du temps. On demontre que l'instabilite est semblable a l'instabilite de Jeans pour la matiere non relativiste du type poussiere. Les effets «hydrodynamiques» peuvent modifier considerablement le caractere de l'instabilite. Application au calcul de la probabilite de formation de trous noirs originels

/pdf/gravitational-instability-of-scalar-fields-and-formation-of-1n7u9dc67b.pdf

Gravitational instability of scalar fields and formation of primordial black holes

Primordial black holes (PBHs) are a profound signature of primordial cosmological structures and provide a theoretical tool to study nontrivial physics of the early Universe. The mechanisms of PBH formation are discussed and observational constraints on the PBH spectrum, or effects of PBH evaporation, are shown to restrict a wide range of particle physics models, predicting an enhancement of the ultraviolet part of the spectrum of density perturbations, early dust-like stages, first order phase transitions and stages of superheavy metastable particle dominance in the early Universe. The mechanism of closed wall contraction can lead, in the inflationary Universe, to a new approach to galaxy formation, involving primordial clouds of massive BHs created around the intermediate mass or supermassive BH and playing the role of galactic seeds.

M. Yu. Khlopov

Papers

Is it easy to save the gravitino

Gravitational instability of scalar fields and formation of primordial black holes

Primordial Black Holes

On the concentration of relic magnetic monopoles in the universe

Primordial black holes as a cosmological test of grand unification