Clustering of Primordial Black Holes. II. Evolution of Bound Systems

Primordial Black Holes (PBHs) that form from the collapse of density perturbations are more clustered than the underlying density field. In a previous paper, we showed the constraints that this has on the prospects of PBH dark matter. In this paper we examine another consequence of this clustering: the formation of bound systems of PBHs in the early universe. These would hypothetically be the earliest gravitationally collapsed structures, forming when the universe is still radiation dominated. Depending upon the size and occupation of the clusters, PBH merging occurs before they would have otherwise evaporated due to Hawking evaporation.Comment: 23 pages, 1 figure. Submitted to PR

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

Astrophysical constraints on primordial black holes in Brans-Dicke theory

We consider cosmological evolution in Brans-Dicke theory with a population of primordial black holes. Hawking radiation from the primordial black holes impacts various astrophysical processes during the evolution of the Universe. The accretion of radiation by the black holes in the radiation dominated era may be effective in imparting them a longer lifetime. We present a detailed study of how this affects various standard astrophysical constraints coming from the evaporation of primordial black holes. We analyze constraints from the present density of the Universe, the present photon spectrum, the distortion of the cosmic microwave background spectrum and also from processes affecting light element abundances after nucleosynthesis. We find that the constraints on the initial primordial black hole mass fractions are tightened with increased accretion efficiency.Comment: 15 page

Primordial black hole constraints in cosmologies with early matter domination

Moduli fields, a natural prediction of any supergravity and superstring-inspired supersymmetry theory, may lead to a prolonged period of matter domination in the early Universe. This can be observationally viable provided the moduli decay early enough to avoid harming nucleosynthesis. If primordial black holes form, they would be expected to do so before or during this matter dominated era. We examine the extent to which the standard primordial black hole constraints are weakened in such a cosmology. Permitted mass fractions of black holes at formation are of order $10^{-8}$, rather than the usual $10^{-20}$ or so. If the black holes form from density perturbations with a power-law spectrum, its spectral index is limited to $n \lesssim 1.3$, rather than the $n \lesssim 1.25$ obtained in the standard cosmology.Comment: 7 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/infcos_papers.htm

Cosmological constraints on primordial black holes produced in the near-critical gravitational collapse

The mass function of primordial black holes created through the near-critical gravitational collapse is calculated in a manner fairly independent of the statistical distribution of underlying density fluctuation, assuming that it has a sharp peak on a specific scale. Comparing it with various cosmological constraints on their mass spectrum, some newly excluded range is found in the volume fraction of the region collapsing into black holes as a function of the horizon mass.Comment: 9 pages. Typos corrected. To appear in Physical Review

Supersymmetry and primordial black hole abundance constraints

We study the consequences of supersymmetry for primordial black hole (PBH) abundance constraints. PBHs with mass less than about 10^{11}g will emit supersymmetric particles when they evaporate. In most models of supersymmetry the lightest of these particles, the lightest supersymmetric particle (LSP), is stable and will hence survive to the present day. We calculate the limit on the initial abundance of PBHs from the requirement that the present day LSP density is less than the critical density. We apply this limit, along with those previously obtained from the effects of PBH evaporation on nucleosynthesis and the present day density of PBHs, to PBHs formed from the collpase of inflationary density perturbations, in the context of supersymmetric inflation models. If the reheat temperature after inflation is low, so as to avoid the overproduction of gravitinos and moduli, then the lightest PBHs which are produced in significant numbers will be evaporating around the present day and there are therefore no constraints from the effects of the evaporation products on nucleosynthesis or from the production of LSPs. We then examine models with a high reheat temperature and a subsequent period of thermal inflation. In these models avoiding the overproduction of LSPs limits the abundance of low mass PBHs which were previously unconstrained. Throughout we incorporate the production, at fixed time, of PBHs with a range of masses, which occurs when critical collapse is taken into account.Comment: 8 pages RevTeX file with 3 figures incorporated (uses RevTeX and epsf). Version to appear in Phys. Rev. D: minor change to calculation and added discussio

Lugar, região, nação, mundo: explorações históricas do debate acerca das escalas da ação política

A partir de uma revisão teórica da noção de escala e de uma recuperação do debate socialista no século XIX a respeito de nacionalismo e internacionalismo, o artigo pretende lançar um novo olhar sobre a discussão contemporânea acerca da escala pertinente da ação política e do planejamento. Rejeitando a possibilidade de que qualquer estratégia efetivamente transformadora se inscreva numa única e privilegiada escala – local, regional, nacional ou global –, a conclusão sugere que o poder, mais do que nunca, não está nem no local nem no regional, nem no nacional nem no global… mas na capacidade de articular escalas, de analisar e intervir de modo transescalar.

Planejamento territorial e projeto nacional: os desafios da fragmentação

A história recente do planejamento territorial no Brasil poderia ser narrada como uma trajetória continuada, embora não linear, de desconstituição – política, intelectual e institucional. Este processo é resultado e fator de aceleração do processo de fragmentação territorial que desafia todos os que se preocupam com a necessidade de um projeto nacional digno desta abrangência. O presente trabalho busca identificar e analisar os principais vetores do processo de fragmentação, a saber: grandes projetos de investimento (GPIs), neo-localismo competitivo e o velho regionalismo, com suas redes de clientela-patronagem. Em seguida, são examinados rapidamente os referentes teórico-conceituais dos GPIs e, em particular, do neo-localismo competitivo, que constitui hoje a principal receita distribuída aos países periféricos e dependentes por agências multilaterais e consultores internacionais. Ao final, busca-se explorar em que medida estariam emergindo no processo social contemporâneo tendências e forças capazes de neutralizarem os vetores da fragmentação e conduzirem um projeto nacional, no qual, necessariamente, o planejamento territorial deverá ocupar lugar central.

Primordial Black Holes: sirens of the early Universe

Primordial Black Holes (PBHs) are, typically light, black holes which can form in the early Universe. There are a number of formation mechanisms, including the collapse of large density perturbations, cosmic string loops and bubble collisions. The number of PBHs formed is tightly constrained by the consequences of their evaporation and their lensing and dynamical effects. Therefore PBHs are a powerful probe of the physics of the early Universe, in particular models of inflation. They are also a potential cold dark matter candidate.Comment: 21 pages. To be published in "Quantum Aspects of Black Holes", ed. X. Calmet (Springer, 2014