83 research outputs found
Black hole formation from massive scalar field collapse in the Einstein-de Sitter universe
We study the spherically symmetric collapse of a real, minimally coupled,
massive scalar field in an asymptotically Einstein-de Sitter spacetime
background. By means of an eikonal approximation for the field and metric
functions, we obtain a simple analytical criterion---involving the physical
size and mass scales (the field's inverse Compton wavelength and the spacetime
gravitational mass) of the initial matter configuration---for generic
(non-time-symmetric) initial data to collapse to a black hole. This analytical
condition can then be used to place constraints on the initial primordial black
hole spectrum, by considering spherical density perturbations that re-entered
the horizon during an early matter-dominated phase that immediately followed
inflation.Comment: 9 pages, RevTeX, 3 eps figures; to appear in Phys. Rev.
Gravitational Collapse and Cosmological Constant
We consider here the effects of a non-vanishing cosmological term on the
final fate of a spherical inhomogeneous collapsing dust cloud. It is shown that
depending on the nature of the initial data from which the collapse evolves,
and for a positive value of the cosmological constant, we can have a globally
regular evolution where a bounce develops within the cloud. We characterize
precisely the initial data causing such a bounce in terms of the initial
density and velocity profiles for the collapsing cloud. In the cases otherwise,
the result of collapse is either formation of a black hole or a naked
singularity resulting as the end state of collapse. We also show here that a
positive cosmological term can cover a part of the singularity spectrum which
is visible in the corresponding dust collapse models for the same initial data.Comment: 18 pages, no figure
Search for composite and exotic fermions at LEP 2
A search for unstable heavy fermions with the DELPHI detector at LEP is
reported. Sequential and non-canonical leptons, as well as excited leptons and
quarks, are considered. The data analysed correspond to an integrated
luminosity of about 48 pb^{-1} at an e^+e^- centre-of-mass energy of 183 GeV
and about 20 pb^{-1} equally shared between the centre-of-mass energies of 172
GeV and 161 GeV. The search for pair-produced new leptons establishes 95%
confidence level mass limits in the region between 70 GeV/c^2 and 90 GeV/c^2,
depending on the channel. The search for singly produced excited leptons and
quarks establishes upper limits on the ratio of the coupling of the excited
fermio
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