210 research outputs found

### The form of cosmic string cusps

We classify the possible shapes of cosmic string cusps and how they transform
under Lorentz boosts. A generic cusp can be brought into a form in which the
motion of the cusp tip lies in the plane of the cusp. The cusp whose motion is
perpendicular to this plane, considered by some authors, is a special case and
not the generic situation.
We redo the calculation of the energy in the region where the string overlaps
itself near a cusp, which is the maximum energy that can be released in
radiation. We take into account the motion of a generic cusp and the resulting
Lorentz contraction of the string core. The result is that the energy scales as
$\sqrt {rL}$ instead of the usual value of $r^{1/3} L^{2/3}$, where $r$ is the
string radius and $L$ and is the typical length scale of the string. Since $r
<< L$ for cosmological strings, the radiation is strongly suppressed and could
not be observed.Comment: 15 pages, ReVTex, 2 postscript figures with eps

### Field theory simulation of Abelian-Higgs cosmic string cusps

We have performed a lattice field theory simulation of cusps in Abelian-Higgs
cosmic strings. The results are in accord with the theory that the portion of
the strings which overlaps near the cusp is released as radiation. The radius
of the string cores which must touch to produce the evaporation is
approximately $r = 1$ in natural units. In general, the modifications to the
string shape due to the cusp may produce many cusps later in the evolution of a
string loop, but these later cusps will be much smaller in magnitude and more
closely resemble kinks.Comment: 9 pages, RevTeX, 13 figures with eps

### Evolution of Primordial Black Hole Mass Spectrum in Brans-Dicke Theory

We investigate the evolution of primordial black hole mass spectrum by
including both accretion of radiation and Hawking evaporation within
Brans-Dicke cosmology in radiation, matter and vacuum-dominated eras. We also
consider the effect of evaporation of primordial black holes on the expansion
dynamics of the universe. The analytic solutions describing the energy density
of the black holes in equilibrium with radiation are presented. We demonstrate
that these solutions act as attractors for the system ensuring stability for
both linear and nonlinear situations. We show, however, that inclusion of
accretion of radiation delays the onset of this equilibrium in all radiation,
matter and vacuum-dominated eras.Comment: 18 pages, one figur

### 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

### Black Hole Constraints on Varying Fundamental Constants

Here we apply the Generalized Second Law of Thermodynamics and derive upper
limits on the variation in the fundamental constants. The maximum variation in
the electronic charge permitted for black holes accreting and emitting in the
present cosmic microwave background corresponds to a variation in the fine
structure constant of ((Delta alpha) / alpha) ~ 2 x 10^-23 per second. This
value matches the variation measured by Webb et al. using absorption lines in
the spectra of distant quasars and suggests the variation mechanism may be a
coupling between the electron and the cosmic photon background.Comment: 5 pages, published versio

### Relativistic Viscous Fluid Description of Microscopic Black Hole Wind

Microscopic black holes explode with their temperature varying inversely as
their mass. Such explosions would lead to the highest temperatures in the
present universe, all the way to the Planck energy. Whether or not a
quasi-stationary shell of matter undergoing radial hydrodynamic expansion
surrounds such black holes is been controversial. In this paper relativistic
viscous fluid equations are applied to the problem. It is shown that a
self-consistent picture emerges of a fluid just marginally kept in local
thermal equilibrium; viscosity is a crucial element of the dynamics.Comment: 11 pages, revte

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