1,763 research outputs found
First results from the Pierre Auger Observatory
We review in these notes the status of the construction of the Pierre Auger
Observatory and present the first Physics results, based on the data collected
during the first year and a half of operation. These results are preliminary,
once the work to understand the systematics of the detectors are still
underway. We discuss the cosmic ray spectrum above 3 EeV, based on the
measurement done using the Surface Detector and the Fluorescence Detector,
both, components of the observatory. We discuss, as well, the search for
anisotropy near the Galactic Center and the limit on the photon fraction at the
highest energies.Comment: 10 pages, 16 figures, Brazilian National Meeting on Particle and
Fields 200
Topological Defects in Contracting Universes
We study the behaviour and consequences of cosmic string networks in
contracting universes. They approximately behave during the collapse phase as a
radiation fluids. Scaling solutions describing this are derived and tested
against high-resolution numerical simulations. A string network in a
contracting universe, together with the gravitational radiation it generates,
can affect the dynamics of the universe both locally and globally, and be an
important source of radiation, entropy and inhomogeneity. We discuss possible
implications for bouncing and cyclic models.Comment: Shorter version of astro-ph/0206287. To appear in Phys. Rev. Let
Radiation from Excited Vortex in the Abelian Higgs Model
Excitation of a vortex in the Abelian Higgs model is investigated with the
help of a polynomial approximation. The excitation can be regarded as a
longitudinal component of the vector field trapped by the vortex. The energy
and profile of the excitation are found. Back-reaction of the excitation on the
vortex is calculated in the small limit. It turns out that in the
presence of the excitation the vortex effectively becomes much wider - its
radius oscillates in time and for all times it is not smaller than the radius
of the unexcited vortex. Moreover, we find that the vector field of the excited
vortex has long range radiative component. Bound on the amplitude of the
excitation is also found.Comment: Latex, 20 pages. 2 figures attached as .uu file to be decoded and
used as input for epsfbox command which is already included in the main Latex
fil
Interactions between Cosmic Strings: An Analytical Study
We derive analytic expressions for the interaction energy between two general
cosmic strings as the function of their relative orientation and the
ratio of the coupling constants in the model. The results are relevant to the
statistic description of strings away from critical coupling and shed some
light on the mechanisms involved in string formation and the evolution of
string networks.Comment: 31 pages,REVTEX, Imperial/TP/93-94/3
Cosmic strings, loops, and linear growth of matter perturbations
We describe the detailed study and results of high-resolution numerical
simulations of string-induced structure formation in open universes and those
with a non-zero cosmological constant. The effect from small loops generated
from the string network has also been investigated. We provide a
semi-analytical model which can reproduce these simulation results. A detailed
study of cosmic string network properties regarding structure formation is also
given, including the correlation time, the topological analysis of the source
spectrum, the correlation between long strings and loops, and the evolution of
long-string and loop energy densities. For models with 8 h^{-1}\sigma_8$, and an overall shape which are consistent within
uncertainties with those currently inferred from galaxy surveys. The cosmic
string scenario with hot dark matter requires a strongly scale-dependent bias
in order to agree with observations.Comment: 60 pages, 24 figure
Vorton Formation
In this paper we present the first analytic model for vorton formation. We
start by deriving the microscopic string equations of motion in Witten's
superconducting model, and show that in the relevant chiral limit these
coincide with the ones obtained from the supersonic elastic models of Carter
and Peter. We then numerically study a number of solutions of these equations
of motion and thereby suggest criteria for deciding whether a given
superconducting loop configuration can form a vorton. Finally, using a recently
developed model for the evolution of currents in superconducting strings we
conjecture, by comparison with these criteria, that string networks formed at
the GUT phase transition should produce no vortons. On the other hand, a
network formed at the electroweak scale can produce vortons accounting for up
to 6% of the critical density. Some consequences of our results are discussed.Comment: 41 pages; color figures 3-6 not included, but available from authors.
To appear in Phys. Rev.
A Note on the evolution of cosmic string/superstring networks
In the context of brane world scenario, cosmic superstrings can be formed in
D-brane annihilation at the end of the brane inflationary era. The cosmic
superstring network has a scaling solution and the characteristic scale of the
network is proportional to the square root of the reconnection probability.Comment: 13 pages, 12 figures (revised version
Vortex Dynamics in Selfdual Maxwell-Higgs Systems with Uniform Background Electric Charge Density
We introduce selfdual Maxwell-Higgs systems with uniform background electric
charge density and show that the selfdual equations satisfied by topological
vortices can be reduced to the original Bogomol'nyi equations without any
background. These vortices are shown to carry no spin but to feel the Magnus
force due to the shielding charge carried by the Higgs field. We also study the
dynamics of slowly moving vortices and show that the spin-statistics theorem
holds to our vortices.Comment: 24 pages + 2 figures ( not included), Cu-TP-611, IASSNS-HEP-93/33,
NSF-ITP-93-13
Non-Gaussianities in two-field inflation
We study the bispectrum of the curvature perturbation on uniform energy
density hypersurfaces in models of inflation with two scalar fields evolving
simultaneously. In the case of a separable potential, it is possible to compute
the curvature perturbation up to second order in the perturbations, generated
on large scales due to the presence of non-adiabatic perturbations, by
employing the -formalism, in the slow-roll approximation. In this
case, we provide an analytic formula for the nonlinear parameter . We
apply this formula to double inflation with two massive fields, showing that it
does not generate significant non-Gaussianity; the nonlinear parameter at the
end of inflation is slow-roll suppressed. Finally, we develop a numerical
method for generic two-field models of inflation, which allows us to go beyond
the slow-roll approximation and confirms our analytic results for double
inflation.Comment: 29 pages, 6 figures. v2, comparison with previous estimates. v3, JCAP
version; Revisions based on Referee's comment, corrected typos, added few eqs
and refs, conclusions unchange
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