5,487 research outputs found
Scalar perturbations in regular two-component bouncing cosmologies
We consider a two-component regular cosmology bouncing from contraction to
expansion, where, in order to include both scalar fields and perfect fluids as
particular cases, the dominant component is allowed to have an intrinsic
isocurvature mode. We show that the spectrum of the growing mode of the Bardeen
potential in the pre-bounce is never transferred to the dominant mode of the
post-bounce. The latter acquires at most a dominant isocurvature component,
depending on the relative properties of the two fluids. Our results imply that
several claims in the literature need substantial revision.Comment: 10 pages, 1 figur
Regular two-component bouncing cosmologies and perturbations therein
We present a full investigation of scalar perturbations in a rather generic
model for a regular bouncing universe, where the bounce is triggered by an
effective perfect fluid with negative energy density. Long before and after the
bounce the universe is dominated by a source with positive energy density,
which may be a perfect fluid, a scalar field, or any other source with an
intrinsic isocurvature perturbation. Within this framework, we present an
analytical method to accurately estimate the spectrum of large-scale scalar
perturbations until their reentry, long after the bounce. We also propose a
simple way to identify non-singular gauge-invariant variables through the
bounce and present the results of extensive numerical tests in several possible
realizations of the scenario. In no case do we find that the spectrum of the
pre-bounce growing mode of the Bardeen potential can be transferred to a
post-bounce constant mode.Comment: 19 pages, 9 figure
Scalar fluctuations in dilatonic brane-worlds
We derive and solve the full set of scalar perturbation equations for a class
of five-dimensional brane--world solutions, with a dilaton scalar field coupled
to the bulk cosmological constant and to a 3-brane. The spectrum contains one
localized massless scalar mode, to be interpreted as an effective dilaton on
the brane, inducing long--range scalar interactions. Two massive scalar modes
yield corrections to Newton's law at short distances, which persist even in the
limit of vanishing dilaton (namely, in the standard Randall--Sundrum
configuration).Comment: 10 pages. Talk presented by V. Bozza at COSMO-01 conference,
Rovaniemi, 200
The Price of an Exact, Gauge-Invariant RG-Flow Equation
We combine old ideas about exact renormalization-group-flow (RGF) equations
with the Vilkovisky-De Witt (VDW) approach to reparametrization invariant
effective actions and arrive at a new, exact, gauge-invariant RGF equation. The
price to be paid for such a result is that both the action and the RGF equation
depend explicitly upon the base point (in field space) needed for the VDW
construction. We briefly discuss the complications originating from this fact
and possible ways to overcome them.Comment: 12 pages. To appear in Phys. Lett.
Assisting pre-big bang phenomenology through short-lived axions
We present the results of a detailed study of how isocurvature axion
fluctuations are converted into adiabatic metric perturbations through axion
decay, and discuss the constraints on the parameters of pre-big bang cosmology
needed for consistency with present CMB-anisotropy data. The large-scale
normalization of temperature fluctuations has a non-trivial dependence both on
the mass and on the initial value of the axion. In the simplest, minimal models
of pre-big bang inflation, consistency with the COBE normalization requires a
slightly tilted (blue) spectrum, while a strictly scale-invariant spectrum
requires mild modifications of the minimal backgrounds at large curvature
and/or string coupling.Comment: 14 pages, latex, 1 figure included using epsfig. A few typos
corrected, two references added, the figure slightly improved. To appear in
Phys. Lett.
Constraints on pre-big bang parameter space from CMBR anisotropies
The so-called curvaton mechanism --a way to convert isocurvature
perturbations into adiabatic ones-- is investigated both analytically and
numerically in a pre-big bang scenario where the role of the curvaton is played
by a sufficiently massive Kalb--Ramond axion of superstring theory. When
combined with observations of CMBR anisotropies at large and moderate angular
scales, the present analysis allows us to constrain quite considerably the
parameter space of the model: in particular, the initial displacement of the
axion from the minimum of its potential and the rate of evolution of the
compactification volume during pre-big bang inflation. The combination of
theoretical and experimental constraints favours a slightly blue spectrum of
scalar perturbations, and/or a value of the string scale in the vicinity of the
SUSY-GUT scale.Comment: 63 pages in Latex style with 14 figures include
Control of gastrointestinal strongyles in goats
Gastrointestinal (GI) parasitism are the most serious problem affecting sheep and goats worldwide. Economic losses caused by GI strongyles are related to decreased production, costs for treatment and prophylaxis and animal death. Effective control of internal parasites in small ruminants is one of the most difficult challenges encountered by veterinary in practice. For control of helminth parasites in grazing animals it is important knowledge of epidemiology of the parasite as it interacts with the host in a specific climatic, management and production environment. Sheep and goats are infected by many of the same GI nematodes, but feeding and management practices alter levels of parasitism between the two ruminants. The most commonly anthelmintics used for helminth control in small ruminants include three chemical groups: Imidazothiazoles/ Pyrimidines (Im/Pm), Benzimidazoles / Probenzimidazoles (Bz/Pbz) and Macrocyclic Lactones (ML). The control of gastrointestinal strongyles infections in goats shows specific patterns. The use of anthelmintics in goats is based upon anthelmintics goats-suited dose rates taking into account the specific pharmacokinetics features of some anthelmintics in this species. Several types of control strategies: deworming programs, grazing management, biological control, supplementary feeding and breeding approaches are discusse
Black holes from high-energy beam--beam collisions
Using a recent technique, proposed by Eardley and Giddings, we extend their
results to the high-energy collision of two beams of massless particles, i.e.
of two finite-front shock waves. Closed (marginally) trapped surfaces can be
determined analytically in several cases even for collisions at non-vanishing
impact parameter in D\ge 4 space-time dimensions. We are able to confirm and
extend earlier conjectures by Yurtsever, and to deal with arbitrary
axisymmetric profiles, including an amusing case of ``fractal'' beams. We
finally discuss some implications of our results in high-energy experiments and
in cosmology.Comment: 17 pages Revtex, 1 figure, references adde
Effects of strategic anthelmintic treatments on the milk production of dairy sheep naturally infected by gastrointestinal strongyles
Adubacao mineral de cafeeiro Conilon (Coffea canephora) em producao no Estado de Rondonia.
O trabalho foi realizado com o objetivo de determinar os niveis mais adequados de NPK, para cafeeiros em producao da cultivar Conilon, em sistemas de plantio tradicionais (espacamentos largos), nos municipios de Nova Uniao e Presidente Medici.bitstream/item/67389/1/CPAF-RO-DOCUMENTOS-28-ADUBACAO-MINERAL-DE-CAFEEIROS-CONILON-COFFEA-CANEPHORA-EM-PRODUCAO-NO-ESTAD.pd
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