991 research outputs found
Black hole and de Sitter solutions in a covariant renormalizable field theory of gravity
It is shown that Schwarzschild black hole and de Sitter solutions exist as
exact solutions of a recently proposed relativistic covariant formulation of
(power-counting) renormalizable gravity with a fluid. The formulation without a
fluid is also presented here. The stability of the solutions is studied and
their corresponding entropies are computed, by using the covariant Wald method.
The area law is shown to hold both for the Schwarzschild and for the de Sitter
solutions found, confirming that, for the case, one is dealing with a
minimal modification of GR.Comment: 7 paages, latex fil
Dark energy in modified Gauss-Bonnet gravity: late-time acceleration and the hierarchy problem
Dark energy cosmology is considered in a modified Gauss-Bonnet (GB) model of
gravity where an arbitrary function of the GB invariant, , is added to
the General Relativity action. We show that such theory is endowed with a quite
rich cosmological structure: it may naturally lead to an effective cosmological
constant, quintessence or phantom cosmic acceleration, with a possible
transition from deceleration to acceleration. It is demonstrated in the paper
that this theory is perfectly viable, since it is compliant with Solar System
constraints. Specific properties of gravity in a de Sitter universe,
such as dS and SdS solutions, their entropy and its explicit one-loop
quantization are studied. The issue of a possible solution of the hierarchy
problem in modified gravities is addressed too.Comment: LaTeX file 20 pages, new subsections are adde
String-inspired Gauss-Bonnet gravity reconstructed from the universe expansion history and yielding the transition from matter dominance to dark energy
We consider scalar-Gauss-Bonnet and modified Gauss-Bonnet gravities and
reconstruct these theories from the universe expansion history. In particular,
we are able to construct versions of those theories (with and without ordinary
matter), in which the matter dominated era makes a transition to the cosmic
acceleration epoch. It is remarkable that, in several of the cases under
consideration, matter dominance and the deceleration-acceleration transition
occur in the presence of matter only. The late-time acceleration epoch is
described asymptotically by de Sitter space but may also correspond to an exact
CDM cosmology, having in both cases an effective equation of state
parameter close to -1. The one-loop effective action of modified
Gauss-Bonnet gravity on the de Sitter background is evaluated and it is used to
derive stability criteria for the ensuing de Sitter universe.Comment: LaTeX20 pages, 4 figures, version to apear in PR
Influence of Temperature on Mutagenicity in Plants Exposed to Surface Disinfected Drinking Water.
Disinfection of surface drinking water, particularly water chlorination, produces by-products with potential genotoxic and/or carcinogenic activity. A study carried out at a pilot plant for drinking water disinfection of lake water revealed mutagenic activity of three different disinfectants (sodium hypochlorite, chlorine dioxide and peracetic acid) in different seasons using in situ mutagenicity assays, both in animal (micronucleus test) and in plant organisms (anaphase chro- mosomal aberration and micronucleus tests). The effects of the disinfectants appeared to be modulated by the season of exposure. In this study, we tried to understand if (and to what extent) the temperature parameter could actually play an independent role in the registered seasonal variation of mutagenic effects, neglecting the variation of other parameters, e.g. physical conditions and chemical composition of the lake water. Therefore plants (Allium cepa for chromosomal aberration test and Vicia faba for micronucleus test) were exposed to the same disinfected lake-water samples at differ- ent temperatures (10°C, 20°C and 30°C), according the ones registered during the in situ experiment. Long-term expo- sure at the temperatures of 20°C (both Vicia faba and Allium cepa) and 30°C (Vicia faba only) to disinfected waters in- duced clear mutagenic effects. These results show that temperature is an important variable which should be taken into account when in situ exposure of plants is planned for mutagenicity testing. Also, different plant systems clearly show specific temperature ranges suitable for their growth, thereby indicating the need for an accurate selection of the test organism for a specific experimental plan
Technology transfer. Multi-purpose cows for milk, meat and traction in smallholder farming systems. Proceedings of a consultation
The aim of this consultation is to explore the practicality of extending technologies that enable the use of dairy cows for multiple purposes, to help develop a regional project to transfer these technologies to relevant countries in east and Central Africa. The focus of the consultation is on new technologies developed by the International Livestock Research Institute (ILRI) and the Ethiopian Institute of Agricultural Research (IAR) to help introduce multi-purpose crossbred cows into smallholder production systems, focussing on traction in addition to milk and meat production. Topics of discussion include development of cow traction technologies, social and cultural altitudes towards adoption of cow traction, extension efforts to spread the technology, draft power use in smallholder farming systems, research on the nutrition of cows, and potential and extent of use of cows for draft work. Countries involved in the study include Kenya, Uganda, Tanzania, Malawi, Ethiopia, Mozambique, Indonesia, Philippines, Thailand, Vietnam, China and India
Quantum Fields in Hyperbolic Space-Times with Finite Spatial Volume
The one-loop effective action for a massive self-interacting scalar field is
investigated in -dimensional ultrastatic space-time ,
being a non-compact hyperbolic manifold with finite volume. Making
use of the Selberg trace formula, the -function related to the small
disturbance operator is constructed. For an arbitrary gravitational coupling,
it is found that has a simple pole at . The one-loop effective
action is analysed by means of proper-time regularisations and the one-loop
divergences are explicitly found. It is pointed out that, in this special case,
also -function regularisation requires a divergent counterterm, which
however is not necessary in the free massless conformal invariant coupling
case. Finite temperature effects are studied and the high-temperature expansion
is presented. A possible application to the problem of the divergences of the
entanglement entropy for a free massless scalar field in a Rindler-like
space-time is briefly discussed.Comment: 13 pages, LaTex. The contribution of hyperbolic elements has been
added. Other minor corrections and reference
Occurrence of geminivirus in tomato-producing areas in Submedio Sao Francisco.
This is the first report of geminivirus in Submedio Sao Francisco and reveals a wide dispersal of this virus that was previously described in the Federal District (1994) and state of Sao Paulo (1997), Minas Gerais (1996) and Bahia (1996).Suplemento. Edição dos Resumos do 30 Congresso Brasileiro de Fitopatologia, Poços de Caldas, 1997
Metric gravity theories and cosmology:II. Stability of a ground state in f(R) theories
A fundamental criterion of viability of any gravity theory is existence of a
stable ground-state solution being either Minkowski, dS or AdS space. Stability
of the ground state is independent of which frame is physical. In general, a
given theory has multiple ground states and splits into independent physical
sectors. All metric gravity theories with the Lagrangian being a function of
Ricci tensor are dynamically equivalent to Einstein gravity with a source and
this allows us to study the stability problem using methods developed in GR. We
apply these methods to f(R) theories. As is shown in 13 cases of Lagrangians
the stability criterion works simply and effectively whenever the curvature of
the ground state is determined. An infinite number of gravity theories have a
stable ground state and further viability criteria are necessary.Comment: A modified and expanded version of a second part of the paper which
previously appeared as gr-qc/0702097v1. The first, modified part is now
published as gr-qc/0702097v2 and as a separate paper in Class. Qu. Grav. The
present paper matches the published versio
One-loop Effective Potential for a Fixed Charged Self-interacting Bosonic Model at Finite Temperature with its Related Multiplicative Anomaly
The one-loop partition function for a charged self-interacting Bose gas at
finite temperature in D-dimensional spacetime is evaluated within a path
integral approach making use of zeta-function regularization. For D even, a new
additional vacuum term ---overlooked in all previous treatments and coming from
the multiplicative anomaly related to functional determinants-- is found and
its dependence on the mass and chemical potential is obtained. The presence of
the new term is shown to be crucial for having the factorization invariance of
the regularized partition function. In the non interacting case, the
relativistic Bose-Einstein condensation is revisited. By means of a suitable
charge renormalization, for D=4 the symmetry breaking phase is shown to be
unaffected by the new term, which, however, gives actually rise to a non
vanishing new contribution in the unbroken phase.Comment: 25 pages, RevTex, a new Section and several explanations added
concering the non-commutative residue and the physical discussio
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