Dark energy as a kinematic effect

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Constante cosmológica: algumas consequências algébricas e dinâmicas

Pós-graduação em Física - IFT

Two-branes with variable tension model and the effective Newtonian constant

It is shown that, in the two brane time variation model framework, if the hidden brane tension varies according to the phenomenological Eotvos law, the visible brane tension behavior is such that its time derivative is negative in the past and positive after a specific time of cosmological evolution. This behavior is interpreted in terms of a useful mechanical system analog and its relation with the variation of the Newtonian (effective) gravitational constant is explored.

Cosmological constraints on an invisibly decaying Higgs

Working in the context of a proposal for collisional dark matter, we derive bounds on the Higgs boson coupling g' to a stable light scalar particle, which we refer to as phion (phi), required to solve problems with small scale structure formation which arise in collisionless, dark matter models. We discuss the behaviour of the phion in the early universe for different ranges of its mass. We find that a phion in the mass range of 100 MeV is excluded and that a phion in the mass range of I GeV requires a large coupling constant, g' greater than or similar to 2, and m(h) less than or similar to 130 GeV in order to avoid overabundance, in which case the invisible decay mode of the Higgs boson would be dominant. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Consequences of dark matter-dark energy interaction on cosmological parameters derived from type Ia supernova data

Models where the dark matter component of the Universe interacts with the dark energy field have been proposed as a solution to the cosmic coincidence problem, since in the attractor regime both dark energy and dark matter scale in the same way. In these models the mass of the cold dark matter particles is a function of the dark energy field responsible for the present acceleration of the Universe, and different scenarios can be parametrized by how the mass of the cold dark matter particles evolves with time. In this article we study the impact of a constant coupling delta between dark energy and dark matter on the determination of a redshift dependent dark energy equation of state w(DE)(z) and on the dark matter density today from SNIa data. We derive an analytical expression for the luminosity distance in this case. In particular, we show that the presence of such a coupling increases the tension between the cosmic microwave background data from the analysis of the shift parameter in models with constant w(DE) and SNIa data for realistic values of the present dark matter density fraction. Thus, an independent measurement of the present dark matter density can place constraints on models with interacting dark energy.

Fertility life table of Trichogramma pretiosum and Trichogramma acacioi (Hymenoptera : Trichogrammatidae) on Sitotroga cerealella (Lepidoptera : Gelechiidae) eggs at different constant temperatures

Fertility life tables were developed for both Trichogramma pretiosum and Trichogramma acacioi reared on Sitotroga cerealella eggs as an alternative host at five different temperatures. The egg parasitoids were first collected from Nipteria panacea eggs, a lepidopterous pest of avocado. Egg parasitoid females were individualized in small glass vials along with 40 eggs of the host during 24 h for parasitization. For evaluation of the parasitism capacity, a similar procedure was adopted, but cardboards with eggs were replaced every day. The net reproductive rate (Ro), intrinsic rate of increase (rm), finite rate of increase (lambda), and mean generation time (T) were estimated. Temperature affected all parameters for both Trichogramma species. The highest fecundity for both species was observed at 25degreesC. Extreme temperatures such as 15degreesC or 35degreesC negatively affect the development rate of both species.

Application of the Potentiometric Stripping Analysis with Constant Current for the Determination of Lithium Ions Using a Spinel-Type Manganese (IV) Oxide-Modified Carbon Paste Electrode

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

DC Electric Field Dependence of the Dielectric Constant of Pzt Thin Films Prepared by Polymeric Precursor Method

This work reports dielectric measurements performed on Pb(Zr0.53Ti0.47)O3 (PZT) thin films prepared by a polymeric precursor method. The -E curves obtained for the PZT film measured at 100 kHz, under a small ac 0.2 kV/cm signal-test and a dc scan featured a typical butterfly curve. However, the -E curves obtained for PZT film under a dc scan, with a scan rate of 0.003 V/s, shows a pronounced asymmetry. The absence of a symmetric secondary peak in -E curves could be an indication of essentially 180 domain switching.

Physiologic and productive responses of Holstein dairy cows with access to the constant or limited shade

The work: was carried out to evaluate the physiologic and productive responses of 16 Holstein breed cows, in different lactating stages and production levels, maintained in two free stall corral types, with or without plastic sheet covering, in the southeast-northwest of the covered area edges. The animals were confined in free stall system, during the months of the summer, with access to the constant or Limited shade. A complete randomized experimental design was: used. The physiological variables measured were respiratory frequency (morning an afternoon) and rectal temperature (morning and afternoon). The productive variables were milk production (morning, afternoon and daily), dry matter (DM) intake (% live weight) and efficiency of milk production (kg of milk/kg DM intake). The animals with access to the constant shade presented respiratory frequency (74.1 vs 81.0 breath/min.) and rectal temperature (39.5 vs 39.7 degrees C) lower and mirk production (22.6 vs 20.9 kg/day) and efficiency of milk production (1.3 vs 1.2 kg of milk/kg DM ingested) higher than the animals with access to the limited shade. There was no effect on the dry matter intake.

The effect of changes in the bulk dielectric constant on the DNA torsional properties

The effect of changes in the bulk dielectric constant on the DNA torsional properties was evaluated from plasmid circularization reactions. In these reactions, pUC18 previously linearized by EcoRI digestion was recircularized with T4 DNA ligase. The bulk dielectric constant of the reaction medium was decreased by the addition of different concentrations of neutral solutes: ethylene glycol, glycerol, sorbitol, and sucrose, or increased by the addition of glycine. The topoisomers generated by the ligase reaction were resolved by agarose-gel electrophoresis. The DNA twist energy parameter (K), which is an apparent torsional constant, was determined by linearization of the Gaussian topoisomers' distribution. It was observed that the twist energy parameter for the given solutes is almost linearly dependent on the bulk dielectric constant. In the reaction buffer, the twist energy parameter was determined to be 1100 +/- 100. By decreasing the dielectric constant to 74 with the addition of sorbitol, the value of the parameter reaches K = 900 +/- 100, whereas the addition of ethylene glycol leads to kappa = 400 +/- 50. Upon addition of glycine, which resulted in a dielectric constant equal to 91, the value of the twist energy parameter increased to K 1750 +/- 100. (c) 2007 Wiley Periodicals.

Freezing of the QCD coupling constant and the pion form factor

The possibility that the QCD coupling constant (alpha(s)) has an infrared finite behavior (freezing) has been extensively studied in recent years. We compare phenomenological values of the frozen QCD running coupling between different classes of solutions obtained through non-perturbative Schwinger-Dyson Equations. With these solutions were computed QCD predictions for the asymptotic pion form factor which, in turn, were compared with experiment.

Analysis of the Hb(b)over-bar coupling constant and CP-violation effects at the future e(+)e(-) collider

The e(+)e(-)-->b (B) over bar nu(ν) over bar process, where nu is an electron, muon, or tau-lepton neutrino, is analyzed in detail for the general form of the coupling constant of a Higgs boson with b quarks, with the (m(b)/v)(a + igamma(5)b) parameterization of the Hb (b) over bar interaction. This process is shown to be highly sensitive to this coupling constant. Experiments at the future with roots = 500-GeV linear collider will provide limits of 2 and 20% for deviations of the parameters a and b, respectively, from their Standard Model values. Results concerning the e(+)e(-)-->b (b) over bar nu(ν) over bar process in combination with the independent measurements of the partial width Gamma(H --> b (b) over bar) can testify to the CP origin of the Higgs sector of the theory. (C) 2003 MAIK Nauka/Interperiodica.

Freezing of the QCD coupling constant and solutions of Schwinger-Dyson equations

We compare phenomenological values of the frozen QCD running coupling constant (alpha(s)) with two classes of infrared finite solutions obtained through nonperturbative Schwinger-Dyson equations. We use these same solutions with frozen coupling constants as well as their respective nonperturbative gluon propagators to compute the QCD prediction for the asymptotic pion form factor. Agreement between theory and experiment on alpha(s)(0) and F (pi)(Q(2)) is found only for one of the Schwinger-Dyson equation solutions.

Structure formation in the presence of dark energy perturbations

We study non-linear structure formation in the presence of dark energy. The influence of dark energy on the growth of large-scale cosmological structures is exerted both through its background effect on the expansion rate, and through its perturbations. In order to compute the rate of formation of massive objects we employ the spherical collapse formalism, which we generalize to include fluids with pressure. We show that the resulting non-linear evolution equations are identical to the ones obtained in the pseudo-Newtonian approach to cosmological perturbations, in the regime where an equation of state serves to describe both the background pressure relative to density, and the pressure perturbations relative to the density perturbations. We then consider a wide range of constant and time-dependent equations of state (including phantom models) parametrized in a standard way, and study their impact on the non-linear growth of structure. The main effect is the formation of dark energy structure associated with the dark matter halo: non-phantom equations of state induce the formation of a dark energy halo, damping the growth of structures; phantom models, on the other hand, generate dark energy voids, enhancing structure growth. Finally, we employ the Press-Schechter formalism to compute how dark energy affects the number of massive objects as a function of redshift (number counts).

QCD tests with an infrared finite gluon propagator and coupling constant

Recent progress in the solution of Schwinger-Dyson equations, as well as lattice simulation of pure glue QCD, indicate that the gluon propagator and coupling constant are infrared finite. Such non-perturbative information can be introduced in the QCD perturbative expansion in the scheme named Dynamical Perturbation Theory. We exemplify this procedure with the calculation of some two-body non-leptonic annihilation B meson decays, which show agreement with the experimental data in the case of a gluon propagator characterized by a dynamical gluon mass of 500MeV, compatible with the value found in several processes computed with this method. We give a. preliminary account of the application of this procedure at the loop level in the case of the Bjorken sum rule.