Thick domain wall universes

We investigate the spacetime of a thick gravitating domain wall for a general potential $V(\Phi)$. Using general analytical arguments we show that all nontrivial solutions fall into two categories: those interpretable as an isolated domain wall with a cosmological event horizon, and those which are pure false vacuum de Sitter solutions. Although this latter solution is always unstable to the field rolling coherently to its true vacuum, we show that there is an additional instability to wall formation if the scalar field does not couple too strongly to gravity. Using the $\lambda \Phi^4$ and sine-Gordon models as illustrative examples, we investigate the phase space of the gravitating domain wall in detail numerically, following the solutions from weak to strong gravity. We find excellent agreement with the analytic work. Then, we analyse the domain wall in the presence of a cosmological constant finding again the two kinds of solutions, wall and de Sitter, even in the presence of a negative cosmological constant.Comment: 20 pages revtex, epsfig, references added, some conclusions altere

Analytic continuations of de Sitter thick domain wall solutions

We perform some analytic continuations of the de Sitter thick domain wall solutions obtained in our previous paper hep-th/0201130 in the system of gravity and a scalar field with an axion-like potential. The obtained new solutions represent anti-de Sitter thick domain walls and cosmology. The anti-de Sitter domain wall solutions are periodic, and correspondingly the cosmological solutions represent cyclic universes. We parameterize the axion-like scalar field potential and determine the parameter regions of each type of solutions.Comment: Additons in section 5, 8 pages, 7 figures, RevTe

Thick Domain Walls and Charged Dilaton Black Holes

We study a black hole domain wall system in dilaton gravity which is the low-energy limit of the superstring theory. We solve numerically equations of motion for real self-interacting scalar field and justify the existence of static axisymmetric field configuration representing the thick domain wall in the background of a charged dilaton black hole. It was also confirmed that the extreme dilaton black hole always expelled the domain wall.Comment: 10 pages, 8 figures; to be published in Phys. Rev. D1

Thick domain walls around a black hole

We discuss the gravitationally interacting system of a thick domain wall and a black hole. We numerically solve the scalar field equation in the Schwarzschild spacetime and obtain a sequence of static axi-symmetric solutions representing thick domain walls. We find that, for the walls near the horizon, the Nambu--Goto approximation is no longer valid.Comment: 18 pages, 11 figures, one reference adde

Models for the Brane-Bulk Interaction: Toward Understanding Braneworld Cosmological Perturbation

Using some simple toy models, we explore the nature of the brane-bulk interaction for cosmological models with a large extra dimension. We are in particular interested in understanding the role of the bulk gravitons, which from the point of view of an observer on the brane will appear to generate dissipation and nonlocality, effects which cannot be incorporated into an effective (3+1)-dimensional Lagrangian field theoretic description. We explicitly work out the dynamics of several discrete systems consisting of a finite number of degrees of freedom on the boundary coupled to a (1+1)-dimensional field theory subject to a variety of wave equations. Systems both with and without time translation invariance are considered and moving boundaries are discussed as well. The models considered contain all the qualitative feature of quantized linearized cosmological perturbations for a Randall-Sundrum universe having an arbitrary expansion history, with the sole exception of gravitational gauge invariance, which will be treated in a later paper.Comment: 47 pages, RevTeX (or Latex, etc) with 5 eps figure

Reissner-Nordstrom Black Holes and Thick Domain Walls

We solve numerically equations of motion for real self-interacting scalar fields in the background of Reissner-Nordstrom black hole and obtained a sequence of static axisymmetric solutions representing thick domain walls charged black hole systems. In the case of extremal Reissner-Nordstrom black hole solution we find that there is a parameter depending on the black hole mass and the width of the domain wall which constitutes the upper limit for the expulsion to occur.Comment: 18 pages, 10 figures, accepted for Phys. Rev.

Vortices and black holes in dilatonic gravity

We study analytically black holes pierced by a thin vortex in dilatonic gravity for an arbitrary coupling of the vortex to the dilaton in an arbitrary frame. We show that the horizon of the charged black hole supports the long-range fields of the Nielsen-Olesen vortex that can be considered as black hole hair for both massive and massless dilatons. We also prove that extremal black holes exhibit a flux expulsion phenomenon for a sufficiently thick vortex. We consider the gravitational back-reaction of the thin vortex on the spacetime geometry and dilaton, and discuss under what circumstances the vortex can be used to smooth out the singularities in the dilatonic C-metrics. The effect of the vortex on the massless dilaton is to generate an additional dilaton flux across the horizon.Comment: 16 pages revtex, published versio

Critical phenomena of thick branes in warped spacetimes

We have investigated the effects of a generic bulk first-order phase transition on thick Minkowski branes in warped geometries. As occurs in Euclidean space, when the system is brought near the phase transition an interface separating two ordered phases splits into two interfaces with a disordered phase in between. A remarkable and distinctive feature is that the critical temperature of the phase transition is lowered due to pure geometrical effects. We have studied a variety of critical exponents and the evolution of the transverse-traceless sector of the metric fluctuations.Comment: revtex4, 4 pages, 4 figures, some comments added, typos corrected, published in PR

Produção de leite em pastagem de capim-elefante sob diferentes períodos de ocupação dos piquetes.

Este trabalho foi realizado com o objetivo de avaliar o efeito de diferentes períodos de ocupação de piquetes de capimelefante (Pennisetum purpureum, Shum cv. Napier) por vacas em sistema de pastejo rotativo. A área de cada unidade experimental de 0,5 ha foi dividida em 11, 7 e 5 piquetes necessários para permitir 3, 5 e 7 dias de ocupação dos piquetes com 30, 30 e 28 dias de descanso, respectivamente. O delineamento experimental foi de blocos ao acaso com três repetições. A taxa de lotação da pastagem foi de quatro vacas leiteiras/ha, correspondendo a duas vacas com peso médio de 500 kg PV por tratamento (0,5 ha). A área experimental foi inicialmente fertilizada no sulco com 100 kg/ha de P2O5 e anualmente, nas águas, em cobertura, com 200 kg/ha de N, 50 kg/ha de P2O5 e 200 kg/ha de K2O, nas formas de sulfato de amônia, superfosfato simples and cloreto de potássio, respectivamente. Na época seca do ano, além da pastagem, as vacas receberam, à vontade, cana-de-açúcar picada mais 1% de uréia e concentrado. Disponibilidade de forragem, altura das plantas, cobertura do solo, relação lâmina foliar/colmo e composição química de forragens dentro de cada ano, nas épocas de chuva e seca foram influenciadas pelos períodos de ocupação dos piquetes, conforme o ano e as épocas de chuva e seca. Entretanto, a produção de leite, nos três anos, dentro de cada época, não diferiu entre os tratamentos com média de 8,3; 8,6; e 8,8 kg/(vaca·dia) e de 7,7; 8,3; e 8,4 kg/(vaca·dia), na época chuvosa e seca, respectivamente, para 3, 5 e 7 dias de ocupação. O uso de cinco dias de ocupação com 30 dias de descanso ou sete dias de ocupação e 28 de descanso dos piquetes de capim-elefante, respectivamente, resultou em menor investimento em cercas, bebedouros e facilidade de manejo das vacas