Type-II defects in integrable classical field theories

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Fonte escalar acoplada ao campo de Klein-Gordon orbitando um objeto estelar

Neste trabalho determinamos, utilizando Teoria Quântica de Campos em nível de árvore, a radiação escalar emitida por uma fonte em movimento circular uniforme no espaço-tempo plano de Minkowski, assumindo Gravitação Newtoniana, e no espaço-tempo curvo de um buraco negro sem carga e com momento angular nulo, assumindo Relatividade Geral. Efetuamos este cálculo analiticamente para o caso de Minkowski e numericamente no âmbito do espaço-tempo de Schwarzschild, sendo que neste espaço-tempo curvo obtivemos a forma analítica e a normalização dos modos nas regiões assintóticas. Verificamos que, para as órbitas circulares estáveis de acordo com a Relatividade Geral, a potência irradiada no caso de um buraco negro de Schwarzschild é menor do que a obtida no espaço-tempo de Minkowski assumindo a Gravitação Newtoniana. Obtemos também que apenas uma pequena parcela da radiação emitida é absorvida pelo buraco negro. Verificamos que a diferença entre as potências irradiadas em Schwarzschild e Minkowski diminui na medida em que aumentamos o valor da massa do campo. Em Schwarzschild, uma parcela cada vez maior da radiação emitida é absorvida pelo buraco negro na medida em que aumentamos o valor da massa do campo.

Application of open string ?eld theory to the in?ationary scenario

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Domain wall description of superconductivity

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Quantum versus classical instability of scalar fields in curved backgrounds

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A real-time thermal field theoretical analysis of Kubo-type shear viscosity: Numerical understanding with simple examples

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Campos espinoriais ELKO

Pós-graduação em Física - FEG

Um estudo sobre teorias de dimensões extras: modelos de branas geradas por campos escalares

In this work we study extra dimensional theories, taking emphasis in braneworld models generated by real scalar fields. Firstly, we revise the Randall-Sundrum models and we discuss about some thick braneworld scenarios already considered in the literature. We introduce a new thick brane model in order to address the Standard Model hierarchy problem. Furthermore, we show that there exists a class of scalar fields models which are very interesting for analytical studies of thick brane scenarios. Finally, we analyze the braneworld consistency conditions in the context of f(R) and Brans-Dicke gravities, where we show that it is possible to evade a no-go theorem regarding thick brane scenarios

Aspectos quânticos e clássicos da instabilidade de campos fundamentais em espaços-tempos astrofísicos

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

D-oscillons in the standard model extension

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Tópicos em teoria das perturbações cosmológicas

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Cordas cósmicas e gravitação planar de ordem superior

The possibility of generalizing gravity in 2+1 dimensions to include higher-derivative terms, thereby allowing for a dynamical theory, opens up a variety of new interesting questions. This is in great contrast with pure Einstein gravity which is a generally covariant theory that has no degrees of freedom - a peculiarity that, in a sense, renders it a little insipid and odorless. The research on gravity of particles moving in a plane, that is, living in flatland, within the context of higher-derivative gravity, leads to novel and interesting effects. For instance, the generation of gravity, antigravity, and gravitational shielding by the interaction of massive scalar bosons via a graviton exchange. In addition, the gravitational deffection angle of a photon, unlike that of Einstein gravity, is dependent of the impact parameter. On the other hand, the great drawback to using linearized general relativity for describing a gravitating string is that this description leads to some unphysical results such as: (i) lack of a gravity force in the nonrelativistic limit; (ii) gravitational deffection independent of the impact parameter. Interesting enough, the effective cure for these pathologies is the replacement of linearized gravity by linearized higher-derivative gravity. We address these issues here

Analytic perturbation theory for bound states in the transfer matrix spectrum of weakly correlated lattice ferromagnetic spin systems

We consider general d-dimensional lattice ferromagnetic spin systems with nearest neighbor interactions in the high temperature region ('beta' << 1). Each model is characterized by a single site apriori spin distribution taken to be even. We also take the parameter 'alfa' = ('S POT.4') - 3 '(S POT.2') POT.2' > 0, i.e. in the region which we call Gaussian subjugation, where ('S POT.K') denotes the kth moment of the apriori distribution. Associated with the model is a lattice quantum field theory known to contain a particle of asymptotic mass -ln 'beta' and a bound state below the two-particle threshold. We develop a 'beta' analytic perturbation theory for the binding energy of this bound state. As a key ingredient in obtaining our result we show that the Fourier transform of the two-point function is a meromorphic function, with a simple pole, in a suitable complex spectral parameter and the coefficients of its Laurent expansion are analytic in 'beta'.

On the motion of particles in covariant Horava-Lifshitz gravity and the meaning of the A-field

We studied the low energy motion of particles in the general covariant. version of Horava-Lifshitz gravity proposed by Horava and Melby-Thompson. Using a scalar field coupled to gravity according to the minimal substitution recipe proposed by da Silva and taking the geometrical optics limit, we could write an effective relativistic metric for a general solution. As a result, we discovered that the equivalence principle is not in general recovered at low energies, unless the spatial Laplacian of A vanishes. Finally, we analyzed the motion on the spherical symmetric solution proposed by Horava and Melby-Thompson, where we could find its effective line element and compute spin-0 geodesics. Using standard methods we have shown that such an effective metric cannot reproduce Newton's gravity law even in the weak gravitational field approximation. (C) 2011 Elsevier B.V All rights reserved.

Localizability in de Sitter space

An analogue of the Newton-Wigner position operator is defined for a massive neutral scalar field in de Sitter space. The one-particle subspace of the theory, consisting of positive-energy solutions of the Klein-Gordon equation selected by the Hadamard condition, is identified with an irreducible representation of the de Sitter group. Postulates of localizability analogous to those written by Wightman for fields in Minkowski space are formulated on it, and a unique solution is shown to exist. Representations in both the principal and the complementary series are considered. A simple expression for the time evolution of the Newton-Wigner operator is presented.