Fresnel analysis of wave propagation in nonlinear electrodynamics

We study wave propagation in local nonlinear electrodynamical models. Particular attention is paid to the derivation and the analysis of the Fresnel equation for the wave covectors. For the class of local nonlinear Lagrangian nondispersive models, we demonstrate how the originally quartic Fresnel equation factorizes, yielding the generic birefringence effect. We show that the closure of the effective constitutive (or jump) tensor is necessary and sufficient for the absence of birefringence, i.e., for the existence of a unique light cone structure. As another application of the Fresnel approach, we analyze the light propagation in a moving isotropic nonlinear medium. The corresponding effective constitutive tensor contains nontrivial skewon and axion pieces. For nonmagnetic matter, we find that birefringence is induced by the nonlinearity, and derive the corresponding optical metrics.

Natural Peccei-Quinn symmetry in the 3-3-1 model with a minimal scalar sector

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

A simple model for quintessential inflation

We propose a simple toy model for quintessential inflation where a complex scalar field described by a Lagrangian with a U(1)(PQ) symmetry spontaneously broken at a high energy scale and explicitly broken by instanton effects at a much lower energy can account for both the early inflationary phase and the recent accelerated expansion of the Universe. The real part of the complex field plays the role of the in flaton whereas the imaginary part, the 'axion', is the quintessence field.

Áxions, májorons e neutrinos em extensões do modelo padrão

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Aging voice and the laryngeal muscle atrophy

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

Search for a spin-dependent short-range force between nucleons with a 3 He, 129 Xe clock-comparison experiment

Light pseudoscalar bosons, such as the axion that was originally proposed as a solution of the strong CP problem, would cause a new spin-dependent short-range interaction. In this thesis, an experiment is presented to search for axion mediated short-range interaction between a nucleon and the spin of a polarized bound neutron. This interaction cause a shift in the precession frequency of nuclear spin-polarized gases in the presence of an unpolarized mass. To get rid of magnetic field drifts co-located, nuclear spin polarized 3He and 129Xe atoms were used. The free nuclear spin precession frequencies were measured in a homogeneous magnetic guiding field of about 350nT using LTc SQUID detectors. The whole setup was housed in a magnetically shielded room at the Physikalisch Technische Bundesanstalt (PTB) in Berlin. With this setup long nuclear spin-coherence times, respectively, transverse relaxation times of 5h for 129Xe and 53h for 3He could be achieved. The results of the last run in September 2010 are presented which give new upper limits on the scalar-pseudoscalar coupling of axion-like particles in the axion-mass window from 10^(-2) eV to 10^(-6) eV. The laboratory upper bounds were improved by up to 4 orders of magnitude.

Dark Matter 2014

This article gives an overview on the status of experimental searches for dark matter at the end of 2014. The main focus is on direct searches for weakly interacting massive particles (WIMPs) using underground-based low-background detectors, especially on the new results published in 2014. WIMPs are excellent dark matter candidates, predicted by many theories beyond the standard model of particle physics, and are expected to interact with the target nuclei either via spin-independent (scalar) or spin-dependent (axial-vector) couplings. Non-WIMP dark matter candidates, especially axions and axion-like particles are also briefly discussed.

Particle components of dark matter

Particle candidates for astrophysical dark matter are reviewed, with particular emphasis on the lightest supersymmetric particle and the axion. The former is now constrained by accelerator experiments to have a mass above about 40 GeV, and ongoing searches at accelerators, in space, and in underground experiments have a good chance to detect it. A reevaluation of the constraint on the axion from supernova 1987a leaves open an interesting window where it may be detected if it constitutes the galactic halo.

Direct searches for dark matter: Recent results

There is abundant evidence for large amounts of unseen matter in the universe. This dark matter, by its very nature, couples feebly to ordinary matter and is correspondingly difficult to detect. Nonetheless, several experiments are now underway with the sensitivity required to detect directly galactic halo dark matter through their interactions with matter and radiation. These experiments divide into two broad classes: searches for weakly interacting massive particles (WIMPs) and searches for axions. There exists a very strong theoretical bias for supposing that supersymmetry (SUSY) is a correct description of nature. WIMPs are predicted by this SUSY theory and have the required properties to be dark matter. These WIMPs are detected from the byproducts of their occasional recoil against nucleons. There are efforts around the world to detect these rare recoils. The WIMP part of this overview focuses on the cryogenic dark matter search (CDMS) underway in California. Axions, another favored dark matter candidate, are predicted to arise from a minimal extension of the standard model that explains the absence of the expected large CP violating effects in strong interactions. Axions can, in the presence of a large magnetic field, turn into microwave photons. It is the slight excess of photons above noise that signals the axion. Axion searches are underway in California and Japan. The axion part of this overview focuses on the California effort. Brevity does not allow me to discuss other WIMP and axion searches, likewise for accelerator and satellite based searches; I apologize for their omission.

Gravidade de Lovelock e a correspondência AdS/CFT

A correspondência AdS/CFT é uma notável ferramenta no estudo de teorias de gauge fortemente acopladas que podem ser mapeadas em uma descrição gravitacional dual fracamente acoplada. A correspondência é melhor entendida no limite em que ambos $N$ e $\\lambda$, o rank do grupo de gauge e o acoplamento de \'t Hooft da teoria de gauge, respectivamente, são infinitos. Levar em consideração interações com termos de curvatura de ordem superior nos permite considerar correções de $\\lambda$ finito. Por exemplo, a primeira correção de acoplamento finito para supergravidade tipo IIB surge como um termo de curvatura com forma esquemática $\\alpha\'^3 R^4$. Neste trabalho investigamos correções de curvatura no contexto da gravidade de Lovelock, que é um cenário simples para investigar tais correções pois as suas equações de movimento ainda são de segunda ordem em derivadas. Esse cenário também é particularmente interessante do ponto de vista da correspondência AdS/CFT devido a sua grande classe de soluções de buracos negros assintoticamente AdS. Consideramos um sistema de gravidade AdS-axion-dilaton em cinco dimensões com um termo de Gauss-Bonnet e encontramos uma solução das equações de movimento, o que corresponde a uma black brane exibindo uma anisotropia espacial, onde a fonte da anisotropia é um campo escalar linear em uma das coordenadas espaciais. Estudamos suas propriedades termodinâmicas e realizamos a renormalização holográfica usando o método de Hamilton-Jacobi. Finalmente, usamos a solução obtida como dual gravitacional de um plasma anisotrópico fortemente acoplado com duas cargas centrais independentes, $a eq c$. Calculamos vários observáveis relevantes para o estudo do plasma, a saber, a viscosidade de cisalhamento sobre densidade de entropia, a força de arrasto, o parâmetro de jet quenching, o potencial entre um par quark-antiquark e a taxa de produção de fótons.