Quantum radiation by electrons in lasers and the Unruh effect

In addition to the Larmor radiation known from classical electrodynamics, electrons in a laser field may emit pairs of entangled photons -- which is a pure quantum effect. We investigate this quantum effect and discuss why it is suppressed in comparison with the classical Larmor radiation (which is just Thomson backscattering of the laser photons). Further, we provide an intuitive explanation of this process (in a simplified setting) in terms of the Unruh effect.Comment: 4 pages, 3 figure

Dynamical Casimir effect with Dirichlet and Neumann boundary conditions

We derive the radiation pressure force on a non-relativistic moving plate in 1+1 dimensions. We assume that a massless scalar field satisfies either Dirichlet or Neumann boundary conditions (BC) at the instantaneous position of the plate. We show that when the state of the field is invariant under time translations, the results derived for Dirichlet and Neumann BC are equal. We discuss the force for a thermal field state as an example for this case. On the other hand, a coherent state introduces a phase reference, and the two types of BC lead to different results.Comment: 12 page

Gauge Theories with Cayley-Klein SO(2;j)SO(2;j) and SO(3;j)SO(3;j) Gauge Groups

Gauge theories with the orthogonal Cayley-Klein gauge groups $SO(2;j)$ and $SO(3;{\bf j})$ are regarded. For nilpotent values of the contraction parameters ${\bf j}$ these groups are isomorphic to the non-semisimple Euclid, Newton, Galilei groups and corresponding matter spaces are fiber spaces with degenerate metrics. It is shown that the contracted gauge field theories describe the same set of fields and particle mass as $SO(2), SO(3)$ gauge theories, if Lagrangians in the base and in the fibers all are taken into account. Such theories based on non-semisimple contracted group provide more simple field interactions as compared with the initial ones.Comment: 14 pages, 5 figure

Radiation Pressure as a Source of Decoherence

We consider the interaction of an harmonic oscillator with the quantum field via radiation pressure. We show that a `Schrodinger cat' state decoheres in a time scale that depends on the degree of `classicality' of the state components, and which may be much shorter than the relaxation time scale associated to the dynamical Casimir effect. We also show that decoherence is a consequence of the entanglement between the quantum states of the oscillator and field two-photon states. With the help of the fluctuation-dissipation theorem, we derive a relation between decoherence and damping rates valid for arbitrary values of the temperature of the field. Coherent states are selected by the interaction as pointer states.Comment: 14 pages, 3 figures, RevTex fil

Lateral Casimir-Polder force with corrugated surfaces

We derive the lateral Casimir-Polder force on a ground state atom on top of a corrugated surface, up to first order in the corrugation amplitude. Our calculation is based on the scattering approach, which takes into account nonspecular reflections and polarization mixing for electromagnetic quantum fluctuations impinging on real materials. We compare our first order exact result with two commonly used approximation methods. We show that the proximity force approximation (large corrugation wavelengths) overestimates the lateral force, while the pairwise summation approach underestimates it due to the non-additivity of dispersion forces. We argue that a frequency shift measurement for the dipolar lateral oscillations of cold atoms could provide a striking demonstration of nontrivial geometrical effects on the quantum vacuum.Comment: 12 pages, 6 figures, contribution to QFEXT07 proceeding

Tracking beats and microtiming in Afro-Latin American music using conditional random fields and deep learning

Trabajo presentado en ISMIR 2019 : 20th Conference of the International Society for Music Information Retrieval, Delft, Netherlands, 4-8 nov, 2019PostprintEvents in music frequently exhibit small-scale temporal deviations (microtiming), with respect to the underlying regular metrical grid. In some cases, as in music from the Afro-Latin American tradition, such deviations appear systematically, disclosing their structural importance in rhythmic and stylistic configuration. In this work we explore the idea of automatically and jointly tracking beats and microtiming in timekeeper instruments of Afro-Latin American music, in particular Brazilian samba and Uruguayan candombe. To that end, we propose a language model based on conditional random fields that integrates beat and onset likelihoods as observations. We derive those activations using deep neural networks and evaluate its performance on manually annotated data using a scheme adapted to this task. We assess our approach in controlled conditions suitable for these timekeeper instruments, and study the microtiming profiles’ dependency on genre and performer, illustrating promising aspects of this technique towards a more comprehensive understanding of these music traditions

Gravitational decoherence of planetary motions

We study the effect of the scattering of gravitational waves on planetary motions, say the motion of the Moon around the Earth. Though this effect has a negligible influence on dissipation, it dominates fluctuations and the associated decoherence mechanism, due to the very high effective temperature of the background of gravitational waves in our galactic environment.Comment: 6 pages, no figure, to appear in EuroPhysics Letters; needs `epl.cls

On the embedding of branes in five-dimensional spaces

We investigate the embedding of four-dimensional branes in five-dimensional spaces. We firstly consider the case when the embedding space is a vacuum bulk whose energy-momentum tensor consists of a Dirac delta function with support in the brane. We then consider the embedding in the context of Randall-Sundrum-type models, taking into account $Z_{2}$ symmetry and a cosmological constant. We employ the Campbell-Magaard theorem to construct the embeddings and are led to the conclusion that the content of energy-matter of the brane does not necessarily determine its curvature. Finally, as an application to illustrate our results, we construct the embedding of Minkowski spacetime filled with dust.Comment: 12 pages - REVTEX To appear in Classical and Quantum Gravit

Minifábricas: tecnologia social para processamento de castanha de caju.

O objetivo principal dessa sistematização é avaliar uma experiência de intervenção para o desenvolvimento local, gerando aprendizado para subsidiar futuras ações de TT, por meio de erros e acertos. Para tanto, buscou-se identificar e compreender os fatores que influenciaram a paralisação de 90% das minifábricas de castanha-de-caju, a partir de uma análise em três níveis: o papel da organização social; as relações de poder; e a gestão administrativa, econômica e financeira. Ao mesmo tempo, analisou-se o método de transferência de tecnologia e construção do conhecimento.bitstream/item/176503/1/OLV18001.pd