Remarks on the Collective Quantization of the SU(2) Skyrme Model

We point out the question of ordering momentum operator in the canonical \break quantization of the SU(2) Skyrme Model. Thus, we suggest a new definition for the momentum operator that may solve the infrared problem that appears when we try to minimize the Quantum Hamiltonian.Comment: 8 pages, plain tex, IF/UFRJ/9

Inertial forces in the Casimir effect with two moving plates

We combine linear response theory and dimensional regularization in order to derive the dynamical Casimir force in the low frequency regime. We consider two parallel plates moving along the normal direction in $D-$dimensional space. We assume the free-space values for the mass of each plate to be known, and obtain finite, separation-dependent mass corrections resulting from the combined effect of the two plates. The global mass correction is proportional to the static Casimir energy, in agreement with Einstein's law of equivalence between mass and energy for stressed rigid bodies.Comment: 9 pages, 1 figure; title and abstract changed; to appear in Physical Review

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

Electronic transport in graphene: A semi-classical approach including midgap states

Using the semi-classical Boltzmann theory, we calculate the conductivity as function of the carrier density. As usually, we include the scattering from charged impurities, but conclude that the estimated impurity density is too low in order to explain the experimentally observed mobilities. We thus propose an additional scattering mechanism involving midgap states which leads to a similar k-dependence of the relaxation time as charged impurities. The new scattering mechanism can account for the experimental findings such as the sublinear behavior of the conductivity versus gate voltage and the increase of the minimal conductivity for clean samples. We also discuss temperature dependent scattering due to acoustic phonons.Comment: 10 pages, 4 figure

Renormalizability of the Dynamical Two-Form

A proof of renormalizability of the theory of the dynamical non-Abelian two-form is given using the Zinn-Justin equation. Two previously unknown symmetries of the quantum action, different from the BRST symmetry, are needed for the proof. One of these is a gauge fermion dependent nilpotent symmetry, while the other mixes different fields with the same transformation properties. The BRST symmetry itself is extended to include a shift transformation by use of an anticommuting constant. These three symmetries restrict the form of the quantum action up to arbitrary order in perturbation theory. The results show that it is possible to have a renormalizable theory of massive vector bosons in four dimensions without a residual Higgs boson.Comment: revtex, 35p. additional discussion about the auxiliary vector field and possible gauge choices, relevant to the question of validity of perturbative expansion, version to be published in Phys.Rev.

Theory of Spin Fluctuations in Striped Phases of Doped Antiferromagnetic Cuprates

We study the properties of generalized striped phases of doped cuprate planar quantum antiferromagnets. We invoke an effective, spatially anisotropic, non-linear sigma model in two space dimensions. Our theoretical predictions are in quantitative agreement with recent experiments in La_{2-x}Sr_xCuO_4 with $0 \leq x \leq 0.018$. We focus on (i) the magnetic correlation length, (ii) the staggered magnetization at $T=0$ and (iii) the N\'eel temperature, as functions of doping, using parameters determined previously and independently for this system. These results support the proposal that the low doping (antiferromagnetic) phase of the cuprates has a striped configuration.Comment: 4 pages, Revtex. To appear in the Proceedings of the International Conference "Stripes, Lattice Instabilities and High Tc Superconductivity", (Rome, Dec. 1996

Estimativas de parâmetros genéticos e ganho de seleção para produção de frutos em progênies de polinização aberta de pupunheira no Estado do Pará, Brasil.

O estudo objetivou estimar parâmetros e valores genéticos para os caracteres número de cachos (NC), peso médio do cacho (PMC) e peso total do cacho (PTC) aos seis anos, pelo método de modelos mistos (REML/BLUP). O teste de progênies foi estabelecido sob o delineamento de blocos ao acaso com 50 tratamentos (progênies), 10 blocos e uma planta por parcela, no espaçamento de 5 x 5 m, além de uma bordadura externa ao experimento. As estimativas de herdabilidade individual e médias no sentido restrito para PTC (0,213 e 0,360) e NC (0,286 e 0,435), respectivamente, foram de boas magnitudes. O coeficiente de variação genética individual exibiu valores elevados para PTC (19,86) e NC (17,59). A raiz quadrada da herdabilidade ao nível de médias das progênies resulta em acurácia seletiva na ordem de 0,60 para PTC e 0,66 para NC, atestando boa precisão e confiança nos parâmetros genéticos estimados, promovendo segurança na seleção. O potencial da população para fins de melhoramento pode ser observado por meio dos ganhos genéticos para PTC, que oscilaram de 8,3 a 19,9 kg, elevando a nova média populacional para o caráter após um ciclo de seleção, para 40,4 kg, equivalente a 25,8%

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