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.

Causal propagators for algebraic gauges

Applying the principle of analytic extension for generalized functions we derive causal propagators for algebraic non-covariant gauges. The so-generated manifestly causal gluon propagator in the light-cone gauge is used to evaluate two one-loop Feynman integrals which appear in the computation of the three-gluon vertex correction. The result is in agreement with that obtained through the usual prescriptions.

Hamilton-Jacobi formulation for singular systems with second-order Lagrangians

Recently, the Hamilton-Jacobi formulation for first-order constrained systems has been developed. In such formalism the equations of motion are written as total differential equations in many variables. We generalize the Hamilton-Jacobi formulation for singular systems with second-order Lagrangians and apply this new formulation to Podolsky electrodynamics, comparing with the results obtained through Dirac's method.

Ps-H scattering using the three-state positronium close-coupling approximation

Positronium scattering off a hydrogen target has been studied employing a three-state positronium model close-coupling approximation (CCA) with and without electron exchange. Elastic, excitation and quenching cross sections are reported at low and medium energies. The effect of electron exchange is found to be significant at low energies. The ratio of quenching to the total cross section (the conversion ratio) approaches the value of 0.25 with increase of energy, as expected.

THE PHYSICAL CONTENT OF THE SP(1,R) MODEL

We analyse the properties of the Sp(1, R) model states using a basis obtained from the deformed harmonic oscillator wavefunctions. We make an Sp(1, R) calculation for C-12 and consider bases obtained from oblate, triaxial and prolate intrinsic states. The model states are given by angular momentum projection of vibrational phonons, which are associated with giant monopole and quadrupole resonances.

Nonadiabatic calculations of the oscillator strengths for the helium atom in the hyperspherical adiabatic approach

Energies and wavefunctions are calculated for the bound states of the helium atom in the hyperspherical adiabatic approach by the full inclusion of nonadiabatic couplings. We show that the use of appropriate asymptotic radial boundary conditions not only allows the efficient calculation of energies accurate up to a few ppm for the ground state but also gives increasingly precise results for high-lying excited states with a unique set of equations. The accuracy of the wavefunctions is demonstrated by the calculation of oscillator strengths in the length form for transitions between stares ii S-1(e) and (n + 1) P-1(0) up to n = 29, in agreement with variational calculations.

Microscopic generalization of the standard interacting boson model Hamiltonian in the restricted dynamics approach

The evaluation of the microscopic generalized interacting boson model (GIBM) Hamiltonian, deduced from the general microscopic nuclear Hamiltonian via the collective O-A-1 invariant microscopic Hamiltonian of the general restricted dynamics model (RDM) in the case of central multipole and multipole-Gauss type effective NN-potential is briefly discussed. The GIBM version, which includes all sixth-order terms in the expansion of the collective part of the NN-potential, has been obtained. This GIBM Hamiltonian contains additional terms compared with the standard (sd-boson) interacting boson model (IBM). The microscopic expressions for the standard IBM Hamiltonian parameters in terms of the employed effective NN-potential parameters have also been obtained.

Comparison of Lagrangian Bounds for One Class of Generalized Assignment Problems

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Interaction potential between vortex lines for uniaxial superconductors in the London approximation

Two distinct expressions of the interaction potential between arbitrarily oriented curved vortex lines with respect to the crystal c axis are derived within the London approximation. One of these expressions is used to compute the eigenvalues of the elasticity matrix. We examine the elastic properties of the vortex chain lattice, recently proposed, concerning shearing deformation.

Scaling in the BCS to Bose crossover problem in different partial waves

The BCS superconductivity to Bose condensation crossover problem is studied in two dimensions in S, P, and D waves, for a simple anisotropic pairing, with a finite-range separable potential at zero temperature. The gap parameter and the chemical potential as a function of Cooper-pair binding B c exhibit universal scaling. In the BCS limit the results for coherence length ξ and the critical temperature T c are appropriate for highT c cuprate superconductors and also exhibit universal scaling as a function of B c.

Frequency upconversion in Er3+-doped fluoroindate glasses pumped at 1.48 μm

We report on efficient frequency upconversion in Er3+-doped fluoroindate glass. The process is observed under 1.48 μm laser diode excitation and results in fluorescence generation in the range from ultraviolet to near-infrared radiation. The study was performed for samples containing 1, 2, and 3 ErF3 mol % in the range of temperatures from 24 to 448 K. The upconverted signals were studied as a function of the laser intensity, and their dynamical behavior is described using a rate equation model which allows us to obtain the energy transfer rates between Er3+ ions in pairs and triads.

Optical properties of chromium-doped fluoroindate glasses

This work reports on the optical properties of Cr3+ ions in the pseudoternary system InF3-GdF3-GaF3. Linear properties, investigated through absorption and emission spectra, provide information on the crystal field, the frequency, and number of phonons emitted during the absorption to the 4T2 band and the emission to the 4A2 ground state, and the Fano antiresonance line shape in the vicinity of the 4A2→2E transition. A study of the nonlinear refractive index as a function of the wavelength, carried out with the Z-scan technique, provides spectroscopic data about electronic transitions starting from the excited state.

Generalized simulated annealing: Application to silicon clusters

We have compared the recently introduced generalized simulated annealing (GSA) with conventional simulated annealing (CSA). GSA was tested as a tool to obtain the ground-state geometry of molecules. We have used selected silicon clusters (Sin, n=4-7,10) as test cases. Total energies were calculated through tight-binding molecular dynamics. We have found that the replacement of Boltzmann statistics (CSA) by Tsallis's statistics (GSA) has the potential to speed up optimizations with no loss of accuracy. Next, we applied the GSA method to study the ground-state geometry of a 20-atom silicon cluster. We found an original geometry, apparently lower in energy than those previously described in the literature.

Highly excited states for the helium atom in the hyperspherical adiabatic approach

The hyperspherical adiabatic approach is used to obtain the highly excited series 1sns 1S e and 1s(n + 1)p 1P o of the helium atom. The introduction of appropriate asymptotic conditions at large values of the hyperspherical radius results in a stable algorithm that allows the calculation of the full atomic spectrum with precision of a few parts per million. Comparison with the variational calculations available in the literature shows that the accuracy of the results improves with increasing principal quantum number. We present the energies up to n = 31 which is the typical value used in multiphoton excitation experiments.