Abstract:
Using the non-perturbative method of {\it dressed} states introduced in previous publications [N.P.Andion, A.P.C. Malbouisson and A. Mattos Neto, J.Phys.{\bf A34}, 3735, (2001); G. Flores-Hidalgo, A.P.C. Malbouisson, Y.W. Milla, Phys. Rev. A, {\bf 65}, 063314 (2002)], we study the evolution of a confined quantum mechanical system embedded in a {\it ohmic} environment. Our approach furnishes a theoretical mechanism to control inhibition of the decay of excited quantum systems in cavities, in both weak and strong coupling regimes.

Abstract:
We employ a dressed state approach to perform a study on the behavior of the uncertainty principle for a system in a heated cavity. We find, in a small cavity for a given temperature, an oscillatory behavior of the momentum--coordinate product, $(\Delta\,p)\,(\Delta\,q)$, which attains periodically finite absolute minimum (maximum) values, no matter large is the elapsed time. This behavior is in a sharp contrast with what happens in free space, in which case, the product $(\Delta\,p)\,(\Delta\,q)$ tends asymptotically, for each temperature, to a constant value, independent of time.

Abstract:
By considering the large-N Ginzburg-Landau model, compactified in one of the spatial dimensions, we determine the beta-function and find an infrared stable fixed point for a superconducting film for dimensions $4

Abstract:
Using the Matsubara formalism, we consider the massive $(\lambda \phi^{4})_{D}$ vector $N$-component model in the large $N$ limit, the system being confined between two infinite paralell planes. We investigate the behavior of the coupling constant as a function of the separation $L$ between the planes. For the Wick-ordered model in $D = 3$ we are able to give an exact formula to the $L$-dependence of the coupling constant. For the non-Wick-ordered model we indicate how expressions for the coupling constant and the mass can be obtained for arbitrary dimension $D$ in the small-$L$ regime. Closed exact formulas for the $L$-dependent renormalized coupling constant and mass are obtained in $D = 3$ and their behaviors as functions of $L$ are displayed. We are also able to obtainn in generic dimension $D$, an equation for the critical value of $L$ corresponding to a second order phase transition in terms of the Riemann $zeta$-function. In $D = 3$ a renormalization is done and an explicit formula for the critical $L$ is given.

The Hartree-Fock equation is non-linear and
has, in principle, multiple solutions. The ω^{th}HF extreme and its associated virtual spin-orbitals furnish an orthogonal base B^{ω} of the full configuration
interaction space. Although all B^{ω} bases generate the same CI space, the corresponding configurations of each B^{ω} base have distinct quantum-mechanical
information contents. In previous works, we have introduced
a multi-reference configuration interaction method, based on the multiple extremes

Abstract:
We study the behavior of two diferent models at finite temperature in a $D$-dimensional spacetime. The first one is the $\lambda\varphi^{4}$ model and the second one is the Gross-Neveu model. Using the one-loop approximation we show that in the $\lambda\varphi^{4}$ model the thermal mass increase with the temperature while the thermal coupling constant decrese with the temperature. Using this facts we establish that in the $(\lambda\varphi^{4})_{D=3}$ model there is a temperature $\beta^{-1}_{\star}$ above which the system can develop a first order phase transition, where the origin corresponds to a metastable vacuum. In the massless Gross-Neveu model, we demonstrate that for $D=3$ the thermal correction to the coupling constant is zero. For $D\neq 3$ our results are inconclusive. Pacs numbers: 11.10.Ef, 11.10.Gh

Abstract:
The degree of nonclassicality of states of a field mode is analysed considering both phase-space and distance-type measures of nonclassicality. By working out some general examples, it is shown explicitly that the phase-space measure is rather sensitive to superposition of states, with finite superpositions possessing maximum nonclassical depth (the highest degree of nonclassicality) irrespective to the nature of the component states. Mixed states are also discussed and examples with nonclassical depth varying between the minimum and the maximum allowed values are exhibited. For pure Gaussian states, it is demonstrated that distance-type measures based on the Hilbert-Schmidt metric are equivalent to the phase-space measure. Analyzing some examples, it is shown that distance-type measures are efficient to quantify the degree of nonclassicality of non-Gaussian pure states.

Abstract:
we consider the n-component tri-dimensional massive gross-neveu model at finite temperature and with compactified spatial coordinates. we study the behavior of the renormalized large-n effective coupling constant, investigating its dependence on the compactification length and the temperature. we show that spatial confinement exists for the model at t = 0, which is destroyed by raising the temperature.

Abstract:
We study the time evolution of a superposition of product states of two dressed atoms in a spherical cavity in the situations of an arbitrarily large cavity (free space) and of a small one. In the large-cavity case, the system dissipates, whereas, for the small cavity, the system evolves in an oscillating way and never completely decays. We verify that the von Neumann entropy for such a system does not depend on time, nor on the size of the cavity

Abstract:
We consider the $N$-component Ginzburg-Landau model in the large $N$ limit, the system being embedded in an external constant magnetic field and confined between two parallel planes a distance $L$ apart from one another. On physical grounds, this corresponds to a material in the form of a film in the presence of an external magnetic field. Using techniques from dimensional and $zeta$-function regularization, modified by the external field and the confinement conditions, we investigate the behavior of the system as a function of the film thickness $L$. This behavior suggests the existence of a minimal critical thickness below which superconductivity is suppressed.