The Kantowski-Sachs Quantum Model with Stiff Matter Fluid

In this paper, we study the quantum cosmological Kantowski-Sachs model and we solve the Wheeler-DeWitt equation in minisuperspace to obtain the wave function of the corresponding universe. The perfect fluid is described by Schutz’s canonical formalism, which allows to attribute dynamical degrees of freedom to matter. The time is introduced phenomenologically using the fluid’s degrees of freedom. In particular, we adopt a stiff matter fluid. The viability of this model is analyzed and discussed.     

Classical and quantum cosmology with two perfect fluids: stiff matter and radiation

In this work the homogeneous and isotropic Universe of Friedmann–Robertson–Walker is studied in the presence of two fluids: stiff matter and radiation described by the Schutz’s formalism. We obtain to the classic case the behaviour of the scale factor of the universe. For the quantum case the wave packets are constructed and the wave function of the universe is found.     

Schrödinger–Wheeler–DeWitt Equation in Chaplygin Gas FRW Cosmological Model

We present a Chaplygin gas Friedmann–Robertson–Walker quantum cosmological model. In this work the Schutz’s variational formalism is applied with positive, negative, and zero constant spatial curvature. In this approach the notion of time can be recovered. These give rise to Schrödinger–Wheeler–DeWitt equation for the scale factor. We use the eigenfunctions in order to construct wave packets for each case. We study the time dependent behavior of the expectation value of the scale factor, using the many-worlds interpretations of quantum mechanics.     

Perfect fluid quantum anisotropic universe: merits and challenges

The present paper deals with quantization of perfect fluid anisotropic cosmological models. Bianchi type V and IX models are discussed following Schutz’s method of expressing fluid velocities in terms of six potentials. The wave functions are found for several examples of equations of state. In one case a complete wave packet could be formed analytically. The initial singularity of a zero proper volume can be avoided in this case, but it is plagued by the usual problem of non-unitarity of anisotropic quantum cosmological models. It is seen that a particular operator ordering alleviates this problem.     

Troubles with Quantum Anisotropic Cosmological Models: Loss of Unitarity

The anisotropic Bianchi I cosmological model coupled with perfect fluid is quantized in the minisuperspace. The perfect fluid is described by using the Schutz formalism which allows to attribute dynamical degrees of freedom to matter. A Schrödinger-type equation is obtained where the matter variables play the role of time. However, the signature of the kinetic term is hyperbolic. This Schrödinger-like equation is solved and a wave packet is constructed. The norm of the resulting wave function comes out to be time dependent, indicating the loss of unitarity in this model. The loss of unitarity is due to the fact that the effective Hamiltonian is hermitian but not self-adjoint. The expectation value and the bohmian trajectories are evaluated leading to different cosmological scenarios, what is a consequence of the absence of a unitary quantum structure. The consistency of this quantum model is discussed as well as the generality of the absence of unitarity in anisotropic quantum models.     

A Note on Q-algebras and Quantization

In this note, we study Schwarz’s conjecture on application of Q-algebras to strict quantization. We prove that in the case of a torus with a constant Poisson structure, Schwarz’s formalism gives the same star product as Rieffel [10]. We construct twisted Fock modules as examples of quantization dg-modules in the case of a compact Kähler manifold. In particular, we relate this construction on $\mathbb{CP}^1In this note, we study Schwarz’s conjecture on application of Q-algebras to strict quantization. We prove that in the case of a torus with a constant Poisson structure, Schwarz’s formalism gives the same star product as Rieffel [10]. We construct twisted Fock modules as examples of quantization dg-modules in the case of a compact K?hler manifold. In particular, we relate this construction on to representations of a fuzzy sphere Mathematics Subject Classification (2000). 53D55, 46L65     

BRST analysis of the gauged SU(2) WZW model and Darboux’s transformations

The four dimensional SU(2) WZW model coupled to electromagnetism is treated as a constraint system in the context of the Batalin-Fradkin-Vilkovisky formalism. Common features with the Faddeev-Jackiw approach are stressed and the same results are obtained. The Darboux’s transformations which are used to diagonalize the canonical one-form in the Faddeev-Jackiw formalism, are shown to transform the fields of the model into BRST and σ closed. The same analysis is also carried out in the case of spinor electrodynamics.     

On the Langevin formalism for nonlinear and nonequilibrium hydrodynamic fluctuations

The Landau-Lifshitz method of fluctuating hydrodynamics is generalized to the cases of nonlinear and nonequilibrium fluctuations. For a simple one-component fluid, the multiplicative random fluxes are constructed by using universal Gaussian variables with variances independent of the specific parameters of a fluid. It is shown that the nonlinear Langevin formalism proposed is equivalent to the approach based on the hydrodynamic Fokker-Planck equation derived earlier by statistical-mechanical methods. Then, the scheme is extended to the case of two-component fluids, where cross effects must be taken into account. In conclusion, the connection of the present formalism with the Keizer approach to nonequilibrium fluctuations is discussed.     

Developments in excited-state density functional theory

This article discusses the reasons behind the apparent lack of success of density functional theory (DFT), during the past three decades, with excited states of many-electron systems. It describes various variational and non-variational approaches developed so far for dealing with this problem. Those include Theophilou’s equiensemble approach, extended to unequally weighted ensembles by Gross et al., Fritsche’s wavefunction partitioning approach, local scaling transformation theory by Kryachko et al., the work-function formalism developed by Harbola and Sahni, etc. Through intimate connections between time-dependence and excited states, under a perturbation, various time-dependent (TD) DFT approaches to excited states, e.g., a quantum fluid dynamical approach, a TD density-functional response theory and a TD optimized effective potential approach, are also reviewed.     

Structure formation in the presence of relativistic heat conduction: corrections to the Jeans wave number with a stable, first order in the gradients, formalism

The problem of structure formation in relativistic dissipative fluids was analyzed in a previous work within Eckart’s framework, in which the heat flux is coupled to the hydrodynamic acceleration, additional to the usual temperature gradient term. It was shown that in such case, the pathological behavior of fluctuations leads to the disappearance of the gravitational instability responsible for structure formation (Mondragon-Suarez and Sandoval-Villalbazo in Gen Relativ Gravit 44:139–145, 2012). In the present work the problem is revisited using a constitutive equation derived from relativistic kinetic theory. This new relation, in which the heat flux is not coupled to the hydrodynamic acceleration, leads to a consistent first order in the gradients formalism. In this case the gravitational instability remains, and only relativistic corrections to the Jeans wave number are obtained. In the calculation here shown the non-relativistic limit is recovered, opposite to what happens in Eckart’s case (Hiscock and Lindblom in Phys Rev D 31:725–733, 1985).     

Simultaneous tracer diffusion and interdiffusion in a sandwich-type configuration to provide the composition dependence of the tracer diffusion coefficients

In this paper, a new formalism of a combined tracer and interdiffusion experiment for a binary interdiffusion couple is developed. The analysis requires an interdiffusion couple that initially contains a thin layer of tracers of one or both of the constituent elements at the original interface of the couple (sandwich interdiffusion experiment). This type of interdiffusion experiment was first performed in 1958 by J.R. Manning. The theoretical analysis presented in this paper is based on a newly developed phenomenological theory of isotopic interdiffusion combined with the Boltzmann–Matano formalism. This new analysis now provides the means to obtain the composition dependent interdiffusion coefficient and tracer diffusion coefficients simultaneously from analysis of the interdiffusion and tracer profiles in a single sandwich interdiffusion experiment. The new analysis is successfully applied to the results of Manning’s original ‘sandwich interdiffusion’ experiment in the Ag–Cd system (six couples in total) and is validated with an independent determination of the Ag and Cd tracer diffusion coefficients by Schoen using the conventional thin film technique. Suggestions for further development of the sandwich interdiffusion experiment and analysis to the case of multicomponent alloys are provided.     

A quantum Hamilton–Jacobi proof of the nodal structure of the wave functions of supersymmetric partner potentials

Quantum Hamilton–Jacobi formalism is used to give a proof for Gozzi’s criterion, which states that for eigenstates of the supersymmetric partners, corresponding to the same energy, the difference in the number of nodes is equal to one when supersymmetry (SUSY) is unbroken and is zero when SUSY is broken. We also show that this proof is also applicable to the case, where isospectral deformation is involved.     

Multipressure regularization for multiphase flow

The standard theory of ideal single-pressure multiphase fluid dynamics, which is known to be ill-posed, is regularized via the hamiltonian formalism by extending the noncanonical Poisson brackets for the standard single-pressure equations to the case of multiple pressures. This formalism is used to find Lyapunov stability conditions for the regularized system.     

Finite-dimensional quantum mechanics of a particle. II

The finite-dimensional quantum mechanics (FDQM) based on Weyl’s form of Heisenberg’s canonical commutation relations, developed for the case of one-dimensional space, is extended to three-dimensional space. This FDQM is applicable to the physics of particles confined to move within finite regions of space and is significantly different from the current quantum mechanics in the case of atomic and subatomic particles only when the region of confinement is extremely small—of the order of nuclear or even smaller dimensions. The configuration space of such a particle has a quantized eigenstructure with a characteristic dependence on its rest mass and dimension of the region of confinement, and the current Schrödinger-Heisenberg formalism of quantum mechanics becomes an asymptotic approximation of this FDQM. As an example, a spherical harmonic oscillator with a particular radius of confinement is considered.     

Gauge interaction as periodicity modulation

The paper is devoted to a geometrical interpretation of gauge invariance in terms of the formalism of field theory in compact space–time dimensions (Dolce, 2011) [8]. In this formalism, the kinematic information of an interacting elementary particle is encoded on the relativistic geometrodynamics of the boundary of the theory through local transformations of the underlying space–time coordinates. Therefore gauge interactions are described as invariance of the theory under local deformations of the boundary. The resulting local variations of the field solution are interpreted as internal transformations. The internal symmetries of the gauge theory turn out to be related to corresponding space–time local symmetries. In the approximation of local infinitesimal isometric transformations, Maxwell’s kinematics and gauge invariance are inferred directly from the variational principle. Furthermore we explicitly impose periodic conditions at the boundary of the theory as semi-classical quantization condition in order to investigate the quantum behavior of gauge interaction. In the abelian case the result is a remarkable formal correspondence with scalar QED.     

On gauge-invariant variables in QED

Exploiting the path-dependence of the gaugeinvariant variables formalism, we illustrate how the gaugefixing procedure correspond, in this formalism, to choose the path. In particular, we consider two propagators for the gauge field. QED is formulated in terms of gauge-invariant variables and its quantization is carried out using the Dirac’s method for constrained systems.     

A novel secular equation for the coupled-band envelope-function approximation for superlattices and application to InAs/InxGa1 − xSb superlattices

This paper derives and demonstrates a new secular equation for the coupled-band envelope-function approximation (EFA) formalism for superlattices in order to overcome the difficulty of handling rapidly growing or decaying wavefunction components, in particular, the ‘wing solutions’. In a second development, the generally nonHermitian secular equation is made Hermitian, making it easier to locate multiply degenerate roots. In the process, the simple Kronig–Penney model is recast into a form closely related to that for the underlying quantum well (QW) problem. The present method is applicable to Burt's EFA formalism. An InAs/InGaSb type-II superlattice is used to demonstrate the method.