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At least 1,045 records · Page 58Linked to original sources

arXiv2013

On nonlinear coherent states properties for electron-phonon dynamics

This work addresses a construction of a dual pair of nonlinear coherent states (NCS) in the context of changes of bases in the underlying Hilbert space for a model pertaining to the condensed matter physics, which obeys a $f$-deformed Heisenberg algebra. The existence and properties of reproducing kernel in the NCS Hilbert space are studied and discussed; the probability density and its dynamics in the basis of constructed coherent states are provided. A Glauber-Sudarshan $P$-representation of the density matrix and relevant issues related to the reproducing kernel properties are presented. Moreover, a NCS quantization of classical phase space observables is performed and illustrated in a concrete example of $q$-deformed coherent states. Finally, an exposition of quantum optical properties is given.

math-ph↗

arXiv2013

Thermomechanics of hydrogen storage in metallic hydrides: modeling and analysis

A thermodynamically consistent mathematical model for hydrogen adsorption in metal hydrides is proposed. Beside hydrogen diffusion, the model accounts for phase transformation accompanied by hysteresis, swelling, temperature and heat transfer, strain, and stress. We prove existence of solutions of the ensuing system of partial differential equations by a carefully-designed, semi-implicit approximation scheme. A generalization for a drift-diffusion of multi-component ionized "gas" is outlined, too.

math-ph↗

arXiv2013

Uniformity of the late points of random walk on Z_n^d for d >= 3

Suppose that $X$ is a simple random walk on $\Z_n^d$ for $d \geq 3$ and, for each $t$, we let $\U(t)$ consist of those $x \in \Z_n^d$ which have not been visited by $X$ by time $t$. Let $\tcov$ be the expected amount of time that it takes for $X$ to visit every site of $\Z_n^d$. We show that there exists $0 < α_0(d) \leq α_1(d) < 1$ and a time $t_* = \tcov(1+o(1))$ as $n \to \infty$ such that the following is true. For $α> α_1(d)$ (resp.\ $α< α_0(d)$), the total variation distance between the law of $\U(αt_*)$ and the law of i.i.d.\ Bernoulli random variables indexed by $\Z_n^d$ with success probability~$n^{-αd}$ tends to~$0$ (resp.\ $1$) as $n \to \infty$. Let $τ_α$ be the first time $t$ that $|\U(t)| = n^{d-αd}$. We also show that the total variation distance between the law of $\U(τ_α)$ and the law of a uniformly chosen set from $\Z_n^d$ with size $n^{d-αd}$ tends to $0$ (resp.\ $1$) for $α> α_1(d)$ (resp.\ $α< α_0(d)$) as $n \to \infty$.

math.PR↗

arXiv2013

Quantum ordering for quantum geodesic functions of orbifold Riemann surfaces

We determine the explicit quantum ordering for a special class of quantum geodesic functions corresponding to geodesics joining exactly two orbifold points or holes on a non-compact Riemann surface. We discuss some special cases in which these quantum geodesic functions form sub--algebras of some abstract algebras defined by the reflection equation and we extend our results to the quantisation of matrix elements of the Fuchsian group associated to the Riemann surface in Poincaré uniformization. In particular we explore an interesting relation between the deformed $U_q(\mathfrak{sl}_2)$ and the Zhedanov algebra AW(3).

math.QA↗

arXiv2013

Agmon-type estimates for a class of jump processes

In the limit epsilon to 0 we analyze the generators H_epsilon of families of reversible jump processes in R^d associated with a class of symmetric non-local Dirichlet-forms and show exponential decay of the eigenfunctions. The exponential rate function is a Finsler distance, given as solution of a certain eikonal equation. Fine results are sensitive to the rate function being C^2 or just Lipschitz. Our estimates are analog to the semi-classical Agmon estimates for differential operators of second order. They generalize and strengthen previous results on the lattice epsilon Z^d. Although our final interest is in the (sub)stochastic jump process, technically this is a pure analysis paper, inspired by PDE techniques.

math.PR↗

arXiv2013

On the algebraic structure of isotropic generalized elasticity theories

In this paper the algebraic structure of the isotropic nth-order gradient elasticity is investigated. In the classical isotropic elasticity it is well-known that the constitutive relation can be broken down into two uncoupled relations between elementary part of the strain and the stress tensors (deviatoric and spherical). In this paper we demonstrate that this result can not be generalized and since 2nd-order isotropic elasticity there exist couplings between elementary parts of higher-order strain and stress tensors. Therefore, and in certain way, nth-order isotropic elasticity have the same kind of algebraic structure as anisotropic classical elasticity. This structure is investigated in the case of 2nd-order isotropic elasticity, and moduli characterizing the behavior are provided.

math-ph↗

arXiv2013

Cartan algorithm and Dirac constraints for Griffiths variational problems

Dirac algorithm allows to construct Hamiltonian systems for singular systems, and so contributing to its successful quantization. A drawback of this method is that the resulting quantized theory does not have manifest Lorentz invariance. This motivated the quest of alternatives to the usual Hamiltonian theory on the space of sections; a particular instance of this search is the so called restricted Hamiltonian theory, where the equations of motion of a field theory are formulated by means of a multisymplectic structure, a kind of generalization of the symplectic form to the multidimensional context, and even a constraint algorithm working in this context has been proposed. In the present article we will try to provide partial aswers to two questions intimately related with these issues: First, to assign multisymplectic spaces to variational problems in the Griffiths formalism in such a way that the equations of motion can be written as restricted Hamiltonian systems, and second, to propose a covariant Dirac-like algorithm suitable to work with them; it must be recalled that given the Griffiths formalism contains the classical variational problems as particular instances, it yields to a novel covariant algorithm for deal with constraints in field theory. Moreover, in this formulation the constraint algorithm becomes simply the Cartan algorithm designed for deal with Pfaffian systems.

math-ph↗

arXiv2013

Convergence of normal form transformations: The role of symmetries

We discuss the convergence problem for coordinate transformations which take a given vector field into Poincaré-Dulac normal form. We show that the presence of linear or nonlinear Lie point symmetries can guaranteee convergence of these normalizing transformations, in a number of scenarios. As an application, we consider a class of bifurcation problems.

math-ph↗

arXiv2013

Additional symmetry of the modified extended Toda hierarchy

In this paper, one new integrable modified extended Toda hierarchy(METH) is constructed with the help of two logarithmic Lax operators. With this modification, the interpolated spatial flow is added to make all flows complete. To show more integrable properties of the METH, the bi-Hamiltonian structure and tau symmetry of the METH will be given. The additional symmetry flows of this new hierarchy are presented. These flows form an infinite dimensional Lie algebra of Block type.

math-ph↗

arXiv2013

Generalized forms, vector fields and superspace

Vector fields with components which are generalized zero-forms are constructed. Inner products with generalized forms, Lie derivatives and Lie brackets are computed. The results are shown to generalize previously reported results for generalized vector fields. Hamiltonian vector fields are discussed. Generalized affine connections and metrics are defined and the fundamental theorem of metric differential geometry is extended. The global structure of the exterior derivative of generalized forms is investigated.

math-ph↗

arXiv2013

The Spectrum of Non-Local Discrete Schroedinger Operators with a delta-Potential

The behaviour of the spectral edges (embedded eigenvalues and resonances) is discussed at the two ends of the continuous spectrum of non-local discrete Schrödinger operators with a $δ$-potential. These operators arise by replacing the discrete Laplacian by a strictly increasing $C^1$-function of the discrete Laplacian. The dependence of the results on this function and the lattice dimension are explicitly derived. It is found that while in the case of the discrete Schrödinger operator these behaviours are the same no matter which end of the continuous spectrum is considered, an asymmetry occurs for the non-local cases. A classification with respect to the spectral edge behaviour is also offered.

math-ph↗

arXiv2013

Zero-curvature condition in Calogero model

We consider the mutual commutativity of Dunkl operators of the rational Calogero model as zero-curvature condition and calculate the non-local operator, related to these flat connections. This operator has physical meaning of particular scattering matrix of Calogero model and maps the eigenfunctions of Dunkl operator to the wave function of $N$ free particles (plane waves).

math-ph↗

arXiv2013

Evolving black hole horizons in General Relativity and alternative gravity

From the microscopic point of view, realistic black holes are time-dependent and the teleological concept of event horizon fails. At present, the apparent or the trapping horizon seem its best replacements in various areas of black hole physics. We discuss the known phenomenology of apparent and trapping horizons for analytical solutions of General Relativity and alternative theories of gravity. These specific examples (we focus on spherically symmetric inhomogeneities in a background cosmological spacetime) may be useful as toy models for research on various aspects of black hole physics.

gr-qc↗

arXiv2013

Classification of degree three polynomial solutions to the Polubarinova-Galin equation

The Polubarinova-Galin equation is derived from zero-surface-tension Hele-Shaw flow driven by injection. In this paper, we classify degree three polynomial solutions to the Polubarinova-Galin equation into three categories: global solutions, solutions which can be continued after blow-up and solutions which cannot be continued after blow-up. The coefficient region of the initial functions in each category is obtained.

math-ph↗

arXiv2013

Nonlinear dependence of the renormalization scale on test functions

Quantum electrodynamics exhibits an informal nonlinear dependence on Lorentz invariant test function properties that determine the renormalization scale, such as Mandelstam variables, contrary to the linear dependence on test functions that is required by the Wightman axioms. A first example of an alternative interacting quantum field formalism that has a comparable weakly nonlinear dependence on Dirac spinor test functions is constructed, using U(1)-gauge connections and U(1)-gauge invariant Dirac spinor test functions.

quant-ph↗

arXiv2013

Dynamics of periodic Toda chains with a large number of particles

For periodic Toda chains with a large number $N$ of particles we consider states which are $N^{-2}-$close to the equilibrium and constructed by discretizing any given $C^2-$functions with mesh size $N^{-1}$. For such states we derive asymptotic expansions of the Toda frequencies $(ω^N_n)_{0 < n < N}$ and the actions $(I^N_n)_{0 < n < N},$ both listed in the standard way, in powers of $N^{-1}$ as $N \to \infty$. %listed in accordance with the ordering of the frequencies at the equilibrium, %$(2 \sin \frac{nπ} {N})_{0 < n < N}$. At the two edges $n \sim 1$ and $N -n \sim 1$, the expansions of the frequencies are computed up to order $N^{-3}$ with an error term of higher order. Specifically, the coefficients of the expansions of $ω^N_n$ and $ω^N_{N-n}$ at order $N^{-3}$ are given by a constant multiple of the n'th KdV frequencies $ω^-_n$ and $ω^+_n$ of two periodic potentials, $q_{-}$ respectively $q_+$, constructed in terms of the states considered. The frequencies $ω^N_n$ for $n$ away from the edges are shown to be asymptotically close to the frequencies of the equilibrium. For the actions $(I^N_n)_{0 < n < N},$ asymptotics of a similar nature are derived.

math.AP↗

arXiv2013

Super-Critical and Sub-Critical Hopf bifurcations in two and three dimensions

Hopf bifurcations have been studied perturbatively under two broad headings, viz., super-critical and sub-critical. The criteria for occurrences of such bifurcations have been investigated using the renormalization group. The procedure has been described in details for both two and three dimensions and has been applied to several important models, including those by Lorenz and Rossler.

nlin.CD↗

arXiv2013

Some fourth order nonlinear elliptic problems related to epitaxial growth

This paper deals with some mathematical models arising in the theory of epitaxial growth of crystal. We focalize the study on a stationary problem which presents some analytical difficulties. We study the existence of solutions. The central model in this work is given by the following fourth order elliptic equation, $$\begin{array}{rclll} Δ^2 u=\text{det} \left(D^2 u \right) &+&λf, \quad & x\in Ω\subset\mathbb{R}^2\\ \hbox{conditions on} &\quad& & \partial Ω. \end{array} $$ The framework to study the problem deeply depends on the boundary conditions.

math.AP↗