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At least 1,135 records · Page 63Linked to original sources
arXiv2013

Optimal Wegner estimate and the density of states for N-body, interacting Schrodinger operators with random potentials

We prove an optimal one-volume Wegner estimate for interacting systems of $N$ quantum particles moving in the presence of random potentials. The proof is based on the scale-free unique continuation principle recently developed for the 1-body problem by Rojas-Molina and Veselic \cite{RM-V1} and extended to spectral projectors by Klein \cite{klein1}. These results extend of our previous results in \cite{CHK:2003,CHK:2007}. We also prove a two-volume Wegner estimate as introduced in \cite{chulaevsky-suhov1}. The random potentials are generalized Anderson-type potentials in each variable with minimal conditions on the single-site potential aside from positivity. Under additional conditions, we prove the Lipschitz continuity of the integrated density of states (IDS) This implies the existence and local finiteness of the density of states. We also apply these techniques to interacting $N$-particle Schrödinger operators with Delone-Anderson type random external potentials.

math-ph↗
arXiv2013

The Effect of the Low Energy Constants on the Spectral Properties of the Wilson Dirac Operator

We summarize recent analytical results obtained for lattice artifacts of the non-Hermitian Wilson Dirac operator. Hereby we discuss the effect of all three low energy constants. In particular we study the limit of small lattice spacing and also consider the regime of large lattice spacing which is closely related to the mean field limit. Thereby we extract simple relations between measurable quantities like the average number of additional real modes and the low energy constants. These relations may improve the fitting for the low energy constants.

hep-lat↗
arXiv2013

A Remark on Wick Ordering of Random Variables

This paper is a small note on the notation $\,:\! q(X)\!:\,$, for the Wick ordering of polynomials $q$ of random variables $X = (X_1,\dotsc,X_n)$, as introduced by Segal in [6]. We argue that expressing $q(X)$ as another polynomial $p$ of a different set of random variables $Y = (Y_1,\dotsc,Y_m)$, does not give rise to a different Wick ordered random variable $\, : \! p(Y) \! : \,$, provided the new random variables $Y_j$ are linear combinations of the $X_i$'s.

math-ph↗
arXiv2013

PT symétrie et puits de potentiel

In this work we consider PT-symmetric perturbations of a self-adjoint semi-classical Schrödinger operator on the real axis in the case of a simple potential well. We assume that the potential is analytic and show that the eigenvalues remain real under the perturbation. Dans ce travail, on considère des perturbations PT -symétriques d'un opérateur de Schrödinger semi-classique auto-adjoint sur la droite réel dans le cas d'un puits de potentiel simple. On suppose que le potentiel soit analytique et on montre que les valeurs propres restent réelles sous la perturbation.

math.SP↗
arXiv2013

Rescaled Magnetization for Critical Bipartite Mean-Fields Models

We consider a bipartite generalization of the Curie-Weiss model in a critical regime. In order to study the asymptotic behavior of the random vector of the total magnetization we apply the change of variables that diagonalizes the Hessian matrix of the pressure functional associated to the model. We obtain a new vector that, suitably rescaled, weakly converges to the product of a Gaussian distribution and a distribution proportional to $\exp(-ξx^{4})$, where the positive constant $ξ$ can be computed from the pressure functional.

math-ph↗
arXiv2013

Differential cohomology in a cohesive infinity-topos

We formulate differential cohomology and Chern-Weil theory -- the theory of connections on fiber bundles and of gauge fields -- abstractly in the context of a certain class of higher toposes that we call "cohesive". Cocycles in this differential cohomology classify higher principal bundles equipped with cohesive structure (topological, smooth, synthetic differential, supergeometric, etc.) and equipped with connections, hence higher gauge fields. We discuss various models of the axioms and applications to fundamental notions and constructions in quantum field theory and string theory. In particular we show that the cohesive and differential refinement of universal characteristic cocycles constitutes a higher Chern-Weil homomorphism refined from secondary caracteristic classes to morphisms of higher moduli stacks of higher gauge fields, and at the same time constitutes extended geometric prequantization -- in the sense of extended/multi-tiered quantum field theory -- of hierarchies of higher dimensional Chern-Simons-type field theories, their higher Wess-Zumino-Witten-type boundary field theories and all further higher codimension defect field theories. We close with an outlook on the cohomological quantization of such higher boundary prequantum field theories by a kind of cohesive motives.

math-ph↗
arXiv2013

Spectral dimension in graph models of causal quantum gravity

The phenomenon of scale dependent spectral dimension has attracted special interest in the quantum gravity community over the last eight years. It was first observed in computer simulations of the causal dynamical triangulation (CDT) approach to quantum gravity and refers to the reduction of the spectral dimension from 4 at classical scales to 2 at short distances. Thereafter several authors confirmed a similar result from different approaches to quantum gravity. Despite the contribution from different approaches, no analytical model was proposed to explain the numerical results as the continuum limit of CDT. In this thesis we introduce graph ensembles as toy models of CDT and show that both the continuum limit and a scale dependent spectral dimension can be defined rigorously. First we focus on a simple graph ensemble, the random comb. It does not have any dynamics from the gravity point of view, but serves as an instructive toy model to introduce the characteristic scale of the graph, study the continuum limit and define the scale dependent spectral dimension. Having defined the continuum limit, we study the reduction of the spectral dimension on more realistic toy models, the multigraph ensembles, which serve as a radial approximation of CDT. We focus on the (recurrent) multigraph approximation of the two-dimensional CDT whose ensemble measure is analytically controlled. The latter comes from the critical Galton-Watson process conditioned on non-extinction. Next we turn our attention to transient multigraph ensembles, corresponding to higher-dimensional CDT. Firstly we study their fractal properties and secondly calculate the scale dependent spectral dimension and compare it to computer simulations. We comment further on the relation between Horava-Lifshitz gravity, asymptotic safety, multifractional spacetimes and CDT-like models.

hep-th↗
arXiv2013

Spinor derivation of quasilocal mean curvature mass in General Relativity

A spinor derivation is presented for quasilocal mean-curvature mass of spacelike 2-surfaces in General Relativity. The derivation is based on the Sen-Witten spinor identity and involves the introduction of novel nonlinear boundary conditions related to the Dirac current of the spinor at the 2-surface and the tangential flux of a boundary Dirac operator, as well the use of a spin basis adapted to the mean curvature frame of the 2-surface normal space. This setting may provide an alternative approach to a positivity proof for mean-curvature mass based on showing that Witten's equation admits a spinor solution satisfying the proposed nonlinear boundary conditions.

math-ph↗
arXiv2013

Fourier transform of a Bessel function multiplied by a Gaussian

An analytical result is given for the exact evaluation of an integral which arises in the analysis of acoustic radiation from wave packet sources: $ I_{mn}(β,q) = \int_{-\infty}^{\infty} e^{-β^{2}x^{2}-i q x}x^{m+1/2}J_{n+1/2}(x) \,d x, $ where $m$ and $n$ are non-negative integers, and $J_{n+1/2}(\cdot)$ is a Bessel function of order $n+1/2$.

math-ph↗
arXiv2013

Canonical equations of Hamilton for the nonlinear Schrödinger equation

We define two different systems of mathematical physics: the second-order differential system (SODS) and the first-order differential system (FODS). The Newton's second law of motion and the nonlinear Schrödinger equation (NLSE) are the exemplary SODS and FODS, respectively. We obtain a new kind of canonical equations of Hamilton (CEH), which are of some kind of symmetry in form and are formally different with the conventional CEH without symmetry [H. Goldstein, C. Poole, J. Safko, Classical Mechanics, third ed., Addison-Wesley, 2001]. We also prove that the number of the CEHs is equal to the number of the generalized coordinates for the FODS, but twice the number of the generalized coordinates for the SODS. We show that the FODS can only be expressed by the new CEH, but do not by the conventional CEH, while the SODS can be done by both the new and the conventional CEHs. As an example, we prove that the nonlinear Schrödinger equation can be expressed with the new CEH in a consistent way.

physics.class-ph↗
arXiv2013

Random flights governed by Klein-Gordon-type partial differential equations

In this paper we study random flights in R^d with displacements possessing Dirichlet distributions of two different types and uniformly oriented. The randomization of the number of displacements has the form of a generalized Poisson process whose parameters depend on the dimension d. We prove that the distributions of the point X(t) and Y(t), t \geq 0, performing the random flights (with the first and second form of Dirichlet intertimes) are related to Klein-Gordon-type partial differential equations. Our analysis is based on McBride theory of integer powers of hyper-Bessel operators. A special attention is devoted to the three-dimensional case where we are able to obtain the explicit form of the equations governing the law of X(t) and Y(t). In particular we show that that the distribution of Y(t) satisfies a telegraph-type equation with time-varying coefficients.

math.PR↗
arXiv2013

Polynomial solutions for a class of second-order linear differential equations

We analyze the polynomial solutions of the linear differential equation $p_2(x)y''+p_1(x)y'+p_0(x)y=0$ where $p_j(x)$ is a $j^{\rm th}$-degree polynomial. We discuss all the possible polynomial solutions and their dependence on the parameters of the polynomials $p_j(x)$. Special cases are related to known differential equations of mathematical physics. Classes of new soluble problems are exhibited. General results are obtained for weight functions and orthogonality relations.

math-ph↗
arXiv2013

The relativistic causal Newton gravity law vs general relativity

The equations of the relativistic causal Newton gravity law for the planets of the solar system are studied in the approximation when the Sun rests at the coordinate origin and the planets do not interact between each other. The planet orbits of general relativity are also studied in the same approximation.

math-ph↗
arXiv2013

Plancherel-Rotach formulae for average characteristic polynomials of products of Ginibre random matrices and the Fuss-Catalan distribution

Formulae of Plancherel-Rotach type are established for the average characteristic polynomials of certain Hermitian products of rectangular Ginibre random matrices on the region of zeros. These polynomials form a general class of multiple orthogonal hypergeometric polynomials generalizing the classical Laguerre polynomials. The proofs are based on a multivariate version of the complex method of saddle points. After suitable rescaling the asymptotic zero distributions for the polynomials are studied and shown to coincide with the Fuss-Catalan distributions. Moreover, introducing appropriate coordinates, elementary and explicit characterizations are derived for the densities as well as for the distribution functions of the Fuss-Catalan distributions of general order.

math.CA↗
arXiv2013

Stretching and folding processes in the 3D Euler and Navier-Stokes equations

Stretching and folding dynamics in the incompressible, stratified 3D Euler and Navier-Stokes equations are reviewed in the context of the vector $\bdB = \nabla q\times\nablaθ$ where $q=\bom\cdot\nablaθ$. The variable $θ$ is the temperature and $\bdB$ satisfies $\partial_{t}\bdB = \mbox{curl}\,(\bu\times\bdB)$. These ideas are then discussed in the context of the full compressible Navier-Stokes equations where $q$ takes the two forms $q = \bom\cdot\nablaρ$ and $q = \bom\cdot\nabla(\lnρ)$.

math-ph↗
arXiv2013

A pattern-forming instability co-driven by distinct mechanisms increases pattern diversity

We use the context of dryland vegetation to study a general problem of complex pattern forming systems - multiple pattern-forming instabilities that are driven by distinct mechanisms but share the same spectral properties. We find that the co-occurrence of such instabilities results in the growth of a single mode rather than two interacting modes. The interplay between the two mechanisms, which promote or counteract each other, compensates for the simpler dynamics of a single mode by inducing higher pattern diversity. Possible implications to biodiversity of ecosystems are discussed.

nlin.PS↗
arXiv2013

Periodic orbits in cosmological billiards: the Selberg trace formula for asymptotic Bianchi IX universes, evidence for scars in the wavefunction of the quantum universe and large-scale structure anisotropies of the present universe

The Selberg trace formula is specified for cosmological billiards in $4=3+1$ spacetime dimensions. The spectral formula is rewritten as an exact sum over the initial conditions for the Einstein field equations for which periodic orbits are implied. For this, a suitable density of measure invariant under the billiard maps has been defined, within the statistics implied by the BKL paradigm. The trace formula has also been specified for the stochastic limit of the dynamics, where the sum over initial conditions has been demonstrated to be equivalent to a sum over suitable symmetry operations on the generators of the groups that define the billiard dynamics, and acquires different features for the different statistical maps. Evidence for scars at the quantum regime is provided. The validity of the Selberg trace formula at the classical level and in the quantum regime enforces the validity of the semiclassical descriptions of these systems, thus offering further elements for the comparison of quantum-gravity effects and the present observed structure of the universe. This procedure also constitutes a new approach in hyperbolic geometry for the application of the Selberg trace formula for a chaotic system whose orbits are associated to precise statistical distributions, for both billiard tables corresponding to the desymmetrized fundamental domain and to that a a congruence subgroup of it.

gr-qc↗