Integrable Structure of Ginibre’s Ensemble of Real Random Matrices and a Pfaffian Integration Theorem

In the recent publication (E. Kanzieper and G. Akemann in Phys. Rev. Lett. 95:230201, 2005), an exact solution was reported for the probability p _n,k to find exactly k real eigenvalues in the spectrum of an n×n real asymmetric matrix drawn at random from Ginibre’s Orthogonal Ensemble (GinOE). In the present paper, we offer a detailed derivation of the above result by concentrating on the proof of the Pfaffian integration theorem, the key ingredient of our analysis of the statistics of real eigenvalues in the GinOE. We also initiate a study of the correlations of complex eigenvalues and derive a formula for the joint probability density function of all complex eigenvalues of a GinOE matrix restricted to have exactly k real eigenvalues. In the particular case of k=0, all correlation functions of complex eigenvalues are determined.     

Anharmonic oscillators in higher dimension: Accurate energy eigenvalues and matrix elements

Energy eigenvalues and matrix elements of various anharmonic oscillators are determined to a high accuracy by applying a method for determining the eigenvalues and eigenvectors of real symmetric para-p diagonal matrices (described in the preceding paper). Our results for the 2- and 3-dimensional oscillators are new and complement similar accurate results for the one dimensional oscillators available in the literature.     

Alternative method of calculating the eigenvalues of the transfer matrix of the τ<Subscript>2</Subscript> model for <Emphasis Type="Italic">N</Emphasis> = 2

It has been shown that the τ₂ (Baxter-Bazhanov-Stroganov) model for N = 2 with arbitrary parameters is a particular case of the generalized Ising model. The model satisfies the free-fermion condition, which enables one to solve it by the method of the auxiliary Grassmann field. Explicit expressions have been derived for the partition function on a finite-size lattice and eigenvalues of the transfer matrix. In this approach, in contrast to the functional relation method, there is no problem with the multiplicities of the eigenvalues of transfer matrix.     

A study of the generalized density matrix in the SU(3) model of Elliott for an arbitrary oscillator n-shell

The SU(3) model of Elliott for an arbitrary oscillator n-shell is considered. Exact solutions corresponding to the low-lying collective SU(3) multiplets are obtained. These multiplets exhibiting distinct collective properties are used as a “collective band”. All the matrix elements from the one-particle density matrix operator inside a given band are investigated. The so-formed matrix R, i.e. the generalized density matrix (GDM), is diagonalized and an explicit expression for the eigenvalues of the GDM in the case of low-lying multiplets is found. The GDM diagonal form contains a number of vanishing eigenvalues (the number of such “zero” eigenvalues is equal to that of the occupied orbits in the oscillator n-shell). Most of the remaining eigenvalues are close to unity. The asymptotic behaviour of the nonzero eigenvalues is analyzed in the limit of large nucleon number and the accuracy of the normalization condition R²= R is estimated.     

Group theory,Markov chains,and excluded volume effect in polymers

A restricted walk of orderr on a lattice is defined as a random walk in which polygons withr vertices or less are excluded. A study of restricted walks for increasingr provides an understanding of how the transition in properties is effected from random to self-avoiding walks which is important in our understanding of the excluded volume effect in polymers and in the study of many other problems. Here the properties of restricted walks are studied by the transition matrix method based on the theory of Markov chains. A group theoretical method is used to reduce the transition matrix governing the walk in a systematic manner and to classify the eigenvalues of the transition matrix according to the various representations of the appropriate group. It is shown that only those eigenvalues corresponding to two particular representations of the group contribute to the correlations among the steps of the walk. The distributions of eigenvalues for walks of various ordersr on the two-dimensional triangular lattice and the three-dimensional face-centered cubic lattice are presented, and they are shown to have some remarkable features.     

On the computation of a very large number of eigenvalues for selfadjoint elliptic operators by means of multigrid methods

Recent results in the study of quantum manifestations in classical chaos raise the problem of computing a very large number of eigenvalues of selfadjoint elliptic operators. The standard numerical methods for large eigenvalue problems cover the range of applications where a few of the leading eigenvalues are needed. They are not appropriate and generally fail to solve problems involving a number of eigenvalues exceeding a few hundreds. Further, the accurate computation of a large number of eigenvalues leads to much larger problem dimension in comparison with the usual case dealing with only a few eigenvalues. A new method is presented which combines multigrid techniques with the Lanczos process. The resulting scheme requires O(mn) arithmetic operations and O(n) storage requirement, where n is the number of unknowns and m, the number of needed eigenvalues. The discretization of the considered differential operators is realized by means of p-finite elements and is applicable on general geometries. Numerical experiments validate the proposed approach and demonstrate that it allows to tackle problems considered to be beyond the range of standard iterative methods, at least on current workstations. The ability to compute more than 9000 eigenvalues of an operator of dimension exceeding 8 million on a PC shows the potential of this method. Practical applications are found, e.g. in the numerical simulation of quantum billiards.     

Higher excited states of acceptors in cubic semiconductors

For the first time, higher excited states of shallow acceptors up to the 3s and 4s states are calculated based on the Balderschi and Lipari theory including the cubic correction. The eigenvalues and eigenvectors of the effective mass Hamiltonian for shallow acceptor states were obtained by the finite element method. The resultant sparse matrix is diagonalized by a newly developed Saad's method based on Arnoldi's algorithm. Comparison with experimental spectra on ZnTe:Li and ZnTe:P gives best valence band parameters for ZnTe; μ = 0.60 and δ = 0.12.     

具有非对角开边界的SU(2)不变Thirring模型的精确解

利用量子反散射方法研究了1+1维时空中具有非对角开边界条件下的SU(2)不变Thirring模型. 于辅助空间引入独立于谱参量的规范变换,找到了适当的Fock真空态. 通过Bethe Ansatz方法得到了系统相应转移矩阵的本征值和本征态,及其谱参数所满足的Bethe Ansatz方程,并讨论了体系的边界自由度. 关键词： SU(2)不变Thirring模型')" href="#">SU(2)不变Thirring模型 非对角开边界 量子反散射方法     

Reduction of the XXZ model with twisted boundary conditions

The XXZ model with twisted boundary conditions is considered. The method of energy spectrum calculation based on the functional equation for the transfer matrix is analyzed. The Hamiltonian eigenvalues are obtained in an explicit form.     

Probability density function of the sum of N partially correlated speckle patterns

A method is developed which allows exact calculation of the probability density function of the sum of N correlated speckle patterns. To find the density function, it is only necessary to first find the eigenvalues of an N × N coherence matrix. When the eigenvalues are distinct, the density function can be expressed as a simple sum of N exponential terms.     

On Eigenvalues of the Sum of Two Random Projections

We study the behavior of eigenvalues of matrix P _N +Q _N where P _N and Q _N are two N-by-N random orthogonal projections. We relate the joint eigenvalue distribution of this matrix to the Jacobi matrix ensemble and establish the universal behavior of eigenvalues for large N. The limiting local behavior of eigenvalues is governed by the sine kernel in the bulk and by either the Bessel or the Airy kernel at the edge depending on parameters. We also study an exceptional case when the local behavior of eigenvalues of P _N +Q _N is not universal in the usual sense.     

Spectral Statistics of Erdős-Rényi Graphs II: Eigenvalue Spacing and the Extreme Eigenvalues

We consider the ensemble of adjacency matrices of Erd?s-Rényi random graphs, i.e. graphs on N vertices where every edge is chosen independently and with probability p ≡ p(N). We rescale the matrix so that its bulk eigenvalues are of order one. Under the assumption \({p N \gg N^{2/3}}\), we prove the universality of eigenvalue distributions both in the bulk and at the edge of the spectrum. More precisely, we prove (1) that the eigenvalue spacing of the Erd?s-Rényi graph in the bulk of the spectrum has the same distribution as that of the Gaussian orthogonal ensemble; and (2) that the second largest eigenvalue of the Erd?s-Rényi graph has the same distribution as the largest eigenvalue of the Gaussian orthogonal ensemble. As an application of our method, we prove the bulk universality of generalized Wigner matrices under the assumption that the matrix entries have at least 4 + ε moments.     

Exactly Complete Solutions of the Pseudoharmonic Potential in N-Dimensions

We present analytically the exact solutions of the Schrödinger equation in the N-dimensional spaces for the pseudoharmonic oscillator potential by means of the ansatz method. The energy eigenvalues of the bound states are easily calculated from this eigenfunction ansatz. The normalized wavefunctions are also obtained. A realization of the ladder operators for the wavefunctions is studied and we deduced that these operators satisfy the commutation relations of the generators of the dynamical group SU(1,1). Some expectation values for 〈r ^?2〉, 〈r ²〉, 〈T〉, 〈V〉, 〈H〉, 〈p ²〉 and the virial theorem for the pseudoharmonic oscillator potential in an arbitrary number of dimensions are obtained by means of the Hellmann–Feynman theorems. Each solution obtained is dimensions and parameters dependent.     

Scalars coupled to fermions in 1+1 dimensions

Using a method introduced in an earlier paper, we study a Bose field coupled to a Fermi field in 1+1 space-time dimensions. We employ the standard Hamiltonian formalism in which one computes the eigenvalues and eigenvectors of the Hamiltonian matrix. The matrix elements are computed using states defined on a lattice in momentum space. The results are compared with known strong and weak coupling limits. Bound states and renormalization effects are studied. We find that the choice of bare masses which give specified physical masses can be non-unique once a critical couplingλ _μ has been exceeded.     

Bethe ansatz for the XXX-S chain with non-diagonal open boundaries

We consider the algebraic Bethe ansatz solution of the integrable and isotropic XXX-S Heisenberg chain with non-diagonal open boundaries. We show that the corresponding K-matrices are similar to diagonal matrices with the help of suitable transformations independent of the spectral parameter. When the boundary parameters satisfy certain constraints we are able to formulate the diagonalization of the associated double-row transfer matrix by means of the quantum inverse scattering method. This allows us to derive explicit expressions for the eigenvalues and the corresponding Bethe ansatz equations. We also present evidences that the eigenvectors can be build up in terms of multiparticle states for arbitrary S.     

Rydberg transition dipole matrix elements from sum frequency generation spectra

A new method for determination of relative dipole matrix elements for transitions between excited states is presented, using sum frequency generation spectroscopy. The method is based on measuring the frequency spacing of related extrema in the dispersion like shapes within the SFG-spectrum, caused by interference between resonant and nonresonant parts in the third order polarizability. It is applied to CdI with the generated frequency in the range of the principal series 5s¹S₀ → np¹P₁, n = 12–28. Values of the products μ_6snpμ_{np5 s} are presented obeying the n^1-3 law.     

Long-range coulomb interaction in ionic crystals

Expressions have been proposed for calculating the matrix elements of the Coulomb interaction of p and d electrons in a chosen ion of a crystal with an infinite crystal lattice. The matrix elements have been calculated at Gaussian-type orbitals. The Coulomb interaction energy per molecular unit of the ????-NaV₂O₅ crystal has been calculated in the ionic approximation for homogeneous and chain orderings. It has been shown that the more correct determination of the energetic favorability of one or other ordering requires calculation of the Coulomb interaction energy with an infinite crystal lattice of electrons that are at different orbitals of the ion under consideration.     

An exponential transverse momentum phase-space event generator

A method for generating multi-particle phase space suitable for approximately exponential p_⊥ matrix elements is proposed. A method of longitudinal momentum generation which allows one to easily sample the importance of certain mass combinations is also proposed.     

Quark masses

We review the current information about the eigenvalues of the quark mass matrix. The theoretical problems involved in a determination of the running masses m_u, m_d, m_s, m_c and m_b from experiment are discussed with the aim of getting reliable numerical values equipped with error bars that represent a conservative estimate of remaining uncertainties.     

Transfer Matrix Functional Relations for the Generalized τ2 (t q ) Model

The N-state chiral Potts model in lattice statistical mechanics can be obtained as a “descendant” of the six-vertex model, via an intermediate “Q” or “τ₂ (t _q )” model. Here we generalize this to obtain a column-inhomogeneous τ₂ (t _q ) model, and derive the functional relations satisfied by its row-to-row transfer matrix. We do not need the usual chiral Potts relations between the Nth powers of the rapidity parameters a _p , b _p , c _p , d _p of each column. This enables us to readily consider the case of fixed-spin boundary conditions on the left and right-most columns. We thereby re-derive the simple direct product structure of the transfer matrix eigenvalues of this model, which is closely related to the superintegrable chiral Potts model with fixed-spin boundary conditions.