The Heisenberg model, a quantum mechanical analogue of the Ising model, has a large ground state degeneracy, due to the symmetry generated by the total spin. This symmetry is also responsible for degeneracies in the rest of the spectrum. We discuss the global structure of the spectrum of Heisenberg models with arbitrary couplings, using group theoretical methods. The Hilbert space breaks up in ...

The critical behaviour of anisotropic Heisenberg models with two kinds of antiferromagnetically exchange-coupled centers are studied numerically by using finite-size calculations and conformal invariance. These models exhibit the interesting property of ferrimagnetism instead of antiferromagnetism. Most of our results are centered in the mixed Heisenberg chain where we have at even (odd) sites ...

We present a study of the Drude weightD(T ) of the spin-1/2XXZ chain in the gapless regime. The thermodynamic Bethe ansatz (TBA) is applied in two different ways. In the first application we employ the particle basis of magnons and their bound states. In this case we rederive and considerably extend earlier work in the literature. However, in the course of our investigation we find arguments th...

It is shown that, with an appropriate scaling, the energy of low-lying excitations of the (1; 1; : : : ; 1) interface in the d-dimensional quantum Heisenberg model are given by the spectrum of the d ? 1-dimensional Lapla-cian on an suitable domain. of this article in its entirety, by any means, is permitted for non-commercial purposes.

The form of the spectral curve for 4d N = 2 supersymmetric Yang-Mills theory with matter fields in the fundamental representation of the gauge group suggests that its 1d integrable counterpart should be looked for among (inhomogeneous) sl(2) spin chains with the length of the chain being equal to the number of colours Nc. For N f < 2Nc the relevant spin chain is the simplest XXX-model, and this...

We introduce four types of SU(2M + 1) spin chains which can be regarded as the BC N versions of the celebrated Haldane–Shastry chain. These chains depend on two free parameters and, unlike the original Haldane–Shastry chain, their sites need not be equally spaced. We prove that all four chains are solvable by deriving an exact expression for their partition function using Polychronakos's " free...

The finite temperature transition of QCD with two degenerate light quarks is studied on the lattice with a renormalization group improved gauge action and the Wilson quark action. We have made simulations on an 8 3 × 4 lattice near the chiral transition point. It is shown that the chiral condensate which is the order parameter of chiral symmetry satisfies remarkably a scaling relation with the ...

Customary lattice methods are considered suitable for the description of the static, or low energy, nonperturbative properties of hadrons. Even though some progress has been made in studying the scattering length, form factors and the deep inelastic structure functions, the finite ultraviolet cut-off a ∼ 2GeV limits the application of classical lattice techniques mainly to the static phenomena....

We present a field-theoretic renormalization group calculation in two loop order for classical O(N)-models with an inverse square interaction in the vicinity of their lower critical dimensionality one. The magnetic susceptibility at low temperatures is shown to diverge like T−a exp(b/T ) with a = (N−2)/(N−1) and b = 2π/(N − 1). From a comparison with the exactly solvable Haldane-Shastry model w...

In this paper, we show the integrability of spin-1/2 XXZ Heisenberg chain with two arbitrary spin boundary Impurities. By using the fusion method, we generalize it to the spin-1 XXZ chain. Then the eigenvalues of Hamiltonians of these models are obtained by the means of Bethe ansatz method. Pacs: 75.20H, 12.40E, 75.10D