The spectral density method is used to study the thermodynamic properties of an anisotropic antiferromagnetic Heisenberg linear chain in an external magnetic field. Insecond order approximation without the decoupling procedure for the two particle correlation function, we are able to obtain many...

The paper is devoted to an investigation of the damping effects of the Fermion elementary excitations in the Jordan-Wigner representation of a one-dimensional anisotropic spin-12 model in an external field. This is realized on the basis of the “Gaussian ansatz”, recently proposed by Nolting...

We study the properties of a d-dimensional sine-Gordon model in the presence of a random field that couples linearly to the sine-Gordon field using the Wilson renormalization group approach via the replica trick. No stable fixed point is found for dimensionalities d4, corresponding to the...

In this paper, a class of product-sum covariance models has been introduced for estimating and modeling space-time correlation structures. It is shown how the coefficients of this class of models are related to the global sill and "partial" spatial and temporal sills; moreover, some constraints...

Motived by the necessity of explicit and reliable calculations, as a valid contribution to clarify the effectiveness and, possibly, the limits of the Tsallis thermostatistics, we formulate the Two-Time Green Functions Method in nonextensive quantum statistical mechanics within the optimal...