F. Cosenza

Thermodynamic properties of a classical d-dimensional spin-S Heisenberg ferromagnet with long-range interactions via the spectral density method

The thermodynamic properties of a classical d-dimensional spin-S Heisenberg ferromagnet, with long-range interactions decaying as r−p and in the presence of an external magnetic field, is investigated by means of the spectral density method in the framework of classical statistical mechanics. We find that long-range order exists at finite temperature for dd with d>2, consistently with known theorems. Besides, the related critical temperature is determined and a study of the critical properties is performed.

Two-time Green's functions and spectral density method in nonextensive quantum statistical mechanics

We extend the formalism of the thermodynamic two-time Greens functions to nonextensive quantum statistical mechanics. Working in the optimal Lagrangian multiplier representation, the q -spectral properties and the methods for a direct calculation of the two-time q Greens functions and the related q -spectral density ( q measures the nonextensivity degree) for two generic operators are presented in strict analogy with the extensive (q=1) counterpart. Some emphasis is devoted to the nonextensive version of the less known spectral density method whose effectiveness in exploring equilibrium and transport properties of a wide variety of systems has been well established in conventional classical and quantum many-body physics. To check how both the equations of motion and the spectral density methods work to study the q -induced nonextensivity effects in nontrivial many-body problems, we focus on the equilibrium properties of a second-quantized model for a high-density Bose gas with strong attraction between particles for which exact results exist in extensive conditions. Remarkably, the contributions to several thermodynamic quantities of the q -induced nonextensivity close to the extensive regime are explicitly calculated in the low-temperature regime by overcoming the calculation of the q grand-partition function.

Spectral density method in quantum nonextensive thermostatistics and magnetic systems with long-range interactions

Abstract.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 Lagrange multiplier framework, focusing on the basic ingredients of the related Spectral Density Method (SDM). Besides, to show how the SDM works, we have performed, to the lowest order of approximation, explicit calculations of the low-temperature properties for a quantum d-dimensional spin-1/2 Heisenberg ferromagnet with long-range interactions decaying as 1/rp ( r is the distance between spins in the lattice).

Spectral density approach to the one-dimensional classical Heisenberg ferromagnet with long-range interactions

Abstract The thermodynamic properties of a classical spin- S Heisenberg ferromagnetic chain with long-range interactions decaying as r − α and in the presence of an external magnetic field, are investigated by means of the spectral density method. In particular, we find that long-range order exists at finite temperature for 1 α

Two-time Green function technique in Tsallis’ classical statistical mechanics

The two-time Green function technique is formulated in nonextensive classical statistical mechanics within the optimal Lagrange multiplier framework. We introduce also the nonextensive classical version of the spectral density method, for a direct calculation of the Green functions, and its effectiveness is tested exploring the equilibrium properties of the classical ferromagnetic Heisenberg spin chain.

Nonperturbative vertex corrections for superconductivity in the Frohlich model

Abstract A nonperturbative calculation of the vertex corrections for the electron–phonon Frohlich model beyond the Migdal regime is performed within a modified version of the conventional gauge technique. We find that they show tendency to depress the critical temperature and other relevant quantities increasing the Migdal parameter m . Moreover, a comparison with the results recently obtained for the BCS pairing model using the same method suggests that, varying the coupling constant λ at fixed m , the sign of the vertex corrections may depend sensibly on the effective pairing interaction between the charge carriers.

A multiplicity trigger based on the Time of Flight detector for the ALICE experiment

The goal of the ALICE Time of Flight detector, based on MRPC technology, is to perform charged particle identification in |η|<1. This large area (150 m), finely segmented detector (~160,000 channels), provides fast signals which will contribute to the Level 0 and Level 1 trigger decisions. We use the TOF detector information to perform an online estimate of the total track multiplicity and to identify simple and peculiar topologies like those produced by peripheral collisions and by cosmic muons. The system architecture foresees a first layer of 72 VME boards interfacing the detector front-end to a second layer, which receives and processes all the information and takes trigger decisions.