Phase diagram of the ANNNI model in the Hamiltonian limit

The Hamiltonian limit of the ANNNI model in (1+1) dimensions is studied by using the Quantum Statistical Monte Carlo method. Even if recent results suggest that Monte Carlo calculations may prove unreliable in the study of this system, the phase diagram of the quantum version of the model was successfully obtained. In particular, the clusive transitions between the disordered, the floating incommensurate and the degenerate 2, 2 are determined by analysing the correlation length behaviour in finite lattices.Partially supported by CONICET Argentina     

Nuclear pions and the Gottfried and Bjorken sum rules

The thermodynamic potential (TDP) of the boson sector of the Weinberg-Salam model in an external uniform magnetic field at finite temperature and nonzero chemical potential is calculated in one-loop approximation. In the high temperature limit with the use of Mellin summation technique explicit expressions for the thermodynamic potential are obtained to analyze its new minimum, different from the ordinary Higgs one. This new minimum is due to the root singularity in the oneloop expression for the TDP, originating as a consequence of the tachyonic mode in the spectrum of gauge boson in the magnetic field. It is demonstrated that in the high temperature limit the Higgs minimum possesses properties common with the ordinary superconductors and Abelian Higgs model. The influence of the magnetic field on the Higgs minimum is indirect and has a sufficiently complicated character. The presence of the non-zero chemical potential lowers the critical temperature leading to the disappearance of the Higgs minimum.     

The ideal mixing departure in vector meson physics

In this work we study the departure from the ideal - mixing angle within the framework of the Nambu-Jona-Lasinio model. In this context we show that the flavor symmetry breaking is unable to produce the shifting of the ideal mixing. We found that a nonet symmetry breaking in the neutral vector sector is necessary to regulate the non-strange content of the meson. The phenomenology is well described by our proposal.Received: 14 November 2002, Revised: 22 April 2003, Published online: 11 July 2003     

Radiative decays of mesons in the NJL model

We revisit the theoretical predictions for anomalous radiative decays of pseudoscalar and vector mesons. Our analysis is performed in the framework of the Nambu–Jona–Lasinio model, introducing adequate parameters to account for the breakdown of chiral symmetry. The results are comparable with those obtained in previous approaches. Received: 14 September 2000 / Revised version: 1 March 2001 / Published online: 8 June 2001     

Rigorous absolute bounds for pion-pion scattering (1). Solving a first extremum problem

This paper is the first of a series of three where we reconsider the derivation of rigorous absolute bounds for strong interactions. It is devoted to the solution of a preliminary extremum problem. From the knowledge, at a given physical energy s and unphysical angle cos θ₀ > 1, of the absorptive part A (s, cos θ₀) of the elastic scattering amplitude for two spinless particles, we find, by exploiting the unitarity condition, the least upper bound of the modulus |F(s, cos θ₁)| of the scattering amplitude for the same energy s and various angles θ₁. Upper (but not least upper) bounds given by previous authors are numerically compared with ours.     

Ferromagnetic and antiferromagnetic properties of the blume-capel model in (1+1) and (2+1) dimensions

A renormalization group realization, allowing the simultaneous and analytic study of both the ferromagnetic and antiferromagnetic phases of the Blume-Capel model, is applied in (1+1)_and (2+1) dimensions. The model is also analyzed by using a variational technique. Critical and tricritical parameters are determined and the phase diagram is exhibited.Partially supported by CONICET, CIC Pcia. de Buenos Aires and SUBCYT, Argentina     

The manifold of solutions of Roy's S- and P-wave equations for pion-pion scattering: The neighbourhood of the physical amplitudes

We study the solutions of the coupled S- and P-wave Roy equations for low-energy pion-pion scattering which are in the neighbourhood of a given solution. We give a general method for constructing these solutions for fixed inelasticities and driving terms and variable S-wave scattering lengths. In the case of the neighbourhood of the physical amplitudes, our procedure leads to a seven-dimensional manifold of solutions. If we omit variations affecting only the I = 0 S-wave around the $\text{K}\text{K}$ threshold, the number of dimensions is reduced to five, in accordance with the results of the phenomenological analysis of low-energy pion-pion scattering. Our solutions allow a study of the correlations between S- and P-waves implied by the Roy equations. This work completes a previous one dealing with the single-channel problem of the I = 1 P-wave.     

Monopolium production from photon fusion at the Large Hadron Collider

Magnetic monopoles have attracted the attention of physicists since the founding of the electromagnetic theory. Their search has been a constant endeavor which was intensified when Dirac established the relation between the existence of monopoles and charge quantization. However, these searches have been unsuccessful. We have recently proposed that monopolium, a monopole–antimonopole bound state, so strongly bound that it has a relatively small mass, could be easier to find and become an indirect but clear signature for the existence of magnetic monopoles. Here we extend our previous analysis for its production to two photon fusion at LHC energies.     

Multichannel framework for singular quantum mechanics

A multichannel S-matrix framework for singular quantum mechanics (SQM) subsumes the renormalization and self-adjoint extension methods and resolves its boundary-condition ambiguities. In addition to the standard channel accessible to a distant (“asymptotic”) observer, one supplementary channel opens up at each coordinate singularity, where local outgoing and ingoing singularity waves coexist. The channels are linked by a fully unitary S-matrix, which governs all possible scenarios, including cases with an apparent nonunitary behavior as viewed from asymptotic distances.     

Monopolium: the key to monopoles

Dirac showed that the existence of one magnetic pole in the universe could offer an explanation for the discrete nature of the electric charge. Magnetic poles appear naturally in most grand unified theories. Their discovery would be of the greatest importance for particle physics and cosmology. The intense experimental search carried out thus far has not met with success. Moreover, if the monopoles are very massive their production is outside the range of present day facilities. A way out of this impasse would be if the monopoles bind to form monopolium, a monopole–antimonopole bound state, which is so strongly bound that it has a relatively small mass. Under these circumstances it could be produced with present day facilities and the existence of monopoles could be indirectly proven. We study the feasibility of detecting monopolium in present and future accelerators. PACS  14.80.Hv; 95.30.Cq; 98.70.-f; 98.80.-k