Unitarized pion-nucleon scattering amplitude from inverse amplitude method

In a recent work on low energy pion-nucleon scattering, instead of using chiral perturbation theory (ChPT) amplitude, we started from a pion-nucleon {\it soft-pion} result and used elastic unitarity directly as a dynamical constraint to construct first-order unitarity corrected amplitudes. The resulting amplitudes are crossing symmetric but, as the ChPT ones, satisfy only approximate unitarity relation. In the present work, we reconsider our approach and we apply the inverse amplitude method (IAM) in order to access the energy resonance region. We present the resulting S- and P-wave phase shifts that are shown to be in qualitative agreement with experimental data.Comment: 6 pages, 3 figure

Two loops calculation in chiral perturbation theory and the unitarization program of current algebra

In this paper we compare two loop Chiral Perturbation Theory (ChPT) calculation of pion-pion scattering with the unitarity second order correction to the current algebra soft-pion theorem. It is shown that both methods lead to the same analytic structure for the scattering amplitude.Comment: 13 pages, Revtex 3.0, no figures, submitted to Phys. Lett.

Symmetry breaking patterns of the 3-3-1 model at finite temperature

We consider the minimal version of an extension of the standard electroweak model based on the $SU(3)_c \times SU(3)_L \times U(1)_X$ gauge symmetry (the 3-3-1 model). We analyze the most general potential constructed from three scalars in the triplet representation of $SU(3)_L$, whose neutral components develop nonzero vacuum expectation values, giving mass for all the model's massive particles. {}For different choices of parameters, we obtain the particle spectrum for the two symmetry breaking scales: one where the $SU(3)_L \times U(1)_X$ group is broken down to $SU(2)_L\times U(1)_Y$ and a lower scale similar to the standard model one. Within the considerations used, we show that the model encodes two first-order phase transitions, respecting the pattern of symmetry restoration. The last transition, corresponding to the standard electroweak one, is found to be very weak first-order, most likely turning second-order or a crossover in practice. However, the first transition in this model can be strongly first-order, which might happen at a temperature not too high above the second one. We determine the respective critical temperatures for symmetry restoration for the model.Comment: 13 pages, 8 figures. Minor changes to match published versio

Top quark forward-backward asymmetry from the 3−3−13-3-1 model

The forward-backward asymmetry $A_{FB}$ in top quark pair production, measured at the Tevatron, is probably related to the contribution of new particles. The Tevatron result is more than a $2\sigma$ deviation from the standard model prediction and motivates the application of alternative models introducing new states. However, as the standard model predictions for the total cross section $\sigma_{tt}$ and invariant mass distribution $M_{tt}$ for this process are in good agreement with experiments, any alternative model must reproduce these predictions. These models can be placed into two categories: One introduces the s-channel exchange of new vector bosons with chiral couplings to the light quarks and to the top quark and another relies on the t-channel exchange of particles with large flavor-violating couplings in the quark sector. In this work we employ a model which introduces both s- and t-channel nonstandard contributions for the top quark pair production in proton antiproton collisions. We use the minimal version of the $SU(3)_C \otimes SU(3)_L \otimes U (1)_X$ model (3-3-1 model) that predicts the existence of a new neutral gauge boson, called $Z^\prime$. This gauge boson has both flavor-changing couplings to up and top quarks and chiral coupling to the light quarks and to the top quark. This very peculiar model coupling can correct the $A_{FB}$ for top quark pair production for two ranges of $Z^\prime$ mass while leading to cross section and invariant mass distribution quite similar to the standard model ones. This result reinforces the role of the 3-3-1 model for any new physics effect.Comment: 12 pages, 4 figures, 2 table

Ciencia y sociedad : la educación en tiempos de fronteras paradigmáticas

Este artigo faz uma ponte entre as idéias de Boaventura de Sousa Santos, a respeito do papel da universidade pública na construção de um projeto de sociedade contrahegemônico à globalização capitalista, e as idéias de István Mészáros, a respeito da radicalidade de uma educação para além do capital. Na costura dessas duas visões da mudança social, utilizamos a visão de Edgar Morin sobre a natureza complexa dos paradigmas e as condições socioculturais de sua transformação. Indagam-se aqui as possibilidades de produção de um novo conhecimento enraizado nas lutas sociais pela superação da hegemonia da lógica do capital e de sua determinação sobre a produção material, cultural e educacional de nossa sociedade. A universidade pública é considerada como espaço privilegiado de democratização da produção do saber científico e de contribuição à construção de um projeto de sociedade revolucionário. _______________________________________________________________________________ ABSTRACTThis study bridges the ideas of Boaventura de Sousa Santos with regards to the role of the public university in the construction of a project for a society, one that is counterhegemonic to capitalist globalization and those of István Mészáros dealing with the radicality of education beyond capital. To bring together those two views of social change, the vision of Edgar Morin on the complex nature of paradigms and the social and cultural conditions for their transformation was used. The article inquires about the possibilities of production of a new knowledge rooted in the social struggles for the overthrow of the hegemony of the logic of capital and its determination over material, cultural and educational production in our society. The public university is considered a privileged space for democratizing the production of scientific knowledge and contributing to the construction of a revolutionary project of society. _______________________________________________________________________________ RÉSUMÉCette étude fait le pont entre les idées de Boaventura de Sousa Santos au sujet du rôle de l’université publique dans la construction d’un projet de société qui soit contrehégémonique à la globalisation capitaliste et celles de István Mészáros qui traitent de la radicalité de l’éducation au delà du capital. Pour rapprocher ces idées sur le changement social, la vision d’Edgar Morin sur la nature complexe des paradigmes et les conditions sociales et culturelles pour leur transformation a été utilisée. L’étude pose la question sur les possibilités de la production d’un nouveau savoir enraciné dans les luttes pour la suppléance de l’hégémonie de la logique du capital et sa détermination sur la production matérielle, culturelle et éducationnelle dans notre société. L’université publique est considérée un espace privilégié pour la démocratisation de la production du savoir scientifique et la construction d’un projet révolutionnaire de société. _______________________________________________________________________________ RESUMENEste artículo hace un puente entre las ideas de Boaventura de Sousa Santos con respecto del papel de la universidad pública en la construcción de un proyecto de sociedad contrahegemónico a la globalización capitalista, y las ideas de István Mészáros, a respecto de la radicalidad de una educación para más allá del capital. En la costura de estas dos visiones del cambio social, utilizamos la visión de Edgar Morin sobre la naturaleza compleja de los paradigmas y las condiciones socioculturales de su transformación. Se indagan aquí las posibilidades de producción de un nuevo conocimiento enraizado en las luchas sociales por la superación de la hegemonía de la lógica del capital y de su determinación sobre la producción material, cultural y educacional de nuestra sociedad. La universidad pública es considerada un espacio privilegiado de democratización de la producción del saber científico y de contribución a la construcción de un proyecto de sociedad revolucionario

Pion-Pion Phase-Shifts and the Value of Quark-Antiquark Condensate in the Chiral Limit

We use low energy pion-pion phase-shifts in order to make distinction between the alternatives for the value of the quark-antiquark condensate $B_0$ in the chiral limit. We will consider the amplitude up to and including ${\cal O}(p^4)$ contributions within the Standard and Generalized Chiral Perturbation Theory frameworks. They are unitarized by means of Pad\'e approximants in order to fit experimental phase-shifts in the resonance region. As the best fits correspond to $\alpha = \beta = 1$, we conclude that pion-pion phase-shift analysis favors the standard ChPT scenario, which assumes just one, large leading order parameter $_{_0}$.Comment: 5 pages, 3 figures and 1 tabl