28,777 research outputs found

    Interplay between chiral and axial symmetries in a SU(2) Nambu--Jona-Lasinio Model with the Polyakov loop

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    We consider a two flavor Polyakov--Nambu--Jona-Lasinio (PNJL) model where the Lagrangian includes an interaction term that explicitly breaks the UA(1)_A(1) anomaly. At finite temperature, the restoration of chiral and axial symmetries, signaled by the behavior of several observables, is investigated. We compare the effects of two regularizations at finite temperature, one of them, that allows high momentum quarks states, leading to the full recovery of chiral symmetry. From the analysis of the behavior of the topological susceptibility and of the mesonic masses of the axial partners, it is found in the SU(2) model that, unlike the SU(3) results, the recovery of the axial symmetry is not a consequence of the full recovery of the chiral symmetry. Thus, one needs to use an additional idea, by means of a temperature dependence of the anomaly coefficient, that simulates instanton suppression effects.Comment: 21 pages, 5 figures; PRD versio

    Periodical press and port cities: Creation of knowledge, representations and networks

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    Port cities constituted dynamic axes of national territories and stood out for their opening to the outside world for the transaction of goods, the reception of the new and the exchange of ideas. They were also free spaces for new technological experiences and the foundation of modern economic, scientific, social and political projects. They stood out as privileged territories for the establishment of networks of knowledge and through these networks maintained the contact with distant lands. Intellectual production in them is remarkable and the periodical press, providing general or specialized information, as an information industry at the service of new political, scientific and economic projects, finds space for its development within the port cities. This Special Section brings together researchers working on these subjects, allowing a multidisciplinary approach involving scholars from such scientific areas as communication, information, history, literature and international relations. The objective is to analyse the relationship between the periodic press and port cities and how these urban spaces fostered public opinion and debate projects, as well as new specialized information.info:eu-repo/semantics/acceptedVersio

    Some properties of two Nambu--Jona-Lasinio -type models with inputs from lattice QCD

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    We investigate the phase diagram of the so-called Polyakov--Nambu--Jona-Lasinio (PNJL) model at finite temperature and nonzero chemical potential. The calculations are performed in the light and strange quark sectors (uu, dd, ss), which includes the 't Hooft instanton induced interaction term that breaks the axial symmetry, and the quarks are coupled to the (spatially constant) temporal background gauge field. On one hand, a special attention is payed to the critical end point (CEP). The strength of the flavor-mixing interaction alters the CEP location, since when it becomes weaker the CEP moves to low temperatures and can even disappear. On the other hand, we also explore the connection between QCD, a nonlocal Nambu--Jona-Lasinio type model and the Landau gauge gluon propagator. Possible links between the quenched gluon propagator and low energy hadronic phenomenology are investigated.Comment: Contribution to the International Meeting "Excited QCD", Peniche, Portugal, 06 - 12 May 201

    Non-collinear coupling between magnetic adatoms in carbon nanotubes

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    The long range character of the exchange coupling between localized magnetic moments indirectly mediated by the conduction electrons of metallic hosts often plays a significant role in determining the magnetic order of low-dimensional structures. In addition to this indirect coupling, here we show that the direct exchange interaction that arises when the moments are not too far apart may induce a non-collinear magnetic order that cannot be characterized by a Heisenberg-like interaction between the magnetic moments. We argue that this effect can be manipulated to control the magnetization alignment of magnetic dimers adsorbed to the walls of carbon nanotubes.Comment: 13 pages, 5 figures, submitted to PR
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