Representations in Density Dependent Hadronic Field Theory and compatibility with QCD sum-rules

Different representations of an effective, covariant theory of the hadronic interaction are examined. For this purpose we have introduced nucleon-meson vertices parametrized in terms of scalar combinations of hadronic fields, extending the conceptual frame of the Density Dependent Hadronic Field Theory. Nuclear matter properties at zero temperature are examined in the Mean Field Approximation, including the equation of state, the Landau parameters, and collective modes. The treatment of isospin channels in terms of QCD sum rules inputs is outlined.Comment: 23 pages, 6 PostScript figures, Revtex4 clas

Characterizing correlations and synchronization in collective dynamics

Synchronization, that occurs both for non-chaotic and chaotic systems, is a striking phenomenon with many practical implications in natural phenomena. However, even before synchronization, strong correlations occur in the collective dynamics of complex systems. To characterize their nature is essential for the understanding of phenomena in physical and social sciences. The emergence of strong correlations before synchronization is illustrated in a few piecewise linear models. They are shown to be associated to the behavior of ergodic parameters which may be exactly computed in some models. The models are also used as a testing ground to find general methods to characterize and parametrize the correlated nature of collective dynamics.Comment: 37 pages, 37 figures, Late

Schemata as Building Blocks: Does Size Matter?

We analyze the schema theorem and the building block hypothesis using a recently derived, exact schemata evolution equation. We derive a new schema theorem based on the concept of effective fitness showing that schemata of higher than average effective fitness receive an exponentially increasing number of trials over time. The building block hypothesis is a natural consequence in that the equation shows how fit schemata are constructed from fit sub-schemata. However, we show that generically there is no preference for short, low-order schemata. In the case where schema reconstruction is favoured over schema destruction large schemata tend to be favoured. As a corollary of the evolution equation we prove Geiringer's theorem. We give supporting numerical evidence for our claims in both non-epsitatic and epistatic landscapes.Comment: 17 pages, 10 postscript figure

Propagation of mesons in asymmetric nuclear matter in a density dependent coupling model

We study the propagation of the light mesons sigma, omega, rho, and a0(980) in dense hadronic matter in an extended derivative scalar coupling model. Within the scheme proposed it is possible to unambiguously define effective density-dependent couplings at the Lagrangian level. We first apply the model to study asymmetric nuclear matter with fixed isospin asymmetry, and then we pay particular attention to hypermatter in beta-equilibrium. The equation of state and the potential contribution to the symmetry coefficient arising from the mean field approximation are investigated.Comment: 17 pages, 15 PostScript figure

Neutron matter under strong magnetic fields: a comparison of models

The equation of state of neutron matter is affected by the presence of a magnetic field due to the intrinsic magnetic moment of the neutron. Here we study the equilibrium configuration of this system for a wide range of densities, temperatures and magnetic fields. Special attention is paid to the behavior of the isothermal compressibility and the magnetic susceptibility. Our calculation is performed using both microscopic and phenomenological approaches of the neutron matter equation of state, namely the Brueckner--Hartree--Fock (BHF) approach using the Argonne V18 nucleon-nucleon potential supplemented with the Urbana IX three-nucleon force, the effective Skyrme model in a Hartree--Fock description, and the Quantum Hadrodynamic formulation with a mean field approximation. All these approaches predict a change from completely spin polarized to partially polarized matter that leads to a continuous equation of state. The compressibility and the magnetic susceptibility show characteristic behaviors, which reflect that fact. Thermal effects tend to smear out the sharpness found for these quantities at T=0. In most cases a thermal increase of 10 MeV is enough to hide the signals of the change of polarization. The set of densities and magnetic field intensities for which the system changes it spin polarization is different for each model. However, there is an overall agreement between the three theoretical descriptions.Comment: updated to correspond with the published versio

A supersymmetric exotic field theory in (1+1) dimensions. One loop soliton quantum mass corrections

We consider one loop quantum corrections to soliton mass for the ${\cal N}=1$ supersymmetric extension of the (1+1)-dimensional scalar field theory with the potential $U(\phi) = \phi^2 \cos^2\left(\ln \phi^2\right)$. First, we compute the one loop quantum soliton mass correction of the bosonic sector. To do that, we regularize implicitly such quantity by subtracting and adding its corresponding tadpole graph contribution, and use the renormalization prescription that the added term vanishes with the corresponding counterterms. As a result we get a finite unambiguous formula for the soliton quantum mass corrections up to one loop order. Afterwards, the computation for the supersymmetric case is extended straightforwardly and we obtain for the one loop quantum correction of the SUSY kink mass the expected value previously derived for the SUSY sine-Gordon and $\phi^4$ models. However, we also have found that for a particular value of the parameters, contrary to what was expected, the introduction of supersymmetry in this model worsens ultraviolet divergences rather than improving them.Comment: 16 pages, 8 figures; Major modifications included to match version published in JHE