Variational fits to the lattice energy of heavy-light mesons

We perform variational calculations of heavy-light meson masses using a fitted formula to a lattice two-quark potential. We examine the light quark mass dependence of the meson mass using the Schrodinger equation and the Dirac equation. For the Dirac equation, a saddle-point variational principle is employed, since the Dirac Hamiltonian is not bound from below.

Three-pion-exchange potential

Using the chiral symmetry, we calculated the dominant contribution to the nucleon - nucleon potential due to the exchange of three non-correlated pions. This contribution is isovetor with pseudoscalar and axial components. The pseudoscalar component is dominant, it has a range of 1.0 fm and it contributes in the pion channel.

Four-fermion contact interactions at one-loop and the new atomic parity violation results.

We investigate the possibility that four-fermion contact interactions give rise to the observed deviation from the Standard Model prediction for the weak charge of cesium, through one-loop contributions. We show that the presence of loops involving the third generation quarks can explain such deviation.

Schwinger-Dyson equations and dynamical gluon mass generation

We obtain a solution for the gluon propagador in Landau gauge within two distinct approximations for the Schwinger-Dyson equations (SIDE). The first, named Mandelstam's approximation, consist in neglecting all contributions that come from fermions and ghosts fields while in the second, the ghosts fields are taken into account leading to a coupled system of integral equations. In both cases we show that a dynamical mass for the gluon propagator can arise as a solution.

Qcd Sum Rules for the G(KK*pi)(Q(2)) form factor

The QCD Sum Rules have been used to evaluate the form factor in the vertex KK*pi. The method of QCD Sum Rules is based on the duality principle in which it is assumed that the hadrons can simultaneously be described in two levels: quarks and hadrons. This work showed that the, axial current, used to describe the meson K is not appropriated to study the form factor.

Quark condensates and high density quark matter

We consider a Coulomb gauge quark model which includes an explicit construct for a nontrivial vacuum structure in QCD. The dynamics is described by a Hamiltonain that contains a linearly rising confining potential and longitudinal and transverse Coulomb-type interactions. The Coulomb potential gives rise to ultraviolate divergences which are non-perturbatively renormalized by adding appropriate counter terms to the Hamiltonian. The equation of state for u and d quark matter at zero temperature is derived in the Hartree-Fock approximation.

Gauge groups from brane-anti-brane systems at angles

We discuss a system formed by two pairs of brane-anti-brane that form an arbitrary angle in a plane. We identify the gauge groups from this system which presumably could be used to construct gauge theories.

Temporal correlator in YM32 and reflection-positivity violation

We consider numerical data for the lattice Landau gluon propagator obtained at very large lattice volumes in three-dimensional pure SU(2) Yang-Mills gauge theory (YM32). We find that the temporal correlator C(t) shows an oscillatory pattern and is negative for several values of t. This is an explicit violation of reflection positivity and can be related to gluon confinement. We also obtain a good fit for this quantity in the whole time interval using a sum of Stingl-like propagators.

Dynamic critical behavior of percolation observables in the 2d Ising model

We present preliminary results of our numerical study of the critical dynamics of percolation observables for the two-dimensional Ising model. We consider the (Monte-Carlo) short-time evolution of the system obtained with a local heat-bath method and with the global Swendsen-Wang algorithm. In both cases, we find qualitatively different dynamic behaviors for the magnetization and Omega, the order parameter of the percolation transition. This may have implications for the recent attempts to describe the dynamics of the QCD phase transition using cluster observables.

Scalar field theory at finite temperature in D=2+1

We discuss the phi(6) theory defined in D = 2 + 1-dimensional space-time and assume that the system is in equilibrium with a thermal bath at temperature beta(-1). We use the 1/N expansion and the method of composite operator (CJT) for summing a large set of Feynman graphs. We demonstrate explicitly the Coleman-Mermin-Wagner theorem at finite temperature.

Chiral symmetry and pion-nucleon scattering

In this work, we study the influence of the way pious couple to nucleons in perturbative calculation of an observable in the pion-nucleon scattering.

A Study of Scattering Amplitude Regularization in the NN System: Two Pions Contributions

In a simplest case we employ dimensional regularization method in order to evaluate the contribution of two pion exchanges to the NN interaction. The method allows one to treat the infinities of scattering amplitude in a way consistent with the symmetries of the theory.

Density-dependent coupling constants and charge symmetry breaking

The effect of the medium in the coupling constants implicate in a charge symmetry breaking on nuclear interactions. The amount of energy due to this modification can explain the Nolen-Schiffer anomaly.

Spin and pseudospin symmetries of the Dirac equation with confining central potentials

We derive the node structure of the radial functions which are solutions of the Dirac equation with scalar S and vector V confining central potentials, in the conditions of exact spin or pseudospin symmetry, i.e., when one has V=±S+C, where C is a constant. We show that the node structure for exact spin symmetry is the same as the one for central potentials which go to zero at infinity but for exact pseudospin symmetry the structure is reversed. We obtain the important result that it is possible to have positive energy bound solutions in exact pseudospin symmetry conditions for confining potentials of any shape, including naturally those used in hadron physics, from nuclear to quark models. Since this does not occur for potentials going to zero at large distances, which are used in nuclear relativistic mean-field potentials or in the atomic nucleus, this shows the decisive importance of the asymptotic behavior of the scalar and vector central potentials on the onset of pseudospin symmetry and on the node structure of the radial functions. Finally, we show that these results are still valid for negative energy bound solutions for antifermions. © 2013 American Physical Society.

Scattering Amplitudes Interpolating Between Instant Form and Front Form of Relativistic Dynamics

Among the three forms of relativistic Hamiltonian dynamics proposed by Dirac in 1949, the front form has the largest number of kinematic generators. This distinction provides useful consequences in the analysis of physical observables in hadron physics. Using the method of interpolation between the instant form and the front form, we introduce the interpolating scattering amplitude that links the corresponding time-ordered amplitudes between the two forms of dynamics and provide the physical meaning of the kinematic transformations as they allow the invariance of each individual time-ordered amplitude for an arbitrary interpolation angle. We discuss the rationale for using front form dynamics, nowadays known as light-front dynamics (LFD), and present a few explicit examples of hadron phenomenology that LFD uniquely can offer from first-principles quantum chromodynamics. In particular, model-independent constraints are provided for the analyses of deuteron form factors and the N Delta transition form factors at large momentum transfer squared Q(2). The swap of helicity amplitudes between the collinear and non-collinear kinematics is also discussed in deeply virtual Compton scattering.