Pedro Bicudo

Chirally symmetric quark description of low-energy pi pi scattering

Weinberg’s theorem for π-π scattering, including the Adler zero at threshold in the chiral limit, is analyticall proved for microscopic quark models that preserve chiral symmetry. Implementing Ward-Takahashi identities, the isospin 0 and 2 scattering lengths are derived in exact agreement with Weinberg’s low energy results. Our proof applies to alternative quark formulations including the Hamiltonian and Euclidean space Dyson-Schwinger approaches. Finally, the threshold π-π scattering amplitudes are calculated using the Dyson- Schwinger equations in the rainbow-ladder truncation, confirming the formal derivation.

The Θ+ (1540) as a heptaquark with the overlap of a pion, a kaon and a nucleon

We study the very recently discovered Theta+ (1540) at SPring-8, at ITEP and at CLAS-Thomas Jefferson Lab. We apply the same RGM techniques that already explained with success the repulsive hard core of nucleon-nucleon, kaon-nucleon exotic scattering, and the attractive hard core present in pion-nucleon and pion-pion non-exotic scattering. We find that the K-N repulsion excludes the Theta+ as a K-N s-wave pentaquark. We explore the Theta+ as a heptaquark, equivalent to a N+pi+K borromean bound-state, with positive parity and total isospin I=0. We find that the kaon-nucleon repulsion is cancelled by the attraction existing both in the pion-nucleon and pion-kaon channels. Although we are not yet able to bind the total three body system, we find that the Theta^+ may still be a heptaquark state. We conclude with predictions that can be tested experimentally.

Gluon screening mass at finite temperature from the Landau gauge gluon propagator in lattice QCD

We address the interpretation of the Landau gauge gluon propagator at finite temperature as a massive-type bosonic propagator. Using pure gauge SU(3) lattice simulations at a fixed lattice volume

The lattice gluon propagator in renormalizable

\ensuremath{\sim}(6.5\text{ }\text{ }\mathrm{fm}{)}^{3}

\xi

, we compute the electric and magnetic form factors, extract a gluon mass from Yukawa-like fits, and study its temperature dependence. This is relevant both for the Debye screening at high temperature

gauges

T

Evidence for the existence of

and for confinement at low

u d \bar{b} \bar{b}

T

and the non-existence of

.

s s \bar{b} \bar{b}

We study the SU(3) gluon propagator in renormalizable