Taking dibaryon fields seriously

We propose a low energy effective field theory of QCD at the scale of pion mass for the $N_B=2$ sector, $N_B$ being the baryon number, which contains two dibaryon fields in addition to the nucleons and pions. It has a well defined counting, is renormalizable and the nucleon-nucleon scattering amplitudes are manifestly unitary at leading order. We work out a lower energy effective theory for nucleons with energy much lower than the pion mass and three momentum comparable to it, which also has a well defined counting and is renormalizable. The dibaryon fields must also be kept as explicit degrees of freedom in this theory. We calculate the scattering amplitudes at next-to-leading order for the $^1S_0$ and $^3S_1$ channels in this framework and obtain an excellent description of the phase shifts for center of mass energies in the $0-50 MeV$ range.Comment: 20 pages, 5 figures; misprints corrected, explanations enlarged, references added. Journal versio

On the factorization of chiral logarithms in the pion form factors

The recently proposed hard-pion chiral perturbation theory predicts that the leading chiral logarithms factorize with respect to the energy dependence in the chiral limit. This claim has been successfully tested in the pion form factors up to two loops in chiral perturbation theory. In the present paper we explain this factorization property at two loops and even show that it is valid to all orders for a subclass of diagrams. We also demonstrate that factorization is violated starting at three loops.Comment: 20 pages, 4 figures. A few misprints corrected and references added, version appeared in JHE

Chiral effective theory with a light scalar and lattice QCD

We extend the usual chiral perturbation theory framework ($\chi$PT) to allow the inclusion of a light dynamical isosinglet scalar. Using lattice QCD results, and a few phenomenological inputs, we explore the parameter space of the effective theory. We discuss the S-wave pion-pion scattering lengths, extract the average value of the two light quark masses and evaluate the impact of the dynamical singlet field in the low--energy constants $\bar{l}_1$, $\bar{l}_3$ and $\bar{l}_4$ of $\chi$PT. We also show how to extract the mass and width of the sigma resonance from chiral extrapolations of lattice QCD data.Comment: Journal version. Added the study of the scalar two-point function and a discussion of the analytical properties of the sigma pole and its dependence on the quark masses. We clarified the relation of $chi$PT$_S$ with unitarized $chi$PT. Figures 6 and 8 have been improved. 28 pages, 2 tables, 8 figure

The late Roman villa of Vilauba and its context: a first report on field-work and excavation in Catalunya, North-East Spain, 1978–81

The first three seasons of a joint Anglo-Catalan research project in north-eastern Spain have concentrated on the Roman villa of Vilauba. It has been shown that the site was occupied for some nine centuries, but the most important discoveries have been the elucidation of substantial phases of occupation from the fifth to seventh centuries A.D., which included in the latest phase a large press building for olive oil. These findings have pointed to the problems of the transition from the Roman to the early medieval period, which have also been met in the field survey of the surrounding region. The medieval settlement pattern had emerged by the ninth or tenth centuries, but its relationship with the Roman pattern remains to be clearly established. Important discoveries have also been made about considerable geomorphological changes in the area, which can be dated to the post-Roman period. A range of techniques have been used in the survey, including recording of standing buildings, geophysical survey and surface collection, which, added to the environmental and pottery studies from the excavation, are shedding important light on the Roman and early medieval rural development of this part of Spain and on the western Mediterranean more generally

Factorization of leading chiral logarithms in the pion form factors

In the recently proposed framework of hard pion chiral perturbation theory, the leading chiral logarithms are predicted to factorize with respect to the energy dependence in the chiral limit. We have scrutinized this assumption in the case of vector and scalar pion form factors FV;S(s) by means of standard chiral perturbation theory and dispersion relations. We show that this factorization property is valid for the elastic contribution to the dispersion integrals for FV;S(s) but it is violated starting at three loops when the inelastic four-pion contributions arise

A scrutiny of hard pion chiral perturbation theory

In the recently proposed framework of hard pion chiral perturbation theory, the leading chiral logarithms are predicted to factorize with respect to the energy dependence in the chiral limit. We have scrutinized this assumption in the case of vector and scalar pion form factors FV;S(s) by means of standard chiral perturbation theory and dispersion relations. We show that this factorization property is valid for the elastic contribution to the dispersion integrals for FV;S(s) but it is violated starting at three loops when the inelastic four-pion contributions arise