Abdou Abdel-Rehim

Spectrum of quenched twisted mass lattice QCD at maximal twist

Hadron masses are computed from quenched twisted mass lattice QCD for a degenerate doublet of up and down quarks with the twist angle set to {pi}/2, since this maximally-twisted theory is expected to be free of linear discretization errors. Two separate definitions of the twist angle are used, and the hadron masses for these two cases are compared. The flavor breaking, that can arise due to twisting, is discussed in the context of mass splittings within the {delta}(1232) multiplet.

Effects of light scalar mesons in eta ---> three pi decay

We study the role of a possible nonet of light scalar mesons in the still interesting � ! 3� decay process, with the primary motivation of learning more about the scalars themselves. The framework is a conventional non-linear chiral Lagrangian of pseudoscalars and vectors, extended to include the scalars. The parameters involving the scalars were previously obtained to fit the s-wave �� and �K scatterings in the region up to about 1 GeV as well as the strong decay � ! ���. At first, one might expect a large enhancement from diagrams including a light �(560). However there is an amusing cancellation mechanism which prevents this from occurring. In the simplest model there is an enhancement of about 13 per cent in the � ! 3� decay rate due to the scalars. In a more complicated model which includes derivative type symmetry breakers, the cancellation is modified and the scalars contribute about 30 percent of the total decay rate (although the total is not significantly changed). The vectors do not contribute much. Our model produces a reasonable estimate for the related a0(980) f0(980) mixing strength, which has been a topic of current debate. Promising directions for future work along the present line are suggested.

Chiral Lagrangian Treatment of the Scalar Mesons: an Overview

In this talk a brief overview of the chiral Lagrangian framework for scalar mesons of refs. [1, 2, 3, 4, 5, 6, 7, 8] together with several low energy processes that have been studied in this framework, is presented.

TWISTED MASS LATTICE QCD AND HADRON PHENOMENOLOGY

Lattice QCD simulations with a twisted mass term (tmLQCD) offer solutions to problems associated with simulations using Wilson fermions and a standard mass term. A summary of recent results from quenched simulations using tmLQCD at maximal twist for the pion form factor and hadron spectrum is presented.

Effect of light scalar mesons in η → 3π

We discuss the decay η → 3π, for which the observed branching ratio is larger than the simplest predictions from chiral symmetry. This process occurs primarily due to strong isospin violation and so is in principle a sensitive measure of the up‐down quark mass difference. We study the role of a possible nonet of light scalar mesons in the η → 3π decay. Using a non‐linear chiral Lagrangian approach which successfully describes several other strong processes, we find that the inclusion of the scalar mesons leads to a modest increase relative to the simplest prediction. The main effect of the scalar mesons is due to a light broad σ meson.

Role of light scalar mesons in η, η' → 3π

We study the role of a light scalar nonet in the interesting decay η → 3π. The framework is a Chiral effective Lagrangian of pseudo‐scalars, scalars and vectors. At leading order , the scalars increase the predicted width by about 14%. We note that although individual scalar contributions are not small, there are cancellations among the scalar diagrams. Including higher order symmetry breaking terms reduce the amount of cancellations among the scalar diagrams but the total predicted width remain the same. The vectors contribution is found to be very small. A preliminary discussion of the related decay η′ → 3π is given. We found that the leading order results of pseudo‐scalars alone are reasonable and close to the experimental data. Including the scalars or the vectors gives a huge enhancement indicating the importance of higher order corrections in this case.

Comparing linear sigma model K‐matrix studies of σ/f0 and the Higgs boson

We present a description of the low energy ππ scattering data using the Linear Sigma Model with K‐matrix unitarization. Then we carry out an analogous study of the strongly‐coupled minimal Higgs sector of the electroweak theory. We discuss the effect of the unitarization prescription on the WW or ZZ fusion processes and also suggest a related treatment for other Higgs production processes such as gluon fusion.