Factorization in graviton scattering and the natural value of the g factor

The factorization property of graviton scattering amplitudes is reviewed and shown to be valid only if the natural value of the gyromagnetic ratio gS=2 is employed—independent of spin

Weak and electromagnetic interactions of hyperons: A chiral approach

A range of issues in the field of weak and electromagnetic interactions of hyperons is presented from the perspective of (broken) chiral symmetry, together with an assessment of where important challenges remain

Effective interactions are effective interactions

In recent years it has been realized that effective interactions—those valid over a limited range of energy-momentum—are often preferable even when more complete theories are available. We shall here present examples of such methods over a range of physical applications—from classical and quantum mechanics, to quantum gravity

Chiral anomaly and eta-eta \u27 mixing

We determine the η-η′ mixing angle via a procedure relatively independent of theoretical assumptions by simultaneously fitting η,η′ reactions involving the anomaly η,η′→γγ, π+π-γ. We extract reasonably precise renormalized values of the octet and singlet pseudoscalar decay constants F8, F0, as well as the mixing angle θ

Electromagnetic properties of nucleons and hyperons in a Lorentz covariant quark model

We calculate magnetic moments of nucleons and hyperons and N -\u3e Delta + gamma transition characteristics using a manifestly Lorentz covariant chiral quark approach for the study of baryons as bound states of constituent quarks dressed by a cloud of pseudoscalar mesons

Decay pi(0)-\u3egamma gamma to next to leading order in chiral perturbation theory

The π0→γγ decay width is analyzed within the combined framework of chiral perturbation theory and the 1/Nc expansion up to O(p6) and O(p4×1/Nc) in the decay amplitude. The η′ is explicitly included in the analysis. It is found that the decay width is enhanced by about 4.5% due to the isospin-breaking induced mixing of the pure U(3) states. This effect, which is of leading order in low energy expansion, is shown to persist nearly unchanged at next to leading order. The chief prediction with its estimated uncertainty is Γπ0→γγ=8.10±0.08eV. This prediction at the 1% level makes the upcoming precision measurement of the decay width even more urgent. Observations on the η and η′ can also be made, especially about their mixing, which is shown to be significantly affected by next to leading order corrections

SU(3) baryon chiral perturbation theory and long distance regularization

The use of SU(3) chiral perturbation theory in the analysis of low energy meson-baryon interactions is discussed. It is emphasized that short distance effects, arising from propagation of Goldstone bosons over distances smaller than a typical hadronic size, are modeldependent and can lead to a lack of convergence in the SU(3) chiral expansion if they are included in loop diagrams. In this paper we demonstrate how to remove such effects in a chirally consistent fashion by use of a cutoff and demonstrate that such removal ameliorates problems which have arisen in previous calculations due to large loop effects

Systematic 1/M expansion for spin 3/2 particles in baryon chiral perturbation theory

Starting from a relativistic formulation of the pion-nucleon-delta system, the most general structure of 1/M corrections for a heavy baryon chiral lagrangian including spin 3/2 resonances is given. The heavy components of relativistic nucleons and delta fields are integrated out and their contributions to the next-to-leaing order lagrangians are constructed explicitly. The effective theory obtained admits a systematic expansion in terms of soft momenta, the pion mass $m_\pi$ and the delta-nucleon mass difference $\Delta$. As an application, we consider neutral pion photoproduction at threshold to third order in this small scale expansion

Coulomb interactions within Halo Effective Field Theory

I present preliminary results of effective field theory applied to nuclear cluster systems, where Coulomb interactions play a significant role.Comment: Talk given at the 20th European Conference on Few-Body Problems in Physics, Pisa, Italy, September 10-14, 200