The baryon axial vector current is computed at one-loop order in heavy baryon chiral perturbation theory in the large-Nc limit, where Nc is the number of colors. Loop graphs with octet and decuplet intermediate states cancel to various orders in Nc as a consequence of the large-Nc spin-flavor symmetry of QCD baryons. These cancellations are explicitly shown for the general case of N f flavors of light quarks. In particular, a new generic cancellation is identified in the renormalization of the baryon axial vector current at one-loop order. A comparison with conventional heavy baryon chiral perturbation theory is performed at the physical values Nc = 3, N f = 3.
Nonrelativistic systems exhibiting collective magnetic behavior are analyzed in the framework of effective Lagrangians. The method, formulating the dynamics in terms of Goldstone bosons, allows to investigate the consequences of spontaneous symmetry breaking from a unified point of view. Low energy theorems concerning spin-wave scattering in ferro-and antiferromagnets are established, emphasizing the simplicity of actual calculations. The present work includes approximate symmetries and discusses the modification of the low energy structure imposed by an external magnetic and an anisotropy field, respectively. Throughout the paper, analogies between condensed matter physics and Lorentz-invariant theories are pointed out, demonstrating the universal feature of the effective Lagrangian technique.
We show how to compute loop graphs in heavy baryon chiral perturbation theory including the full functional dependence on the ratio of the Delta-nucleon mass difference to the pion mass, while at the same time automatically incorporating the 1/N c cancellations that follow from the large-N c spin-flavor symmetry of baryons in QCD. The one-loop renormalization of the baryon axial vector current is studied to demonstrate the procedure. A new cancellation is identified in the one-loop contribution to the baryon axial vector current. We show that loop corrections to the axial vector currents are exceptionally sensitive to deviations of the ratios of baryon-pion axial couplings from SU (6) values.
The quantum dimer model on the square lattice is equivalent to a U (1) gauge theory. Quantum Monte Carlo calculations reveal that, for values of the Rokhsar-Kivelson (RK) coupling λ < 1, the theory exists in a confining columnar phase. The interfaces separating distinct columnar phases display plaquette order, which, however, is not realized as a bulk phase. Static "electric" charges are confined by flux tubes that consist of multiple strands, each carrying a fractionalized flux 1 4 . A soft pseudo-Goldstone mode emerges around λ ≈ 0, long before one reaches the RK point at λ = 1.
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