Investigating and optimizing the chiral properties of lattice fermion actions

We study exceptional modes of both the Wilson and the clover action in order to understand why quenched clover spectroscopy suffers so severely from exceptional configurations, We show that, in contrast to the case of the Wilson action, a large clover coefficient can make the exceptional modes extremely localized and thus very sensitive to short distance fluctuations. We describe a way to optimize the chiral behavior of Wilson-type lattice fermion actions by studying their low energy real eigenmodes. We find a candidate action, the clover action with fat links with a tuned clover term. We present a calculation of spectroscopy and matrix elements at Wilson gauge coupling beta = 5.7. When compared to simulations with the standard (non-perturbatively improved) clover action at small lattice spacing, the action shows good scaling behavior, with an apparent great reduction in the number of exceptional configurations. (C) 1999 Published by Elsevier Science B.V.