Weonjong Lee

Partial flavor symmetry restoration for chiral staggered fermions

We study the leading discretization errors for staggered fermions by first constructing the continuum effective Lagrangian, including terms of O(a{sup 2}), and then constructing the corresponding effective chiral Lagrangian. The terms of O(a{sup 2}) in the continuum effective Lagrangian completely break the SU(4) flavor symmetry down to the discrete subgroup respected by the lattice theory. We find, however, that the O(a{sup 2}) terms in the potential of the chiral Lagrangian maintain an SO(4) subgroup of SU(4). It follows that the leading discretization errors in the pion masses are SO(4) symmetric, implying three degeneracies within the seven lattice irreducible representations. These predictions hold also for perturbatively improved versions of the action. These degeneracies are observed, to a surprising degree of accuracy, in existing data. We argue that the SO(4) symmetry does not extend to the masses and interactions of other hadrons (vector mesons, baryons, etc.) or to higher order in a{sup 2}. We show how it is possible that, for physical quark masses of O(a{sup 2}), the new SO(4) symmetry can be spontaneously broken, leading to a staggered analogue of the Aoki phase of Wilson fermions. This does not, however, appear to happen for presently studied versions of the staggered action.morexa0» (c) 1999 The American Physical Society.«xa0less

Breakdown of cluster decomposition in instanton calculations of the gluino condensate

Abstract A longstanding puzzle concerns the calculation of the gluino condensate tr λ 2 16π 2 =cΛ 3 in N =1 supersymmetric SU ( N ) gauge theory: so-called weak-coupling instanton (WCI) calculations give c =1, whereas strong-coupling instanton (SCI) calculations give, instead, c=2 (N−1)!(3N−1) −1/N . By examining correlators of this condensate in arbitrary multi-instanton sectors, we cast serious doubt on the SCI calculation of tr λ 2 16π 2 by showing that an essential step—namely cluster decomposition—is invalid. We also show that the addition of a so-called Kovner-Shifman vacuum (in which tr λ 2 16π 2 =0 ) cannot straightforwardly resolve this mismatch.

Weak matrix elements for CP violation.

We present preliminary results of matrix elements of four fermion operators relevant to the determination of e and E / E using staggered fermions. To calculate the matrix elements relevant to CP violation in Kaon decays it is important to use a lattice formulation which preserves (some) chiral symmetry.

Scaling behavior of improvement and renormalization constants.

This talk summarizes results for all the scale independent renormalization constants for bilinear currents ( Z A, ZV, and Zs/Zp), the improvement constants (CA, CV, and CT), the quark mass dependence of 20, and the coefficients of the equation of motion operators for O(a) improved lattice QCD. Using data at p = 6.0, 6.2 and 6.4 we study the scaling behavior of these quantities and quantify residual discretization errors.

One-loop matching coefficients for improved staggered bilinears

We calculate one-loop matching factors for bilinear operators composed of improved staggered fermions. We compare the results for different improvement schemes used in the recent literature, all of which involve the use of smeared links. These schemes aim to reduce, though not completely eliminate,

NON-PERTURBATIVE RENORMALIZATION CONSTANTS USING WARD IDENTITIES

{O(a}^{2})

Kaon mixing matrix elements from beyond-the-standard-model operators in staggered chiral perturbation theory

discretization errors. We find that all these improvement schemes substantially reduce the size of matching factors compared to unimproved staggered fermions. The resulting corrections are comparable to, or smaller than, those found with Wilson and domain-wall fermions. In the best case (``Fat-7 and mean-field improved hypercubic fat links) the corrections are

Non-perturbative improvement of bilinears in unquenched QCD

10%

Perturbative matching of the staggered four-fermion operators for {epsilon}'/{epsilon}

or smaller at

Order a improved renormalization constants

1/a=2mathrm{GeV}.