193 research outputs found
Including electromagnetism in decay calculations
Because of the small size of the ratio A_2/A_0 of the I=2 to I=0 K -> pipi
decay amplitudes (the Delta I=1/2 rule) the effects of electromagnetism on A_2
may be a factor of 20 larger than given by a naive O(alpha) estimate. Thus, if
future calculations of A_2 and epsilon'/epsilon are to achieve 10% accuracy,
these effects need to be included. Here we present the first steps toward
including electromagnetism in a calculation of the standard model K -> pipi
decay amplitudes using lattice QCD.Comment: 8 pages, 1 figures, presented at the 35th International Symposium on
Lattice Field Theory (Lattice 2017
Dirac Spectrum, Axial Anomaly and the QCD Chiral Phase Transition
The QCD phase transition is studied on and lattices
both with and without quark loops. We introduce a new zero-flavor or quenched
species of quark and study the resulting chiral condensate, \azbz as
a function of the mass, . By examining \azbz for we gain considerable information about the spectrum of
Dirac eigenvalues. A comparison of and 0.025 shows little dependence
of the Dirac spectrum on such a light, dynamical quark mass, after an overall
shift in is removed. The presence of sufficient small eigenvalues to
support anomalous chiral symmetry breaking in the high temperature phase is
examined quantitatively. In an effort to enhance these small eigenvalues,
\azbz is also examined in the pure gauge theory in the region of the
deconfinement transition with unexpected results. Above the critical
temperature, the three phases show dramatically different chiral
behavior. Surprisingly, the real phase shows chiral symmetry, suggesting that a
system with one flavor of staggered fermion at will possess a chiral a
phase transition---behavior not expected in the continuum limit.Comment: Contribution to Lattice 95. 8 pages. Latex source file Individual
figures available from [email protected] and also submitted seperately
as figures.uu as required
Relativistic Heavy Quark Effective Action
We study the fermion action needed to accurately describe the low energy
physics of systems including heavy quarks in lattice QCD even when the heavy
fermion mass is on the order of, or larger than, the inverse lattice
spacing: . We carry out an expansion through first order in (where is the heavy quark momentum) and all orders in ,
refining the analysis of the Fermilab and Tsukuba groups. We demonstrate that
the spectrum of heavy quark bound states can be determined accurately through
and for arbitrary exponent by using a lattice action
containing only three unknown coefficients: , and (a
generalization of ), which are functions of . In a companion paper,
we show how these three coefficients can be precisely determined using
non-perturbative techniques.Comment: 40 pages, 1 figur
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