Speaker: Christopher Aubin (William and Mary)

Title:
A Tasteless Ghost Story: The $a_0$ in Mixed-Action Lattice QCD

Abstract:
I discuss the calculation of the isovector scalar correlator, 
which is particularly sensitive to lattice artifacts, using 
domain-wall valence quarks on a staggered sea (generated by 
the MILC collaboration). With the mixed-action formalism, 
there are large unphysical contributions which arise due to 
the non-unitary nature of the theory. This can be understood 
using the prediction from chiral perturbation theory determined 
by Prelovsek, which indicates that the leading unitarity 
violations come from taste breaking effects. In particular, 
although these effects cannot be removed from all quantities, 
one can at least show that they are under control, and we can 
theoretically understand their origin.