We present a valence calculation of the electric polarizability of the neutron, neutral pion, and neutral kaon on two dynamically generated nHYP-clover ensembles. The pion masses for these ensembles are 227(2) MeV and 306(1) MeV, which are the lowest
ones used in polarizability studies. This is part of a program geared towards determining these parameters at the physical point. We carry out a high statistics calculation that allows us to: (1) perform an extrapolation of the kaon polarizability to the physical point; we find $alpha_K =0.269(43)times10^{-4}$fm$^{3}$, (2) quantitatively compare our neutron polarizability results with predictions from $chi$PT, and (3) analyze the dependence on both the valence and sea quark masses. The kaon polarizability varies slowly with the light quark mass and the extrapolation can be done with high confidence.
A direct calculation of the mixed-action parameter $Delta_{mix}$ with valence overlap fermions on a domain-wall fermion sea is presented. The calculation is performed on four ensembles of the 2+1-flavor domain-wall gauge configurations: $24^3 times 6
4$ ($a m_l= 0.005$, $a=0.114fm$) and $32^3 times 64$ ($a m_l = 0.004, 0.006, 0.008$, $a=0.085fm$). For pion masses close to $300MeV$ we find hbox{$Delta_{mix}=0.030(6)GeV^4$} at $a=0.114fm$ and $Delta_{mix}=0.033(12)GeV^4$ at $a=0.085fm$. The results are quite independent of the lattice spacing and they are significantly smaller than the results for valence domain-wall fermions on Asqtad sea or those of valence overlap fermions on clover sea. Combining the results extracted from these two ensembles, we get $Delta_{mix}=0.030(6)(5)GeV^4$, where the first error is statistical and the second is the systematic error associated with the fitting method.
