Study of pentaquarks on the lattice with overlap fermions

Abstract

We present a quenched lattice QCD calculation of spin-1/2 five-quark states with uudds quark content for both positive and negative parities. We do not observe any bound pentaquark state in these channels for either I = 0 or I = 1. The states we found are consistent with KN scattering states which are checked to exhibit the expected volume dependence of the spectral weight. The results are based on overlap-fermion propagators on two lattices, 12 3 × 28 and 16 3 × 28, with the same lattice spacing of 0.2 fm, and pion mass as low as ∼ 180 MeV.

Scalar glueball, scalar quarkonia, and their mixing

“…Possible SU(3) breaking effects are characterized by the subscripts "s" and "ss". As noticed in passing, lattice calculations [6] of the a 0 (1450) and K * 0 (1430) masses indicate a good SU(3) symmetry for the scalar meson sector above 1 GeV. This means that M S should be close to M U or M D .…”

“…It goes further in [26] to assume that the observed heavy scalar mesons form another 4-quark nonet. We note, however, the quenched lattice calculations in [6], which presumably gives the bare qq states before mixing with q 2q2 via sea quark loops in the dynamical fermion calculation, already seem to suggest the near degenercy between a 0 (1450) and K * 0 (1430).…”

“…This suggests that M G should be close to 1700 MeV rather than 1500 MeV [2] from the earlier lattice calculations 1 . Second, the recent quenched lattice calculation of the isovector scalar meson a 0 mass has been carried out for a range of low quark masses [6]. With the lowest one corresponding to m π as low as 180 MeV, it is found that, when the quark mass is smaller than that of the strange, a 0 mass levels off, in contrast to those of a 1 and other hadrons that have been calculated on the lattice.…”

“…[20] seriously. We shall rely on the conclusion from the other calculations in both the quenched and unquenched calculations [6,7,8,9,10]. light scalar nonet is known to have a reversed ordering, namely, the scalar strange meson κ is lighter than the non-strange one such as f 0 (980), it has been proposed in [25] to consider the mixing of the qq heavy scalar nonet with the light nonet to make a 0 (1450) and K * 0 (1430) closer.…”

“…However, there are several serious problems with this scenario. First, the isovector scalar meson a 0 (1450) is confirmed to be a qq meson in lattice calculations [6,7,8,9, 10] which will be discussed later. As such, the degeneracy of a 0 (1450) and K * 0 (1430), which has a strange quark, cannot be explained if M S is larger than M N by ∼ 250 MeV.…”