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Register a new userDerivation of Luschers finite size formula for $Npi$ and $NN$ system
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N. Ishizuka
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I present derivation of Luschers finite size formula for the elastic $Npi$ and the $NN$ scattering system for several angular momenta from the relativistic quantum field theory.
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A sanity check rules out certain types of obviously false results, but does not catch every possible error. After reviewing such a sanity check for $NN$ bound states with the Luschers finite volume formula[1-3], we give further evidences for the operator dependence of plateaux, a symptom of the fake plateau problem, against the claim in [4]. We then present our critical comments on [5] by NPLQCD: (i) Operator dependences of plateaux in NPL2013[6,7] exist with the $P$-values of 4--5%. (ii) The volume independence of plateaux in NPL2013 does not prove their correctness. (iii) Effective range expansion (ERE) fits in NPL2013 violate the physical pole condition. (iv) Ref.[5] is partly based on new data and analysis different from the original ones[6,7]. (v) A new ERE in Refs.[5,8] does not satisfy the Luschers finite volume formula. [1] T. Iritani et al., JHEP 10 (2016) 101. [2] S. Aoki et al., PoS (LATTICE2016) 109. [3] T. Iritani et al., 1703.0720. [4] T. Yamazaki et al., PoS (LATTICE2017) 108. [5] S.R. Beane et al., 1705.09239. [6] S.R. Beane et al., PRD87 (2013) 034506. [7] S.R. Beane et al., PRC88 (2013) 024003. [8] M.L. Wagman et al., 1706.06550.
We investigate an application of twisted boundary conditions for study of low-energy hadron-hadron interactions with Lushcers finite size method. It allows us to calculate the phase shifts for elastic scattering of two hadrons at any small value of the scattering momentum even in a finite volume. We then can extract model independent information of low-energy scattering parameters such as the scattering length, the effective range and the effective volume from the $S$-wave and $P$-wave scattering phase shifts through the effective range expansion. This approach also enables us to examine the existence of near-threshold and narrow resonance states, of which characteristic is observed in many of newly discovered charmonium-like $XYZ$ mesons. As a simple example, we demonstrate our method for low-energy $J/psi$-$phi$ scatterings to search for Y(4140) resonance using 2+1 flavor PACS-CS gauge configurations at the lightest pion mass, $m_{pi}=156$ MeV.
On the basis of the Luschers finite volume formula, a simple test (consistency check or sanity check) is introduced and applied to inspect the recent claims of the existence of the nucleon-nucleon ($NN$) bound state(s) for heavy quark masses in lattice QCD. We show that the consistency between the scattering phase shifts at $k^2 > 0$ and/or $k^2 < 0$ obtained from the lattice data and the behavior of phase shifts from the effective range expansion (ERE) around $k^2=0$ exposes the validity of the original lattice data, otherwise such information is hidden in the energy shift $Delta E$ of the two nucleons on the lattice. We carry out this sanity check for all the lattice results in the literature claiming the existence of the $NN$ bound state(s) for heavy quark masses, and find that (i) some of the $NN$ data show clear inconsistency between the behavior of ERE at $k^2 > 0$ and that at $k^2 < 0$, (ii) some of the $NN$ data exhibit singular behavior of the low energy parameter (such as the divergent effective range) at $k^2<0$, (iii) some of the $NN$ data have the unphysical residue for the bound state pole in S-matrix, and (iv) the rest of the $NN$ data are inconsistent among themselves. Furthermore, we raise a caution of using the ERE in the case of the multiple bound states. Our finding, together with the fake plateau problem previously pointed out by the present authors, brings a serious doubt on the existence of the $NN$ bound states for pion masses heavier than 300 MeV in the previous studies.
In this comment, we address a number of erroneous discussions and conclusions presented in a recent preprint by the HALQCD collaboration, arXiv:1703.07210. In particular, we demonstrate that lattice QCD determinations of bound states at quark masses corresponding to a pion mass of $m_pi = 806$ MeV are robust, and that the phases shifts extracted by the NPLQCD collaboration for these systems pass all of the sanity checks introduced in arXiv:1703.07210.
Determinations of the couplings of $N N (n pi) (n geq 1)$ are reported. The study is based on both a quark model of nucleon and a chiral field theory of mesons. The coupling of $N N pi$ is predicted and is in agreement with current value. It shows that the coupling $ N N 2 pi $ is resulted in the nature that pion is a Goldstone boson. The couplings of $N N (n pi) (n geq 2)$ are predicted by this approach.
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