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Register a new userQuark mass dependence of nucleon mass and axial-vector coupling constant
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We present an updated analysis of the quark mass dependence of the nucleon mass and nucleon axial-vector coupling g_A, comparing different formulations of SU(2) Baryon Chiral Effective Field Theory, with and without explicit delta (1232) degrees of freedom. We discuss the outcome of the corresponding interpolations between lattice QCD data and the physical values for these two nucleon observables. It turns out that in order to obtain successful interpolating functions at one-loop order, the inclusion of explicit delta (1232) degrees of freedom is not decisive for the nucleon mass but crucial for g_A. A chiral extrapolation of recent lattice results by the LHP collaborations is also shown.
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We examine the quark mass dependence of the pion vector form factor, particularly the curvature (mean quartic radius). We focus our study on the consequences of assuming that the coupling constant of the rho to pions is largely independent of the quark mass while the quark mass dependence of the rho--mass is given by recent lattice data. By employing the Omnes representation we can provide a very clean estimate for a certain combination of the curvature and the square radius, whose quark mass dependence could be determined from lattice computations. This study provides an independent access to the quark mass dependence of the rho-pi-pi coupling and in this way a non-trivial check of the systematics of chiral extrapolations. We also provide an improved value for the curvature for physical values for the quark masses, namely <r^4> = 0.73 +- 0.09 fm^4 or equivalently c_V=4.00pm 0.50 GeV^{-4}.
We present state-of-the-art results from a lattice QCD calculation of the nucleon axial coupling, $g_A$, using Mobius Domain-Wall fermions solved on the dynamical $N_f = 2 + 1 + 1$ HISQ ensembles after they are smeared using the gradient-flow algorithm. Relevant three-point correlation functions are calculated using a method inspired by the Feynman-Hellmann theorem, and demonstrate significant improvement in signal for fixed stochastic samples. The calculation is performed at five pion masses of $m_pisim {400, 350, 310, 220, 130}$~MeV, three lattice spacings of $asim{0.15, 0.12, 0.09}$~fm, and we do a dedicated volume study with $m_pi Lsim{3.22, 4.29, 5.36}$. Control over all relevant sources of systematic uncertainty are demonstrated and quantified. We achieve a preliminary value of $g_A = 1.285(17)$, with a relative uncertainty of 1.33%.
We carry out a perturbative determination of mass dependent renormalization factors and $O(a)$ improvement coefficients for the vector and axial vector currents with a relativistic heavy quark action, which we have designed to control $m_Qa$ errors by extending the on-shell $O(a)$ improvement program to the case of $m_Q gg Lambda_{rm QCD}$ with $m_Q$ the heavy quark mass. We discuss what kind of improvement operators are required for the heavy-heavy and the heavy-light cases under the condition that the Euclidean rotational symmetry is not retained anymore because of the $m_Qa$ corrections. Our calculation is performed employing the ordinary perturbation theory with the fictitious gluon mass as an infrared regulator. We show that all the improvement coefficients are determined free from infrared divergences. Results of the renormalization factors and the improvement coefficients are presented as a function of $m_Q a$ for various improved gauge actions as well as the plaquette action.
Nucleon isovector vector, $g_V$, and axialvector, $g_A$, charges calculated on a 2+1-flavor dynamical domain-wall-fermions (DWF) ensemble at physical mass jointly generated by RIKEN-BNL-Columbia (RBC) and UKQCD Collaborations with lattice cut off of 1.730(4) GeV, are reported with about a percent statistical errors, along with isovector ``scalar, $g_S$, and ``tensor charges, $g_T$, with larger statistical errors. Nucleon mass is estimated as 947(6) MeV. A few standard-deviation systematics is seen in the vector charge, likely from $O(a^2)$ discretization error through small excited-state contamination. The axialvector charge is found with a few to several standard-deviation systematic deficit, depending on calculation methods, in comparison with the experiment. Nucleon signal is likely lost as early as 10 lattice units or about 1.1 fm in time from the source.
Lattice QCD in a dual formulation with staggered fermions is well established in the strong coupling limit and allows to perform Monte Carlo simulations at finite baryon chemical potential. We have recently addressed the dependence of the nuclear critical end point as a function of the quark mass $am_q$, and separately as a function of the lattice gauge coupling $beta$ in the chiral limit. Here we proceed to determine the dependence of the nuclear transition on both, $am_q$ and $beta$, on isotropic lattices and attempt to pinpoint the critical end point for various $beta$ where the sign problem is still manageable.
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