Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userImproving the lattice axial vector current
206
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
For Wilson and clover fermions traditional formulations of the axial vector current do not respect the continuum Ward identity which relates the divergence of that current to the pseudoscalar density. Here we propose to use a point-split or one-link axial vector current whose divergence exactly satisfies a lattice Ward identity, involving the pseudoscalar density and a number of irrelevant operators. We check in one-loop lattice perturbation theory with SLiNC fermion and gauge plaquette action that this is indeed the case including order $O(a)$ effects. Including these operators the axial Ward identity remains renormalisation invariant. First preliminary results of a nonperturbative check of the Ward identity are also presented.
rate research
Read More
We investigate implications of the use of the point-split axial vector current derived from a Wilson like fermionic action. We compute the corresponding renormalization factor nonperturbatively for one beta value. The axial charge gA calculated from this nonlocal current is found to be nearer to the physical value than computed with the local axial vector current -- computed both on the same lattice with the same action.
Previous lattice QCD calculations of axial vector and pseudoscalar form factors show significant deviation from the partially conserved axial current (PCAC) relation between them. Since the original correlation functions satisfy PCAC, the observed deviations from the operator identity cast doubt on whether all the systematics in the extraction of form factors from the correlation functions are under control. We identify the problematic systematic as a missed excited state, whose energy as a function of the momentum transfer squared, $Q^2$, is determined from the analysis of the 3-point functions themselves. Its mass is much smaller than those of the excited states previously considered and including it impacts the extraction of all the ground state matrix elements. The form factors extracted using these mass/energy gaps satisfy PCAC and other consistency conditions, and validate the pion-pole dominance hypothesis. We also show that the extraction of the axial charge $g_A$ is very sensitive to the value of the mass gaps of the excited states used and current lattice data do not provide an unambiguous determination of these, unlike the $Q^2 eq 0$ case. To highlight the differences and improvement between the conventional versus the new analysis strategy, we present a comparison of results obtained on a physical pion mass ensemble at $aapprox 0.0871,mathrm{fm}$. With the new strategy, we find $g_A = 1.30(6)$. A very significant improvement over previous lattice results is found for the axial charge radius $r_A = 0.74(6),mathrm{fm}$, extracted using the $z$-expansion to parameterize the $Q^2$ behavior of $G_A(Q^2)$, and $g_P^ast = 8.06(44)$ obtained using the pion pole-dominance ansatz to fit the $Q^2$ behavior of the induced pseudoscalar form factor $widetilde{G}_P(Q^2)$.
Using the axial-vector coupling and the electromagnetic form factors of the D and D* mesons in 2+1 flavor Lattice QCD, we compute the D*Dpi, DDrho and D*D*rho coupling constants, which play an important role in describing the charm hadron interactions in terms of meson-exchange models. We also extract the charge radii of D and D* mesons and determine the contributions of the light and charm quarks separately.
We report on a non-perturbative computation of the renormalization factor Z_A of the axial vector current in three-flavour O(a) improved lattice QCD with Wilson quarks and tree-level Symanzik improved gauge action and also recall our recent determination of the improvement coefficient c_A. Our normalization and improvement conditions are formulated at constant physics in a Schrodinger functional setup. The normalization condition exploits the full, massive axial Ward identity to reduce finite quark mass effects in the evaluation of Z_A and correlators with boundary wave functions to suppress excited state contributions in the pseudoscalar channel.
We are calculated the expectation value of the axial-vector current induced by the vacuum polarization effect of the Dirac field in constant external electromagnetic field. In calculations we use Schwingers proper time method. The effective Lagrangian has very simple Lorenz invariant form. Along with the anomaly term, it also contains two Lorenz invariant terms. The result is compared with our previous calculation of the photon - Z boson mixing in the magnetic field.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
