arXiv subjects

Rajan Gupta

Publications and source records attributed to Rajan Gupta.

152 records · Page 9Linked to original sources

arXiv1995

Topological Density and Instantons on a Lattice

We present an update on the study of topological structure of QCD. Issues addressed include a comparison between the plaquette and the geometric methods of calculating the topological density. We show that the improved gauge action based on sqrt(3) blocking transformation suppresses the formation of topologically charged dislocations with low action. Using a cooling method we identify the instantons' location, estimate their size and density, and calculate the renormalization constant Z_Q for the plaquette method.

hep-lat↗

arXiv1994

Semi-leptonic form-factors from lattice qcd

We present results for semi-leptonic form-factors obtained on a statistical sample of $66$ $32^3 \times 64$ lattices at $β= 6.0$ using quenched Wilson fermions. We find $f_+^{D \to K l ν}(q^2 = 0) = 0.73 \pm 0.06$, $A_2/A_1({D \to K^* l ν}) = 0.72 \pm 0.22$, $V/A_1({D_s \to ϕl ν}) = 1.91 \pm 0.04$, and $A_2/A_1({D_s \to ϕl ν}) = 0.68 \pm 0.09$, where the error estimate includes statistical errors and errors due to extrapolation to $q^2 =0$ and to physical values of $(m_u + m_d)/2$ and $m_s$. The remaining sources of systematic errors are those due to $O(a)$ discretization errors and those due to quenching, which our results indicate may be small. We also comment on the validity of pole-dominance in these form-factors. Source available from http://nqcd.lanl.gov/Lattice_QCD/papers/dpf94/

hep-ph↗

arXiv1994

A pot-pourri of results in QCD from large lattice simulations on the CM5

We present a status report on simulations being done on $32^3 \times 64$ lattices at $β= 6.0$ using quenched Wilson fermions. Results for the spectrum, decay constants, the kaon B-parameter $B_K$, and semi-leptonic form factors are given based on the current statistical sample of 28 configurations. These ``Grand Challenge'' calculations are being done on the CM5 at Los Alamos in collaboration with G. Kilcup, S. Sharpe and P. Tamayo. We end with a brief statement of code performance.

hep-lat↗

arXiv1993

Geometric Measurement of Topological Susceptibility on Large Lattices

The topological susceptibility of the quenched QCD vacuum is measured on large lattices for three $β$ values from $6.0$ to $6.4$. Charges possibly induced by $O(a)$ dislocations are identified and shown to have little effect on the measured susceptibility. As $β$ increases, fewer such questionable charges are found. Scaling is checked by examining the ratios of the susceptibility to previously existing values of the rho mass, string tension, F-pi, and lambda-lattice.

hep-lat↗

arXiv1993

Semileptonic form factors of heavy-light mesons from lattice QCD

The form factors for the semileptonic decays of heavy-light pseudoscalar mesons of the type $D \to Keν$ are studied in quenched lattice QCD at $β=6.0$ using Wilson fermions. We explore new numerical techniques for improving the signal and study $O(a)$ corrections using three different lattice transcriptions of the vector current. We present a detailed discussion of the relation of these lattice currents to the continuum vector current and show that the disagreement between the previous results is to a large extent due to the value of $Z_V$ used in the calculations. We also present results for the decay constants of light-light, heavy-light and heavy-heavy mesons.

hep-lat↗

arXiv1993

Calculations of hadronic matrix elements using lattice qcd

I give a brief introduction to the scope of lattice QCD calculations in our effort to extract the fundamental parameters of the standard model. This goal is illustrated by two examples. First I discuss the extraction of CKM matrix elements from measurements of form factors for semi-leptonic decays of heavy-light pseudoscalar mesons such as $D \to Keν$. Second, I present the status of results for the kaon $B$ parameter relevant to CP violation. I conclude the talk with a short outline of our experiences with optimizing QCD codes on the CM5.

hep-lat↗

arXiv1993

Bethe-Salpeter Amplitudes and Density Correlations for Mesons with Wilson Fermions

We present an investigation of various gauge invariant definitions of the $q\bar q$ Bethe-Salpeter (BS) amplitude for mesons in lattice QCD, and compare them to the Coulomb and Landau gauge BS amplitudes. We show that the gauge invariant BS amplitude is considerably broadened by the use of ``fat'' gauge links (constructed by smearing the links of the original lattice). A qualitative demonstration of the Lorentz contraction of the pion wavefunction at non-zero momentum is given. We also calculate density-density correlations and discuss the limitations in extracting the charge radius of the pion from these observables. Lastly, the polarization dependence of the BS amplitude for the $ρ$ meson is exhibited, and we extract the relative admixture of $l=0$ and $l=2$ states showing that simple hydrogen-like wavefunctions provide a good fit.

hep-lat↗

arXiv1993

$I=2$ pion scattering amplitude with Wilson fermions

We present an exploratory calculation of the $I=2$ $π-π$ scattering amplitude at threshold using Wilson fermions in the quenched approximation, including all the required contractions. We find good agreement with the predictions of chiral perturbation theory even for pions of mass 560-700 MeV. Within the 10\% errors, we do not see the onset of the bad chiral behavior expected for Wilson fermions. We also derive rigorous inequalities that apply to 2-particle correlators and as a consequence show that the interaction in the antisymmetric state of two pions has to be attractive.

hep-lat↗