arXiv subjects
Publications and source records attributed to R. Gupta.
We give here a compilation of papers presented at Lattice 2000 (XVIII Intl. Symposium on Lattice Field Theory, Bangalore, India, 17-22 August 2000). The table of contents provides links to papers on the e-print arXiv.
Artificial neural networks are algorithms which have been developed to tackle a range of computational problems. These range from modelling brain function to making predictions of time-dependent phenomena to solving hard (NP-complete) problems. In this introduction we describe a single, yet very important, type of network known as a feedforward network. This network is a mathematical model which can be trained to learn an arbitrarily complex relationship between a data and a parameter domain, so can be used to solve interpolation and classification problems. We discuss the structure, training and interpretation of these networks, and their implementation, taking the classification of stellar spectra as an example.
We describe how the improvement of quark bilinears generalizes from quenched to unquenched QCD, and discuss which of the additional improvement constants can be determined using Ward Identities.
We impose the axial and vector Ward identities on local fermion bilinear operators in the Sheikholesalami-Wohlert discretization of fermions. From this we obtain all the coefficients needed to improve the theory at O(a), as well as the scale and scheme independent renormalization constants, Z_A, Z_V and Z_S/Z_P.
We extend the application of vector and axial Ward identities to calculate $b_A$, $b_P$ and $b_T$, coefficients that give the mass dependence of the renormalization constants of the corresponding bilinear operators in the quenched theory. The extension relies on using operators with non-degenerate quark masses. It allows a complete determination of the $O(a)$ improvement coefficients for bilinears in the quenched approximation using Ward Identities alone. Only the scale dependent normalization constants $Z_P^0$ (or $Z_S^0$) and $Z_T$ are undetermined. We present results of a pilot numerical study using hadronic correlators.
Preliminary results from an extensive lattice calculation of the B, B_c, and Υspectrum at quenched β= 6.0 are presented. The study includes radially and orbitally excited mesons, and baryons containing b quarks. The b quarks are formulated using NRQCD; for light and c quarks, a tadpole-improved clover action is used.
We present quenched results for B meson decay constants using NRQCD b quarks and O(a) tadpole improved clover light quarks. For the first time, one-loop matching factors between lattice and continuum currents are incorporated through O(α/M) taking operator mixing fully into account. This includes an important O(αa) discretization correction to the heavy-light axial vector current. We find f_B = 0.147(11)(^{+8}_{-12})(9)(6) MeV and f_{B_s}/f_B = 1.20(4)(^{+4}_{-0}). PACS numbers: 12.38.Gc, 12.39.Hg, 13.20.He, 14.40.Nd
We present results on the spectrum of B and D mesons including radial excitations and discuss the pseudoscalar decay constant. The results are obtained at beta=5.7 in the quenched approximation using NRQCD for the heavy quark. To study scaling violations we also compare to results obtained at beta=6.0.
We present estimates of light quarks masses using lattice data. Our main results are based on a global analysis of all the published data for Wilson and Staggered fermions, both in the quenched approximation and with $n_f=2$ dynamical flavors. The Wilson and Staggered results agree after extrapolation to the continuum limit for both the $n_f=0,2$ theories. Our best estimates, in the MSbar scheme at scale $2 GeV$, are $mbar=3.2(4) MeV$ and $m_s = 90(20) MeV$ in the quenched approximation, and $mbar ~ 2.7 MeV$ and $m_s ~ 70 MeV$ for the $n_f=2$ theory. These estimates are significantly smaller than phenomenological estimates based on sum rules, but maintain the ratios predicted by chiral perturbation theory. Along with the new estimates of 4-fermion operators, lower quark masses have a significant impact on the extraction of $ε'/ε$ from the Standard Model.
Muon Colliders have unique technical and physics advantages and disadvantages when compared with both hadron and electron machines. They should thus be regarded as complementary. Parameters are given of 4 TeV and 0.5 TeV high luminosity μ^+ μ^- colliders, and of a 0.5 TeV lower luminosity demonstration machine. We discuss the various systems in such muon colliders, starting from the proton accelerator needed to generate the muons and proceeding through muon cooling, acceleration and storage in a collider ring. Detector background, polarization, and nonstandard operating conditions are discussed.
We study a class of 2D non-equilibrium Ising models based on competing dynamics induced by contact with heat-baths at two different temperatures. We make a comparative study of the non-equilibrium versions of Metropolis, heat bath/Glauber and Swendsen-Wang dynamics and focus on their critical behavior in order to understand their universality classes. We present strong evidence that some of these dynamics have the same critical exponents and belong to the same universality class as the equilibrium 2D Ising model. We show that the bond version of the Swendsen-Wang update algorithm can be mapped into an equilibrium model at an effective temperature.
Results for semi-leptonic form-factors for processes like $D \to K l ν$ and the Bethe-Salpeter amplitudes (BSA) for pion and rho mesons are presented. The form-factor data is consistent with previous calculations. We find that the long distance fall-off of BSA for both $π$ and $ρ$ is very well fit by an exponential, but surprisingly the effective mass governing this fall-off is lighter than the pion's. Lastly, by studying the dependence of $ρ$ polarization on separation direction we show that there is a measureable $l=2$ state in addition to $l=0$ in the BSA for the rho. (Talk presented by R. Gupta at LATTICE92. Latex needs macro package espcrc2.sty)
We investigate the use of two types of non-local (``smeared'') sources for quark propagators in quenched lattice QCD at $β=6.0$ using Wilson fermions at $κ=0.154$ and $0.155$. We present results for the hadron mass spectrum, meson decay constants, quark masses, the chiral condensate and the quark distribution amplitude of the pion. The use of smeared sources leads to a considerable improvement over previous results. We find a disturbing discrepancy between the baryon spectra obtained using Wuppertal and wall sources. We find good signals in the ratio of correlators used to calculate the quark mass and the chiral condensate and show that the extrapolation to the chiral limit is smooth.