arXiv subjects

D. Du

Publications and source records attributed to D. Du.

25 records · Page 2Linked to original sources

arXiv2012

Two-point Correlator Fits on HISQ Ensembles

We present our methods to fit the two point correlators for light, strange, and charmed pseudoscalar meson physics with the highly improved staggered quark (HISQ) action. We make use of the least-squares fit including the full covariance matrix of the correlators and including Gaussian constraints on some parameters. We fit the correlators on a variety of the HISQ ensembles. The lattice spacing ranges from 0.15 fm down to 0.06 fm. The light sea quark mass ranges from 0.2 times the strange quark mass down to the physical light quark mass. The HISQ ensembles also include lattices with different volumes and with unphysical values of the strange quark mass. We use the results from this work to obtain our preliminary results of $f_D$, $f_{D_s}$, $f_{D_s}/f_{D}$, and ratios of quark masses presented in another talk [1].

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arXiv2012

Charm semileptonic decays and |V_{cs(d)}| from heavy clover quarks and 2+1 flavor asqtad staggered ensembles

By combining experimentally measured partial branching fractions for the semileptonic decays D to K l nu and D to pi l nu with lattice calculations of the form factors f_+^{D to K}(q^2) and f_+^{D to pi}(q^2), one can extract the CKM matrix elements |V_{cs}| and |V_{cd}|. We are calculating the form factors by using Fermilab charm and asqtad staggered light and strange quarks on 2+1 flavor asqtad staggered ensembles generated by the MILC Collaboration. We vary the light valence quark masses from 0.4m_s to 0.05m_s (m_s is the strange sea-quark mass), and the lattice spacings, from about 0.12 fm to about 0.045 fm. We extrapolate to the physical light-quark mass and the continuum limit using heavy-light meson staggered chiral perturbation theory about the SU(2) and SU(3) limits, compare the resulting (preliminary) form factor shapes with experiment, and discuss our errors.

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arXiv2012

Kaon semileptonic decay form factors with HISQ valence quarks

We report on the status of our kaon semileptonic form factor calculations using the highly-improved staggered quark (HISQ) formulation to simulate the valence fermions. We present results for the form factor f_+^{K π}(0) on the asqtad N_f=2+1 MILC configurations, discuss the chiral-continuum extrapolation, and give a preliminary estimate of the total error. We also present a more preliminary set of results for the same form factor but with the sea quarks also simulated with the HISQ action; these results include data at the physical light quark masses. The improvements that we expect to achieve with the use of the HISQ configurations and simulations at the physical quark masses are briefly discussed.

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arXiv2012

Pseudoscalar meson physics with four dynamical quarks

We present preliminary results for light, strange and charmed pseudoscalar meson physics from simulations using four flavors of dynamical quarks with the highly improved staggered quark (HISQ) action. These simulations include lattice spacings ranging from 0.15 to 0.06 fm, and sea-quark masses both above and at their physical value. The major results are charm meson decay constants f_D, f_{D_s} and f_{D_s}/f_D and ratios of quark masses. This talk will focus on our procedures for finding the decay constants on each ensemble, the continuum extrapolation, and estimates of systematic error.

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arXiv2007

Fisher's Zeros and Perturbative Series in Gluodynamics

We study the zeros of the partition function in the complex beta plane (Fisher's zeros) in SU(2) and SU(3) gluodynamics. We discuss their effects on the asymptotic behavior of the perturbative series for the average plaquette. We present new methods to infer the existence of these zeros in region of the complex beta plane where MC reweighting is not reliable. These methods are based on the assumption that the plaquette distribution can be approximated by a phi^4 type distribution. We give new estimates of the locations for a 4^4 lattice. For SU(2), we found zeros at beta =2.18(1) \pm i0.18(2) (which differs from previous estimates), and at beta =2.18(1) \pm i0.22(2). For SU(3), we confirm beta =5.54(2)\pm i0.10(2) and found additional zeros at beta =5.54(2)\pm i0.16(2). Some of the technical material can be found in recent preprints, in the following we emphasize the motivations (why it is important to know the locations of the zeros) and the challenges (why it is difficult to locate the zeros when the volume increases)

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arXiv2007

Fisher's zeros of quasi-Gaussian densities of states

We discuss apparent paradoxes regarding the location of the zeros of the partition function in the complex $β$ plane (Fisher's zeros) of a pure SU(2) lattice gauge theory in 4 dimensions. We propose a new criterion to draw the region of the complex $β$ plane where reweighting methods can be trusted when the density of states is almost but not exactly Gaussian. We propose new methods to infer the existence of zeros outside of this region. We demonstrate the reliability of these proposals with quasi Gaussian Monte Carlo distributions where the locations of the zeros can be calculated by independent numerical methods. The results are presented in such way that the methods can be applied for general lattice models. Applications to specific lattice models will be discussed in a separate publication.

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arXiv2006

Definition and parametrization of non-perturbative effects in quenched QCD

The notion of a non-perturbative effect is ambiguous if it requires the subtraction of a perturbative part defined by a diverging series. A common procedure consists in dropping the order of minimal contribution and the higher orders. This allows us to isolate very accurately the one-instanton effect for the double-well potential. For the one plaquette gauge theory, an exact analytical expression can be written for the non-perturbative part. We report recent attempts to extend this approach to the average plaquette of quenched QCD. Our goal is to express the non-perturbative effects in terms of expressions of the form beta^B exp(-A beta) calculable semi-classically. The situation is complicated by zeroes of the partition function in the complex $β$ plane (presumably near 5.75 pm i 0.2). We discuss two methods to describe the intermediate and large order behavior of the perturbative series. One is inspired by mean field theory (logarithmic specific heat) and reproduces accurately the known perturbative series with only two free parameters. A diagrammatic interpretation of this fact is still lacking. The other is based on infra-red renormalons with a factorial growth showing up at order larger than 20 and a possible effective theory interpretation. These extrapolations are compatible with the non-perturbative part of the plaquette being proportional to a^4. We propose an exponential parametrization to the corrections to the universal part of the beta function and find results compatible with the suggestion of a^2 corrections made by C. Allton.

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