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E. Eichten

Publications and source records attributed to E. Eichten.

At least 37 records · Page 2Linked to original sources
arXiv1999

Physical Effects of Infrared Quark Eigenmodes in LQCD

A truncated determinant algorithm is used to study the physical effects of the quark eigenmodes associated with eigenvalues below 400 MeV. This initial study focuses on coarse lattices (with O(a^2) improved gauge action), light internal quark masses and large physical volumes. Four bellwether full QCD processes are discussed: topological charge distributions, the eta prime propagator, string breaking as observed in the static energy and the rho decay into two pions.

hep-lat↗
arXiv1999

Modelling the Quark Determinant in Full QCD Simulations

The computational requirements and dynamics of Monte Carlo simulations of unquenched QCD incorporating the infrared quark eigenmodes (up to $\approx Λ_{QCD}$) exactly and UV modes via a loop representation are discussed. The accuracy of such a loop representation is studied for a variety of lattice volumes and quark masses. The method has been successfully applied for lattices up to 10$^3$x20 at $a \simeq$0.17F with improved (clover) action, and allows simulations at or near kappa critical.

hep-lat↗
arXiv1999

Loop Representations of the Quark Determinant in Lattice QCD

The modelling of the ultraviolet contributions to the quark determinant in lattice QCD in terms of a small number of Wilson loops is examined. Complete Dirac spectra are obtained for sizeable ensembles of SU(3) gauge fields at $β$=5.7 on 6$^4$, 8$^4$, and 10$^4$ lattices allowing for the first time a detailed study of the volume dependence of the effective loop action generating the quark determinant. The connection to the hopping parameter expansion is examined in the heavy quark limit. We compare the efficiency and accuracy of various methods- specifically, Lanczos versus stochastic approaches- for extracting the quark determinant on an ensemble of configurations.

hep-lat↗
arXiv1998

Evidence for quenched chiral logs

Using the pole shifting procedure of the modified quenched approximation (MQA) to cure the exceptional configuration problem, accurate hadron hadron spectrum calculations can be obtained at very light quark mass. Here we use the MQA to extend and improve our previous investigation of chiral logs in the pion mass. At beta=5.7 for Wilson fermion, we see clear evidence for quenched chiral logarithms in the pion mass as a function of quark mass. The size of the observed chiral log exponent delta is in good agreement with the value obtained from a direct calculation of the eta' hairpin diagram.

hep-lat↗
arXiv1998

Truncated Determinant Approach to Light Dynamical Quarks

Virtual quark effects in lattice QCD are studied in an approach where the infrared modes are included in a precise and gauge-invariant manner. At fixed physical volume the required number of modes does not increase in the continuum limit, and the acceptance is tolerable even for very light quark masses. Topological charge distributions at varying quark mass, and the static quark potential, showing the onset of string-breaking, are presented in both QED2 and QCD4.

hep-lat↗
arXiv1998

An Efficient Algorithm for QCD with Light Dynamical Quarks

A new approach to the inclusion of virtual quark effects in lattice QCD simulations is presented. Infrared modes which build in the chiral physics in the light quark mass limit are included exactly and in a gauge invariant way. At fixed physical volume the number of relevant infrared modes does not increase as the continuum limit is approached. The acceptance of our procedure does not decrease substantially in the limit of small quark masses. Two alternative approaches are discussed for including systematically the remaining ultraviolet modes. In particular, we present evidence that these modes are accurately described by an effective action involving only small Wilson loops.

hep-lat↗
arXiv1998

Quenched Chiral Artifacts for Wilson-Dirac Fermions

We examine artifacts associated with the chiral symmetry breaking induced through the use of Wilson-Dirac fermions in lattice Monte Carlo computations. For light quark masses, the conventional quenched theory can not be defined using direct Monte Carlo methods due to the existence of nonintegrable poles in physical quantities. These poles are associated with the real eigenvalue spectrum of the Wilson-Dirac operator. We show how this singularity structure can be observed in the analysis of both QED in two dimensions and QCD in four dimensions.

hep-lat↗
arXiv1997

The eta-prime propagator in quenched QCD

The calculation of the eta-prime hairpin diagram is carried out in the modified quenched approximation (MQA) in which the lattice artifact which causes exceptional configurations is removed by shifting observed poles at kappa<kappa_c in the quark propagators to the critical value of hop ping parameter. By this method, the eta-prime propagator can be accurately calculated even for very light quark mass. A determination of the topological susceptibility for quenched QCD is also obtained, using the fermionic method of Smit and Vink to calculate winding numbers.

hep-lat↗
arXiv1997

Resolving Exceptional Configurations

In lattice QCD with Wilson fermions, exceptional configurations arise in the quenched approximation at small quark mass. The origin of these large previously uncontrolled lattice artifacts is identified. A simple well-defined procedure (MQA) is presented which removes the artifacts while preserving the correct continuum limit.

hep-lat↗
arXiv1997

QED2 as a testbed for interpolations between quenched and full QCD

Lattice QED2 with the Wilson formulation of fermions is used as a convenient model system to study artifacts of the quenched approximation on a finite lattice. The quenched functional integral is shown to be ill-defined in this system as a consequence of the appearance of exactly real modes for physical values of the fermion mass. The location and frequency of such modes is studied as a function of lattice spacing, lattice volume, topological charge and improved action parameters. The efficacy of the recently proposed modified quenched approximation is examined, as well as a new approach to the interpolation from the quenched to full dynamical theory employing a truncated form of the fermion determinant.

hep-lat↗
arXiv1997

Quenched Approximation Artifacts: A study in 2-dimensional QED

The spectral properties of the Wilson-Dirac operator in 2-dimensional QED responsible for the appearance of exceptional configurations in quenched simulations are studied in detail. The mass singularity structure of the quenched functional integral is shown to be extremely compicated, with multiple branch points and cuts. The connection of lattice topological charge and exactly real eigenmodes is explored using cooling techniques. The lattice volume and spacing dependence of these modes is studied, as is the effect of clover improvement of the action. A recently proposed modified quenched approximation is applied to the study of meson correlators, and the results compared with both naive quenched and full dynamical calculations of the same quantity.

hep-lat↗
arXiv1997

Light Quarks, Zero Modes, and Exceptional Configurations

In continuum QCD, nontrivial gauge topologies give rise to zero eigenvalues of the massless Dirac operator. In lattice QCD with Wilson fermions, these zero modes appear as exactly real eigenvalues of the Wilson-Dirac operator and hence as poles in the quark propagator in the vicinity of critical hopping parameter. It is shown that "exceptional configurations" which arise in the quenched approximation at small quark mass are the result of the fluctuation of the position of zero mode poles to sub-critical values of the hopping parameter on particular gauge configurations. We describe a procedure for correcting these lattice artifacts by first isolating the contribution of zero mode poles to the quark propagator and then shifting the sub-critical poles to the critical point. This procedure defines a modified quenched approximation in which accurate calculations can be carried out for arbitrarily small quark masses.

hep-lat↗
arXiv1996

Electromagnetic Splittings and Light Quark Masses

A method for computing electromagnetic properties of hadrons in lattice QCD is described. The electromagnetic field is introduced dynamically, using a noncompact formulation. Employing enhanced electric charges, the dependence of the pseudoscalar meson mass on the (anti)quark charges and masses can be accurately calculated. At $β=5.7$ with Wilson action, the $π^+-π^0$ splitting is found to be $4.9(3)$ MeV. Using the measured $K^0-K^+$ splitting, we also find $m_u/m_d = .512(6)$. Systematic errors are discussed. Preliminary results for vector meson splittings are also presented.}

hep-lat↗
arXiv1996

Electromagnetic Structure of Light Baryons in Lattice QCD

A method in which electromagnetic properties of hadrons are studied by direct simulation of dynamical photon effects is applied to the extraction of the isomultiplet structure of the octet baryons. Using 187 configurations at $β=5.7$ with Wilson action, and up and down quark masses determined from the meson spectrum, the nucleon splitting is found to be $1.55(\pm 0.56\; \rm stat)$ MeV; the hyperon splittings are found to be $Σ^{0}-Σ^{+}=2.47\pm 0.39$, $Σ^{-}-Σ^{0}=4.63\pm 0.36$, $Ξ^{-}-Ξ^{0}=5.68\pm 0.24$ MeV. Estimated systematic corrections arising from finite volume and the quenched approximation are included in these results.

hep-lat↗
arXiv1996

Quenched Chiral Logs, the $η'$ Mass, and the Hairpin Diagram

Limits on the size of quenched chiral logs in the pion mass for Wilson fermions are investigated. The smallness of chiral logs is shown to be a result of the suppression of the hairpin diagram for small $p^2$, such that the value of the hairpin on the pion mass shell is much smaller than the physical $m_{η'}^2$. A direct calculation of the topological susceptibility from the same data gives $m_{η'}\approx 1$ GeV.

hep-lat↗
arXiv1996

Electromagnetic Structure of Light Baryons in Lattice QCD

A method for computing electromagnetic properties of hadrons in lattice QCD is applied to the extraction of electromagnetic properties of the octet baryons. This allows a determination of the full dependence of the baryon masses on the charges and masses of the valence quarks. Results of a first numerical study (at $β=5.7$ with Wilson action and light quark masses fixed from the pseudoscalar meson spectrum) are reported. The octet baryon isomultiplet splittings (with statistical errors) are found to be: ${\rm N} - {\rm P} = 1.55(\pm 0.56)$, $Σ^0 - Σ^+ = 2.47(\pm 0.39)$, $Σ^- - Σ^0 = 4.63(\pm 0.36)$ and $Ξ^- - Ξ^0 = 5.68(\pm 0.24)$ MeV. Estimates of the systematic corrections arising from finite volume and the quenched approximation are included in these results.

hep-lat↗
arXiv1996

Electromagnetic Splittings and Light Quark Masses in Lattice QCD

A method for computing electromagnetic properties of hadrons in lattice QCD is described and preliminary numerical results are presented. The electromagnetic field is introduced dynamically, using a noncompact formulation. Employing enhanced electric charges, the dependence of the pseudoscalar meson mass on the (anti)quark charges and masses can be accurately calculated. At $β=5.7$ with Wilson action, the $π^+-π^0$ splitting is found to be $4.9(3)$ MeV. Using the measured $K^0-K^+$ splitting, we also find $m_u/m_d = .512(6)$. Systematic errors are discussed.

hep-lat↗