arXiv subjects

Mike Peardon

Publications and source records attributed to Mike Peardon.

At least 19 recordsLinked to original sources

arXiv2022

The static energy of a quark-antiquark pair from Laplacian eigenmodes

We test a method for computing the static quark-antiquark potential in lattice QCD, which is not based on Wilson loops, but where the trial states are formed by eigenvector components of the covariant lattice Laplace operator. The runtime of this method is significantly smaller than the standard Wilson loop calculation, when computing the static potential not only for on-axis, but also for many off-axis quark-antiquark separations, i.e., when a fine spatial resolution is required. We further improve the signal by using multiple eigenvector pairs, weighted with Gaussian profile functions of the eigenvalues, providing a basis for a generalized eigenvalue problem (GEVP), as it was recently introduced to improve distillation in meson spectroscopy. We show results with the new method for the static potential with dynamical fermions and demonstrate its efficiency compared to traditional Wilson loop calculations. The method presented here can also be applied to compute hybrid or tetra-quark potentials and to static-light systems.

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arXiv2022

Implementing noise reduction techniques into theOpenQ*D package

We present the results of testing a new technique for stochastic noise reduction in the calculation of propagators by implementing it in OpenQ*D for two ensembles with O(a) improved Wilson fermion action, with periodic boundary conditions and pion masses of 437 MeV and 331 MeV, for the connected vector and pseudoscalar correlators. We find that the technique yields no speedup compared to traditional methods, owning to the failure of its underlying assumption that the spectra of the spatial Laplacian and Dirac operators are sufficiently similar for the technique's purposes.

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arXiv2021

Optimizing Distillation for charmonium and glueballs

We study the charmonium spectrum on an ensemble with two heavy dynamical quarks with a mass at half the physical charm quark mass. Operators for different quantum numbers are used in the framework of distillation with different smearing profiles to increase the overlap with ground and excited states. The use of exact distillation, large statistics and the absence of light quarks gives robust results for the charmonium spectrum. We also present preliminary results for the glueball spectrum in this theory.

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arXiv2019

String breaking by light and strange quarks in QCD

The energy spectrum of a system containing a static quark anti-quark pair is computed for a wide range of source separations using lattice QCD with $N_\mathrm{f}=2+1$ dynamical flavours. By employing a variational method with a basis including operators resembling both the gluon string and systems of two separated static mesons, the first three energy levels are determined up to and beyond the distance where it is energetically favourable for the vacuum to screen the static sources through light- or strange-quark pair creation, enabling both these screening phenomena to be observed. The separation dependence of the energy spectrum is reliably parameterised over this saturation region with a simple model which can be used as input for subsequent investigations of quarkonia above threshold and heavy-light and heavy-strange coupled-channel meson scattering.

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arXiv2018

String breaking with 2+1 dynamical fermions using the stochastic LapH method

The static potential $V(r)$ between a static quark and a static antiquark separated by a distance r is defined as the energy of the ground state of the system. As a consequence of confinement, the energy between the quark-antiquark pair is contained inside a color flux tube, which will break due to pair creation as soon as the energy is high enough. String breaking is manifested as a quantum-mechanical mixing phenomenon between different states containing two infinitely heavy quarks. We investigate this phenomenon with $N_\mathrm{f}=2+1$ flavors of dynamical fermions in the stochastic LapH framework, using an ensemble of gauge configurations generated through the CLS effort. We observe the effect of the third sea-quark flavor, which results in a second mixing-phenomenon.

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arXiv2016

Towards string breaking with 2+1 dynamical fermions using the stochastic LapH method

We investigate the use of stochastically estimated light quark propagators in correlation functions involving a static color source. To this end we compute the static-light meson pseudoscalar correlation function in the stochastic LapH framework, using an ensemble of $N_f= 2+1$ gauge configurations generated through the CLS effort. We extract the static-light as well as the static-strange mass with good statistical precision. Together with the static potential, we obtain a preliminary estimate for the expected mixing region.

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arXiv2012

A comparison of analysis techniques for extracting resonance parameters from lattice Monte Carlo data

Different methods for extracting resonance parameters from Euclidean lattice field theory are tested. Monte Carlo simulations of the O(4) non-linear sigma model are used to generate energy spectra in a range of different volumes both below and above the inelastic threshold. The applicability of the analysis methods in the elastic region is compared. Problems which arise in the inelastic region are also emphasised.

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arXiv2011

Charmonium spectroscopy from an anisotropic lattice study

We present a progress report on our study of the charmonium spectrum in full QCD on anisotropic lattices generated by the Hadron Spectrum Collaboration. We adopt a large basis of interpolating operators to extract the excited charmonium states using the variational method. A detailed spectrum of excited charmonium mesons in many $J^{PC}$ channels is obtained. Hybrid states with exotic and non-exotic quantum numbers are determined and preliminary results from a study of disconnected contributions to the $η_c$ are presented.

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arXiv2011

Polynomial Filtered HMC -- an algorithm for lattice QCD with dynamical quarks

Polynomial approximations to the inverse of the fermion matrix are used to filter the dynamics of the upper energy scales in HMC simulations. The use of a multiple time-scale integration scheme allows the filtered pseudofermions to be evolved using a coarse step size. We introduce a novel generalisation of the nested leapfrog which allows for far greater flexibility in the choice of time scales. We observe a reduction in the computational expense of the molecular dynamics integration of between 3--5 which improves as the quark mass decreases.

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arXiv2011

Improved stochastic estimation of quark propagation with Laplacian Heaviside smearing in lattice QCD

A new method of stochastically estimating the low-lying effects of quark propagation is proposed which allows accurate determinations of temporal correlations of single-hadron and multi-hadron operators in lattice QCD. The method is well suited for calculations in large volumes. Contributions involving quark propagation connecting hadron sink operators at the same final time can be handled in a straightforward manner, even for a large number of final time slices. The method exploits Laplacian Heaviside (LapH) smearing. ZN noise is introduced in a novel way, and variance reduction is achieved using judiciously-chosen noise dilution projectors. The method is tested using isoscalar mesons in the scalar, pseudoscalar, and vector channels, and using the two-pion system of total isospin I=0,1,2 on large anisotropic 24^3 x 128 lattices with spatial spacing a_s~0.12 fm and temporal spacing a_t~0.034 fm for pion masses mpi~390 and 240 MeV.

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arXiv2010

Hadronic decay width from finite-volume energy spectrum in lattice QCD

The standard approach to determine the parameters of a resonance is based on the study of the volume dependence of the energy spectrum. In this work we study a non-linear sigma model coupled to a scalar field in which a resonance emerges. Using an analysis method introduced recently, based on the concept of probability distribution, it is possible to determine the mass and the width of the resonance.

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arXiv2010

Extracting resonance parameters from lattice data

Monte Carlo simulations of the 4d O(4) model in the broken phase are performed to determine the parameters of a resonance. The standard method for extracting them on the lattice is through Lüscher's formula; recently a new method, based on the probability distribution concept, has been proposed. We study the application of these methods and compare them with Monte Carlo data.

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arXiv2009

Exploring the Spectrum of QCD using the Lattice

The calculation of the spectrum of QCD is key to an understanding of the strong interactions, and vital if we are to capitalize on the experimental study of the spectrum. In this paper, we describe progress towards understanding the spectrum of resonances of both mesons and baryons from lattice QCD, focusing in particular on the resonances of the $I=1/2$ nucleon states, and of charmonium mesons composed of the heavy charmed quarks.

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arXiv2007

Charmonium at high temperature in two-flavor QCD

We compute charmonium spectral functions in 2-flavor QCD on anisotropic lattices using the maximum entropy method. Our results suggest that the S-waves (J/psi and eta_c) survive up to temperatures close to 2Tc, while the P-waves (chi_c0 and chi_c1) melt away below 1.2Tc.

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arXiv2007

Radial and orbital excitations of static-light mesons

We present results for the spectrum of static-light mesons from Nf=2 lattice QCD. These results were obtained using all-to-all light quark propagators on an anisotropic lattice, yielding an improved signal resolution when compared to more conventional lattice techniques. With a light quark mass close to the strange quark, we have measured the splittings between the ground-state S-wave static-light meson and higher excitations. We attempt to identify the quantum numbers of the excited states in the context of the reduced spatial symmetries of the lattice.

hep-lat↗

arXiv2006

Static-light mesons on a dynamical anisotropic lattice

We present results for the spectrum of static-light mesons from Nf=2 lattice QCD. These results were obtained using all-to-all light quark propagators on an anisotropic lattice, yielding an improved signal resolution when compared to more conventional lattice techniques. In particular, we consider the inversion of orbitally-excited multiplets with respect to the `standard ordering', which has been predicted by some quark models.

hep-lat↗

arXiv2006

Dynamical QCD simulations on anisotropic lattices

The simulation of QCD on dynamical (Nf=2) anisotropic lattices is described. A method for nonperturbative renormalisation of the parameters in the anisotropic gauge and quark actions is presented. The precision with which this tuning can be carried out is determined in dynamical simulations on 8^3x48 and 8^3x80 lattices.

hep-lat↗

arXiv2005

Mesons at high temperature in Nf=2 QCD

We report first results for spectral functions of charmonium in 2-flavour QCD. The spectral functions are determined from vector and pseudoscalar correlators on a dynamical, anisotropic lattice. J/psi and eta_c are found to survive well into the deconfined phase before melting away at T<~2T_c. Current systematic uncertainties prevent us from drawing any definite conclusions at this stage.

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