Bulletin of the American Physical Society
APS April Meeting 2021
Volume 66, Number 5
Saturday–Tuesday, April 17–20, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Y08: Advances in Computation: Lattice QCD and MoreLive

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Sponsoring Units: DCOMP Chair: Anna Hasenfratz, University of Colorado 
Tuesday, April 20, 2021 1:30PM  1:42PM Live 
Y08.00001: Validation of the Lüscher Method on the Lattice Frank Lee, Andrei Alexandru, Ruairí Brett The L\"{u} scher method for twoparticle scattering is a critical tool for connecting finitevolume spectrum with infinitevolume scattering phaseshifts. We investigate the efficacy of the method in a simple quantum mechanical model. The quantization condition is numerically examined, including the effects of higher partial waves. Various setups used in practice are explored: cubic and elongated lattices, moving frames, and systems with integer and halfinteger spin. [Preview Abstract] 
Tuesday, April 20, 2021 1:42PM  1:54PM Live 
Y08.00002: Machine Learning Algorithms for faster determination of Lattice QCD Hadron Correlators Giovanni Pederiva, Andrea Shindler A big portion of Lattice QCD calculations requires the calculation of hadronic twopoint correlation functions. These can be computationally challenging mostly depending on the size of the systems that are simulated and on the physical parameters. We present a new procedure that allows for reduced computational resources to calculate hadronic twopoint functions on the lattice. We apply a variety of machine learning regression algorithms, to relate propagators obtained with the BiCGStab linear solver with different convergence parameters. A mapping between low precision propagator data to high precision propagators is investigated and an assessment of the systematic uncertainty over the gauge field configuration ensemble of the procedure is discussed. The validity of the method is assessed based on derived quantities such as effective masses of hadrons, together with the potential gain in computer time, and on the robustness of the results to the different models that are tested. The method is found to be stable and to produce results that are comparable with traditional computations while requiring significantly less computer time. [Preview Abstract] 
Tuesday, April 20, 2021 1:54PM  2:06PM Live 
Y08.00003: Calculation of Gluon PDF using PseudoPDF Technique Tanjib Khan We present our calculation of the unpolarized gluon parton distribution function (PDF) in the nucleon using PseudoPDF technique on a $32^3 \times 64$ isotropic lattice with a pion mass of 358 MeV. The nucleon interpolating fields are constructed using the distillation method while the sGEVP method is used to calculate the gluonic matrix elements. We implement the gradientflow technique to compute the flowed matrix elements and using the double ratio, calculate the flowed reduced Ioffetime distribution (rITD). We extrapolate the results to the flowtime independent rITD and calculate the lightcone ITD in $\overline{MS}$ scheme, at the small zseparation limit, using NLO matching formula. Finally, the gluon PDF is calculated from the lightcone ITD by applying appropriate kernel form. [Preview Abstract] 
Tuesday, April 20, 2021 2:06PM  2:18PM Live 
Y08.00004: A novel nonperturbative renormalization scheme for local operators Christopher Monahan, Anna Hasenfratz, Matthew Rizik, Andrea Shindler, Oliver Witzel Lattice quantum chromodynamics (QCD) provides the only systematic nonperturbative approach to calculating the properties of the strong nuclear force at low energies. Lattice calculations discretize spacetime on a Euclidean lattice and sample the path integral stochastically to obtain Monte Carlo estimates of QCD correlation functions. One common challenge for lattice calculations is constructing nonperturbative renormalization schemes and relating those schemes to the standard MSbar scheme typically used in perturbative calculations. The gradient flow, which exponentially suppresses ultraviolet field fluctuations and removes ultraviolet divergences (up to a multiplicative fermionic wavefunction renormalization), can be used to describe realspace Wilsonian renormalization group transformations and determine the corresponding beta function. We propose a new nonperturbative renormalization scheme for local operators that uses the gradient flow and is amenable to lattice QCD calculations, and present some preliminary results for quark bilinear operators. [Preview Abstract] 
Tuesday, April 20, 2021 2:18PM  2:30PM Live 
Y08.00005: Selflearning MonteCarlo for nonabelian gauge theory with dynamical fermions Akio Tomiya, Yuki Nagai, Akinori Tanaka In this talk, we introduce the selflearning MonteCarlo (SLMC) algorithm for nonabelian gauge theory with dynamical fermions in four dimensions to resolve the autocorrelation problem in lattice QCD. We performed simulations with the dynamical staggered fermions and plaquette gauge action by both in HMC and SLMC for zero and finite temperature to examine the validity of SLMC. We confirmed that SLMC can reduce autocorrelation time in nonabelian gauge theory and reproduces results from HMC. For finite temperature runs, we confirmed that SLMC reproduces correct results with HMC, including higherorder moments of the Polyakov loop and the chiral condensate. Besides, our finite temperature calculations indicate that four flavor QC${}_2$D with $\hat{m} = 0.5$ is likely in the crossover regime in the Colombia plot. This talk is based on arXiv 2010.11900. [Preview Abstract] 
Tuesday, April 20, 2021 2:30PM  2:42PM Live 
Y08.00006: Quirks of QCD: Twist2 Operators on the Lattice Tangereen Claringbold, Chris Monahan To probe the structure of hadrons, we often use high energy electrons in scattering experiments, called Deep Inelastic Scattering or DIS. When doing theoretical calculations of the scattering cross section of a DIS process, we apply the operator product expansion to introduce the rotationallyinvariant twist2 operators, where twist is dimension minus spin. To move to numerical calculations, we break up space and time into discrete points on a lattice, rather than a continuum, which breaks rotational symmetry leading to the twist2 operators having powerdivergent mixing under renormalization. We propose that applying the gradient flow prescription to these operators on the lattice will remove the powerdivergent mixing. The gradient flow is a regulator that smears the fields in a new parameter called the flow time. We give an example of two twist2 operators that have a powerdivergent mixing on the lattice, but where this powerdivergence is removed under the gradient flow. [Preview Abstract] 
Tuesday, April 20, 2021 2:42PM  2:54PM Live 
Y08.00007: NTCL: The Nuclear Tensor Contraction Library Justin Lietz, Gustav Jansen, Xingze Mao Tensor contractions are a ubiquitous mathematical operation in theoretical physics and are frequently the dominant computational cost in codes that implement these theories. Additionally, scientists use a diverse range of computational hardware to perform these calculations: from humble laptops to leadership class supercomputing facilities. Writing an application which can perform well on a variety of computational platforms is time consuming for scientists, and frequently impossible if a large amount of legacy code is being used. The Nuclear Tensor Contraction Library (NTCL) is a library that solves these challenges by providing a single tensor contraction interface which implements the actual tensor contraction via plugins, where plugins for many popular existing libraries like cuTensor (for Nvidia GPUs) and Tencile (for AMD GPus) have been included. Here we present benchmarks for some tensor contractions typical in nuclear physics, using a variety of hardware, a variety of algorithms, and a variety of asynchronous data management schemes, all of which are accessed through a single NTCL interface. [Preview Abstract] 
Tuesday, April 20, 2021 2:54PM  3:06PM On Demand 
Y08.00008: The AtiyahPatodiSinger Index Theorem and Lattice Simulations Sadataka Furui Atiyah, Patodi and Singer (APS) considered a system in a heat bath with proper boundary conditions. In the Hamiltonian formulation, difference of the number of zero modes in the time t\textgreater 0 and that in the time t\textless 0 are defined as AtiyahPatodiSinger Index. In Domain wall lattice simulation of QCD, difference of number of chirality $+$ zero modes and chirality  zero modes was discussed by Fukaya et al.[1]. We replace zero modes of Dirac spinors to those of Weyl spinors and study 2 D convolutions of a soliton wave and time reversed soliton wave which belong to the AltlandZirnbauer symmetry class DIII[2,3] . When beam directions of KhokhlovZaboltskaya soliton and that of its time reversed soliton are not parallel, there appear points where the convolution of the two solitons becomes negative near the boundary [4], which is related to the APS index in a bounded Riemann manifold. Relations to finite temperature lattice QCD will be discussed. [1] H. Fukaya et al, Phys. Rev. D 96, 125004 (2017). [2] S. Ryu et al, Phys. Rev. B 85, 045104 (2012). [3] I.A. Gruzberg et al, Phys. Rev. B 71, 245124 (2005). [4] S. Furui and S. Dos Santos, arXiv:2010.09487[physics.genph] [Preview Abstract] 
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