92 research outputs found
Job Management and Task Bundling
High Performance Computing is often performed on scarce and shared computing
resources. To ensure computers are used to their full capacity, administrators
often incentivize large workloads that are not possible on smaller systems.
Measurements in Lattice QCD frequently do not scale to machine-size workloads.
By bundling tasks together we can create large jobs suitable for gigantic
partitions. We discuss METAQ and mpi_jm, software developed to dynamically
group computational tasks together, that can intelligently backfill to consume
idle time without substantial changes to users' current workflows or
executables.Comment: 8 pages, 3 figures, LATTICE 2017 proceeding
The Electromagnetic Self-Energy Contribution to M_p - M_n and the Isovector Nucleon Magnetic Polarizability
We update the determination of the isovector nucleon electromagnetic
self-energy, valid to leading order in QED. A technical oversight in the
literature concerning the elastic contribution to Cottingham's formula is
corrected and modern knowledge of the structure functions is used to precisely
determine the inelastic contribution. We find \delta M_{p-n}^\gamma =
1.30(03)(47) MeV. The largest uncertainty arises from a subtraction term
required in the dispersive analysis, which can be related to the isovector
magnetic polarizability. With plausible model assumptions, we can combine our
calculation with additional input from lattice QCD to constrain this
polarizability as: \beta_{p-n} = -0.87(85) x 10^{-4} fm^3.Comment: 5 pages, version accepted for publication in PR
A Lattice Test of 1/N_c Baryon Mass Relations
1/N_c baryon mass relations are compared with lattice simulations of baryon
masses using different values of the light-quark masses, and hence different
values of SU(3) flavor-symmetry breaking. The lattice data clearly display both
the 1/N_c and SU(3) flavor-symmetry breaking hierarchies. The validity of 1/N_c
baryon mass relations derived without assuming approximate SU(3)
flavor-symmetry also can be tested by lattice data at very large values of the
strange quark mass. The 1/N_c expansion constrains the form of discretization
effects; these are suppressed by powers of 1/N_c by taking suitable
combinations of masses. This 1/N_c scaling is explicitly demonstrated in the
present work.Comment: 13 pages, 20 figures; v2 version to be published in PR
Nucleon and Delta masses in twisted mass chiral perturbation theory
We calculate the masses of the nucleons and deltas in twisted mass heavy
baryon chiral perturbation theory. We work to quadratic order in a power
counting scheme in which we treat the lattice spacing and the quark masses to
be of the same order. We give expressions for the mass and the mass splitting
of the nucleons and deltas both in and away from the isospin limit. We give an
argument using the chiral Lagrangian treatment that, in the strong isospin
limit, the nucleons remain degenerate and the delta multiplet breaks into two
degenerate pairs to all orders in chiral perturbation theory. We show that the
mass splitting between the degenerate pairs of the deltas first appears at
quadratic order in in the lattice spacing. We discuss the subtleties in the
effective chiral theory that arise from the inclusion of isospin breaking.Comment: 21 pages, 4 figures, version published in PR
Finite volume corrections to pi-pi scattering
Lattice QCD studies of hadron-hadron interactions are performed by computing
the energy levels of the system in a finite box. The shifts in energy levels
proportional to inverse powers of the volume are related to scattering
parameters in a model independent way. In addition, there are non-universal
exponentially suppressed corrections that distort this relation. These terms
are proportional to exp(-m_pi L) and become relevant as the chiral limit is
approached. In this paper we report on a one-loop chiral perturbation theory
calculation of the leading exponential corrections in the case of I=2 pi-pi
scattering near threshold.Comment: 17 pages, 2 figures, 1 table. Version published in PR
Universality of Mixed Action Extrapolation Formulae
Mixed action theories with chirally symmetric valence fermions exhibit very
desirable features both at the level of the lattice calculations as well as in
the construction and implementation of the low energy mixed action effective
field theory. In this work we show that when such a mixed action effective
field theory is projected onto the valence sector, both the Lagrangian and the
extrapolation formulae become universal in form through next to leading order,
for all variants of discretization methods used for the sea fermions. Our
conclusion relies on the chiral nature of the valence quarks. The result
implies that for all sea quark methods which are in the same universality class
as QCD, the numerical values of the physical coefficients in the various mixed
action chiral Lagrangians will be the same up to lattice spacing dependent
corrections. This allows us to construct a prescription to determine the mixed
action extrapolation formulae for a large class of hadronic correlation
functions computed in partially quenched chiral perturbation theory at the
one-loop level. For specific examples, we apply this prescription to the
nucleon twist--2 matrix elements and the nucleon--nucleon system. In addition,
we determine the mixed action extrapolation formula for the neutron EDM as this
provides a nice example of a theta-dependent observable; these observables are
exceptions to our prescription.Comment: 36 pages, appendix on twisted mass sea fermions added, expanded
discussion of NLO operators, version published in JHEP; typographical errors
corrected in Eqs. (68) and (69
Gate Based Implementation of the Laplacian with BRGC Code for Universal Quantum Computers
We study the gate-based implementation of the binary reflected Gray code
(BRGC) and binary code of the unitary time evolution operator due to the
Laplacian discretized on a lattice with periodic boundary conditions. We find
that the resulting Trotter error is independent of system size for a fixed
lattice spacing through the Baker-Campbell-Hausdorff formula. We then present
our algorithm for building the BRGC quantum circuit. For an adiabatic evolution
time with this circuit, and spectral norm error , we find the
circuit cost (number of gates) and depth required are \mc{O}(t^2 n A D
/\epsilon) with auxiliary qubits for a system with lattice points
per dimension and particle number ; an improvement over binary position
encoding which requires an exponential number of -local operators. Further,
under the reasonable assumption that bounds , with the
kinetic energy and a non-trivial potential, the cost of QFT (Quantum
Fourier Transform ) implementation of the Laplacian scales as
\mc{O}\left(n^2\right) with depth \mc{O}\left(n\right) while BRGC scales as
\mc{O}\left(n\right), giving an advantage to the BRGC implementation
Finite volume corrections to ππ scattering
Abstract Lattice QCD studies of hadron-hadron interactions are performed by computing the energy levels of the system in a finite box. The shifts in energy levels proportional to inverse powers of the volume are related to scattering parameters in a model independent way. In addition, there are non-universal exponentially suppressed corrections that distort this relation. These terms are proportional to e −mπ L and become relevant as the chiral limit is approached. In this paper we report on a one-loop chiral perturbation theory calculation of the leading exponential corrections in the case of I = 2 ππ scattering near threshold
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