Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Infinite Variance in Fermion Quantum Monte Carlo Calculations   For important classes of many-fermion problems, quantum Monte Carlo (QMC)
methods allow exact calculations of ground-state and finite-temperature
properties, without the sign problem. The list spans condensed matter, nuclear
physics, and high-energy physics, including the half-filled repulsive Hubbard
model, the spin-balanced atomic Fermi gas, lattice QCD calculations at zero
density with Wilson Fermions, and is growing rapidly as a number of problems
have been discovered recently to be free of the sign problem. In these
situations, QMC calculations are relied upon to provide definitive answers.
Their results are instrumental to our ability to understand and compute
properties in fundamental models important to multiple sub-areas in quantum
physics. It is shown, however, that the most commonly employed algorithms in
such situations turn out to have an infinite variance problem. A diverging
variance causes the estimated Monte Carlo statistical error bar to be
incorrect, which can render the results of the calculation unreliable or
meaningless. We discuss how to identify the infinite variance problem. An
approach is then proposed to solve the problem. The solution does not require
major modifications to standard algorithms, adding a ``bridge link" to the
imaginary-time path-integral. The general idea is applicable to a variety of
situations where the infinite variance problem may be present. Illustrative
results are presented for the ground state of the Hubbard model at
half-filling.

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The categories of this paper are: quant-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: funct-an
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The categories of this paper are: eess
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The categories of this paper are: q-fin
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The categories of this paper are: cs
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-th
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The categories of this paper are: math-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: chem-ph
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The categories of this paper are: patt-sol
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The categories of this paper are: adap-org
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The categories of this paper are: dg-ga
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The categories of this paper are: stat
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The categories of this paper are: mtrl-th