Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Partially Quenched Chiral Perturbation Theory and a Massless Up Quark: A
  Lattice Calculation of the Light-Quark-Mass Ratio   The nontrivial topological structure of the QCD gauge vacuum generates a CP
breaking term in the QCD Lagrangian. However, measurements of the neutron
electric dipole moment have demonstrated that the term's coefficient is
unnaturally small, a dilemma known as the strong CP problem. A massless up
quark is one potential solution, as the term could then be absorbed through
chiral rotations. Through the light-quark-mass ratio m_u / m_d, leading order
Chiral Perturbation Theory appears to rule this scenario out. However, the
Kaplan-Manohar ambiguity demonstrates that certain strong next-to-leading order
corrections are indistinguishable from an up quark mass. Only a direct
calculation of the Gasser-Leutwyler coefficient combination 2 L_8 - L_5 can
resolve the issue. We carry out such a calculation, using partially quenched
N_f = 3 staggered fermions and hypercubic blocking, and make a quantitative
assessment of our systematic error. We find 2 L_8 - L_5 = (0.22 +/- 0.14) x
10^-3, which corresponds to a light-quark-mass ratio of m_u / m_d = 0.408 +/-
0.035. Thus, the massless-up-quark solution to the strong CP problem is ruled
out. This is the first calculation of its type to use a physical number of
light quarks, N_f = 3, and the first determination of 2 L_8 - L_5 to include a
comprehensive study of statistical error.

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The categories of this paper are: math-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: atom-ph
5
The categories of this paper are: gr-qc
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The categories of this paper are: nucl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: nucl-ex
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The categories of this paper are: patt-sol
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The categories of this paper are: astro-ph
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The categories of this paper are: stat
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The categories of this paper are: comp-gas
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The categories of this paper are: hep-ex
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The categories of this paper are: funct-an
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The categories of this paper are: supr-con
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The categories of this paper are: quant-ph
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The categories of this paper are: cs