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Steve98052 (talk | contribs) →The sign problem in field theory: Adding the footnotes to the section header seems like a better way to footnote section-general references than the "(References for this section:,[][])." line. |
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* Particle physics. It prevents the use of [[Lattice QCD]] to predict the phases and properties of [[quark matter]].<ref name='Philipsen'>O. Philipsen, "Lattice calculations at non-zero chemical potential: The QCD phase diagram", [http://pos.sissa.it//archive/conferences/077/011/Confinement8_011.pdf PoS Confinement8 011 (2008)], Plenary talk at Quark Confinement and the Hadron Spectrum 8, Mainz, Germany, Sept 2008</ref>
==The sign problem in field theory<ref name='Wiese-cluster'/><ref name='Kieu'/>==
In a field theory approach to multi-particle systems, the fermion density is controlled by the value of the fermion [[chemical potential]] <math>\mu</math>. One evaluates the [[Partition function (quantum field theory)|partition function]] <math>Z</math> by summing over all classical field configurations, weighted by <math>\exp(-S)</math> where <math>S</math> is the action of the configuration. The sum over fermion fields can be performed analytically, and one is left with a sum over the [[boson]]ic fields <math>\sigma</math> (which may have been originally part of the theory, or have been produced by a [[Hubbard-Stratonovich transformation]] to make the fermion action quadratic)
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