Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Selfconsistent Approximations in Mori's Theory   The constitutive quantities in Mori's theory, the residual forces, are
expanded in terms of time dependent correlation functions and products of
operators at $t=0$, where it is assumed that the time derivatives of the
observables are given by products of them. As a first consequence the
Heisenberg dynamics of the observables are obtained as an expansion of the same
type. The dynamic equations for correlation functions result to be
selfconsistent nonlinear equations of the type known from mode-mode coupling
approximations. The approach yields a neccessary condition for the validity of
the presented equations. As a third consequence the static correlations can be
calculated from fluctuation-dissipation theorems, if the observables obey a Lie
algebra. For a simple spin model the convergence of the expansion is studied.
As a further test, dynamic and static correlations are calculated for a
Heisenberg ferromagnet at low temperatures, where the results are compared to
those of a Holstein Primakoff treatment.

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The categories of this paper are: mtrl-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-th
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The categories of this paper are: quant-ph
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The categories of this paper are: q-alg
1
The categories of this paper are: cs
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The categories of this paper are: hep-ex
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The categories of this paper are: solv-int
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The categories of this paper are: nucl-ex
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The categories of this paper are: cmp-lg
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The categories of this paper are: math-ph
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The categories of this paper are: physics
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The categories of this paper are: acc-phys
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The categories of this paper are: bayes-an
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The categories of this paper are: astro-ph
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The categories of this paper are: comp-gas