Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Anatomy of a Weak Matrix Element   Although the weak nonleptonic amplitudes of the Standard Model are
notoriously difficult to calculate, we have produced a modified weak matrix
element which can be analyzed using reliable methods. This hypothetical
nonleptonic matrix element is expressible in terms of the isovector vector and
axialvector spectral functions $\rho_{\rm V}(s)$ and $\rho_{\rm A}(s)$, which
can be determined in terms of data from tau lepton decay and $e^+ e^-$
annihilation. Chiral symmetry and the operator product expansion are used to
constrain the spectral functions respectively in the low energy and the high
energy limits. The magnitude of the matrix element thus determined is compared
with its `vacuum saturation' estimate, and in the future may be accessible with
lattice calculations.

16
The categories of this paper are: stat
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
19
The categories of this paper are: eess
18
The categories of this paper are: econ
13
The categories of this paper are: quant-ph
29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
31
The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
37
The categories of this paper are: supr-con
15
The categories of this paper are: nucl-ex
33
The categories of this paper are: plasm-ph