Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Self-duality, helicity and background field loopology   I show that helicity plays an important role in the development of rules for
computing higher loop effective Lagrangians. Specifically, the two-loop
Heisenberg-Euler effective Lagrangian in quantum electrodynamics is remarkably
simple when the background field has definite helicity (i.e., is self-dual).
Furthermore, the two-loop answer can be derived essentially algebraically, and
is naturally expressed in terms of one-loop quantities. This represents a
generalization of the familiar ``integration-by-parts'' rules for manipulating
diagrams involving free propagators to the more complicated case where the
propagators are those for scalars or spinors in the presence of a background
field.

37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
11
The categories of this paper are: hep-lat
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
10
The categories of this paper are: q-bio
3
The categories of this paper are: physics
22
The categories of this paper are: chao-dyn
1
The categories of this paper are: cs
33
The categories of this paper are: plasm-ph
26
The categories of this paper are: bayes-an
29
The categories of this paper are: funct-an
12
The categories of this paper are: nucl-th
18
The categories of this paper are: econ
6
The categories of this paper are: astro-ph