Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Replacing the Breit-Wigner amplitude by the complex delta function to
  describe resonances   Whenever the Breit-Wigner amplitude appears in a calculation,there are many
instances (e.g., Fermi's two-level system and the Weisskopf-Wigner
approximation) where energy integrations are extended from the scattering
spectrum of the Hamiltonian to the whole real line. Such extensions are
performed in order to obtain a desirable, causal result. In this paper, we
recall several of those instances and show that substituting the Breit-Wigner
amplitude by the complex delta function allows us to recover such desirable
results without having to extend energy integrations outside of the scattering
spectrum.

29
The categories of this paper are: funct-an
7
The categories of this paper are: hep-th
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
16
The categories of this paper are: stat
25
The categories of this paper are: patt-sol
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
10
The categories of this paper are: q-bio
22
The categories of this paper are: chao-dyn
33
The categories of this paper are: plasm-ph
15
The categories of this paper are: nucl-ex