Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Two-pion exchange as a leading-order contribution in chiral effective
  field theory   Pion exchange is the central ingredient to nucleon-nucleon interactions used
in nuclear structure calculations, and one pion exchange (OPE) enters at
leading order in chiral effective field theory. In the $^{2S+1}L_J={^1S_0}$
partial wave, however, OPE and a contact term needed for proper renormalization
fail to produce the qualitative, and quantitative, features of the scattering
phase shifts. Cutoff variation also revealed a surprisingly low breakdown
momentum of about 330 MeV in this partial wave. Here we show that potentials
consisting of OPE, two pion exchange (TPE), and a single contact address these
problems and yield accurate and renormalization group (RG) invariant phase
shifts in the $^1S_0$ partial wave. We demonstrate that a leading-order
potential with TPE can be systematically improved by adding a contact quadratic
in momenta. For momentum cutoffs below about 500 MeV, the removal of relevant
physics from TPE loops needs to be compensated by additional contacts to keep
RG invariance. Inclusion of the $\Delta$ isobar degree of freedom in the
potential does not change the strong contributions of TPE.

15
The categories of this paper are: nucl-ex
21
The categories of this paper are: adap-org
1
The categories of this paper are: cs
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
20
The categories of this paper are: acc-phys
25
The categories of this paper are: patt-sol
6
The categories of this paper are: astro-ph
32
The categories of this paper are: atom-ph
30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
29
The categories of this paper are: funct-an