Chiral Lagrangian approach to exchange vector currents in nuclei

Abstract

Exchange vector currents are calculated up to one-loop order (corresponding to next-to-next-to-leading order) in chiral perturbation theory. As an illustration of the power of the approach, we apply the formalism to the classic nuclear process n + p → d + γ at thermal energy. The exchange current correction comes out to be (4.5 ± 0.3) % in amplitude giving a predicted cross section σ = (334 ± 3) mb in excellent agreement with the experimental value (334.2 ± 0.5) mb. Together with the axial charge transitions computed previously, this result provides a strong support for the power of chiral Lagrangians in nuclear physics. As a byproduct of our results, we suggest an open problem in the application of chiral Lagrangian approach to nuclear processes that has to do with giving a physical meaning to the short-range correlations that play an important role in nuclei.(a) Permanent address :

Electromagnetic two-body currents of one- and two-pion range

“…The present study is similar to that of Ref. [16], albeit it uses a different formalism. Various aspects of the calculations are discussed in considerable detail.…”

“…where we have defined 16) and Σ/2 is the spin-3/2 operator. As it will become clear below, terms involving more than two ∆-isobars are not needed in the present study.…”

“…[16]. These currents were used in hybrid calculations of the n-p capture cross section [16,17], spin observables in n-p capture [18], and, more recently, magnetic moments of the deuteron and trinucleons [17].…”

Chiral perturbation theory for electroweak reactions on deuterium

“…These play a role in, e.g. np → dγ [18]. The first MEC effect in ed → ed does not occur until N 2 LO, or O(eP 3 ), where an NNπγ vertex from L (2) πN gets included in an isoscalar two-body contribution to the deuteron charge operator (see Fig.…”

QCD and nuclear physics

“…One of the properties of the pion, as the Nambu-Goldstone boson of chiral symmetry breaking, is the fact that its couplings become weak at low momentum. Thus if one uses an effective chiral theory to describe low energy pionnucleon interactions, and if a cutoff is introduced so that the couplings never grows large, then one can use that effective theory, even in a nonperturbative manner, to make precise calculations [1][2][3][4][5]. Such theories tend to have quite a few parameters since the cutoff is not very high and all the dynamics above the cutoff must be put into parameters of the effective theory.…”