Abstract
The weak structure of the nucleon is the non-perturbative response of the nucleon to a weak- interacting probe. Here, I review the existing experimental data at low energy. In particular, the role of few- body nuclear reactions in constraining the weak response of the nucleon, in vacuum and in nuclear medium, is discussed.
Highlights
The nucleon is the basic component of the nucleus
Adding the contact part of the meson-exchange currents (MEC), which is related to the short range weak correlations of axial character, cures this problem and allows the half-life to reach its experimental value for −0.3 ≤ cD ≤ −0.1
It is clear that the half life of triton presents a very weak sensitivity to the NNN force, and to the strength of the spin-orbit interaction. – Weak dependence on the specific character of the force Complementary to the previous point, a quantitatively similar cD dependence of E1A can be obtained using A = 3 wave-functions produced by the phenomenological Argonne v18 (AV18) NN potential
Summary
The nucleon is the basic component of the nucleus. The nucleon itself is not a point particle, as its structure, i.e., its response to an external probe, varies with the momentum of this probe. The non-perturbative character of QCD at low energies makes a theoretical calculation of this response terribly challenging, a challenge that is only partially met today by means of large scale lattice-QCD calculations, which have a ∼ 5% accuracy, as well as systematic problems originated in the basic assumptions of the method This property of QCD entails that even though the probe can be treated perturbatively, the nucleon itself has to be treated non-perturbatively. The second ingredient, developed in the last two decades, is chiral perturbation theory (χPT) – an effective theory of QCD at low energies, enabling a construction of a nuclear Lagrangian that is consistent with QCD The combination of these two ingredients allows essentially parameter free calculations of weak nuclear reactions, with sub-percentage accuracy. The last three sections are dedicated to describe calculations of three specific reactions, intended to study the weak structure of the nucleon, its evolution inside nuclei, and implications of weak reactions on our understanding of nuclear structure
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