Sum rule approach to the nucleon electric polarizability

Scattering of charged particles off monopole–anti-monopole pairs

“…Lower and upper bounds to the magnetic susceptibility can be found. The so called Feynman bound is given by [33,34],…”

“…We make here the assumption that the previous lower bound can reasonably approximate the magnetic susceptibility for monopolium as established in other contexts [32][33][34], thus…”

Meson exchange and nucleon polarizabilities in the quark model

“…Our starting point to calculate the electric static polarizability, including the effects of the meson and gluon q − q interactions, has to be simple enough to have a direct relation with the potential model and, in addition, independent on the space of states introduced by Eq.(3). In the harmonic oscillator case the sum over excited states can be directly evaluated but in more realistic scenarios one has to resort to other techniques such as variational methods [7] or sum rules [10] 1 . We make use of a sum rule technique which, washing out all the complications of the baryonic spectrum, requires the knowledge of the nucleon wave function only, and constrains the numerical result to satisfy the stringent inequality [12]:…”

“…These observables have been calculated in a wide variety of hadronic models, including bag and soliton models, chiral perturbation theory and dispersion relation methods (see [6] for a review). The non-relativistic constituent quark model seems to present a serious and peculiar problem [7][8][9][10]: it cannot reproduce the spectrum and the experimental values (6) simultaneously. This can be straightforwardly illustrated within the harmonic oscillator model [11].…”

RPA description of the electric polarizability of the nucleon

“…Studies of the polarizability therefore provide a possibility to test the physical content of effective quark models of low energy QCD. In the past calculations have been performed in the Skyrme model [4,5,6], the MIT-Bag model [7,8] and its chiral extensions [9,10], chiral soliton models [11,12,13], chiral perturbation theory [14] and non-relativistic constituent quark models [15]. With quark degrees of freedom only the polarizability is found to range between α N ∼ 8 • 10 −4 f m 3 in the MIT-Bag model to α N ∼ 30•10 −4 f m 3 in the non-relativistic quark models where a quark core root-mean-square (rms) radius of about < r 2 > 1/2 core ∼ 0.7f m was used.…”