The Goldberger-Treiman relation $M=2pi/sqrt{3}f^{rm cl}_pi$ where $M$ is the constituent quark mass in the chiral limit (cl) and $f^{rm cl}_pi$ the pion decay constant in the chiral limit predicts constituent quark masses of $m_u=328.8pm 1.1$ MeV and
$m_d=332.3pm 1.1$ MeV for the up and down quark, respectively, when $f^{rm cl}_pi=89.8pm 0.3$ MeV is adopted. Treating the constituent quarks as bare Dirac particles the following zero order values $mu^{(0)}}_p=2.850pm 0.009$ and $mu^{(0)}}_n= -1.889pm 0.006$ are obtained for the proton and neutron magnetic moments, leading to deviations from the experimental data of 2.0% and 1.3%, respectively. These unavoidable deviations are discussed in terms of contributions to the magnetic moments proposed in previous work.
It is shown that the scalar mesons $sigma$, $f_0(980)$ and $a_0(980)$ as $t$-channel exchanges quantitatively solve the problem of diamagnetism and give an explanation of the large missing part of the electric polarizability $alpha$ showing up when o
nly the pion cloud is taken into account. The electric polarizability of the proton $alpha_p$ confirms a two-photon width of the $sigma$ meson of $Gamma_{sigmagammagamma}=(2.58pm 0.26)$ keV.
The signs and values of the two-photon couplings $F_{Mgammagamma}$ of mesons $(M)$ and their couplings $g_{MNN}$ to the nucleon as entering into the $t$-channel parts of the difference of the electromagnetic polarizabilities $(alpha-beta)$ and the ba
ckward angle spin polarizabilities $gamma_pi$ are determined. The excellent agreement achieved with the experimental polarizabilities of the proton makes it possible to make reliable predictions for the neutron. The results obtained are $alpha_n=13.4pm 1.0$, $beta_n=1.8mp 1.0$ ($10^{-4}$ fm$^3$), and $gamma^{(n)}_pi=57.6pm 1.8$ ($10^{-4}$ fm$^4$). New empirical information on the flavor wave functions of the $f_0(980)$ and the $a_0(980)$ meson is obtained.
The electromagnetic polarizabilities of the nucleon are shown to be essentially composed of the nonresonant $alpha_p(E_{0+})=+3.2$, $alpha_n(E_{0+})=+4.1$,the $t$-channel $alpha^t_{p,n}=-beta^t_{p,n}=+7.6$ and the resonant $beta_{p,n}(P_{33}(1232))=+
8.3$ contributions (in units of $10^{-4}$fm$^3$. The remaining deviations from the experimental data $Deltaalpha_p=1.2pm 0.6$, $Deltabeta_p=1.2mp 0.6$, Deltaalpha_n=0.8pm 1.7$ and $Deltabeta_n=2.0mp 1.8$ are contributed by a larger number of resonant and nonresonant processes with cancellations between the contributions. This result confirms that dominant contributions to the electric and magnetic polarizabilities may be represented in terms of two-photon couplings to the $sigma$-meson having the predicted mass $m_sigma=666$ MeV and two-photon width $Gamma_{gammagamma}=2.6$ keV.
