Predictions of covariant chiral perturbation theory for nucleon polarisabilities and polarised Compton scattering

We update the predictions of the SU(2) baryon chiral perturbation theory for the dipole polarisabilities of the proton, {αE1,βM1}p={11.2(0.7),3.9(0.7)}×10−4fm3, and obtain the corresponding predictions for the quadrupole, dispersive, and spin polarisabilities: {αE2,βM2}p={17.3(3.9),−15.5(3.5)}×10−4fm5, {αE1ν,βM1ν}p={−1.3(1.0),7.1(2.5)}×10−4fm5, and {γE1E1,γM1M1,γE1M2,γM1E2}p={−3.3(0.8),2.9(1.5),0.2(0.2),1.1(0.3)}×10−4fm4. The results for the scalar polarisabilities are in significant disagreement with semi-empirical analyses based on dispersion relations, however the results for the spin polarisabilities agree remarkably well. Results for proton Compton-scattering multipoles and polarised observables up to the Delta(1232) resonance region are presented too. The asymmetries Σ3 and Σ2x reproduce the experimental data from LEGS and MAMI. Results for Σ2z agree with a recent sum rule evaluation in the forward kinematics. The asymmetry Σ1z near the pion production threshold shows a large sensitivity to chiral dynamics, but no data is available for this observable. We also provide the predictions for the polarisabilities of the neutron: {αE1,βM1}n={13.7(3.1),4.6(2.7)}×10−4fm3, {αE2,βM2}n={16.2(3.7),−15.8(3.6)}×10−4fm5, {αE1ν,βM1ν}n={0.1(1.0),7.2(2.5)}×10−4fm5, and {γE1E1,γM1M1,γE1M2,γM1E2}n={−4.7(1.1),2.9(1.5),0.2(0.2),1.6(0.4)}×10−4fm4. The neutron dynamical polarisabilities and multipoles are examined too. We also discuss subtleties related to matching dynamical and static polarisabilities.