We investigate a large angle photodisintegration of two nucleons from the $^3$He nucleus within the framework of the hard rescattering model (HRM). In the HRM a quark of one nucleon knocked out by an incoming photon rescatters with a quark of the oth
er nucleon leading to the production of two nucleons with large relative momentum. Assuming the dominance of the quark-interchange mechanism in a hard NN scattering, the HRM allows to express the amplitude of a two-nucleon break-up reaction through the convolution of photon-quark scattering, $NN$ hard scattering amplitude and nuclear spectral function. The photon-quark scattering amplitude can be explicitly calculated in the high energy regime, whereas for $NN$ scattering one uses the fit of the available experimental data. The HRM predicts several specific features for the hard breakup reaction. First, the cross section will approximately scale as $s^{-11}$. Secondly, the $s^{11}$ weighted cross section will have the shape of energy dependence similar to that of $s^{10}$ weighted $NN$ elastic scattering cross section. Also one predicts an enhancement of the $pp$ breakup relative to the $pn$ breakup cross section as compared to the results from low energy kinematics. Another result is the prediction of different spectator momentum dependencies of $pp$ and $pn$ breakup cross sections. This is due to the fact that same-helicity $pp$-component is strongly suppressed in the ground state wave function of $^3$He. Because of this suppression the HRM predicts significantly different asymmetries for the cross section of polarization transfer $NN$ breakup reactions for circularly polarized photons. For the $pp$ breakup this asymmetry is predicted to be zero while for the $pn$ it is close to ${2over 3}$.
Novel processes probing the decay of nucleus after removal of a nucleon with momentum larger than Fermi momentum by hard probes finally proved unambiguously the evidence for long sought presence of short-range correlations (SRCs) in nuclei. In combin
ation with the analysis of large $Q^2$, A(e,e)X processes at $x>1$ they allow us to conclude that (i) practically all nucleons with momenta $ge$ 300 MeV/c belong to SRCs, consisting mostly of two nucleons, ii) probability of such SRCs in medium and heavy nuclei is $sim 25%$, iii) a fast removal of such nucleon practically always leads to emission of correlated nucleon with approximately opposite momentum, iv) proton removal from two-nucleon SRCs in 90% of cases is accompanied by a removal of a neutron and only in 10% by a removal of another proton. We explain that observed absolute probabilities and the isospin structure of two nucleon SRCs confirm the important role that tensor forces play in internucleon interactions. We find also that the presence of SRCs requires modifications of the Landau Fermi liquid approach to highly asymmetric nuclear matter and leads to a significantly faster cooling of cold neutron stars with neutrino cooling operational even for $N_p/N_n le 0.1$. The effect is even stronger for the hyperon stars. Theoretical challenges raised by the discovered dominance of nucleon degrees of freedom in SRCs and important role of the spontaneously broken chiral symmetry in quantum chromodynamics (QCD) in resolving them are considered. We also outline directions for future theoretical and experimental studies of the physics relevant for SRCs.
