Elena Litvinova

Magnetic dipole, M1, strengths were studied in semimagic ^{50}Ti up to the neutron-separation threshold by combining data from (d,p) one-neutron transfer, (γ,γ^{'}) real-photon scattering, (e,e^{'}) inelastic scattering at extreme backward angles, and (p,p^{'}) at E_{p}=210 MeV and extreme forward angles. The combination of all probes provided unique access to the neutron spin-flip contribution and the possibility to evaluate its role in generating the spin-flip M1 strengths. The small contribution of the neutron (1f_{7/2})^{-1}(1f_{5/2})^{+1} spin-flip transitions, which were probed with the (d,p) reaction, to the overall strength in ^{50}Ti questions the standard picture for the microscopic origin of spin-flip strength in the fp shell. For ^{50}Ti, this Letter shows that J^{π}=1^{+} states with larger neutron (1f_{7/2})^{-1}(1f_{5/2})^{+1} spectroscopic factors do not correspond to the ones with the largest B(M1;0_{1}^{+}→1_{i}^{+}) strengths.

Some recent advancements of the nuclear many-body theory and selected results on nuclear giant and pygmy resonances are presented. The theory is compactly reviewed, with a special focus on the emergent scale of the quasiparticle-vibration coupling (qPVC), which carries the order parameter associated with the qPVC vertex, and an efficient treatment of the nuclear many-body problem organized around the qPVC hierarchy. Self-consistent numerical solutions of the relativistic Bethe-Salpeter-Dyson equation for the nuclear response function in medium-heavy nuclei are discussed. The presented update on the pygmy dipole resonance focuses on establishing the formation of its two-component structure as a result of the fragmentation of the low-energy dipole mode due to the qPVC and its mixing with the similarly fragmented giant dipole resonance. The centroid of the isoscalar giant monopole resonance is also linked to qPVC effects, particularly to its sensitivity to the coupling of the collective breathing mode to the lowest quadrupole vibrations, which is enhanced by quadrupole collectivity. The resolution of the long-standing "fluffiness" puzzle regarding the compressibility of open-shell tin isotopes is summarized. The recently developed thermal variant of the superfluid response theory is briefly introduced and continuously linked to the description of the isoscalar monopole response at finite temperature with the prospect of refining the temperature-dependent nuclear equation of state.

Studying the response of quantum systems is essential for gaining deeper insights into the fundamental nature of matter and its behavior in diverse physical contexts. Computation of nuclear response is critical for many applications, but its spectroscopically accurate description in medium-heavy nuclei in wide energy ranges remains particularly challenging because of the complex nature of nuclear quantum states in the high-level-density regime. Herein, we push the limits of configuration complexity in the classical computation of the nuclear response and present an algorithm with a quantum benefit for treating complex configurations. The classical computational method of approaching spectroscopic accuracy is implemented for medium-heavy nuclei and pioneered for the dipole response of 120Sn, while the quantum algorithm reaching the exact solution is realized for the Lipkin Hamiltonian to unravel the emergence of collectivity at strong coupling.