M. Sambataro

Nuclear excitations as coupled one and two random-phase-approximation modes

We present an extension of the random--phase approximation (RPA) where the RPA phonons are used as building blocks to construct the excited states. In our model, that we call double RPA (DRPA), we include up to two RPA phonons. This is an approximate and simplified way, with respect to the full second random--phase approximation (SRPA), to extend the RPA by including two particle--two hole configurations. Some limitations of the standard SRPA model, related to the violation of the stability condition, are not encountered in the DRPA. We also verify in this work that the energy--weighted sum rules are satisfied. The DRPA is applied to low--energy modes and giant resonances in the nucleus

Isoscalar-isovector proton-neutron pairing and quartet condensation in N = Z nuclei

^{16}

Isovector pairing in a formalism of quartets for N = Z nuclei

O. We show that the model (i) produces a global downwards shift of the energies with respect to the RPA spectra; (ii) provides a shift that is however strongly reduced compared to that generated by the standard SRPA. This model represents an alternative way of correcting for the SRPA anomalous energy shift, compared to a recently developed extension of the SRPA, where a subtraction procedure is applied. The DRPA provides results in good agreeement with the experimental energies, with the exception of those low--lying states that have a dominant two particle--two hole nature. For describing such states, higher--order calculations are needed.

Many-body correlations in a multistep variational approach

We show that the correlations generated in the ground state of

Collective excitations in Random Phase Approximation and beyond

N=Z

Bosonic Treatment of Pairing Correlations in a Solvable Many‐Level Model

nuclei by the isovector and isoscalar pairing forces can be treated with high precision as a condensate of alpha-like quartets. To treat these correlations, the quartet condensation model (QCM) is extended to the treatment of spherically symmetric isovector

Quasiparticle random-phase approximation and {beta}-decay physics: Higher-order approximations in a boson formalism

(T=1,J=0)

Extended random-phase approximation in a boson formalism with Pauli principle.

and isoscalar

Pair condensation in a finite Fermi system

(T=0,J=1)

Extension of the second random-phase approximation

pairing forces. Within the QCM, we discuss the competition between