arXiv subjects

F. Barranco

Publications and source records attributed to F. Barranco.

43 records · Page 3Linked to original sources

arXiv2003

Parity inversion, breakdown of shell closure and particle-vibration coupling in Be-isotopes

The coupling of single-particle motion and of vibrations in $^{11}_4$Be produces dressed neutrons which spend only a fraction of the time in pure single-particle states, and which weighting differently from the bare neutrons, lead to parity inversion. The interaction of the two least bound neutrons in the ground state of $^{12}_4$Be mediated by the $v_{14}$ Argonne nucleon-nucleon potential and by the exchange of the phonon cloud, give rise to a strongly correlated state, where the neutrons spend more than half of the time in (s$^2$+d$^2$)-configurations, resulting in a breaking of the N=8 shell closure.

nucl-th↗

arXiv2002

Stability properties of |Psi|^2 in Bohmian dynamics

According to Bohmian dynamics, the particles of a quantum system move along trajectories, following a velocity field determined by the wave-function Psi(x,t). We show that for simple one-dimensional systems any initial probability distribution of a statistical ensemble approaches asymptotically |Psi(x,t)}|^2 if the system is subject to a random noise of arbitrarily small intensity.

quant-ph↗

arXiv2001

Effect of particle-phonon coupling on pairing correlations in nuclei

The influence of particle-phonon coupling on pairing correlations in nuclei is studied by solving the Dyson equation including the anomalous (pairing) Green function. We develop the formalism for solving the equation with the minimum of approximations. The solution of the Dyson equation is compared with the diagonalization of particle-phonon coupled Hamiltonian in a small space. This comparison reveals that the effect of many-phonon states is incorporated in the Dyson equation. We calculate the pairing gap of the neutron in 120Sn. We compare analytically the present method with a simpler treatment based on Bloch-Horowitz perturbation theory.

nucl-th↗

arXiv2001

Solution of the Dyson equation for nucleons in the superfluid phase

We investigate the role the interweaving of surface vibrations and nucleon motion has on Cooper pair formation in spherical superfluid nuclei. A quantitative calculation of the state-dependent pairing gap requires to go beyond the quasiparticle approximation, treating in detail the breaking of the single-particle strength and of the associated poles. This is done solving self-consistently the Dyson equation, including both a bare nucleon-nucleon interaction (which for simplicity we choose as a monopole-pairing force of constant matrix elements g) and an induced interaction arizing from the exchange of vibrations (calculated microscopically in QRPA) between pairs of nucleons moving in time reversal states. Both the normal and anomalous density Green functions are included, thus treating self-energy and pairing processes on equal footing. We apply the formalism to the superfluid nucleus 120Sn. Adjusting the value of g so as to reproduce, for levels close to the Fermi level, the empirical odd-even mass difference (Delta approx 1.4 MeV), it is found that the pairing gap receives about equal contributions from the monopole-pairing force and from the induced interaction. [More sentences continue. See the main body.]

nucl-th↗

arXiv2000

The halo of the exotic nucleus 11Li: a single Cooper pair

If neutrons are progressively added to a normal nucleus, the Pauli principle forces them into states of higher momentum. When the core becomes neutron-saturated, the nucleus expels most of the wavefunction of the last neutrons outside to form a halo, which because of its large size can have lower momentum. It is an open question how nature stabilizes such a fragile system and provides the glue needed to bind the halo neutrons to the core. Here we show that this problem is similar to that of the instability of the normal state of an electron system at zero temperature solved by Cooper, solution which is at the basis of BCS theory of superconductivity. By mimicking this approach using, aside from the bare nucleon-nucleon interaction, the long wavelength vibrations of the nucleus $^{11}$Li, the paradigm of halo nuclei, as tailored glues of the least bound neutrons, we are able to obtain a unified and quantitative picture of the observed properties of $^{11}$Li.

nucl-th↗

arXiv1998

On the Origin of Nuclear Superfluidity

The induced pairing interaction arising from the exchange of collective surface vibrations among nucleons moving in time reversal states close to the Fermi energy is found to lead to values of the pairing gap which are similar to those experimentally observed.

nucl-th↗

arXiv1998

Semiclassical Approximation to Neutron Star Superfluidity Corrected for Proximity Effects

The inner crust of a neutron star is a superfluid and inhomogeneous system, consisting of a lattice of nuclei immersed in a sea of neutrons. We perform a quantum calculation of the associated pairing gap and compare it to the results one obtains in the Local Density Approximation (LDA). It is found that the LDA overestimates the spatial dependence of the gap, and leads to a specific heat of the system which is too large at low temperatures, as compared with the quantal result. This is caused by the neglect of proximity effects and the delocalized character of the single-particle wavefunctions close to the Fermi energy. It is possible to introduce an alternative, simple semiclassical approximation of the pairing gap which leads to a specific heat that is in good agreement with the quantum calculation.

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