Inhomogeneity growth in two-component fermionic systems

Abstract

The dynamics of fermionic many-body systems is investigated in the framework of BoltzmannLangevin (BL) stochastic one-body approaches. Within the recently introduced BLOB model, we examine the interplay between mean-field effects and two-body correlations, of stochastic nature, for nuclear matter at moderate temperature and in several density conditions, corresponding to stable or mechanically unstable situations. Numerical results are compared to analytic expectations for the fluctuation amplitude of isoscalar and isovector densities, probing the link to the properties of the employed effective interaction, namely symmetry energy (for isovector modes) and incompressibility (for isoscalar modes). For unstable systems, clusterization is observed. The associated features are compared to analytical results for the typical length and time scales characterizing the growth of unstable modes in nuclear matter and for the isotopic variance of the emerging fragments. We show that the BLOB model is generally better suited than simplified approaches previously introduced to solve the BL equation, and it is therefore more advantageous in applications to open systems, like heavy ion collisions.

Dynamic description of ternary and quaternary splits of heavy nuclear systems in the deep-inelastic regime

“…11, in comparison with the study of Ref. [23]), we concluded that for both semi-central and semi-peripheral impact parameters the leading wavelength related to the surface instability is roughly twice larger (λ = 20 f m) and the leading growth time can be up to ten times longer (t rupture = /Γ k ≈ 200 to 300 fm/c). As a consequence, rather massive fragments (roughly up to Germanium) are produced in such process with a formation time which, calculated from the onset of instabilities, extends over roughly 500 fm/c.…”

“…In this work, in the same spirit of Ref. [40], where the 197 Au+ 197 Au system was also simulated, we employed a stochastic one-body approach which, in this new attempt, adopts a full treatment of the Boltzmann-Langevin equation in three dimensions, condensed in the BLOB model [23,42]. Such approach handles shape fluctuations in the dynamical evolution more consistently, while keeping an efficient description of collective behaviour relying on the mean-field formalism.…”

Collision dynamics at medium and relativistic energies

“…The latter was conceived with the purpose of including fluctuations in full phase space, thus improving the treatment of fluctuations and correlations, but preserving, at the same time, mean-field features such as the proper description of spinodal instabilities at low density [116]. The improvement introduced by the BLOB approach is primarily providing a correct sampling of the fluctuation amplitude in full phase space, yielding a faster fragmentation dynamics and also a consistent description of the threshold toward multifragmentation.…”

“…As an illustrative example, Fig.13 shows the action of the isovector terms on the system 136 Xe+ 124 Sn (at 32 MeV/A), looking at fragment isotopic features. Results obtained with BLOB, employing an asystiff EOS, are displayed [116].…”

“…From this point of view, isospin observables could be also exploited as a tracer of the reaction dynamics, to probe pre-equilibrium stage and fragmentation path. Finally, it would be quite appealing to extend the comparison of pre-equilibrium and fragmentation features discussed above to other approaches recently introduced to deal with the nuclear many-body dynamics, namely approaches incorporating explicit light cluster production [76] and new stochastic models [116,66].…”