Tuesday, 30 June 2020

Nuclear soliton review

The latest article in the special topic I am co-editing in Frontiers in Physics appeared today.  It is called "Solitons in Nuclear Time-Dependent Density Functional Theory" and is by Yoritaka Iwata, from Kansei University, Osaka.

It follows on from some of his previous work (including a paper in New Journal of Physics I co-authored with him), combining a review of why one might expect soliton behaviour in nuclei, some existing results, and a new more thorough exploration of relevant parameter space.

The basis of the idea is that the time-dependent density functional theory which describes nuclear systems appears as a non-linear Schr√∂dinger equation which formally is equivalent to the canonical equation with which solitons are described.  Depending, then, on details of the nuclear interaction, and on the boundary conditions – the specific nuclear interaction being explored – one may find soliton solutions.

One particular confounding factor with the existence of solitons in nuclear reactions is the relative speed of the waves which equilibrate the charge and those which move matter.  If neutrons and protons are exchanged too quickly in reactions, then solitons are not possible.  This is something highlighted in Iwata's previous papers, and a hot topic in understanding heavy-ion reactions, with a recent paper in Physical Review Letters studying the same thing from a more nuclear physics (rather than mathematical/solitonic) perspective. 

Here's a picture from the paper (their Figure 4) showing a collisions around the boundary where charge equilibration is important:

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