Bose-Einstein condensation in finite drops of alpha particles

Abstract

Ground-state properties of finite drops of α particles (Q-balls) are studied within a fieldtheoretical approach in the mean-field approximation. The strong interaction of α's is described by the scalar field with a sextic Skyrme-like potential. The radial profiles of scalar-and Coulomb fields are found by solving the coupled system of Klein-Gordon and Poisson equations. A generalized condition for Bose-Einstein condensation in a finite system of charged bosons is formulated in terms of particle effective mass. The formation of shell-like nuclei, with vanishing density around the centre, is predicted at high enough attractive strength of Skyrme potential. The equilibrium values of energy and baryon number of Q-balls and Q-shells are calculated for different sets of interaction parameters. Empirical binding energies of α-conjugate nuclei are reproduced only if the gradient term in the Lagrangian is strongly enhanced. It is demonstrated that this enhancement can be explained by nonzero range of strong αα interaction.