Interaction between nuclear clusters and superfluid phonons in the neutron-star inner crust

TL;DR

This paper derives a microscopic interaction model between nuclear clusters and superfluid phonons in neutron-star crusts, revealing a smaller coupling strength than previously estimated due to phonon amplitude suppression.

Contribution

It provides a microscopic calculation of the cluster-phonon coupling constant using nuclear density functional theory and quasiparticle RPA, clarifying its magnitude.

Findings

Coupling constant is significantly smaller than hydrodynamical estimates.

Superfluid phonon amplitude is suppressed inside and around nuclear clusters.

Microscopic response analysis yields a more accurate interaction parameter.

Abstract

The interaction between lattice vibrations of nuclear clusters and superfluid phonons associated with neutron superfluidity plays an important role in the dynamics of the neutron-star inner crust. While this coupling has been discussed mainly within macroscopic approaches such as hydrodynamics and effective field theory, its microscopic origin and the value of the effective coupling constant have remained unclear. In this work, we derive the interaction between nuclear clusters and superfluid phonons starting from a microscopic description of inner-crust matter. Using nuclear density functional theory, we analyze the response of a neutron superfluid around a single nuclear cluster within the quasiparticle random-phase approximation. From this microscopic response, we obtain the interaction between the cluster and the surrounding superfluid. Matching this result to the long-wavelength effective description, we determine the coupling constant in an effective Hamiltonian describing the mixing between lattice and superfluid phonons. The resulting coupling strength is found to be significantly smaller than previous hydrodynamical estimates. This reduction originates from the suppression of the superfluid phonon amplitude inside and around the nuclear cluster. Our results provide a microscopic determination of the coupling parameter governing lattice-superfluid phonon mixing in the neutron-star inner crust.