Dispersion relation of a polaron in the Yang-Gaudin Bose gas

TL;DR

This paper analytically derives the dispersion relation of a polaron in a one-dimensional Yang-Gaudin Bose gas across weak and strong interactions, revealing a power series form and its implications for spectral response functions.

Contribution

It provides the first explicit analytical expressions for the polaron dispersion in the Yang-Gaudin Bose gas in both interaction regimes.

Findings

Polaron dispersion near dark soliton at weak interaction

Explicit power series form of dispersion at strong interaction

Coefficients decay faster with higher series order

Abstract

We study a one-dimensional Bose gas with two internal states described by the Yang-Gaudin model and calculate analytically the dispersion relation of a polaron quasiparticle, which is the lowest excitation branch. We study the dispersion in the thermodynamic limit in the regimes of weak and strong interaction without limitations on the momentum. At weak interaction the polaron dispersion is in the vicinity of the dark soliton one; we calculate the leading deviation in the parametric form. At strong interaction we find an ansatz for the explicit form of the polaron dispersion. It has the form of a power series of the sine function of the momentum with interaction-dependent coefficients. By increasing the power of the series, the corresponding coefficients show faster decay and thus one practically needs only a few of them; we give the results for the first three. The coefficients of the series are connected to the Maclaurin series of the polaron dispersion and thus it is sufficient to calculate latter quantity to automatically find the power series result for the dispersion at all momenta. The derived results for the dispersion can be used to obtain explicit expressions for the exponents of the power-law singularities in the response functions at the spectral edge.