Exact Matrix Elements of the Field Operator in the Thermodynamic Limit of the Lieb-Liniger Model

We study a matrix element of the field operator in the Lieb-Liniger model using the Bethe ansatz technique coupled with a functional approach to compute Slavnov determinants. We obtain the matrix element exactly in the thermodynamic limit for any coupling constant $c$, and compare our results to known semiclassics at the limit $c\to 0.$