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In this paper we continue the programme initiated in Part I, that is thestudy of entanglement measures in the sine-Gordon model. In both parts, we havefocussed on one specific technique, that is the well-known connection betweenbranch point twist field correlators and measures of entanglement in 1+1Dintegrable quantum field theory. Our papers apply this technique for the firsttime to a non-diagonal theory with an involved particle spectrum, thesine-Gordon model. In this Part II we focus on a different entanglementmeasure, the symmetry resolved entanglement, and develop its associated twistfield description, exploiting the underlying U(1) symmetry of the theory. Inthis context, conventional branch point twist fields are no longer the fieldsrequired, but instead we must work with one of their composite generalisations,which can be understood as the field resulting from the fusion of a standardbranch point twist field and the sine-Gordon exponential field associated withU(1) symmetry. The resulting composite twist field has correlators which asusual admit a form factor expansion. In this paper we write the associated formfactor equations and solve them for various examples in the breather sector byusing the method of angular quantisation. We show that, in the attractiveregime, this is the sector which provides the leading contribution to thesymmetry resolved entropies, both Renyi and von Neumann. We compute the latterin the limit of a large region size and show that they satisfy the property ofequipartition, that is the leading contribution to the symmetry resolvedentanglement is independent of the symmetry sector.

Branch Point Twist Field Form Factors in the sine-Gordon Model II: Composite Twist Fields and Symmetry Resolved Entanglement