A note on four-particle form factors of operators {T}_{2n}{T}_{-2n} in the sinh-Gordon model

The diagonal matrix elements < {θ }₁,{θ }₂| {T}_2n{T}_-2n| {θ }₁,{θ }₂> between two-particle states in the sinh-Gordon model are computed analytically for all integers n\gt 0. This confirms the proposal [1] by Smirnov and Zamolodchikov for these matrix elements and demonstrates the effectiveness of the algebraic approach to form factors.