  In a recent work, Bodineau and Derrida analyzed the phase fluctuations in the
ABC model. In particular, they computed the asymptotic variance and, on the
basis of numerical simulations, they conjectured the presence of a drift, which
they guessed to be an antisymmetric function of the three densities. By
assuming the validity of the fluctuating hydrodynamic approximation, we prove
the presence of such a drift, providing an analytical expression for it. This
expression is then shown to be an antisymmetric function of the three
densities. The antisymmetry of the drift can also be inferred from a symmetry
property of the underlying microscopic dynamics.
