Finite-size effects in one-dimensional Bose–Einstein condensation of photons

The finite-size effect plays a key role in one-dimensional Bose–Einstein condensation (BEC) of photons since such condensation cannot occur in the thermodynamic limit due to the linear dispersion relation of photons. However, since a divergence difficulty arises, the previous theoretical analysis of the finite-size effect often only gives the leading-order contribution. In this article, by using an analytical continuation method to overcome the divergence difficulty, we give an analytical treatment for the finite-size effect in BEC. We show that the deviation between experiment and theory becomes much smaller by taking into account the next-to-leading correction.