Corrections to Conformal Charge at BKT Transitions

The conformal anomaly is key to describing the physics of interacting field theories in two dimensions, and has been shown to obtain finite-size corrections that are useful to numerical and experimental studies. At Berezinskii-Kosterlitz-Thouless transitions, the corrections are logarithmic with previously unknown universal coefficients. In this paper, I reveal the universal, $1^{st}$-order correction to the conformal anomaly for finite-sized systems at BKT transitions. This term results solely from topological defects that are irrelevant in the infrared limit. I compare the result with careful observations of entanglement for the quantum Heisenberg model with periodic boundary conditions in one spatial dimension.