Arguments towards a c-theorem from branch-point twist fields

A fundamental quantity in (1+1)-dimensional quantum field theories is Zamolodchikov's c-function. A function of a renormalization group distance parameter r, which interpolates between ultraviolet and infrared fixed points, its value is usually interpreted as a measure of the number of degrees of freedom of a model at a particular energy scale. The c-theorem establishes that c(r) is a monotonically decreasing function of r and that its derivative. (c) over dot(r) alpha-r(3) may only vanish at quantum critical points (r = 0 and r = infinity). At those points, c(r) becomes the central charge of the conformal field theory which describes the critical point. In this communication, we argue that a different function proposed by Calabrese and Cardy, defined in terms of the two-point function , which involves the branch-point twist field T and the trace of the stress-energy tensor Theta, has exactly the same qualitative features as c(r).