  We discuss the long distance behaviour of the flux tube associated to baryon
vertices and argue that, if the gauge system admits stable k-strings, the
conformal field theory describing this string in the IR has conformal anomaly
c=(d-2)\sigma_k/\sigma, where \sigma_k is the k-string tension and \sigma that
of the fundamental representation. We check this result in a 3D Z_4 gauge model
at finite temperature, where a string effect directly related to "c" can be
clearly identified.
