Universality in effective strings

It is demonstrated that, due to the finite thickness of domain walls and th e consequent ambiguity in defining their locations, the effective string de scription obtained by integrating out bulk degrees of freedom contains ambi guities in the coefficients of the various geometric terms. The only term w ith unambiguous coefficient is the zeroth-order Nambu-Goto term. We argue t hat fermionic ghost fields which implement gauge-fixing act to balance thes e ambiguities. The renormalized string tension, obtained after integrating out both bulk and world sheet degrees of freedom, can be defined in a schem e-independent manner; explicit finite expressions are computed, to one-loop , for the case of compact quantum electrodynamics and phi(4) theory. (C) 19 99 American Institute of Physics. [S0021-3640(99)00307-2].