出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We report the results of a set of high precision simulations performed in the 3d gauge Ising model.
We evaluated the interquark potential and the rst few energy levels and compared them with the
predictions obtained with the effective Nambu-Goto string and with the free bosonic string. The
data are precise enough to unambiguously distinguish between the free string predictions and
those obtained using the N-G effective string. At large distances we nd a remarkable agreement
between Monte Carlo data and N-G predictions for the rst excited energy level, while the free
string picture is denitely excluded. As the interquark distance is decreased (and/or the nite
temperature becomes higher) the Monte Carlo results show larger and larger deviations both from
the N-G and from the free string predictions. In order to better understand this behaviour we rederived
the effective Nambu-Goto theory result for the Polyakov loop correlator using a covariant
quantization. We chose as boundary conditions those of an open string attached to two D0-branes
at spatial distance R, in a target space with compact euclidean time. Obviously our treatment
is fully consistent only in d = 26. The extension to generic d requires taking into account the
Liouville mode of Polyakov's formulation. The analogy with the standard light cone calculation
suggests that the contribution due to the Liouville eld can be neglected for large R. At shorter
scales, the Liouville mode cannot be neglected and its contribution to the interquark potential
might be the source of the discrepancies with respect to the effective N-G results that we observe
in our Monte Carlo simulations.
