Open string derivation of winding states in thermal noncommutative field theories

The 'winding state' behavior appears in the two-loop nonplanar contribution to the partition function in thermal noncommutative field theories. We der ive this feature directly from the purely open string theory analysis in th e presence of the constant background B-field; we compute the two-loop part ition function for worldsheets with a handle and a boundary when the time d irection of the Euclideanized target space is compactified. In contrast to the closed-string-inspired approach, it is not necessary to add infinite nu mber of extra degrees of freedom. Furthermore, we find a piece of supportin g evidence toward the conjecture that, in the UV limit, the noncommutativit y parameter plays the role of the effective string scale in noncommutative held theories. (C) 2001 Published by Elsevier Science B.V.