ABSTRACT
Similarly - if we consider the D-brane as a solitonic solution in supergravity - the metric and the dilaton field ¢ diverge when approaching the D-brane, i.e. as the distance from the brane goes to zero. The considerations presented above suggest that this divergence is in fact not meaningfuL since supergravity is not the right tool in such a regime. Trying to cure this divergence by including the pile-up of massive closed string states in the supergravity effective action - i. e. trying to catch the feat ures of (he region t -+ oc performing a perturbative expansion around t = 0 - is not the most economic procedure. One should instead adopt the more appropriate open string picture. The effective Lagrangian which is suitable in this regime is written in terms of the lightest mode of the stretched string, with mass rn ,...., r / A;. In other words, one should not look for a regular metric and dilaton field. The appropriate description is now in terms of different low energy fields.
