Integral Eisenstein cocycles on GLn, I : Sczechs cocycle and p-adic L-functions of totally real fields

We define an integral version of Sczechs Eisenstein cocycle on GLn by smoothing at a prime ell. As a result we obtain a new proof of the integrality of the values at nonpositive integers of the smoothed partial zeta functions associated to ray class extensions of totally real fields. We also obtain a new construction of the p-adic L-functions associated to these extensions. Our cohomological construction allows for a study of the leading term of these p-adic L-functions at s=0. We apply Spiesss formalism to prove that the order of vanishing at s=0 is at least equal to the expected one, as conjectured by Gross. This result was already known from Wiles proof of the Iwasawa Main Conjecture.