Series representation; Pade' approximants and critical behavior in QCD at nonzero T and mu_B

We discuss the analytic continuation beyond $\mu/T \simeq 1$ in QCD at nonzero T and $\mu$ by use of the Pade' approximants. The slope of the critical line obtained in this way increases at large $\mu$ with respect to the second order Taylor result.In the hot phase Pade' and Taylor approximants coincide, suggesting a very large, and possibly infinite, radius of convergence of the Taylor series in this thermodynamic region.