2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/29507In underdoped cuprates, T_c is thought to be determined by Cooper pair phase fluctuations because of the small superfluid density n_s. Experimentally, T_c is found to scale with n_s. The fluctuation-exchange approximation (FLEX) in its standard form fails to predict this behavior of T_c since it does not include phase fluctuations. We therefore extend the FLEX to include them selfconsistently. We present results for T_c[n_s,x], where x is the doping.(5 pages, 3 figures included, minor changes, to appear in JLTP proceedings MOS99)Superconductivitytext