2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/50245We exhibit a tachyonic mode in a linearized analysis of perturbations of large anti-de Sitter Reissner-Nordstrom black holes in four dimensions. In the large black hole limit, and up to a 0.7% discrepancy which is probably round-off error in the numerical analysis, the tachyon appears precisely when the black hole becomes thermodynamically unstable.6 pages, REVTex 4.0, one figure. For problems viewing or printing the figure, see http://viper.princeton.edu/~ssgubser/tachyon/READMEHigh Energy Physics - Theorytext