p-Brane Tension & Mass Spectrum

In string/M-theory, p-branes are p-dimensional extended objects with tension T_p = 1/(g_s·(2π)^p·l_s^{p+1}). Fundamental strings (p=1) have T_1=1/(2πl_s²), while D-branes have T_p ∝ g_s^{-1}. At strong coupling, Dp-branes become light — key to S-duality. The BPS bound M≥|Z| ensures stability; saturated for supersymmetric branes. The duality web: T-duality maps Dp↔D(p±1), S-duality maps D1↔F1, and M-theory lifts D2→M2, F1→M2.