2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/141883We provide formulas for the entropy of free-string states depending on their mass, charges and size, both in bosonic and superstring theory (IIA or IIB). We properly define these quantities in full-fledged string theory. We then investigate the corrections to the entropy due to self-interactions of the string for states with fixed mass, charge and size, both for BPS and non-BPS configurations. Again, the analysis is performed using string theory techniques.28 pages, 2 figuresHigh Energy Physics - TheoryGeneral Relativity and Quantum Cosmologytext