2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/205584We consider one of the simplest time-dependent backgrounds in M-theory, describing the shrinking away of the M-theory dimension with the other spatial dimensions static. As the M-theory dimension becomes small, the situation becomes well-described by string theory in a singular cosmological background where the string coupling tends to zero but the $α'$-corrections become large, near the cosmic singularity. We compute these $α'$-corrections, both for the background and for linearized perturbations, in heterotic string theory, and show they may be reproduced by a map from eleven-dimensional M-theory.22 pages, 4 figuresHigh Energy Physics - Theorytext