Speaker
Description
Inflationary attractor models yield robust predictions, but these may change when gravity is extended beyond general relativity. To investigate this, we study scalar perturbations in scalar--torsion theories described by $f(T,\phi)+P(\phi)X$. In flat gauge, we expand the action to second order, retaining the tetrad's scalar boost, whose variation imposes an additional constraint. Eliminating the lapse, shift, and boost yields a single propagating scalar mode with sound speed $c_{\rm s}^2=1$. Beyond the TEGR limit, its effective mass can be nonzero due to this constraint. We relate the mode to the curvature perturbation in unitary gauge and recover the general-relativistic limit. This provides a basis for studying $\alpha$-attractor potentials and their primordial spectra in scalar--torsion gravity.