Primordial perturbations from dilaton-induced gauge fields

Understand

We study the primordial scalar and tensor perturbations in inflation scenario involving a spectator dilaton field.

• In our setup, the rolling spectator dilaton causes a tachyonic instability of gauge fields, leading to a copious production of gauge fields in the superhorizon regime, which generates additional scalar and tensor perturbations through gravitational interactions.
• Our prime concern is the possibility to enhance the tensor-to-scalar ratio $r$ relative to the standard result, while satisfying the observational constraints.
• To this end, we allow the dilaton field to be stabilized before the end of inflation, but after the CMB scales exit the horizon.