Inflating without a flat potential: Viscous inflation

We propose a novel inflationary model driven by bulk viscosity, where the negative pressure induced by the viscous term plays the role of an inflaton potential. Unlike conventional slow-roll inflation, where a nearly flat potential governs the inflaton’s dynamics, our model relies on a dissipative mechanism to sustain inflation. Since viscosity does not contribute directly to the Universe’s energy density, the Hubble rate is determined solely by the inflaton’s kinetic energy. The resulting power spectrum is nearly scale-invariant, with its spectral tilt governed by slow-roll parameters intrinsic to the model. We compare our predictions for the scalar spectral index and tensor-to-scalar ratio with the latest Planck 2018 measurements, demonstrating the viability of this alternative inflationary framework.