Steep inflation: ending braneworld inflation by gravitational particle production

We propose a scenario for inflation based upon the braneworld picture, in which high-energy corrections to the Friedmann equation permit inflation to take place with potentials ordinarily too steep to sustain it. Inflation ends when the braneworld corrections begin to lose their dominance. Reheating may naturally be brought about via gravitational particle production, rather than the usual inflaton decay mechanism; the reheat temperature may be low enough to satisfy the gravitino bound and the Universe becomes radiation dominated early enough for nucleosynthesis. We illustrate the idea by considering steep exponential potentials, and show they can give satisfactory density perturbations (both amplitude and slope) and reheat successfully. The scalar field may survive to the present epoch without violating observational bounds, and could be invoked in the quintessential inflation scenario of Peebles and Vilenkin.