Researchers have used numerical simulations to model the dynamic evolution of the early Universe within the framework of the Starobinsky inflationary model. This model, which describes a phase of ultra-rapid exponential expansion of the early Universe, is one of the most successful and serves as a benchmark for other inflationary theories. The study focused on the interaction between the scalaron (the quantum field responsible for inflation) and the production of radiation from its decay, ensuring exact energy conservation in an expanding background.

The simulations, starting with a radiation-free Universe and initial conditions based on standard slow-roll approximations, showed that inflationary dynamics are predominantly governed by the scalaron. Despite continuous radiation production, the radiation component remained subdominant during inflation, which lasted for approximately 60 *e*-folds. Following the inflationary phase, the scalaron entered a damped oscillatory phase, accompanied by rapid radiation growth. This transition represents a "graceful exit" from inflation and a smooth entry into the reheating phase.

During reheating, the radiation energy density continuously increased as the scalaron's energy was depleted. Ultimately, the radiation energy density substantially exceeded the residual scalaron energy, indicating the onset of a hot, radiation-dominated phase. This result satisfies the Kofman-Yi criterion for successful reheating, demonstrating that the coupled scalaron-radiation dynamics provides a self-consistent realization of the graceful exit from inflation and the transition to radiation domination in the Starobinsky model.