Primordial black holes (PBHs) forming prior to big bang nucleosynthesis evolve during the reheating epoch, an environment dominated by an oscillating inflaton field decaying into a relativistic thermal bath. In this work, we track the complete lifecycle of PBHs within this coupled inflaton-radiation background. Utilizing $\alpha$-attractor E models, we analytically anchor the reheating initial conditions directly to cosmic microwave background observations. By matching exact scalar field solutions in a Schwarzschild spacetime to the cosmological far zone, we derive the cycle-averaged mass accretion rate and couple it to the growing radiation bath. We find that this combined accretion induces a highly nonlinear enhancement of the final PBH mass. Because the Hawking evaporation timescale scales cubically with mass, PBHs forming near their critical runaway limits experience a massive extension of their lifespans. Surviving deeper into the radiation-dominated era triggers a multi-order-of-magnitude amplification in their emitted stochastic gravitational wave background.

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• Cosmology
• Gravitational waves
• Inflation
• Primordial black holes