Atomic Dirac energy-level dynamics and redshift in the 4xU(1) gravity gauge field

Gravitational interaction unavoidably influences atoms and their electromagnetic radiation field in strong gravitational fields. Theoretical description of such effects using the curved metric of general relativity is limited due to the classical nature of the metric and the assumption of the local inertial frame, where gravitational interaction is absent. Here we apply unified gravity extension of the Standard Model [Rep. Prog. Phys. 88, 057802 (2025)] to solve the Dirac equation for hydrogen-like atoms in the 4xU(1) gravity gauge field, which appears alongside all other quantum fields. We show that the gravity gauge field shifts the atomic Dirac energy levels by an amount that agrees with the experimentally observable gravitational redshift. Our result for the redshift follows directly from quantum field theory and is strictly independent of the metric-based explanation of general relativity. Furthermore, we present how gravitational potential gradient breaks the symmetry of the electric potential of the atomic nucleus, thus leading to splitting of otherwise degenerate spectral lines in strong gravitational fields. Enabling detailed spectral line analysis, our work opens novel possibilities for future investigations of quantum photonics phenomena in strong gravitational fields.