Quantum 2025 – wissenschaftliches Programm

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TUE: Tuesday Contributed Sessions

TUE 9: Quantum Physics in Strong Fields: Contributed Session to Symposium

TUE 9.8: Vortrag

Dienstag, 9. September 2025, 16:00–16:15, ZHG101

Photon-graviton conversion in a magnetic field — •Naser Ahmadiniaz — Helmholtz Zentrum Dresden Rossendorf, Dresden, Germany

In this talk, I will first give a brief overview of the worldline formalism, a first-quantized approach to quantum field theory that streamlines the computation of scattering amplitudes in gauge theory and gravity. This method is particularly well suited to incorporating background fields non-perturbatively and reveals the underlying geometric structure of amplitudes. The main focus will be on photon--graviton conversion in an external magnetic field. While this process is typically studied at tree level, one-loop corrections due to scalar and spinor fields have also been computed. Unlike the tree-level result, the one-loop amplitude exhibits a dependence on the photon polarization, leading to vacuum dichroism. I will present a worldline-based derivation of this one-loop effect and show how the formalism naturally captures the emergence of dichroism. Furthermore, I will discuss the role of a previously neglected tadpole contribution. Although such diagrams often vanish in conventional treatments, we find that in this context the tadpole gives a finite contribution to the amplitude that must be included to obtain a complete result.

Keywords: Worldline method; Phton graviton conversion