2024/04/10 by Pedro Bittar, Bittar, Pedro, S. Fichet +3 · 3 citations
Earth and Planetary Sciences · Physics and Astronomy · #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #FOS: Physical sciences #Geophysics and Gravity Measurements #High Energy Physics - Theory (hep-th)
paper · pdf · doi:10.48550/arxiv.2404.07254
openalex publication_date 2024/04/10 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We compute the four-photon (F4) operators generated by loops of charged particles of spin 0, (1)/(2), 1 in the presence of gravity and in any spacetime dimension d. To this end, we expand the one-loop effective action via the heat kernel coefficients, which capture both the gravity-induced renormalization of the F4 operators and the low-energy Einstein-Maxwell effective field theory (EFT) produced by massive charged particles. We set positivity bounds on the F4 operators using standard arguments from extremal black holes (for d≥ 4) and from infrared (IR) consistency of four-photon scattering (for d≥ 3). We find that both approaches yield nearly equivalent results, even though in the amplitudes we discard the graviton t-channel pole and use the vanishing of the Gauss-Bonnet term at quadratic order for any d. The positivity bounds constrain the charge-to-mass ratio of the heavy particles. If the Planckian F4 operators are sufficiently small or negative, such bounds produce a version of the d-dimensional Weak Gravity Conjecture (WGC) in most, but not all, dimensions. In the special case of d=6, the gravity-induced beta functions of F4 operators from charged particles of any spin are positive, leading to WGC-like bounds with a logarithmic enhancement. In d=9,10, the WGC fails to guarantee extremal black hole decay in the infrared EFT, thereby requiring the existence of sufficiently large Planckian F4 operators.