Chiroptical effect induced by gravitational waves

Abstract

We propose the gravitational analog of the chiroptical effect for the first time, demonstrating that gravitational waves (GWs) can induce a reversal of photon chirality through the exchange of angular momentum, namely the spin-2-gravitation chiroptical effect. By analyzing the interaction between photon spin angular momentum (SAM) and GWs, we derive the selection rules governing this exchange, which are strictly dictated by the spin-1 and spin-2 nature of the electromagnetic and gravitational fields, respectively. We find that the gravitational chiroptical effect reflects the local nature of SAM which prevents the accumulation of gravitational perturbations over spatial phase windings, and offers a theoretically rigorous tool to probe the chiral structure of GWs. This mechanism provides a novel observational pathway to constrain modified gravity theories, measure the asymmetric properties of compact binaries, and explore parity-violating physics in the early universe.

Figures (3)

• Figure 1: Schematic illustration of three GW effects on the photons: Partial deflection, polarization rotation, and the chiroptical effect.
• Figure 2: A right-circularly polarized GW propagating along the $-z$ axis rotates the light polarization clockwise. Note that the direction of rotation matches the chirality of the GW.
• Figure 3: Schematic of the gravitational chiroptical effect during (a) quasi-parallel ($\theta \rightarrow 0$), (b) antiparallel ($\theta = \pi$), and (c) perpendicular ($\theta = \pi/2$) propagation. Orange and green spheres represent GWs (gravitons) and photons, respectively. The black arrows indicate propagation directions and the blue numbers in boxes represent the $z$-component of AM. The red and purple arrows depict the reversal of photon chirality resulting from the exchange of AM between photons and GWs. The diagrams show that the selection rules governing the exchanges are strictly dictated by the spin-1 and spin-2 nature of the electromagnetic and gravitational fields, respectively.