Hollowood, T., & Shore, G. (2008). The causal structure of QED in curved spacetime: Analyticity and the refractive index. Journal of High Energy Physics, 2008(12), pp. -091. doi:10.1088/1126-6708/2008/12/091

Hollowood, Timothy, and Graham Shore. "The Causal Structure of QED in Curved Spacetime: Analyticity and the Refractive Index." Journal of High Energy Physics 2008, no. 12 (2008): -091.

Hollowood, Timothy, and Graham Shore. "The Causal Structure of QED in Curved Spacetime: Analyticity and the Refractive Index." Journal of High Energy Physics 2008.12 (2008): -091.