English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The effect of vacuum polarization on the propagation of photons in curvedspacetime is studied in scalar QED. A compact formula is given for the fullfrequency dependence of the refractive index for any background in terms of theVan Vleck-Morette matrix for its Penrose limit and it is shown how thesuperluminal propagation found in the low-energy effective action is reconciledwith causality. The geometry of null geodesic congruences is found to imply anovel analytic structure for the refractive index and Green functions of QED incurved spacetime, which preserves their causal nature but violates familiaraxioms of S-matrix theory and dispersion relations. The general formalism isillustrated in a number of examples, in some of which it is found that therefractive index develops a negative imaginary part, implying an amplificationof photons as an electromagnetic wave propagates through curved spacetime.

The Causal Structure of QED in Curved Spacetime: Analyticity and the Refractive Index