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 Plus monthly

Global: Zendy Tools annual

Global: Zendy Tools monthly

Global: Zendy Free Plan

Wick's theorem in the Schwinger-Perel-Keldysh closed-time-loop formalism iswritten in a form where the place of contractions is taken by the linearresponse function of the field. This result demonstrates that the physicalinformation supplied by Wick's theorem for operators is propagation of the freefield in space and time.

Causal signal transmission by quantum fields. IV: The causal Wick theorem