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

We give a simple discussion of ghosts, unitarity violation, negative normstates and quantum vs classical behavior in the simplest model with fourderivative action - the Pais-Uhlenbeck oscillator. We also point out that thenormalizable "vacuum state" (in the sense defined below) of this model can beunderstood as spontaneous breaking of the emergent conformal symmetry. Weprovide an example of an interacting system that couples the "particle" and"ghost" degrees of freedom and nevertheless remains unitary on both classicaland quantum level.

Some Comments on Ghosts and Unitarity: The Pais-Uhlenbeck Oscillator Revisited