# Schwinger-Keldysh techniques (in holography) ## Refs - originals: Schwinger1961 and Keldysh1964 - bulk dual developed in [[2008#Skenderis, van Rees (May)]] and [[2008#Skenderis, van Rees (Dec)]] - see also [[0440 grSK geometry]] ## Applications - used in [[2016#Dong, Lewkowycz, Rangamani]] to derive [[0007 RT surface|HRT]] - it was needed to turn real Euclidean path integrals used for RT surfaces to HRT surfaces - e.g. can use to generalise [[MarolfWangWang2020]] - Lorentzian replica spacetime: [[2020#Colin-Ellerin, Dong, Marolf, Rangamani, Wang]] ## Properties - a paper on relation between Euclidean sources and Lorentzian spacetimes [[2017#Marolf, Parrikar, Rabideau, Rad, van Raamsdonk]] #toread ## Examples - scalar correlation functions in BTZ - [[DimitrovMayersonMin2021]][](https://arxiv.org/pdf/2112.08197.pdf) - [[Melo2021]][](https://arxiv.org/pdf/2112.09119.pdf) - finds additional cross-terms between real and imaginary fields making the propagator matrix 3 by 3 rather than 2 by 2 - higher spins - [[2023#Hao]]