PIRSA:20020061 Scientific Series Quantum Fields and Strings

DOI10.48660/20020061

Series: Quantum Fields and Strings

Chandrasekaran, V. (2020). Entropy Variations and Light Ray Operators from Replica Defects. Perimeter Institute. https://pirsa.org/20020061

Chandrasekaran, Venkatesa. Entropy Variations and Light Ray Operators from Replica Defects. Perimeter Institute, Feb. 18, 2020, https://pirsa.org/20020061 

@misc{ pirsa_PIRSA:20020061,
  doi = {10.48660/20020061},
  url = {https://pirsa.org/20020061},
  author = {Chandrasekaran, Venkatesa},
  keywords = {Quantum Fields and Strings},
  language = {en},
  title = {Entropy Variations and Light Ray Operators from Replica Defects},
  publisher = {Perimeter Institute},
  year = {2020},
  month = {feb},
  note = {PIRSA:20020061 see, \url{https://pirsa.org}}
}

Abstract

We study the defect operator product expansion (OPE) of displacement operators in free and interacting conformal field theories using replica methods. We show that as n approaches 1 a contact term can emerge when the OPE contains defect operators of twist d−2. For interacting theories and general states we give evidence that the only possibility is from the defect operator that becomes the stress tensor in the n→1 limit. This implies that the quantum null energy condition (QNEC) is always saturated for CFTs with a twist gap. As a check, we show independently that in a large class of near vacuum states, the second variation of the entanglement entropy is given by a simple correlation function of averaged null energy operators as studied by Hofman and Maldacena. This suggests that sub-leading terms in the the defect OPE are controlled by a defect version of the spin-3 non-local light ray operator and we speculate about the possible origin of such a defect operator. For free theories this contribution condenses to a contact term that leads to violations of QNEC saturation.

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