# Null states Null states are states with zero norm. They are orthogonal to themselves. In order to obtain an irrep of e.g. [[0032 Virasoro algebra|Virasoro algebra]], one needs to quotient the states by the null states. See e.g. [[Rsc0002 Alday Notes on CFT]] chapter 6. ## Null states in celestial CFT - YM: - [[2020#Banerjee, Ghosh]] - GR: - [[2020#Banerjee, Ghosh, Paul]]: $\overline{S L(2, \mathbb{C})}$ symmetry - [[2021#Banerjee, Ghosh, Paul]]: Virasoro symmetry - [[2021#Banerjee, Ghosh, Samal]]: subsubleading soft graviton - classification: - [[2023#Banerjee, Kulkarni, Paul (Jan)]]