A pair of researchers, one at the Massachusetts Institute of Technology (MIT) and another at California Institute of Technology (Caltech) and the University of Tokyo, have recently investigated a set of old conjectures about symmetries in quantum gravity. The specific conjectures of focus: (1) Quantum gravity does not allow for global symmetries; (2) For gauge symmetry, all possible charges must be realized; (3) Internal gauge groups must be compact. Their paper, published in Physical Review Letters, shows that these old assumptions hold within the anti-de Sitter/conformal field theory (AdS-CFT) correspondence.
Source:
https://phys.org/news/2019-05-constraints-symmetries-holography.html