Higher Spin Gravity and its Applications

Higher spin gravities are theories whose spectrum contains a graviton (i.e. a massless particle with spin 2) together with (infinitely many) massless higher-spin particles (i.e. with spin greater than 2). However, interactions between higher-spin particles have been a challenge for theoretical physicists since the early 70’s, when the first attempts to write down some consistent interaction between them were made after the birth of supergravity. A first set of nonlinear equations, describing an infinite tower of interacting massless totally-symmetric tensor fields of all integer spins in four dimensions was proposed by M. A. Vasiliev in the early 90’s. These equations were extended to arbitrary dimensions in 2003. On top of being a formal solution to the long-standing problem of higher- spin interactions, Vasiliev’s theory attracted a lot of attention due to the holographic duality (proposed by Klebanov, Polyakov, Sezgin and Sundell in 2002) relating it to the critical O(N) vector model - an interacting conformal field theory (CFT) of a large number of massless scalar fields - which is of high importance in statistical physics since it belongs to the universality class of the Ising model. Since then, there has been a great deal of progress in the understanding of higher-spin holographic dualities and the structure of the interactions encoded in Vasiliev’s equations. Nevertheless, many challenging open problems remain such as their locality properties. The purpose of this program is to bring together a broad spectrum of researchers working on higher spin to exchange ideas and develop new insights which will lead to new advances as well as new collaborations across these diverse fields.