universe Review On Exact Solutions and Perturbative Schemes in Higher Spin Theory Carlo Iazeolla 1, Ergin Sezgin 2,* and Per Sundell 3 1 NSR Physics Department, G. Marconi University, via Plinio 44, 00193 Rome, Italy;
[email protected] 2 Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University, College Station, TX 77843, USA 3 Departamento de Ciencias Físicas, Universidad Andres Bello, Sazie 2212, Santiago, Chile;
[email protected] * Correspondence:
[email protected] Received: 9 November 2017; Accepted: 12 December 2017; Published: 1 January 2018 Abstract: We review various methods for finding exact solutions of higher spin theory in four dimensions, and survey the known exact solutions of (non)minimal Vasiliev’s equations. These include instanton-like and black hole-like solutions in (A)dS and Kleinian spacetimes. A perturbative construction of solutions with the symmetries of a domain wall is also described. Furthermore, we review two proposed perturbative schemes: one based on perturbative treatment of the twistor space field equations followed by inverting Fronsdal kinetic terms using standard Green’s functions; and an alternative scheme based on solving the twistor space field equations exactly followed by introducing the spacetime dependence using perturbatively defined gauge functions. Motivated by the need to provide a higher spin invariant characterization of the exact solutions, aspects of a proposal for a geometric description of Vasiliev’s equation involving an infinite dimensional generalization of anti de Sitter space are revisited and improved. Keywords: higher-spin gravity; exact solutions; higher-spin geometry 1. Introduction Higher spin (HS) theory in four dimensions, in its simplest form and when expanded about its (anti-)de Sitter vacuum solution, describes a self-interacting infinite tower of massless particles of spin s = 0, 2, 4 ...