Et al 2006 fotopoulos et al 2007 and fotopoulos and

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Unformatted text preview: os et al. (2007), and Fotopoulos and Tsulaia (2007). It yields deformed Fronsdal actions albeit with Abelian p-form-like vertices that do not contain the non-Abelian interactions characteristic of the higher-spin gravities to be discussed in this review. Whether there exists a refined limit in the spirit of the aforementioned deconstruction by Sagnotti and Taronna (2011), leading to such couplings, remains to be seen. As far as the closed AdS string is concerned, it exhibits a novel physical phenomenon that has no flat-space analog, whereby solitons, carrying quantum numbers of singletons, are formed at cusps (Engquist and Sundell, 2006); in the tensionless limit, their dynamics can be extracted by discretizing the Nambu-Goto action and degenerating spacetime to the Dirac hypercone leading to a direct connection between Vasiliev’s higher-spin gravities and tensionless closed strings in which the graviton on both sides is identified (Engquist and Sundell, 2006). The resulting physical picture is also in accordance with the holographic proposals by Sundborg (2001) and Sezgin and Sundell (2002b) later dubbed ‘‘la grande bouffe’’ (Bianchi, Morales, and Samtleben, 2003). Although these string-related theories are extremely interesting in their own right, here we are mainly concerned with non-Abelian interactions for strictly massless fields in flat spacetime and for their (A)dS analogs with their critical masses and the related higher-spin gravity. In the case of strictly massless fields in flat spacetime, many S-matrix no-go theorems can be found in the literature (Weinberg, 1964; Coleman and Mandula, 1967; Haag, Lopuszanski, and Sohnius, 1975; Grisaru, Pendleton, and van Nieuwenhuizen, 1977; Benincasa and Cachazo, 2007; Porrati, 2008; Benincasa and Conde, 2011) that seemingly forbid interacting massless higher-spin particles. Since the relative strength of no-go theorems is measured by the weakness of their hypotheses, the S-matrix approach is usually advertised because it does not require assumptions about ´ locality nor the Poincare-covariant realization of the incoming quanta. At a closer inspection, however, it turns out that the S-matrix no-go results obtained so far concern only the spin-s couplings involving s derivatives such as, for example, two-derivative couplings between the graviton and other fields. If one accepts that the spin-s couplings contain more than s derivatives, then these S-matrix arguments need to be reconsidered, and since the higher-spin interaction problem presents itself already at the classical level, it is anyway more satisfactory to pursue this analysis starting from purely Lagrangian arguments. And indeed, numerous cubic vertices, consistent at this order, have been found over the years in 990 Xavier Bekaert, Nicolas Boulanger, and Per A. Sundell: How higher-spin gravity surpasses the spin- . . . Minkowski and (A)dS spacetimes. They all exhibit higherderivative couplings and will be reviewed here,...
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This document was uploaded on 09/28/2013.

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