@MISC{Nair710stringtheories, author = {V. P. Nair}, title = {String Theories}, year = {710} }

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Abstract

A new class of twistor string theories were recently constructed by Abou-Zeid, Hull and Mason. The most interesting one of these theories has the particle content of N = 8 supergravity. Arguments are given for the vanishing of the (+ − −)-helicity amplitude for gravitons which suggest that this theory describes a chiral N = 8 supergravity rather than Einstein supergravity. Recently, a new set of twistor string theories has been proposed which has the potential of describing a number of interesting field theories as twistor string theories [1]. This was done by gauging the Berkovits form of the Witten-Berkovits twistor string theory with respect to a holomorphic one-form on twistor space [2, 3]. The Witten-Berkovits string theory describes N = 4 supersymmetric Yang-Mills theory coupled to N = 4 conformal supergravity [4]. There are two reasons why one might seek to modify this string theory. If the twistor string theory is to be used for calculations in Yang-Mills theory, then it is necessary to decouple (or eliminate) the conformal supergravitons which can otherwise contribute in loops. Being conformally coupled, there is no dimensional parameter which can be tuned to eliminate them. Secondly, since conformal gravity is a theory with fourth-order