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Type IIA supergravity

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Type IIA supergravity

In supersymmetry, type IIA supergravity is the unique supergravity in ten dimensions with two supercharges of opposite chirality. It was first constructed in 1984 by a dimensional reduction of eleven-dimensional supergravity on a circle. The other supergravities in ten dimensions are type IIB supergravity, which has two supercharges of the same chirality, and type I supergravity, which has a single supercharge. In 1986 a deformation of the theory was discovered which gives mass to one of the fields and is known as massive type IIA supergravity. Type IIA supergravity plays a very important role in string theory as it is the low-energy limit of type IIA string theory.

After supergravity was discovered in 1976 with pure 4D supergravity, significant effort was devoted to understanding other possible supergravities that can exist with various numbers of supercharges and in various dimensions. The discovery of eleven-dimensional supergravity in 1978 led to the derivation of many lower dimensional supergravities through dimensional reduction of this theory. Using this technique, type IIA supergravity was first constructed in 1984 by three different groups, by F. Giani and M. Pernici, by I.C.G. Campbell and P. West, and by M. Huq and M. A. Namazie. In 1986 it was noticed by L. Romans that there exists a massive deformation of the theory. Type IIA supergravity has since been extensively used to study the low-energy behaviour of type IIA string theory. The terminology of type IIA, type IIB, and type I was coined by J. Schwarz, originally to refer to the three string theories that were known of in 1982.

Ten dimensions admits both and supergravity, depending on whether there are one or two supercharges. Since the smallest spinorial representations in ten dimensions are MajoranaWeyl spinors, the supercharges come in two types depending on their chirality, giving three possible supergravity theories. The theory formed using two supercharges of opposite chiralities is denoted by and is known as type IIA supergravity.

This theory contains a single multiplet, known as the ten-dimensional nonchiral multiplet. The fields in this multiplet are , where is the metric corresponding to the graviton, while the next three fields are the 3-, 2-, and 1-form gauge fields, with the 2-form being the Kalb–Ramond field. There is also a Majorana gravitino and a Majorana spinor , both of which decompose into a pair of Majorana–Weyl spinors of opposite chiralities and . Lastly, there a scalar field .

This nonchiral multiplet can be decomposed into the ten-dimensional multiplet , along with four additional fields . In the context of string theory, the bosonic fields in the first multiplet consists of NSNS fields while the bosonic fields are all RR fields. The fermionic fields are meanwhile in the NSR sector.

The superalgebra for supersymmetry is given by

where all terms on the right-hand side besides the first one are the central charges allowed by the theory. Here are the spinor components of the Majorana supercharges while is the charge conjugation operator. Since the anticommutator is symmetric, the only matrices allowed on the right-hand side are ones that are symmetric in the spinor indices , . In ten dimensions is symmetric only for modulo , with the chirality matrix behaving as just another matrix, except with no index. Going only up to five-index matrices, since the rest are equivalent up to Poincare duality, yields the set of central charges described by the above algebra.

The various central charges in the algebra correspond to different BPS states allowed by the theory. In particular, the , and correspond to the D0, D2, and D4 branes. The corresponds to the NSNS 1-brane, which is equivalent to the fundamental string, while corresponds to the NS5-brane.

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