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254

 

ϕ 4G x1x2abGx1x2

 

 

 

 

6 Supergravity: The Principles

exp

3

24

εabx1

...x8 Gx1x2x3x4 Gx5x6x7x8

 

(6.7.46)

 

4

 

 

 

 

 

1

 

 

 

 

 

 

 

 

 

1

 

 

 

 

 

 

 

 

 

0 = DmG ma1a2a3 +

 

 

fmG ma1a2a3

 

 

 

 

 

 

 

 

3

 

 

+

48

εa1a2a3x1...x7 Gx1x2x3x4 Hx5x6x7

 

+ exp

3

ϕ

2 G m[a1 H a2a3]nηmn

 

2

 

3

 

 

 

 

 

1

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(6.7.47)

Any solution of these bosonic set of equations can be uniquely extended to a full superspace solution involving 32 theta variables by means of the rheonomic conditions. The implementation of such a fermionic integration is the supergauge completion.

6.8 Type IIB Supergravity

The formulation of type IIB supergravity as it appears in string theory textbooks [3033] is tailored for the comparison with superstring amplitudes and is quite appropriate to this goal. Yet, from the viewpoint of the general geometrical set up of supergravity theories this formulation is somewhat unwieldy. Specifically it neither makes the SU(1, 1)/U(1) coset structure of the theory manifest, nor it relates the supersymmetry transformation rules to the underlying algebraic structure which, as in all other instances of supergravities, is a simple and well defined Free Differential algebra.

The Free Differential Algebra of type IIB supergravity was singled out many years ago by Castellani in [35] and the geometric manifestly SU(1, 1) covariant formulation of the theory was constructed by Castellani and Pesando in [34]. In this section we summarize their formulae giving also their transcription from a complex SU(1, 1) basis to a real SL(2, R) basis. Furthermore we provide the translation vocabulary between these intrinsic notations and those of Polchinski’s textbook [32, 33] frequently used in current superstring literature.

6.8.1 The SU(1, 1)/U(1) SL(2, R)/O(2) Coset

As it is later emphasized in Chap. 8, a basic ingredient in all supergravity constructions is the parameterization of the scalar manifold geometry that, with few exceptions, corresponds to a homogeneous scalar manifold. In all these cases the essential building block appearing in the Lagrangian and supersymmetry transformation rules is the coset representative Li ) that provides a parameterization of the coset manifold G/H in terms of some chosen patch of coordinates. A very use-

6.8 Type IIB Supergravity

255

ful choice is given by the so called solvable Lie algebra parameterization.11 This is true also in the present case where the solvable parameterization of the coset SU(1, 1)/U(1) SL(2, R)/O(2) is precisely that which allows for the identification of the massless superstring fields inside the covariant formulation of supergravity.

Our notations are as follows.

SL(2, R) Lie Algebra

[L0, L±] = ±L±; [L+, L] = 2L0

(6.8.1)

with the following explicit 2-dimensional representation:

L0 =

2

 

 

0

 

1

 

;

L+ =

 

0

0

;

L=

 

1

0

 

 

(6.8.2)

 

1

 

 

1

0

 

 

 

 

0

1

 

 

 

 

0

0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Coset Representative of SL(2, R)/O(2) in the Solvable Parameterization

 

L(ϕ, C[0])

 

exp ϕL0

 

exp C[0]eϕ L

C 0[eϕ/2]

exp

ϕ/2

 

(6.8.3)

 

 

 

=

 

[

 

 

]

 

 

=

exp

ϕ/2

 

 

0

 

 

]

 

 

 

 

 

 

 

 

[

]

 

 

[−

 

 

 

where ϕ(x) and C[0] are respectively identified with the dilaton and with the Ramond-Ramond 0-form of the superstring massless spectrum. The isomorphism of SL(2, R) with SU(1, 1) is realized by conjugation with the Cayley matrix:

 

=

 

1

i

 

 

C

 

1

 

1

i

 

(6.8.4)

 

 

 

 

 

 

 

 

 

2

 

 

 

 

 

Introducing the SU(1, 1) coset representative

 

 

 

SU(1, 1) # Λ = C LC 1

(6.8.5)

from the left invariant 1-form Λ1 we can extract the 1-forms corresponding to the scalar vielbein P and the U(1) connection Q

The SU(1, 1)/U(1) Vielbein and Connection

 

 

 

 

Λ1

=

P

iQ

(6.8.6)

 

 

 

iQ P

Explicitly

 

 

 

 

 

 

P =

1

ieϕ dC[0]

scalar vielbein

 

 

 

2

(6.8.7)

Q =

1

exp[ϕ] dC[0]

 

U(1)-connection

 

2

 

 

11For a review see either [25] or [24] and all references therein.

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