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Born-Infeld gravity in any dimension J. A. Nieto* Facultad de Ciencias Fı ´sico-Matema ´ticas de la Universidad Auto ´noma de Sinaloa, Av. de las Ame ´ricas y Blvd. Universitarios, Ciudad Universitaria, C.P. 80010, Culiaca ´n Sinaloa, Me ´xico ~Received 10 February 2004; published 26 August 2004! We develop a Born-Infeld type theory for gravity in any dimension. We show that in four dimensions our formalism allows a self-dual ~or anti-self-dual! Born-Infeld gravity description. Moreover, we show that such a self-dual action is reduced to both the Deser-Gibbons and the Jacobson-Smolin-Samuel action of Ashtekar formulation. A supersymmetric generalization of our approach is outlined. DOI: 10.1103/PhysRevD.70.044042 PACS number~s!: 04.60.2m, 04.65.1e, 11.15.2q, 11.30.Ly I. INTRODUCTION More than 80 years ago, Eddington @1# introduced the action S EDD 5 E d 4 x A det~ R mn ~ G !! , ~1! as a possibility to incorporate affine invariance in a gravita- tional context. Here R mn 5R n m is the Ricci tensor and G mn a 5G n m a becomes the Christoffel symbol, after using the Pala- tini method. In 1934 Born and Infeld ~BI!@2# for different reasons than Eddington proposed a similar action for electrodynamics S BI 5 E d 4 x A det~ g mn 1F mn ! , ~2! where g mn is the space-time metric and F mn is the electro- magnetic field strength. It turns out that the action S BI re- duces to Maxwell action for small amplitudes. Some years ago, the action ~2! became of very much interest because its relation with SUSY ~see @3# and references therein! and string theory ~see @4–7# and references therein! and D-brane physics @8#. At present, the BI theory has been generalized to the supersymmetric non-Abelian case ~see @9# and references therein! and it has been connected with noncommutative ge- ometry @10# and Cayley-Dickson algebras @11#. Moreover, it turns out intriguing that the BI action can be derived from matrix theory @12# and D9-brane @13#. For interesting com- ments and observation about the BI theory the reader is re- ferred to the works of Schwarz @14# and Ketov @15#. Inspired by the interesting properties of the BI theory, Deser and Gibbons @16# proposed in 1998 the analogue of S BI for a gravity, S DG 5 E d 4 x A det~ ag mn 1bR mn 1cX mn ! . ~3! Here, X mn 5X n m stands for higher order corrections in cur- vature and a , b and c are appropriate coupling constants. De- ser and Gibbons determined some possible choices for X mn by imposing three basic criteria to the action ~3!, namely freedom of ghosts, regularization of singularities and super- symmetrizability. In fact, they found that the expression X mn ;R m a R an may provide one interesting choice for X mn , allowing the action ~3! to describe gravitons but no ghosts. From the point of view of string theory both the photon as well as the graviton should be part of the spectrum of a string. Therefore one should expect that just as S BI is used to regularize p-branes the S DG action may be used with similar purpose. However, for this possibility to be viable it is nec- essary to generalize the S DG action to higher dimensions. Moreover, Wohlfarth @17# has pointed out that the supersym- metrizability requirement presumably implied by M-theory, may provide another reason to be interested in such a higher- dimensional extension of S DG . In this work, we use similar technics as the one used in MacDowell-Mansouri formalism @18#~see also @19# and ref- erences therein! in order to generalize the S DG action to higher dimensions. In four dimensions, our approach is re- duced to the theory of Deser-Gibbons. We also show that in four dimensions our action admits self-dual ~anti-self-dual! generalization which is reduced to the Ashtekar action as proposed by Jacobson-Smolin-Samuel @20#. Since Born- Infeld type action has shown to be also useful to study dif- ferent aspects of the brane world scenario, our work may appear interesting in this area of research. The plan of this paper is as follows: In Sec. II, using a MacDowell-Mansouri’s type formalism we establish our pro- posed action for Born-Infeld gravity in any dimension. In Sec. III, we discuss the relationship between our proposed action and the Deser and Gibbons action. In Sec. IV, we consider a self-dual ~anti-self-dual! version of our proposed action in four dimensions and we show that it is reduced to the Jacobson-Smolin-Samuel action for the Ashtekar formal- ism. Finally, in Sec. V we outline a possible supersymmetric generalization of our formalism and we make some final re- marks. II. PROPOSED BORN-INFELD-GRAVITY BIGACTION Consider the extended curvature R mn ab 5R mn ab 1S mn ab , ~4! where *Electronic address: [email protected] PHYSICAL REVIEW D 70, 044042 ~2004! 1550-7998/2004/70~4!/044042~5!/$22.50 ©2004 The American Physical Society 70 044042-1

Born-Infeld gravity in any dimension

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Page 1: Born-Infeld gravity in any dimension

PHYSICAL REVIEW D 70, 044042 ~2004!

Born-Infeld gravity in any dimension

J. A. Nieto*Facultad de Ciencias Fı´sico-Matema´ticas de la Universidad Auto´noma de Sinaloa, Av. de las Ame´ricas y Blvd. Universitarios,

Ciudad Universitaria, C.P. 80010, Culiaca´n Sinaloa, Me´xico~Received 10 February 2004; published 26 August 2004!

We develop a Born-Infeld type theory for gravity in any dimension. We show that in four dimensions ourformalism allows a self-dual~or anti-self-dual! Born-Infeld gravity description. Moreover, we show that sucha self-dual action is reduced to both the Deser-Gibbons and the Jacobson-Smolin-Samuel action of Ashtekarformulation. A supersymmetric generalization of our approach is outlined.

DOI: 10.1103/PhysRevD.70.044042 PACS number~s!: 04.60.2m, 04.65.1e, 11.15.2q, 11.30.Ly

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I. INTRODUCTION

More than 80 years ago, Eddington@1# introduced theaction

SEDD5E d4xAdet~Rmn~G!!, ~1!

as a possibility to incorporate affine invariance in a gravtional context. HereRmn5Rnm is the Ricci tensor andGmn

a

5Gnma becomes the Christoffel symbol, after using the Pa

tini method.In 1934 Born and Infeld~BI! @2# for different reasons than

Eddington proposed a similar action for electrodynamics

SBI5E d4xAdet~gmn1Fmn!, ~2!

wheregmn is the space-time metric andFmn is the electro-magnetic field strength. It turns out that the actionSBI re-duces to Maxwell action for small amplitudes. Some yeago, the action~2! became of very much interest becauserelation with SUSY ~see @3# and references therein! andstring theory~see@4–7# and references therein! and D-branephysics@8#. At present, the BI theory has been generalizedthe supersymmetric non-Abelian case~see@9# and referencestherein! and it has been connected with noncommutativeometry@10# and Cayley-Dickson algebras@11#. Moreover, itturns out intriguing that the BI action can be derived fromatrix theory@12# and D9-brane@13#. For interesting com-ments and observation about the BI theory the reader isferred to the works of Schwarz@14# and Ketov@15#.

Inspired by the interesting properties of the BI theoDeser and Gibbons@16# proposed in 1998 the analogueSBI for a gravity,

SDG5E d4xAdet~agmn1bRmn1cXmn!. ~3!

Here,Xmn5Xnm stands for higher order corrections in cuvature anda,b andc are appropriate coupling constants. Dser and Gibbons determined some possible choices forXmn

*Electronic address: [email protected]

1550-7998/2004/70~4!/044042~5!/$22.50 70 0440

-

-

ss

o

-

e-

,

-

by imposing three basic criteria to the action~3!, namelyfreedom of ghosts, regularization of singularities and supsymmetrizability. In fact, they found that the expressiXmn;Rm

aRan may provide one interesting choice forXmn ,allowing the action~3! to describe gravitons but no ghosts

From the point of view of string theory both the photonwell as the graviton should be part of the spectrum ostring. Therefore one should expect that just asSBI is used toregularizep-branes theSDG action may be used with similapurpose. However, for this possibility to be viable it is neessary to generalize theSDG action to higher dimensionsMoreover, Wohlfarth@17# has pointed out that the supersymmetrizability requirement presumably implied by M-theormay provide another reason to be interested in such a higdimensional extension ofSDG .

In this work, we use similar technics as the one usedMacDowell-Mansouri formalism@18# ~see also@19# and ref-erences therein! in order to generalize theSDG action tohigher dimensions. In four dimensions, our approach isduced to the theory of Deser-Gibbons. We also show thafour dimensions our action admits self-dual~anti-self-dual!generalization which is reduced to the Ashtekar actionproposed by Jacobson-Smolin-Samuel@20#. Since Born-Infeld type action has shown to be also useful to study dferent aspects of the brane world scenario, our work mappear interesting in this area of research.

The plan of this paper is as follows: In Sec. II, usingMacDowell-Mansouri’s type formalism we establish our prposed action for Born-Infeld gravity in any dimension.Sec. III, we discuss the relationship between our propoaction and the Deser and Gibbons action. In Sec. IV,consider a self-dual~anti-self-dual! version of our proposedaction in four dimensions and we show that it is reducedthe Jacobson-Smolin-Samuel action for the Ashtekar formism. Finally, in Sec. V we outline a possible supersymmegeneralization of our formalism and we make some finalmarks.

II. PROPOSED BORN-INFELD-GRAVITY „BIG … ACTION

Consider the extended curvature

R mnab5Rmn

ab1Smnab , ~4!

where

©2004 The American Physical Society42-1

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J. A. NIETO PHYSICAL REVIEW D 70, 044042 ~2004!

Rmnab5]mvn

ab2]nvmab1vm

acvncb2vn

acvmcb ~5!

and

Smnab52~em

a enb2en

aemb !. ~6!

Here,vmab is a SO(d21,1) connection andem

a is a vierbeinfield. It turns out that Eq.~4! can be obtained using thMacDowell-Mansouri formalism@18# ~see also Ref.@19# andreferences therein!. In fact, in such a formalism the gravitational field is represented as a connection one-form assated to some group which contains the Lorentz group asubgroup. The typical example is provided by theSO(d,1)de Sitter gauge theory of gravity. In this case, theSO(d,1)gravitational gauge fieldvm

AB52 vmBA is broken into the

SO(d21,1) connectionvmab and thevm

da5ema vierbein field,

with the dimensiond fixed. Thus the de Sitter~or anti–deSitter! curvature

R mnAB5]mvn

AB2]nvmAB1vm

ACvnCB2vn

ACvmCB ~7!

leads to the curvature~4!.Let us now introduce the definition

R ma [eb

nR mnab , ~8!

whereebn is the inverse vierbien field.

Our proposed action is

S521

d! E ddx«m1 . . . mdea1 . . . adRm1

a1 . . . Rmd

ad , ~9!

-

04404

ci-a

where«m1 . . . md is the completely antisymmetric tensor assciated to the space-time, with«0 . . .d2151 and «0 . . .d2151, whileea1 . . . ad

is also the completely antisymmetric ten

sor but now associated to the internal groupS(d21,1), withe0 . . .d21521. We assume that the internal metric is givby (hab)5diag(21, . . . ,1). So, wehavee0 . . .d2151.

Using Eq.~6! we get

ebnSmn

ab5lema , ~10!

wherel512d. Therefore, Eqs.~4! and~8! and~10! lead to

R ma 5Rm

a 1lema , ~11!

where

Rma [eb

nRmnab . ~12!

Substituting Eq.~11! into Eq. ~9! we obtain

S521

d! E ddx«m1 . . . mdea1 . . . ad~Rm1

a1 1lem1

a1 ! . . . ~Rmd

ad

1lemd

ad !. ~13!

From this action we get

S52ld

d! E ddx«m1 . . . mdea1 . . . adem1

a1 . . . emd

ad 2dld21

d! E ddx«m1 . . . mdea1 . . . adem1

a1 . . . emd21

ad21 Rmd

ad

2d~d21!ld22

2!d! E ddx«m1 . . . mdea1 . . . adem1

a1 . . . emd22

ad22 Rmd21

ad21 Rmd

ad 2•••21

d! E ddx«m1 . . . mdea1 . . . adRm1

a1 . . . Rmd

ad .

~14!

in

Since

«m1 . . . mdea1 . . . ad52e~ea1

[m1 . . . ead

md]!, ~15!

where the bracket@m1 . . . md# means completely antisymmetric ande5det(em

a ), we find that the action~14! can bewritten as

S5ldE ddxe1ld21E ddxeR

1ld22

2! E ddxe~R22RmnRmn!1•••1E ddx det~Rma !.

~16!

Here, R[eamRm

a and Rmn[enaRma ,while Rmn[gmagnbRab ,

wheregab is the matrix inverse ofgab[eaaeb

bhab . We rec-ognize in the first and second terms in the action~16! theEinstein-Hilbert action with cosmological constantd-dimensions.

III. RELATION WITH DESER-GIBBONS TYPE ACTION

Let us define the tensor

Gmn[1

l2R m

a R nbhab . ~17!

Using Eq.~11! we get

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BORN-INFELD GRAVITY IN ANY DIMENSION PHYSICAL REVIEW D 70, 044042 ~2004!

Gmn51

l2~Rm

a 1lema !~Rn

b1lenb!hab

5gmn1LRmn1L2

4Rm

aRan , ~18!

whereL52/l. Here, we used the fact thatRmn5Rnm .From Eq.~17!, it is not difficult to see that

det~Gmn![21

l2dR 2, ~19!

whereR5det(R ma ). Therefore, our proposed action~9! can

be expressed in terms ofGmn as

S521

d! E ddx«m1 . . . mdea1 . . . adRm1

a1 . . . Rmd

ad 5E ddxR

5ldE ddxA2det~Gmn!. ~20!

In virtue of Eq.~18! the action~20! becomes

S52d

LdE ddxA2detS gmn1LRmn1L2

4Rm

aRanD ,

~21!

which is a Born-Infeld type action for gravity in any dimen

04404

sion. In four dimensions, we recognize that the action~21!corresponds to the one proposed by Deser and Gibbons@16#@see Eq.~3! of @16##, with Xmn5Rm

aRan .

IV. SELF-DUAL „ANTI-SELF-DUAL … ACTION IN FOURDIMENSIONS

In four dimensions the action~9! can be generalized to thcase of self-dual~anti-self-dual! gauge gravitational field. Wedefine the self-dual~anti-self-dual! of R mn

cd as

6R mnab5

1

26

McdabR mn

cd , ~22!

where

6Mcdab5

1

2~dcd

ab7 i ecdab!. ~23!

Here,dcdab5dc

addb2dc

bdda . We also define

6R ma [eb

n6R mnab . ~24!

In four dimensions~9! becomes

S521

4!E d4x«m1 . . . m4ea1 . . . a4Rm1

a1 . . . Rm4

a4 . ~25!

Substituting Eq.~11! into this expression lead us to

S521

4!E d4x«m1 . . . m4ea1 . . . a4~Rm1

a1 1lem1

a1 ! . . . ~Rm4

a4 1lem4

a4 !52l4

4!E d4x«m1 . . . m4ea1 . . . a4em1

a1 . . . em4

a4

24l3

4! E d4x«m1m2m3m4ea1a2a3a4em1

a1 em2

a2 em3

a3 Rm4

a4 26l2

4! E d4x«m1m2m3m4ea1a2a3a4em1

a1 em2

a2 Rm3

a3 Rm4

a4

24l

4! E d4x«m1m2m3m4ea1a2a3a4em1

a1 Rm2

a2 Rm3

a3 Rm4

a4 21

4!E d4x«m1m2m3m4ea1a2a3a4Rm1

a1 Rm2

a2 Rm3

a3 Rm4

a4 . ~26!

Simplifying these expressions one finds

S5l4E d4xe1l3E d4xeR1l2

2!E d4xe~R22RmnRmn!

1l

3!E d4xe~R323RRmnRmn12RmaRabRmb !

1E d4xedet~Rmn!. ~27!

Let us now generalize the action~25! in the form

S521

4!E d4x«m1 . . . m4ea1 . . . a4

6Rm1

a1 . . . 6Rm4

a4 . ~28!

It is not difficult to see that

6R ma [6Rm

a 1lema . ~29!

Thus, we have

S521

4!E d4x«m1 . . . m4ea1 . . . a4~6Rm1

a1 1lem1

a1 ! . . . ~ 6Rm4

a4

1lem4

a4 !. ~30!

Therefore, we obtain

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J. A. NIETO PHYSICAL REVIEW D 70, 044042 ~2004!

S5l4E d4xe1l3E d4xe6R1l2

2!E d4xe~ 6R2

2 6Rmn6Rmn!1l

3!E d4xe~ 6R3236R6Rmn6Rmn

126Rma6Rab6Rm

b !1E d4xedet~ 6Rmn!. ~31!

We recognize in the second term of this expression the Atekar action as proposed by Jacobson-Smolin-Samuel@20#.

V. FINAL COMMENTS

In this work, we proposed the action~9! as an alternativeto generalize to higher dimensions the Born-Infeld-gravaction of Deser and Gibbons. We proved that our actionfour dimensions allows a generalization to self-dual~anti-self-dual! action. Moreover, we showed that such a self-daction is reduced to the Jacobson-Smolin-Samuel actiothe Ashtekar formulation.

It is remarkable that the only requirement for the prposed action~9! is the general covariance implied by thtransition SO(d,1)→SO(d21,1). It remains to checkwhether the action~9! satisfies the criteria of ghosts freedoand regularization of singularities used by Deser and Gbons @16# in four dimensions and Wohlfarth@17# in higherdimensions. However, these requirements should be appvery carefully to the action~9! because under compactification ~9! should lead not only to gravity but also to YanMills and scalar fields. From the point of view of M-theorone may even think in a phase in which matter fields aghosts are mixed implying a generalization of the action~9!to some kind of topological theory.

As we mentioned in the Introduction, supersymmetrability provides to Wohlfarth@17# with one of the main mo-tivation for considering BI gravity in higher dimensionWohlfarth’s theory is constructed by using the symmetriesthe Riemann tensor, considering tensors with pair of asymmetrized indices. Specifically, the Wohlfarth’s formution is based on the action*A2g@(det(dB

A1jRBA)§21#,

whereRAB5R[mn][ ab] , dBA5dm

adnb2dm

bdna andj, § are con-

stants~see Ref.@17# for details!. Although interesting, it doesnot seem evident how to supersymmetrize this theory.

In contrast, our treatment admits a straightforward genalization to the supersymmetric version in four dimensioIn fact, in the action~9! we may replace the curvatureR mn

ab

by its supersymmetric extension

R mnab5Rmn

ab1Smnab1Qmn

ab ,

R mni 5Rmn

i 1Smni , ~32!

R mna 5Rmn

a 1Smna ,

where

04404

h-

n

lof

-

-

ed

d

-

fi-

r-.

Qmnab5

1

2f i j

abcmi cn

j , ~33!

Smna 5

1

2f i j

4acmi cn

j , ~34!

Smni 5 f 4a j

i ~ema cn

j 2enacm

j !, ~35!

and

Rmni 5]mcn

i 2]ncmi 1

1

2f cd j

i ~vmcdcn

j 2vncdcm

j !. ~36!

Here,cmi is a spinor field and the quantitiesf cd j

i and so onare the structure constants of algebra associated to thesupergroupOsp(1u4). It may be interesting for further research to see if the resulting supersymmetric Born-Infgravity theory is related to theD54, N51 Born-Infeld su-pergravity proposed by Gates and Ketov@21#.

Since some authors@22,23# have found interesting connections between the non-Abelian Born-Infeld theory aD-branes it may also be interesting for further researchinvestigate the relation of the action~9! with string theoryand withp-branes physics.

Recently, Liu and Li@24# have found an interesting applcation of Born-Infeld and brane worlds and Garcı´a-Salcedoand Breton@25# have studied the possibility that Born-Infelinflates the Bianchi cosmological models. It may be intereing to pursue an application of the action~9! in these direc-tions.

Pilatnik @26# has found spherical static solutions of thBorn-Infeld gravity theory which may also correspond to ttheory described by the action~9!. Feigenbaum@27# foundthat Born regulates gravity in four dimensions, so it appeattractive to see if the action~9! can be used to regulatgravity in higher dimensions. Furthermore, Vollick@28# usedthe Palatini formalism in Born-Infeld Einstein theory in foudimensions and identify the antisymmetric part of the Ritensor with the electromagnetic field. So, if we use simiPalatini’s technics in connection with the action~9! oneshould expect to identify part of the Ricci tensor with geeralized electromagnetic field, perhaps Yang-Mills field.

Finally, it has been shown~see @29#! that dualities inM-theory ~see@30# and references therein! are deeply relatedto Born Infeld theory. Since eleven dimensional supergravmust be part of M-theory one should expect that Born-Infgravity theory in any dimensions may play an important roin this context. In this direction the derivations of BornInfeld theory from supergravity@31# and the Nambu-Gotoaction from Born-Infeld theory@32# may be of particularinterest to continue a further research in connection withaction ~9!.

ACKNOWLEDGMENT

I would like to thank to M. C. Marı´n for helpful com-ments.

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BORN-INFELD GRAVITY IN ANY DIMENSION PHYSICAL REVIEW D 70, 044042 ~2004!

@1# A. S. Eddington,The Mathematical Theory of Relativity~Cam-bridge University Press, Cambridge, UK, 1924!.

@2# M. Born and L. Infeld, Proc. R. Soc. LondonA144, 425~1934!.

@3# A. Silvas, ‘‘Born-Infeld and Supersymmetry,’’ Ph.D. thesis,Plata, hep-th/0012267.

@4# A.A. Tseytlin, Nucl. Phys.B501, 41 ~1997!.@5# G. Karatheodoris, A. Pinzul, and A. Stern, Mod. Phys. Lett

A 18, 1681~2003!.@6# I.Y. Park, Phys. Rev. D64, 081901~2001!.@7# G.W. Gibbons, Rev. Mex. Fis.49S1, 19 ~2003!.@8# R. Emparan, Phys. Lett. B423, 71 ~1998!.@9# E.A. Bergshoeff, A. Bilal, M. de Roo, and A. Sevrin, J. Hig

Energy Phys.07, 029 ~2001!.@10# E. Serie, T. Masson, and R. Kerner, ‘‘Nonabelian generali

tion of Born-Infeld theory by noncommutative geometryhep-th/0307105.

@11# S. Kuwata, ‘‘Born-Infeld Lagrangian using Cayley-Dickson agebras,’’ hep-th/0306271.

@12# E. Keski-Vakkuri and Per Kraus, Nucl. Phys.B518, 212~1998!.

@13# S.F. Kerstan, Class. Quantum Grav.19, 4525~2002!.@14# J.H. Schwarz, ‘‘Comments on Born-Infeld theory,’’ talk give

at Strings 2001: International Conference, Mumbai, Ind2001, hep-th/0103165.

@15# S.V. Ketov, ‘‘Many faces of Born-Infeld theory,’’ Invited talkat 7th International Wigner Symposium~Wigsym 7!, CollegePark, Maryland, 2001, hep-th/0108189.

@16# S. Deser and G.W. Gibbons, Class. Quantum Grav.15, L35~1998!.

04404

-

,

@17# M.N.R. Wohlfarth, ‘‘Gravity a la Born-Infeld,’’hep-th/0310067.

@18# S.W. MacDowell and F. Mansouri, Phys. Rev. Lett.38, 739~1997!; F. Mansouri, Phys. Rev. D16, 2456~1977!.

@19# H. Graca-Compea´n, J.A. Nieto, O. Obrego´n, and C. Ramr´ez,Phys. Rev. D59, 124003~1999!; J.A. Nieto, O. Obrego´n, andJ. Socorro,ibid. 50, R3583~1994!; J.A. Nieto, J. Socorro, andO. Obrego´n, Phys. Rev. Lett.76, 3482~1996!.

@20# T. Jacobson and L. Smolin, Class. Quantum Grav.5, 583~1988!; J. Samuel, Pramana, J. Phys.28, L429 ~1987!.

@21# S.J. Jr. Gates and S.V. Ketov, Class. Quantum Grav.18, 3561~2001!.

@22# S. Nagoaka, ‘‘Fluctuation analysis of the nonAbelian BorInfeld action in the background intersecting D-braneshep-th/0307232.

@23# S. Stieberger and T.R. Taylor, Nucl. Phys.B648, 3 ~2003!.@24# D. Liu and X. Li, Phys. Rev. D68, 067301~2003!.@25# R. Garcia-Salcedo and N. Breton, ‘‘Born-Infeld inflates Bia

chi cosmologies,’’ hep-th/0212130.@26# D. Palatnik, Phys. Lett. B432, 287 ~1998!; 432, 287 ~1998!.@27# J.A. Feigenbaum, Phys. Rev. D58, 124023~1998!.@28# Dan N. Vollick, ‘‘Palatini approach to Born-Infeld-Einstein

theory and a geometric description of electrodynamicgr-qc/0309101.

@29# D. M. Brace, ‘‘Duality in M-theory and Born-Infeld theory,’’Ph.D. thesis~Advisor: Bruno Zumino!.

@30# M.J. Duff, Int. J. Mod. Phys. A11, 5623~1996!.@31# M. Sato and A. Tsuchiya, Prog. Theor. Phys.109, 687 ~2003!.@32# S. Ansoldi, C. Castro, E.I. Guendelman, and E. Spalluc

Class. Quantum Grav.19, L135 ~2002!.

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