DCPT-02/03, FFUOV-02/01 Chern-Simons Couplings for Dielectric F-Strings in Matrix String Theory Dominic Brecher1, Bert Janssen1 and Yolanda Lozano2 1 Centre for Particle Theory, Department of Mathematical Sciences, University of Durham, South Road, Durham DH1 3LE, United Kingdom. email: dominic.brecher, [email protected] 2 0 0 2 Departamento de F´ısica, Universidad de Oviedo 2 Avda. Calvo Sotelo 18, 33007 Oviedo, Spain. n e-mail: [email protected] a J 7 1 Abstract: We compute the non-abelian couplings in the Chern-Simons action for a 2 set of coinciding fundamental strings in both the type IIA and type IIB Matrix string v 7 theories. Starting from Matrix theory in a weakly curved background, we construct the 0 linear couplings of closed string fields to type IIA Matrix strings. Further dualities give a 1 1 type IIB Matrix string theory and a type IIA theory of Matrix strings with winding.1 0 2 0 / 1 Introduction h t - p It is well-known that a collection of D-branes under the influence of a background R-R e field strength can undergo an “expansion” into a single higher-dimensional D-brane. This h : is the so-called dielectric effect, a first analysis of which was performed in [1], at the level v i of the abelian theory relevant to the description of the single expanded D-brane. It was X some years later that the complementary2 description from the point of view of the lower- r a dimensional multiple branes was provided [2]. From this perspective, the expansion takes place because the embedding coordinates of the multiple branes are matrix-valued, and give rise to new non-abelian couplings in the combined Born-Infeld-Chern-Simons action [3, 2]. There is much evidence that the dielectric effect should also exist for fundamental strings, both from the abelian analysis [1] and from the supergravity perspective [4]. However, one would further like to provide the complementary description from the point of view of the fundamental strings. Since, from the strings’ perspective, the dielectric effect should be due to matrix-valued coordinates, one is led to a consideration of Matrix string theory [5]. Moreover, matrix string theory is equivalent to type IIA superstring theory in the light-cone gauge, together with extra degrees of freedom representing D- brane states. Therefore it is the appropriate framework in which to study systems of multiple fundamental strings expanding into higher-dimensional D-branes (see also [6]). 1TalkgivenbyBertJanssen. 2See[2]foradiscussionontherangesofvaliditiesofthetwodescriptions. 1 Starting from Matrix theory in a weakly curved background, we construct the linear couplings of closed string fields to type IIA Matrix strings. Further dualities give a type IIB Matrix string theory and a type IIA theory of Matrix strings with winding. From these actions we identify the couplings that are responsible for the dielectric effect. This letter is a summary of the results published in [7]. 2 Matrix Theory and D0-branes Our starting point is the Chern-Simons action for D0-branes with linear couplings to the R-R background fields, as given in [3]: S = 1 dt STr C(1)Iµ +C(3) Iµνρ + 1 C(5) Iµ1...µ5 + 1 C(7) Iµ1...µ7 , (1) linear R Z n µ 0 µνρ 2 60 µ1...µ5 4 336 µ1...µ7 6 o where STr denotes the symmetrised trace and R the radius of the eleventh dimension. These couplings can be derived from the Matrix theory couplings to linear background fields, as shown in [8]. The indices µ,ν = 0,...,9, the currents I couple to the R-R p (p+1)-form potentials C(p+1) and the potentials C(5) and C(7) have been rescaled relative to [3]3. The currents appearing in (1) are given in terms of the dimensional reduction of the Born-Infeld field strength, i F = F0i = ∂ Xi X˙i, F = Fij = [Xi,Xj], (2) 0i t ij − ≡ β where i,j = 1,...,9 and β = 2πl3/R. We will not give the explicit expression but refer to P [3]. It can be shown [2, 7] that (1) agrees with the linear order expansion of the multiple D0-brane theory [3, 2] S = T dt STr P ei(iXiX)/λ C(n) , (3) 0 Z n h (cid:16)X (cid:17)io with λ = 2πα. Here the interior multiplication is defined as (i Σ) = XiΣ . ′ X µ1...µp iµ1...µp This type of contraction of the embedding scalars with the R-R potentials are the origin of the dielectric effect, as explained in [2]. 3 Multiple D-strings To construct the Matrix string theory of [5], one compactifies Matrix theory on a circle in, say, the x9 direction and performs a T-duality transformation. Taking now i,j = 1,...,8, and denoting the dual coordinate by xˆ, the world volume fields transform as [9] λ F9i = i[X9,Xi] 1 dxˆ D Xi, F09 = X˙9 1 dxˆλA˙ , (4) β −→ 2πRˆ9 Z β xˆ − −→ −2πRˆ9 Z xˆ whereRˆ = α/R istheradiusofthedualcircle. Turningtothelinearaction(1),wemust 9 ′ 9 consider T-duality applied to both the world volume and background fields. As far as the currents are concerned, we just have to consider the transformation of the Born-Infeld field strength (2) under T-duality, as given by (4) above. This is a simple re-writing, for the results we refer to [3]. 3Notethatthereshouldalsobecouplingsto C(9),butthesearenotdeterminedbytheanalysisof[3]. 2 To linear order, the action of T-duality on the R-R fields is: C(p) C(p 1) , (5) a1...ap−19 ←→ a1−...ap−1 where a,b = 0,...,8. A simple application of these rules gives S = 1 dtdxˆ STr C(0)I9 +C(2)Ia +3C(2)Iab9 +C(4) Iabc + 1 C(4) Ia1...a49 linear 2πRRˆ9 Z n 0 a9 0 ab 2 abc9 2 12 a1...a4 4 + 1 C(6) Ia1...a5 + 1 C(6) Ia1...a69 + 1 C(8) Ia1...a7 . (6) 60 a1...a59 4 48 a1...a6 6 336 a1...a79 6 o By construction, the multiple D0-brane action (3) is covariant under T-duality, so the T-dual of the D0-brane action (1) should be equivalent to the linearised version of the D-string action. With the Is as in [3], it is easy to see that the R-R terms can indeed be written as [2] S = T STr P ei(iXiX)/λ C(n) eλF , (7) 1 Z n h (cid:16)X (cid:17)i∧ o where F = A˙ .4 09 xˆ 4 Matrix string theory in type IIA Having constructed the (1+1)-dimensional theory for multiple D-strings, we are now in a position to perform the so-called 9-11 flip, which acts on the background fields as C(0) C(1), C(2) b , C(2) h , −→ − 9 ab −→ ab a9 −→ − a9 C(4) C(5) , C(4) C(3), C(6) N(7) , (8) a1...a4 −→ a1...a49 abc9 −→ abc a1...a6 −→ a1...a69 C(6) ˜b , C(8) C(9) , C(8) C(7) , a1...a59 −→ a1...a59 a1...a8 −→ − a1...a89 a1...a79 −→ − a1...a7 and will give us the type IIA Matrix string theory action in a linear background. Here, b , ˜b and N(7) are the NS-NS 2-form, its Hodge dual and the field that couples µν µ1..µ6 µ1...µ7 minimally to the type IIA Kaluza-Klein monopole, respectively. We take the view here that the currents are invariant under the 9-11 flip, since in the flat space case it does not change the worldvolume fields [5]. Performing the transformations (8) on the linear action (6), one finds S = 1 dτdσα′ STr C(1)I9 h Ia +3b Iab9 +C(3)Iabc + 1 C(5) Ia1...a49 2π Z R2 n− 9 0 − a9 0 ab 2 abc 2 12 a1...a49 4 + 1˜b Ia1...a5 + 1 N(7) Ia1...a69 1 C(7) Ia1...a7 . (9) 60 a1...a59 4 48 a1...a69 6 − 336 a1...a7 6 o Here, we have defined the dimensionless world sheet coordinates σ = 1 xˆ9, τ = R t. (10) Rˆ9 α′ Writing the currents I in terms of the dimensionless quantities τ and σ, this is the action describing Matrix string theory in a weakly curved background [10, 7]. In particular, if we set the Born-Infeld field to zero, we find for the R-R three-form couplings: S = i dτdσ STr √α′ 1 C(3) + √α′ 1 C(3) +X˙iC(3) , (11) C(3) 4πgs Z n R √2 + R √2 − i o 4Weshouldnote thatonlyhalfofthetermsnecessarytoformthepullbackofC(8) arepresentinthelinearaction(6). ThemissingtermscomefromthemissingC(9) couplingintheD0-braneaction(1). 3 where we have defined C(3) = [Xj,Xi]C(3), (12) µ µij and made use of light-cone coordinates. This coupling has been given before in [10]. We showed however in [7] that extra C(3) terms arise if one takes into account the couplings coming from the Born-Infeld part of the action. A dielectric solution involving only the couplingsin(11)wasgivenin[10]whichwehaveinterpretedin[7]intermsofgravitational waves expanding into a transverse D2-brane. It can be seen from (9) that as regards the R-R 5-form potential, only the terms of (5) the form C contribute. Setting the Born-Infeld vector to zero, the remaining 5-form a1...a49 R-R field couplings can be written as: S = i R dτdσ STr √α′C(5) +X˙iC(5) X˙iC(5) , (13) C(5) 4πgs√α′ Z n R +− +i − −io where we have defined C(5) = [Xk,Xj]DXiC(5) . (14) µν ijkµν Similarly, the C(7) couplings only have contributions involving terms of the form C(7) . a1...a7 These can be written as S = i R2 dτdσ STr √α′ 1 C(7) + √α′ 1 C(7) +X˙iC(7) , (15) C(7) 96πgs3 α′ Z n R √2 + R √2 − i o with C(7) = [Xn,Xm][Xl,Xk][Xj,Xi]C(7) . (16) µ ijklmnµ Let us also consider for the sake of completeness the couplings to ˜b(6) and N(7). As for C(5), only the terms with a 9-component appear in the action. The ˜b(6) couplings can be written as: S = 1 R dτdσ STr √α′˜b(6) +X˙i˜b(6) X˙i˜b(6) , (17) ˜b(6) 16πgs2√α′ Z n R +− +i − −io where ˜b(6) = [Xl,Xk][Xj,Xi]˜b(6) , (18) µν ijklµν and the N(7) couplings are given by S = 1 R2 dτdσ STr √α′N(7) X˙iN(7) +X˙iN(7) , (19) N(7) −16πgs2 α′ Z n R +− − +i −i o where N(7) = [Xm,Xl][Xk,Xj]DXiN(7) . (20) µν ijklmµν Note that the couplings of the different fields occur at a different order of the expansion parameter R/√α. Oneshould lookat these couplings when studying fundamental strings ′ expanding into D4-, D6- or NS5-branes, or Kaluza-Klein monopoles. 5 Multiple IIB F-strings To describe fundamental strings in the type IIB theory, we perform another T-duality in the x9 direction, as in (5). As before, we assume that the world volume fields do not change. The linear action (9) becomes SIIB = 1 dτdσα′ STr b Ia C(0)I9 +C(4) Iabc +3b Iab9 linear 2π Z R2 n a9 0 − 0 abc9 2 ab 2 4 + 1 C(4) Ia1...a49 + 1˜b Ia1...a5 + 1˜b Ia1...a69 1 C(8) Ia1...a7 , (21) 12 a1...a4 4 60 a1...a59 4 48 a1...a6 6 − 336 a1...a79 6 o which should describe Matrix strings in the IIB theory. Note that precisely the same action is obtained if one applies the S-duality rules to the D1-brane action (6), although it is not clear a priori how such an S-duality should be done directly, since we are dealing with non-abelian fields. The action above can be rewritten in a more convenient form, filling in the expressions for the currents: S = 1 dτdσ STr P α′b(2) + gs√α′C(0) F + i√α′(i i )C(4) +i(i i )b(2) F 2π Z n hR2 R ∧ gsR X X X X ∧ 1 (i i )2˜b(6) R (i i )2C(4) F+ iR (i i )3C(8) iR2 (i i )3˜b(6) F . (22) −2gs2 X X −2gs√α′ X X ∧ 6gs3√α′ X X −6gs2α′ X X ∧ io Again we note that only half of the terms necessary to form the pullback of C(8) are present in the linear action. Some of the above couplings have been given before in [11]. In [7] it was shown that the C(4) coupling gives rise to a solution of F-strings expanding into a D3-brane. 6 Multiple F-strings with winding in type IIA Type IIA F-strings with winding number can be obtained from IIB strings by performing a T-duality transformation in a direction transverse to the IIB strings. Calling z the T- duality direction and a = (0,i), where now i = 1,...,7, the linear action that is obtained from (21) is given by: SIIA = 1 dτdσα′ STr b Ia +h Iz C(1)I9 +C(5) Iabc 3C Iabz +3b Iab9 linear 2π Z R2 n a9 0 z9 0 − z 0 abc9z 2 − ab9 2 ab 2 6h Iaz9 + 1 N(7) Ia1...a5 + 1˜b Ia1...a4z + 1 C(5) Ia1...a49 + 1C(3)Iabcz9 − az 2 60 a1...a59z 4 12 a1...a4z9 4 12 a1...a4z 4 3 abc 4 1 C(9) Ia1...a7 + 1 C(7) Ia1...a6z + 1 N(7) Ia1...a69 + 1˜b Ia1...a5z9 . (23) −336 a1...a79z 6 48 a1...a69 6 48 a1...a6z 6 8 a1...a5z 6 o The direction z in which the T-duality is performed appears as an isometry direction in thetransverse spaceofthestrings. Wedenotethecorresponding Killing vector askµ = δµ, z k = η +h . Inamanner similar to theKaluza-Kleinmonopole, thenon-abelianstrings µ zµ zµ do not see this special direction, the embedding scalar Xz is not a degree of freedom of the strings, but is transformed under T-duality into a world volume scalar ω 5. Theaction(23)canbewritteninacovariantwayasagaugedsigmamodel,wheregauge covariant derivatives Xµ are used to gauge away the embedding scalar corresponding α D to the isometry direction [12]: Xµ = D Xµ k D Xρkµ, (24) α α ρ α D − with α = σ,τ. These gauge covariant derivatives reduce to the standard covariant deriva- tives D Xµ for µ = z and are zero for µ = z. The pull-backs in the action of the F-strings α 6 with winding are constructed from these gauge covariant derivatives. For example, b(2) = b Xµ Xνdtdx (25) µν Ph i D D 5This world volume scalar forms an invariant field strength with baz (see [11] for the details), and can therefore be associatedtofundamental stringswrappedaroundtheisometrydirectionz,whichthemselvesendontheMatrixstrings. 5 Filling in the expressions for the currents, we can write the Chern-Simons action as: S = 1 dτdσ STr gs√α′i C(1) F + α′b(2) √α′k(1) Dω +i(i )k(1) F linear 2π Z (cid:26)P(cid:20)− R k ∧ R2 − R ∧ [X,ω] ∧ +i√α′(i )C(3) + i (i i )C(3) Dω + R (i i )(i )C(3) F i√α′(i i )i C(5) gsR [X,ω] gs X X ∧ gs√α′ X X [X,ω] ∧ − gsR X X k + R (i i )2i C(5) F + 1 (i )(i i )i ˜b(6) + R (i i )2i ˜b(6) Dω 2gs√α′ X X k ∧ gs2 [X,ω] X X k 2gs2√α′ X X k ∧ + R2 (i )(i i )2i ˜b(6) F 1 (i i )2i N(7) iR2 (i i )3i N(7) F 2gsα′ [X,ω] X X k ∧ − 2gs2 X X k − 6gs2α′ X X k ∧ iR2 (i )(i i )3C(7) + R (i i )3i C(9) , (26) −2gs3α′ [X,ω] X X 6gs3√α′ X X k (cid:21)(cid:27) where we have introduced the following types of interior multiplication: (i Σ) = kρΣ = Σ , (i Σ) = [Xi,ω]Σ . 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