arXiv subjects

Mohammad R. Garousi

Publications and source records attributed to Mohammad R. Garousi.

At least 73 records · Page 4Linked to original sources

arXiv2015

Higher-derivative corrections to type II supergravity:Four Ramond-Ramond terms

It is known that the sphere-level S-matrix element of four type II superstrings has one kinematic factor. At the low energy limit, this factor produces the kinematic factor of the corresponding Feynman amplitudes in the supergravity. It also produces higher-derivative couplings of four strings. In this paper, we explicitly calculate the kinematic factor of four RR states in the supergravity. Using this factor, we then find the eight-derivative P-even and P-odd couplings of four RR fields, including the self-dual RR five-form field strength. We show that the P-even couplings are mapped to the standard $\bar{R}^4$ couplings by linear T-duality and S-duality transformations. We also confirm the P-even couplings with direct calculations in type II superstring theories.

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arXiv2014

Sphere-level Ramond-Ramond couplings in Ramond-Neveu-Schwarz formalism

We calculate in details the sphere-level scattering amplitude of two Ramond-Ramond (RR) and two Neveu-Schwarz-Neveu-Schwarz (NSNS) vertex operators in type II superstring theories in Ramond-Neveu-Schwarz (RNS) formalism. We then compare the expansion of this amplitude at order $α'^3$ with the eight-derivative couplings of the gravity and B-field that have been recently found based on S-dual and T-dual Ward identities. We find exact agreement. Moreover, using the above S-matrix element, we have found various couplings involving the dilaton field, and shown that they are also fully consistent with these Ward identities.

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arXiv2014

S-duality constraint on higher-derivative couplings

The Riemann curvature correction to the type II supergravity at eight-derivative level in string frame is given as e^{-2ϕ}(t_8t_8R^4+\frac{1}{4}\eps_{8}\eps_{8}R^4). For constant dilaton, it has been extended in the literature to the S-duality invariant form by extending the dilaton factor in the Einstein frame to the non-holomorphic Eisenstein series. For non-constant dilaton, however, there are various couplings in the Einstein frame which are not consistent with the S-duality. By constructing the tensors $t_{2n}$ from Born-Infeld action, we include the appropriate Ricci and scalar curvatures as well as the dilaton couplings to make the above action to be consistent with the S-duality.

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arXiv2013

S-duality of D-brane action at order $O(α'^2)$

Using the compatibility of the DBI and the Chern-Simons actions with the T-duality transformations, the curvature corrections to these actions have been recently extended to include the quadratic B-field couplings at order $O(α'^2)$. In this paper, we use the compatibility of the couplings on D$_3$-brane with the S-duality to find the nonlinear RR couplings at order $O(α'^2)$. We confirm the quadratic RR couplings in the DBI part with the disk-level scattering amplitude. Using the regularized non-holomorphic Eisenstein series $E_1$, we then write the results in $SL(2,Z)$ invariant form.

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arXiv2013

Ramond-Ramond S-matrix elements from T-dual Ward identity

Recently it has been speculated that the Ward identities associated with the string dualities and the gauge symmetries can be used as guiding principles to find all components of the scattering amplitude of $n$ supergravitons from a given component of the S-matrix. In this paper, we apply the Ward identities associated with the T-duality and the gauge symmetries on the disk-level S-matrix element of one RR $(p-3)$-form, one NSNS and one NS states, to find the corresponding S-matrix elements of the RR $(p-1)$-form, $(p+1)$-form or the RR$(p+3)$-form on the world volume of a D$_p$-brane. Moreover, we apply these Ward identities on the S-matrix element of one RR $(p-3)$-form and two NSNS states to find the corresponding S-matrix elements of the RR $(p-1)$-form, $(p+1)$-form, $(p+3)$-form or the RR $(p+5)$-form.

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arXiv2013

T-duality of D-brane action at order $α'$ in bosonic string theory

In bosonic string theory, it is known that the Buscher rules for the T-duality transformations receive quantum corrections at order $α'$. In this paper, we use the consistency of the gravity couplings on the D-brane effective action at order $α'$, with the above T-duality transformations to find the B-field and the dilaton couplings. We show that these couplings are fully consistent with the corresponding disk-level S-matrix elements in string theory.

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arXiv2013

T-duality of curvature terms in D-brane actions

We examine the known curvature terms in the DBI part of the D-brane action under the T-duality transformation. Using the compatibility of the action with the standard rules of T-duality at the linear order as a guiding principle, we include the appropriate NS-NS $B$-field terms in the action and show that they reproduce the O(α'^2) terms of the corresponding disk-level scattering amplitude.

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arXiv2013

S-duality invariant dilaton couplings at order $α'^3$

The Riemann curvature correction to the type II supergravity at eight-derivative level is given schematically as $(t_8t_8+{1}{8}\eps_{10}\eps_{10})R^4$ at tree-level. The replacement of the generalized Riemann curvature in $t_8t_8R^4$, proposed by Gross and Sloan, produces various NS-NS couplings which are invariant under T-duality. Recently, using the combination of S-duality and T-duality transformations on these couplings, we have found groups of couplings which are invariant under the S-duality transformation. In this paper, we have examined the couplings involving the dilaton with direct scattering amplitude calculations of four NS-NS vertex operators in the superstring theory and found exact agreement. The coupling $\eps_{10}\eps_{10}R^4$ is a total derivative term at four-field level. The $σ$-model beta function approach implies the presence of this term at the tree-level. By examining the sphere-level scattering amplitude of five gravitons, we have also confirmed the presence of this term in the tree-level effective action.

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arXiv2013

Generalized Riemann curvature corrections to type II supergravity

We observe that the replacement of the Riemann curvature with the generalized Riemann curvature into the corrections to the type II supergravity at order $α'^3$ which are in terms of the contractions of four Riemann curvatures $R^4$, is not fully consistent with the S-matrix elements in the superstring theory. In particular, they produce non-zero S-matrix elements for odd number of B-field strengths which are not consistent with the string theory results. Using the consistency of the couplings with the linear T-duality as a guiding principle, we consider all T-duality invariant couplings and fix their coefficients by requiring them to be consistent with the S-matrix elements. The new Lagrangian density is then equivalent to the replacement of the generalized Riemann curvature into the expression $t_8t_8R^4$.

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arXiv2013

S-duality of tree-level S-matrix elements in D$_3$-brane effective action

Recently it has been speculated that the S-matrix elements on the world volume of D$_3$-branes should satisfy the ward identity corresponding to the S-duality transformations. For a single brane and in the low energy limit, this indicates that in the abelian Dirac-Born-Indeld-Chern-Simons theory the combination of contact terms and tree-level massless poles in an $n$-point function should satisfy the S-duality. In this paper we examine in details the S-matrix element of three gauge bosons and one two-form and the S-matrix element of six gauge bosons in favor of the above proposal.

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arXiv2013

Ramond-Ramond corrections to type II supergravity at order $α'^3$

Recently, it has been shown that the NS-NS corrections to the type II supergravity given by Gross and Sloan are invariant under the linear T-duality. In this paper, we study the invariance of this action under sequence of S-duality and linear T-duality to find the R-R corrections to the supergravity at order $α'^3$, up to field redefinition.

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arXiv2013

S-matrix elements from T-duality

Recently it has been speculated that the S-matrix elements satisfy the Ward identity associated with the T-duality. This indicates that a group of S-matrix elements is invariant under the linear T-duality transformations on the external states. If one evaluates one component of such T-dual multiplet, then all other components may be found by the simple use of the linear T-duality. The assumption that fields must be independent of the Killing coordinate, however, may cause, in some cases, the T-dual multiplet not to be gauge invariant. In those cases, the S-matrix elements contain more than one T-dual multiplet which are intertwined by the gauge symmetry. In this paper, we apply the T-dual Ward identity on the S-matrix element of one RR $(p-3)$-form and two NSNS states on the world volume of a D$_p$-brane to find its corresponding T-dual multiplet. In the case that the RR potential has two transverse indices, the T-dual multiplet is gauge invariant, however, in the case that it has one transverse index the multiplet is not gauge invariant. We find a new T-dual multiplet in this case by imposing the gauge symmetry. We show that the multiplets are reproduced by explicit calculation, and their low energy contact terms at order $α'^2$ are consistent with the existing couplings in the literature.

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arXiv2012

T-duality of the Riemann curvature corrections to supergravity

We examine the known Riemann curvature corrections to the supergravity action at order $α'^3$ under the T-duality transformations. Using the compatibility of the action with the linear T-duality and with the S-matrix calculations as guiding principles, we have found the couplings of four $B$-field strengths and the couplings of two Riemann curvatures and two $B$-field strengths at order $α'^3$. Using the S-matrix calculations we have also found new dilaton couplings in the string frame at this order.

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arXiv2012

Ricci curvature corrections to type II supergravity

We examine the NS-NS corrections to the type II supergravity given by Gross and Sloan, under the linear T-duality transformations. We show that the gravity and the B-field couplings are invariant under off-shell T-duality, whereas the dilaton couplings are invariant under on-shell T-duality. Requiring the compatibility of the dilaton couplings with off-shell T-duality as a guiding principle, we extend them to include the appropriate Ricci curvature and the divergence of the B-field strength.

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arXiv2012

S-duality of color-ordered amplitudes

Recently, it has been proposed that the S-matrix elements on the world volume of an abelian D$_3$-brane are consistent with the Ward identity associated with the S-duality. In this paper we extend this study to the case of multiple D$_3$-branes. We speculate that the S-matrix elements are consistent with the S-dual Ward identity irrespective of the ordering of the external states. Imposing this symmetry on the particular case of the S-matrix element of one Kalb-Ramond, one transverse scalar and two nonabelian gauge bosons, we will find the linear S-duality transformation of the commutator of two nonabelian gauge field strengths. Using this transformation and the standard S-duality transformations of the supergravity fields, all other nonabelian S-matrix elements of one closed and three open string states can be found by the S-duality proposal. We will show that the predicted S-matrix elements are reproduced exactly by explicit calculations.

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arXiv2012

Tree-level S-matrix elements from S-duality

It has been speculated that the S-matrix elements of type IIB superstring theory satisfy the Ward identity associated with the S-duality. This indicates that a group of S-matrix elements at each loop level are invariant under the linear $SL(2,R)$ transformations. If one evaluates one element of such S-dual multiplet, then all other components can be found by the simple use of the linear $SL(2,R)$ transformations. In this paper, we calculate the disk-level S-matrix element of one graviton(dilaton), one B-field and one gauge boson on the word volume of D$_3$-brane. The S-dual multiplet corresponding to the graviton(dilaton) amplitude has three(six) components. In particular, the graviton multiplet has the S-matrix element of one graviton, one R-R two-form and one gauge boson, and the dilaton multiplet has the S-matrix element of one R-R scalar, one B-field and one gauge boson vertex operators. We calculate explicitly these particular components and show that they are precisely the ones predicted by the S-duality. We have also found the low energy contact terms of the dilaton multiplet at order $α'^2$.

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arXiv2011

On S-duality of D$_3$-brane S-matrix

There is a conjecture in the literature that indicates the tree-level S-matrix elements of graviton become symmetric under the $SL(2,Z)$ transformation after including the loops and the nonperturbative effects. Using the Ward identity corresponding to the global S-duality transformations, this conjecture can be extended to other S-matrix elements as well. While the $SL(2,Z)$ transformation on the background dilaton is nonlinear, the Ward identity dictates the S-duality transformations on external states should be the linearized $SL(2,R)$ transformations. We examine in details various S-matrix elements involving massless closed string and/or open string vertex operators on the world volume of D$_3$-brane in favor of this conjecture.

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arXiv2011

S-duality of S-matrix

Recently, it has been observed that the kinematic factor of the disk-level S-matrix element of two RR two-forms and the disk-level S-matrix element of two B-fields on the world volume of D$_3$-brane are compatible with the standard rules of S-duality. Inspired by this observation, we speculate that the S-matrix elements on the world volume of D$_3$-brane are invariant under the $SL(2,Z)$ transformation. Compatibility with S-duality requires the S-matrix elements on the world volume of D$_1$-brane and D$_5$-brane to be extended to the $SL(2,Z)$-covariant form. In particular, this implies the S-matrix elements on the world volume of F$_1$-string and NS$_5$-brane at strong coupling to be related by S-duality to the disk-level S-matrix elements of D$_1$-string and D$_5$-brane, respectively. %The S-matrix elements then dictate that both F$_1$-string and NS$_5$-brane have D$_1$-string excitations. The contact terms of these S-matrix elements at order $O(α'^0)$ produce a Born-Infeld and Chern-Simons type effective action for both F$_1$-string and NS$_5$-brane. They are consistent with the $SL(2,R)$-covariant action appears in the literature.

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