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Alexander Sevrin

Publications and source records attributed to Alexander Sevrin.

At least 37 records · Page 2Linked to original sources
arXiv2009

N=2 world-sheet approach to D-branes on generalized Kaehler geometries: II. Dualities

Following the general formalism reviewed in 0810.5355 [hep-th] we present several examples of possible D3-brane configurations on four-dimensional generalized Kaehler geometries. We will discuss T-duality transformations in N = 2 boundary superspace and apply the duality transformations to the constructed D3-branes. The duality transformations lead to a systematic method to construct coisotropic branes, even on target spaces that are not hyper-Kaehler.

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arXiv2008

N = 2 world-sheet approach to D-branes on generalized Kaehler geometries: I. General formalism

We present an N = 2 world-sheet superspace description of D-branes on bihermitian or generalized Kaehler manifolds. To accomplish this, D-branes are considered as boundary conditions for a nonlinear sigma-model in what we call N = 2 boundary superspace. In this note the general formalism for such an approach is presented and the resulting classification sketched. This includes some remarks regarding target spaces whose parameterization includes semi-chiral superfields which have not appeared in the literature yet. In an accompanying note we turn to some examples and applications of the general setup presented here.

hep-th↗
arXiv2008

An N=2 worldsheet approach to D-branes in bihermitian geometries: I. Chiral and twisted chiral fields

We investigate N=(2,2) supersymmetric nonlinear sigma-models in the presence of a boundary. We restrict our attention to the case where the bulk geometry is described by chiral and twisted chiral superfields corresponding to a bihermitian bulk geometry with two commuting complex structures. The D-brane configurations preserving an N=2 worldsheet supersymmetry are identified. Duality transformations interchanging chiral for twisted chiral fields and vice versa while preserving all supersymmetries are explicitly constructed. We illustrate our results with various explicit examples such as the WZW-model on the Hopf surface S3xS1. The duality transformations provide e.g new examples of coisotropic A-branes on Kahler manifolds (which are not necessarily hyper-Kahler). Finally, by dualizing a chiral and a twisted chiral field to a semi-chiral multiplet, we initiate the study of D-branes in bihermitian geometries where the cokernel of the commutator of the complex structures is non-empty.

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arXiv2008

A and B branes from N=2 superspace

We present a manifestly supersymmetric description of A and B branes on Kaehler manifolds using a completely local N=2 superspace formulation of the world-sheet nonlinear sigma-model in the presence of a boundary. In particular, we show that an N=2 superspace description of type A boundaries is possible. This leads to a concrete realization of the still poorly understood coisotropic A branes. We also discuss briefly how the superspace description of a B brane provides an efficient way to compute higher loop beta-functions. In particular, we sketch how one obtains the fourth order derivative correction to the Born-Infeld action by using a beta-function method.

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arXiv2006

A note on N=(2,2) superfields in two dimensions

Motivated by the results in {\tt hep-th/0508228}, we perform a careful analysis of the allowed linear constraints on $N=(2,2)$ scalar superfields. We show that only chiral, twisted-chiral and semi-chiral superfields are possible. Various subtleties are discussed.

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arXiv2003

Supersymmetric non-linear sigma-models with boundaries revisited

We study two-dimensional supersymmetric non-linear sigma-models with boundaries. We derive the most general family of boundary conditions in the non-supersymmetric case. Next we show that no further conditions arise when passing to the N=1 model. We present a manifest N=1 off-shell formulation. The analysis is greatly simplified compared to previous studies and there is no need to introduce non-local superspaces nor to go (partially) on-shell. Whether or not torsion is present does not modify the discussion. Subsequently, we determine under which conditions a second supersymmetry exists. As for the case without boundaries, two covariantly constant complex structures are needed. However, because of the presence of the boundary, one gets expressed in terms of the other one and the remainder of the geometric data. Finally we recast some of our results in N=2 superspace and discuss applications.

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arXiv2003

Higher order terms in the non-abelian D-brane effective action and magnetic background fields

Recently a proposal for the non-abelian effective D-brane action was given through fourth order in alpha'. As the resulting expressions turned out to be quite involved, some checks of this result are called for. In the present paper we calculate the spectrum in the presence of constant magnetic background fields and compare it to the string theoretical result. Apart from a small typo in the original expression (the overall sign of thefourth order term), we obtain perfect agreement. We discuss potential applications.

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arXiv2002

Strings, gravity and particle physics

This contribution, aimed mostly at experimental particle physicists, reviews some of the main ideas and results of String Theory in a non-technical language. It originates from the talks presented by the authors at the Electro-Weak session of the 2002 Moriond Meeting, here merged in an attempt to provide a more complete and concise view of the subject.

hep-ex↗
arXiv2002

The non-abelian D-brane effective action through order $α'{}^4$

Requiring the existence of certain BPS solutions to the equations of motion, we determine the bosonic part of the non-abelian D-brane effective action through order $α'{}^4$. We also propose an economic organizational principle for the effective action.

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arXiv2002

Testing the fermionic terms in the non-abelian D-brane effective action through order $α'{}^3$

Recently the construction of the non-abelian effective D-brane action was performed through order $α'{}^3$ including the terms quadratic in the gauginos. This result can be tested by calculating the spectrum in the presence of constant magnetic background fields and comparing it to the string theoretic predictions. This test was already performed for the purely bosonic terms. In this note we extend the test to the fermionic terms. We obtain perfect agreement.

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arXiv2001

Getting the D-brane effective action from BPS configurations

We review a method to find the non-abelian open superstring effective action, thereby settling the issue of the ordering ambiguities. We start from solutions to Yang-Mills which, in D-brane context, define certain BPS configurations. Studying their deformations in the abelian case shows that the Born-Infeld action is the unique deformation which admits solutions of this type. By applying the method to the non-abelian case we calculated the full effective action through O(α'^3). The presence of derivative terms turns out to be essential. Testing the result by comparing the spectrum in the presence of a constant magnetic background field with the string theory prediction, we obtain perfect agreement.

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arXiv2001

The non-abelian open superstring effective action through order $α'{}^3$

Using the method developed in {\tt hep-th/0103015}, we determine the non-abelian Born-Infeld action through ${\cal O}(α'{}^3)$. We start from solutions to a Yang-Mills theory which define a stable holomorphic vector bundle. Subsequently we investigate its deformation away from this limit. Through $ {\cal O}(α'{}^2)$, a unique, modulo field redefinitions, solution emerges. At $ {\cal O}(α'{}^3)$ we find a one-parameter family of allowed deformations. The presence of derivative terms turns out to be essential. Finally, we present a detailed comparison of our results to existing, partial results.

hep-th↗
arXiv2001

Testing the $α'{}^3$ term in the non-abelian open superstring effective action

Recently, a proposal for the full non-abelian open superstring effective action through ${\cal O}(α'{}^3)$ has been formulated in {\tt hep-th/0108169}. We test this result by calculating the spectrum in the presence of constant magnetic background fields and by comparing the result to string theoretic predictions. The agreement is perfect. Other proposals for the superstring effective action through this order do not reproduce the spectrum correctly.

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arXiv2001

The Uniqueness of the Abelian Born-Infeld Action

Starting from BPS solutions to Yang-Mills which define a stable holomorphic vector bundle, we investigate its deformations. Assuming slowly varying fieldstrengths, we find in the abelian case a unique deformation given by the abelian Born-Infeld action. We obtain the deformed Donaldson-Uhlenbeck-Yau stability condition to all orders in alpha'. This result provides strong evidence supporting the claim that the only supersymmetric deformation of the abelian d=10 supersymmetric Yang-Mills action is the Born-Infeld action.

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arXiv2001

The non-abelian Born-Infeld action at order F^6

To gain insight into the non-abelian Born-Infeld (NBI) action, we study coinciding D-branes wrapped on tori, and turn on magnetic fields on their worldvolume. We then compare predictions for the spectrum of open strings stretching between these D-branes, from perturbative string theory and from the effective NBI action. Under some plausible assumptions, we find corrections to the Str-prescription for the NBI action at order F^6. In the process we give a way to classify terms in the NBI action that can be written in terms of field strengths only, in terms of permutation group theory.

hep-th↗
arXiv2000

Chiral forms and their deformations

We systematically study deformations of chiral forms with applications to string theory in mind. To first order in the coupling constant, this problem can be translated into the calculation of the local BRST cohomological group at ghost number zero. We completely solve this cohomology and present detailed proofs of results announced in a previous letter. In particular, we show that there is no room for non-abelian, local, deformations of a pure system of chiral p-forms.

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