arXiv subjects

Ali H. Chamseddine

Publications and source records attributed to Ali H. Chamseddine.

84 records · Page 5Linked to original sources

arXiv2001

Non-Abelian vacua in D=5, N=4 gauged supergravity

We study essentially non-Abelian backgrounds in the five dimensional N=4 gauged SU(2)$\times$U(1) supergravity. Static configurations that are invariant under either the SO(4) spatial rotations or with respect to the SO(3) rotations and translations along the fourth spatial coordinate are considered. By analyzing consistency conditions for the equations for supersymmetric Killing spinors we derive the Bogomol'nyi equations and obtain their globally regular solutions. The SO(4) symmetric configurations contain the purely magnetic non-Abelian fields together with the purely electric Abelian field and possess two unbroken supersymmetries. The SO(3) configurations have only the non-Abelian fields and preserve four supersymmetries.

hep-th↗

arXiv2000

Complex Gravity and Noncommutative Geometry

The presence of a constant background antisymmetric tensor for open strings or D-branes forces the space-time coordinates to be noncommutative. An immediate consequence of this is that all fields get complexified. By applying this idea to gravity one discovers that the metric becomes complex. Complex gravity is constructed by gauging the symmetry $U(1,D-1)$. The resulting action gives one specific form of nonsymmetric gravity. In contrast to other theories of nonsymmetric gravity the action is both unique and gauge invariant. It is argued that for this theory to be consistent one must prove the existence of generalized diffeomorphism invariance. The results are easily generalized to noncommutative spaces.

hep-th↗

arXiv2000

Deforming Einstein's Gravity

A deformation of Einstein Gravity is constructed based on gauging the noncommutative ISO(3,1) group using the Seiberg-Witten map. The transformation of the star product under diffeomorphism is given, and the action is determined to second order in the deformation parameter.

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arXiv2000

Complexified Gravity in Noncommutative Spaces

The presence of a constant background antisymmetric tensor for open strings or D-branes forces the space-time coordinates to be noncommutative. This effect is equivalent to replacing ordinary products in the effective theory by the deformed star product. An immediate consequence of this is that all fields get complexified. The only possible noncommutative Yang-Mills theory is the one with U(N) gauge symmetry. By applying this idea to gravity one discovers that the metric becomes complex. We show in this article that this procedure is completely consistent and one can obtain complexified gravity by gauging the symmetry $U(1,D-1)$ instead of the usual $SO(1,D-1)$. The final theory depends on a Hermitian tensor containing both the symmetric metric and antisymmetric tensor. In contrast to other theories of nonsymmetric gravity the action is both unique and gauge invariant. The results are then generalized to noncommutative spaces.

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arXiv1999

Supersymmetric D0-Branes in Curved Backgrounds

An action for supersymmetric D0-branes in curved backgrounds is obtained by dimensional reduction of N=1 ten-dimensional supergravity coupled to super Yang-Mills system to 0+1 dimensions. The resultant action exhibits the coset-space symmetry $\frac{SO(9,9+n)}{SO(9)\times SO(9+n)}\times U(1)$ where $n=N^{2}-1$ is the dimension of the SU(N) gauge group.

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arXiv1998

Chiral Anomalies in the Spectral Action

The definition of the spectral action involves the trace operator over states in the physical Hilbert space. We show that in the presence of chiral fermions there are consistency conditions on the fermionic representations. These conditions are identical to the conditions for absence of gauge and gravitational anomalies obtained in the path integral formalism.

hep-th↗

arXiv1998

Gauged N=4 Supergravity through Compactification and BPS Monopoles

It is shown that N=4 gauged supergravity in four dimensions is obtained by compactifying N=1 supergravity in ten dimensions on the group manifold $S^3\times S^3$. This could be further related to supergravity in eleven dimensions. Analysis of supersymmetry conditions of N=4 gauged supergravity in four dimensions reveals solutions which preserve 1/4 of the supersymmetries and are characterized by a BPS-monopole-type gauge field. These solutions are lifted to solutions of the ten and eleven dimensional theories.

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arXiv1998

Remarks on the Spectral Action Principle

The presence of chiral fermions in the physical Hilbert space implies consistency conditions on the spectral action. These conditions are equivalent to the absence of gauge and gravitational anomalies. Suggestions for the fermionic part of the spectral action are made based on the supersymmetrisation of the bosonic part.

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arXiv1997

Non-Abelian Solitons in N=4 Gauged Supergravity and Leading Order String Theory

We study static, spherically symmetric, and purely magnetic solutions of the N=4 gauged supergravity in four dimensions. A systematic analysis of the supersymmetry conditions reveals solutions which preserve 1/4 of the supersymmetries and are characterized by a BPS-monopole-type gauge field and a globally hyperbolic, everywhere regular geometry. We show that the theory in which these solutions arise can be obtained via compactification of ten-dimensional supergravity on the group manifold. This result is then used to lift the solutions to ten dimensions.

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arXiv1997

Non-Abelian BPS Monopoles in N=4 Gauged Supergravity

We study static, spherically symmetric, and purely magnetic solutions of SU(2) $\times$ SU(2) gauge supergravity in four dimensions. A systematic analysis of the supersymmetry conditions reveals solutions which preserve 1/8 of the supersymmetries and are characterized by a BPS-monopole-type gauge field and a globally hyperbolic, everywhere regular geometry. These present the first known example of non-Abelian backgrounds in gauge supergravity and in leading order effective string theory.

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arXiv1997

An Effective Superstring Spectral Action

A supersymmetric theory in two-dimensions has enough data to define a noncommutative space thus making it possible to use all the tools of noncommutative geometry. In particular, we apply this to the N=1 supersymmetric non-linear sigma model and derive an expression for the generalized loop space Dirac operator, in presence of a general background, using canonical quantization. The spectral action principle is used to show that the superstring partition function is also a spectral action valid for the fluctuations of the string modes.

hep-th↗

arXiv1996

The Spectral Action Principle

We propose a new action principle to be associated with a noncommutative space $(\Ac ,\Hc ,D)$. The universal formula for the spectral action is $(ψ,Dψ) + \Trace (χ(D /$ $\Lb))$ where $ψ$ is a spinor on the Hilbert space, $\Lb$ is a scale and $χ$ a positive function. When this principle is applied to the noncommutative space defined by the spectrum of the standard model one obtains the standard model action coupled to Einstein plus Weyl gravity. There are relations between the gauge coupling constants identical to those of $SU(5)$ as well as the Higgs self-coupling, to be taken at a fixed high energy scale.

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