Ahmed Hindawi

Nontrivial vacua in higher-derivative gravitation.

A discussion of an extended class of higher-derivative classical theories of gravity is presented. A procedure is given for exhibiting the new propagating degrees of freedom, at the full nonlinear level, by transforming the higher-derivative action to a canonical second-order form. For general fourth-order theories, described by actions which are general functions of the scalar curvature, the Ricci tensor and the full Riemann tensor, it is shown that the higher-derivative theories may have multiple stable vacua. The vacua are shown to be, in general, nontrivial, corresponding to de Sitter or anti{endash}de Sitter solutions of the original theory. It is also shown that around any vacuum the elementary excitations remain the massless graviton, a massive scalar field, and a massive ghostlike spin-two field. The analysis is extended to actions which are arbitrary functions of terms of the form {nabla}{sup 2{ital k}}{ital R}, and it is shown that such theories also have a nontrivial vacuum structure. {copyright} {ital 1996 The American Physical Society.}

Consistent spin two coupling and quadratic gravitation

A discussion of the field content of quadratic higher-derivative gravitation is presented, together with a new example of a massless spin-two field consistently coupled to gravity. The full quadratic gravity theory is shown to be equivalent to a canonical second- order theory of a massive scalar field, a massive spin-two symmetric tensor field and gravity. The conditions showing that the tensor field describes only spin-two degrees of freedom are derived. A limit of the second-order theory provides a new example of massless spin-two field consistently coupled to gravity. A restricted set of vacua of the second-order theory is also discussed. It is shown that flat-space is the only stable vacuum of this type, and that the spin-two field around flat space is unfortunately always ghost-like.

Four-dimensional higher-derivative supergravity and spontaneous supersymmetry breaking

Abstract We construct two classes of higher-derivative supergravity theories generalizing Einstein supergravity. We explore their dynamical content as well as their vacuum structure. The first class is found to be equivalent to Einstein supergravity coupled to a single chiral superfield. It has a unique stable vacuum solution except in a special case, when it becomes identical to a simple no-scale theory. The second class is found to be equivalent to Einstein supergravity coupled to two chiral superfields and has a richer vacuum structure. It is demonstrated that theories of the second class can possess a stable vacuum with vanishing cosmological constant that spontaneously breaks supersymmetry. We present an explicit example of this phenomenon and compare the result with the Polonyi model.

Vector-tensor multiplet in N = 2 superspace with central charge

Abstract We use the four-dimensional N = 2 central charge superspace to give a geometrical construction of the Abelian vector-tensor multiplet consisting, under N = 1 supersymmetry, of one vector and one linear multiplet. We derive the component field supersymmetry and central charge transformations, and show that there is a super-Lagrangian, the higher components of which are all total derivatives, allowing us to construct superfield and component actions.

Spherically symmetric solutions in Møller's tetrad theory of gravitation

The general solution of Møllers field equations in case of spherical symmetry is derived. The previously obtained solutions are verified as special cases of the general solution.

Soft supersymmetry breaking induced by higher-derivative supergravitation in the electroweak standard model

Abstract We show how spontaneous supersymmetry breaking in the vacuum state of higher-derivative supergravity is transmitted, as explicit soft supersymmetry-breaking terms, to the effective Lagrangian of the standard electroweak model. The general structure of the soft supersymmetry breaking terms is presented and a new scenario for understanding the gauge hierarchy problem, based on the functional form of these terms, is discussed.

Two-dimensional higher-derivative supergravity and a new mechanism for supersymmetry breaking

Abstract We discuss the general form of quadratic (1,1) supergravity in two dimensions, and show that this theory is equivalent to two scalar supermultiplets coupled to nontrivial supergravity. It is demonstrated that the theory possesses stable vacua with vanishing cosmological constant which spontaneously break supersymmetry.

Higher-Derivative Gravitation and a New Mechanism for Supersymmetry Breaking in Four-Dimensions

A discussion of the number of degrees of freedom, and their dynamical properties, in higher derivative gravitational theories is presented. The complete non-linear sigma model for these degrees of freedom is exhibited using the method of auxiliary fields. As a by-product we present a consistent non-linear coupling of a spin-2 tensor to gravitation. It is shown that non-vanishing

The vector-tensor multiplet in N = 2 superspace

(C_{\mu\nu\alpha\beta})^2

Higher derivative gravitation in bosonic and superstring theories and a new mechanism for supersymmetry breaking

terms arise in