Non-Linear Supergravity and Inflationary Cosmology
We review a series of developments concerning non-linear realizations of supersymmetry coupled to supergravity, with emphasis on some applications to inflationary Cosmology.
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arXiv subjects
Augusto Sagnotti
Publications and source records attributed to Augusto Sagnotti.
String Theory and The Velo-Zwanziger Problem
We examine the behavior of the leading Regge trajectory of the open bosonic string in a uniform electromagnetic background and present a consistent set of Fierz-Pauli conditions for these symmetric tensors that generalizes the Argyres-Nappi spin-2 result. These equations indicate that String Theory does bypass the Velo-Zwanziger problem, i.e. the loss of causality experienced by a massive high-spin field minimally coupled to electromagnetism. Moreover, we provide some evidence that only the first Regge trajectory can be described in isolation and show that the open-string spectrum is free of ghosts in weak constant backgrounds. Finally, we comment on the roles of the critical dimension and of the gyromagnetic ratio.
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Unconstrained Higher Spins of Mixed Symmetry. II. Fermi Fields
This paper is a sequel of arXiv:0810.4350 [hep-th], and is also devoted to the local "metric-like" unconstrained Lagrangians and field equations for higher-spin fields of mixed symmetry in flat space. Here we complete the previous constrained on-shell formulation of Labastida for Fermi fields, deriving the corresponding constrained Lagrangians both via the Bianchi identities and via the requirement of self-adjointness. We also describe two types of unconstrained Lagrangian formulations: a "minimal" one, containing higher derivatives of the compensator fields, and another non-minimal one, containing only one-derivative terms. We identify classes of these systems that are invariant under Weyl-like symmetry transformations.
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Unconstrained Higher Spins of Mixed Symmetry. I. Bose Fields
This is the first of two papers devoted to the local "metric-like" unconstrained Lagrangians and field equations for higher-spin gauge fields of mixed symmetry in flat space. Here we complete the previous constrained formulation of Labastida for Bose fields. We thus recover his Lagrangians via the Bianchi identities, before extending them to their "minimal" unconstrained form with higher derivatives of the compensator fields and to yet another, non-minimal, form with only two-derivative terms. We also identify classes of these systems that are invariant under Weyl-like symmetries.
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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.
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Open strings and their symmetry groups
Much of the recent progress in String Theory can be traced to a precise strategy: a careful study of the few models known since the beginnings of the subject, and the abstraction from them of basic properties that one would like to demand from other models. This could be termed a set of "model-building rules". The approach corresponds to the fact, often a source of embarrassment to specialists, that String Theory, born as a set of rules rather than as a set of principles, has long resisted attempts to reduce it to a logically satisfying structure. Talk presented at the Cargese Summer Institute on Non-Perturbative Methods in Field Theory, Cargese, France, July 16-30, 1987.
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Open Strings
This review is devoted to open strings, and in particular to the often surprising features of their spectra. It follows and summarizes developments that took place mainly at the University of Rome ``Tor Vergata'' over the last decade, and centred on world-sheet aspects of the constructions now commonly referred to as ``orientifolds''. Our presentation aims to bridge the gap between the world-sheet analysis, that first exhibited many of the novel features of these systems, and their geometric description in terms of extended objects, D-branes and O-planes, contributed by many other colleagues, and most notably by J. Polchinski. We therefore proceed through a number of prototype examples, starting from the bosonic string and moving on to ten-dimensional fermionic strings and their toroidal and orbifold compactifications, in an attempt to guide the reader in a self-contained journey to the more recent developments related to the breaking of supersymmetry.
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Self-dual Tensors in Six-Dimensional Supergravity
We review some properties of the field equations of six-dimensional (1,0) supergravity coupled to tensor and vector multiplets, and in particular their relation to covariant and consistent anomalies and a peculiar Noether identity for the energy-momentum tensor. We also describe a lagrangian formulation for this system, obtained applying the Pasti-Sorokin-Tonin prescription.
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Consistent and covariant anomalies in six-dimensional supergravity
In this note we clarify some issues in six-dimensional (1,0) supergravity coupled to vector and tensor multiplets. In particular, we show that, while the low-energy equations embody tensor-vector couplings that contribute only to gauge anomalies, the divergence of the energy-momentum tensor is properly non-vanishing. In addition, we show how to revert to a supersymmetric formulation in terms of covariant non-integrable field equations that embody corresponding covariant anomalies.
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Some Properties of Tensor Multiplets in Six-Dimensional Supergravity
We review some results on the complete coupling between tensor and vector multiplets in six-dimensional $(1,0)$ supergravity.
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Surprises in Open-String Perturbation Theory
The perturbative analysis of models of open and closed superstrings presents a number of surprises. For instance, variable numbers of antisymmetric tensors ensure their consistency via generalized Green-Schwarz cancellations and a novel type of singularity occurs in their moduli spaces. All these features are related, in one way or another, to the presence of boundaries on the world sheet or, equivalently, of extended objects (branes) interacting with the bulk theory in space time. String dualities have largely widened the interest in these models, that exhibit a wealth of generic non-perturbative features of String Theory.
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Twelve-Dimensional Aspects of Four-Dimensional N=1 Type I Vacua
Four-dimensional supergravity theories are reinterpreted in a 12-dimensional F-theory framework. The O(8) symmetry of N=8 supergravity is related to a reduction of F-theory on T_8, with the seventy scalars formally associated, by O(8) triality, to a fully compactified four-form A_4. For the N=1 type I model recently obtained from the type IIB string on the Z orbifold, we identify the Kähler manifold of the untwisted scalars in the unoriented closed sector with the generalized Siegel upper-half plane Sp(8,R)/(SU(4) \times U(1)). The SU(4) factor reflects the holonomy group of Calabi-Yau fourfolds.
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Chiral Asymmetry in Four-Dimensional Open-String Vacua
Starting from the type IIB string on the Z orbifold, we construct some chiral open-string vacua with N=1 supersymmetry in four dimensions. The Chan-Paton group depends on the (quantized) NS-NS antisymmetric tensor. The largest choice, SO(8)xSU(12)xU(1), has an anomalous U(1) factor whose gauge boson acquires a mass of the order of the string scale. The corresponding open-string spectrum comprises only Neumann strings and includes three families of chiral multiplets in the (8,12*) + (1,66) representation. A comparison is drawn with a heterotic vacuum with non-standard embedding, and some properties of the low-energy effective field theory are discussed.
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Low-Energy Analysis of $M$ and $F$ Theories on Calabi-Yau Threefolds
We elucidate the interplay between gauge and supersymmetry anomalies in six-dimensional $N=1$ supergravity with generalized couplings between tensor and vector multiplets. We derive the structure of the five-dimensional supergravity resulting from the $S_1$ reduction of these models and give the constraints on Chern-Simons couplings that follow from duality to $M$ theory compactified on a Calabi-Yau threefold. The duality is supported only on a restricted class of Calabi-Yau threefolds and requires a special type of intersection form. We derive five-dimensional central-charge formulas and discuss briefly the associated phase transitions. Finally, we exhibit connections with $F$-theory compactifications on Calabi-Yau manifolds that admit elliptic fibrations. This analysis suggests that $F$ theory unifies Type-$IIb$ three-branes and $M$-theory five-branes.
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Open Descendants in Conformal Field Theory
Open descendants extend Conformal Field Theory to unoriented surfaces with boundaries. The construction rests on two types of generalizations of the fusion algebra. The first is needed even in the relatively simple case of diagonal models. It leads to a new tensor that satisfies the fusion algebra, but whose entries are signed integers. The second is needed when dealing with non-diagonal models, where Cardy's ansatz does not apply. It leads to a new tensor with positive integer entries, that satisfies a set of polynomial equations and encodes the classification of the allowed boundary operators.
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Completeness Conditions for Boundary Operators in 2D Conformal Field Theory
In non-diagonal conformal models, the boundary fields are not directly related to the bulk spectrum. We illustrate some of their features by completing previous work of Lewellen on sewing constraints for conformal theories in the presence of boundaries. As a result, we include additional open sectors in the descendants of $D_{odd}$ $SU(2)$ WZW models. A new phenomenon emerges, the appearance of multiplicities and fixed-point ambiguities in the boundary algebra not inherited from the closed sector. We conclude by deriving a set of polynomial equations, similar to those satisfied by the fusion-rule coefficients $N_{ij}^k$, for a new tensor $A_{a b}^i$ that determines the open spectrum.
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Some Properties of Open - String Theories
Open-string theories may be related to suitable models of oriented closed strings. The resulting construction of ``open descendants'' is illustrated in a few simple cases that exhibit some of its key features.
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Anomaly Cancellations and Open-String Theories
In models of oriented closed strings, anomaly cancellations are deeply linked to the {\it modular invariance} of the torus amplitude. If open and/or unoriented strings are allowed, there are no non-trivial modular transformations in the additional genus-one amplitudes (Klein bottle, annulus and Möbius strip). As originally recognized by Green and Schwarz, in the ten-dimensional type-I superstring the anomaly cancellation results from a delicate interplay between the contributions of these additional surfaces. In lower-dimensional models, the possible presence of a number of antisymmetric tensors yields a generalization of the Green-Schwarz mechanism. I illustrate these results by referring to some six-dimensional chiral models, and I conclude by addressing the additional difficulties that one meets when trying to extend the construction to chiral four-dimensional models. (Contribution to ''From Superstrings to Supergravity'', Erice, ITALY, december 5-12, 1992)
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