Green-Schwarz Anomaly Cancellation Mechanism Research Articles

Anomaly flows

The Anomaly flow is a flow which implements the Green-Schwarz anomaly cancellation mechanism originating from superstring theory, while preserving the conformally balanced condition of Hermitian metrics. There are several versions of the flow, depending on whether the gauge field also varies, or is assumed known. A distinctive feature of Anomaly flows is that, in $m$ dimensions, the flow of the Hermitian metric has to be inferred from the flow of its $(m-1)$-th power $\omega^{m-1}$. We show how this can be done explicitly, and we work out the corresponding flows for the torsion and the curvature tensors. The results are applied to produce criteria for the long-time existence of the flow, in the simplest case of zero slope parameter.

The heterotic superpotential and moduli

We study the four-dimensional effective theory arising from ten-dimensional heterotic supergravity compactified on manifolds with torsion. In particular, given the heterotic superpotential appropriately corrected at $\mathcal{O}(\alpha')$ to account for the Green-Schwarz anomaly cancellation mechanism, we investigate properties of four-dimensional Minkowski vacua of this theory. Considering the restrictions arising from F-terms and D-terms we identify the infinitesimal massless moduli space of the theory. We show that it agrees with the results that have recently been obtained from a ten-dimensional perspective where supersymmetric Minkowski solutions including the Bianchi identity correspond to an integrable holomorphic structure, with infinitesimal moduli calculated by its first cohomology. As has recently been noted, interplay of complex structure and bundle deformations through holomorphic and anomaly constraints can lead to fewer moduli than may have been expected. We derive a relation between the number of complex structure and bundle moduli removed from the low energy theory in this way, and give conditions for there to be no complex structure moduli or bundle moduli remaining in the low energy theory. The link between Yukawa couplings and obstruction theory is also briefly discussed.

Green-Schwarz mechanism and α′-deformed Courant brackets

We establish that the unusual two-form gauge transformations needed in the Green-Schwarz anomaly cancellation mechanism fit naturally into an $\alpha'$-deformed generalized geometry. The algebra of gauge transformations is a consistent deformation of the Courant bracket and features a nontrivial modification of the diffeomorphism group. This extension of generalized geometry emerged from a `doubled $\alpha'$-geometry', which provides a construction of exactly gauge and T-duality invariant $\alpha'$ corrections to the effective action.

Double field theory at order α′

We investigate α′ corrections of bosonic strings in the framework of double field theory. The previously introduced “doubled α′-geometry” gives α′-deformed gauge transformations arising in the Green-Schwarz anomaly cancellation mechanism but does not apply to bosonic strings. These require a different deformation of the duality-covariantized Courant bracket which governs the gauge structure. This is revealed by examining the α′ corrections in the gauge algebra of closed string field theory. We construct a four-derivative cubic double field theory action invariant under the deformed gauge transformations, giving a first glimpse of the gauge principle underlying bosonic string α′ corrections. The usual metric and b-field are related to the duality covariant fields by non-covariant field redefinitions.

Twisted Differential String and Fivebrane Structures

In the background effective field theory of heterotic string theory, the Green-Schwarz anomaly cancellation mechanism plays a key role. Here we reinterpret it and its magnetic dual version in terms of differential twisted String- and differential twisted Fivebrane-structures that generalize the notion of Spin-structures and Spin-lifting gerbes and their differential refinement to smooth Spin-connections. We show that all these structures can be encoded in terms of nonabelian cohomology, twisted nonabelian cohomology, and differential twisted nonabelian cohomology, extending the differential generalized abelian cohomology as developed by Hopkins and Singer and shown by Freed to formalize the global description of anomaly cancellation problems in higher gauge theories arising in string theory. We demonstrate that the Green-Schwarz mechanism for the H_3-field, as well as its magnetic dual version for the H_7-field define cocycles in differential twisted nonabelian cohomology that may be called, respectively, differential twisted Spin(n)-, String(n)- and Fivebrane(n)-structures on target space, where the twist in each case is provided by the obstruction to lifting the classifying map of the gauge bundle through a higher connected cover of U(n) or O(n). We show that the twisted Bianchi identities in string theory can be captured by the (nonabelian) L-infinity-algebra valued differential form data provided by the differential refinements of these twisted cocycles.

Mixed mediation of supersymmetry breaking with anomalous U(1) gauge symmetry

Models with anomalous U(1) gauge symmetry contain various superfields which can have nonzero supersymmetry breaking auxiliary components providing the origin of soft terms in the visible sector, e.g. the U(1) vector superfield, the modulus or dilaton superfield implementing the Green-Schwarz anomaly cancellation mechanism, U(1)-charged but standard model singlet matter superfield required to cancel the Fayet-Iliopoulos term, and finally the supergravity multiplet. We examine the relative strength between these supersymmetry breaking components in a simple class of models, and find that various different mixed mediations of supersymmetry breaking, involving the modulus, gauge, anomaly and D-term mediations, can be realized depending upon the characteristics of D-flat directions and how those D-flat directions are stabilized with a vanishing cosmological constant. We identify two parameters which represent such properties and thus characterize how the various mediations are mixed. We also discuss the moduli stabilization and soft terms in a variant of KKLT scenario, in which the visible sector Kähler modulus is stabilized by the D-term potential of anomalous U(1) gauge symmetry.

Mixed Mediation of Supersymmetry Breaking in Models with Anomalous U(1) Gauge Symmetry

There can be various built-in sources of supersymmetry breaking in models with anomalous U(1) gauge symmetry, e.g. the U(1) D-term, the F-components of the modulus superfield required for the Green-Schwarz anomaly cancellation mechanism and the chiral matter superfields required to cancel the Fayet-Iliopoulos term, and finally the supergravity auxiliary component which can be parameterized by the F-component of chiral compensator. The relative strength between these supersymmetry breaking sources depends crucially on the characteristics of D-flat direction and also on how the D-flat direction is stabilized at a vacuum with nearly vanishing cosmological constant. We examine the possible pattern of the mediation of supersymmetry breaking in models with anomalous U(1) gauge symmetry, and find that various different mixed mediation scenarios can be realized, including the mirage mediation which corresponds to a mixed modulus-anomaly mediation, D-term domination giving a split sparticle spectrum, and also a mixed gauge-D-term mediation scenario.

K-theory in quantum field theory

We survey three different ways in which K-theory in all its forms enters quantum field theory. In Part 1 we give a general argument which relates topological field theory in codimension two with twisted K-theory, and we illustrate with some finite models. Part 2 is a review of pfaffians of Dirac operators, anomalies, and the relationship to differential K-theory. Part 3 is a geometric exposition of Dirac charge quantization, which in superstring theories also involves differential K-theory. Parts 2 and 3 are related by the Green-Schwarz anomaly cancellation mechanism. An appendix, joint with Jerry Jenquin, treats the partition function of Rarita-Schwinger fields.

THE N=2 VECTOR–TENSOR MULTIPLET, CENTRAL CHARGE SUPERSPACE, AND CHERN–SIMONS COUPLINGS

We present a new, alternative interpretation of the vector–tensor multiplet as a two-form in central charge superspace. This approach provides a geometric description of the (nontrivial) central charge transformations ab initio and is naturally generalized to include couplings of Chern–Simons forms to the antisymmetric tensor gauge field, giving rise to a N=2 supersymmetric version of the Green–Schwarz anomaly cancellation mechanism.

N = 1, D = 6 supergravity: Duality and non-minimal couplings

Six-dimensional supergravity theories and their duality properties play a central role in the context of string duality and string compactifications. Lowering dimensions usually leads to an increasing complexity of theories; in this respect six dimensions seem to constitute an appropriate compromise between the physical four and the presumably more fundamental ten or eleven dimensions. In this paper we present a superspace formulation of N = l, D = 6 supergravity with one tensor multiplet and an arbitrary number of vector- and hypermultiplets, in which the bosonic abelian superforms of the theory, the dilaton, the abelian gauge fields and the two-form are replaced by their S-duals i.e. four-, three- and two-superforms respectively, in compatibility with supersymmetry. As usual this replacement interchanges Bianchi identities with equations of motion. This formulation holds in the presence of one tensor multiplet and arbitrary numbers of hypermultiplets and abelian super-Maxwell multiplets if all couplings are minimal. We determine the consistency conditions for non-minimal couplings in N = 1, D = 6 supergravity, for which we present a particularly significant solution, namely the one associated with the Chem-SimonsLorentz three-form which entails the Green-Schwarz anomaly cancellation mechanism. In the case of non-minimal couplings it is found that the gauge fields and the two-form can still be dualized while the dilaton has to remain a zero-form.

A model of Yukawa hierarchies

We present a model for the observed hierarchies among the Yukawa couplings of the standard model in the context of an effective low enegy theory with an anomalous U (1) symmetry. This symmetry, a generic feature of superstring compactification, is a remnant of the Green-Schwarz anomaly cancellation mechanism. The gauge group is that of the standard model, augmented by X , the anomalous U (1), and two family-dependent phase symmetries Y (1) and Y (2) . The correct hierarchies are reproduced only when sin 2 θ w = 3 8 at the cut-off. To cancel anomalies, right-handed neutrinos and other standard model singlets must be introduced. Independently of the charges of the right-handed neutrinos, this model produces the same neutrino mixing matrix and an inverted hierarchy of neutrino masses. The heaviest is the electron neutrino with a mass ∼ 1 meV, and mixing of the order of λ c 3 with each of the other two neutrinos.

BRST Cohomology of the Chapline–Manton Model

We completely compute the local BRST cohomology $H(s|d)$ of the combined Yang-Mills-2-form system coupled through the Yang-Mills Chern-Simons term ("Chapline-Manton model"). We consider the case of a simple gauge group and explicitely include in the analysis the sources for the BRST variations of the fields ("antifields"). We show that there is an antifield independent representative in each cohomological class of $H(s|d)$ at ghost number 0 or 1. Accordingly, any counterterm may be assumed to preserve the gauge symmetries. Similarly, there is no new candidate anomaly beside those already considered in the literature, even when one takes the antifields into account. We then characterize explicitly all the non-trivial solutions of the Wess-Zumino consistency conditions. In particular, we provide a cohomological interpretation of the Green-Schwarz anomaly cancellation mechanism.

“Anomalous” U( l) symmetry in orbifold string models

“Anomalous” U(1) gauge symmetry with a Green-Schwarz anomaly cancellation mechanism is discussed in the orbifold construction of four-dimensional heterotic string models. Some conditions are given as criteria to have “anomalous” U(1) in orbifold string models. In particular, “anomalous” U(1) is absent if the massless twisted matter has no mixing between visible and hidden sectors or if a certain type of discrete symmetries are found. We then give a general procedure for classifying orbifold models with “anomalous” U(1) and for identifying the “anomalous” U(1) basis. We illustrate our procedure in Z 3 and Z 4 orbifold models. According to our procedure, the classification of “anomalous” U(1) can be reduced to classification in the absence of a Wilson line. We also discuss discrete symmetries left unbroken after the “anomalous” U(1) breaking. This includes a possible relation between “anomalous” U(1) and discrete R symmetries.

The supersymmetric version of the Green-Schwarz anomaly cancellation mechanism

The N = 1, D = 10 Supergravity-Super-Yang-Mills (SUGRA-SYM) theory is plagued by ABBJ gauge and Lorentz anomalies which are cancelled via the Green-Schwarz anomaly cancellation mechanism. Due to the fact that the ABBJ anomalies are not invariant under supersymmetry (SUSY) transformations one concludes that the theory is plagued also by a SUSY anomaly. For the gauge groups SO(32) and E 8 × E 8 we compute this SUSY anomaly, by solving a coupled cohomology problem, and we show that it can be cancelled by subtracting from the action the known Green-Schwarz counterterm, the same which cancels also the ABBJ anomaly, the expected result. Finally, we argue that the corresponding mechanism does not apply in the dual SUGRA-SYM, related to the heterotic five-brane.

All-loop gauge couplings from anomaly cancellation in string effective theories

We derive, to all orders in perturbation theory, the E 8 gauge coupling and the modified dilaton-axion Kähler potential for the effective theories of a class of d = 4, N = 1 heterotic string models. The derivation relies on an extended version of the Green-Schwarz anomaly cancellation mechanism, and exploits target-space duality invariance. Although we deal with field-dependent effective gauge couplings and scales in a non-renormalizable supergravity theory, we derive for them a renormalization group equation as a relation among dynamical fields. When expectation values of these fields are considered, our results agree with those previously obtained in renormalizable theories with N = 1 global supersymmetry. We finally comment on possible generalizations of the present results.

Generalized Green-Schwarz anomaly cancellation mechanism.

We show that the chiral anomaly can be canceled by a single antisymmetric tensor if the anomaly form factorizes into the product of two invariant polynomials of curvature two-forms, R and F. This generalizes the Green-Schwarz cancellation mechanism, where the factorization is of the form (Tr${R}^{2}$-Tr${F}^{2}$) times an invariant polynomial. The Yang-Mills group constraints differ from those obtained by the Green-Schwarz mechanism if the anomaly form is factorized differently and thus new anomaly-free theories emerge. This generalized mechanism works for any theories in D=4k dimensions and nonsupergravity theories in D=4k-2. However, for supergravity-type theories in D=4k-2 only the original Green-Schwarz factorization works. We explicitly construct many anomaly-free theories in D=8 and D=10, using the generalized mechanism.

4D supergravity coupled to an antisymmetric tensor field with Green-Schwarz mechanism

We derive the component lagrangian for general matter coupling to 4D supergravity of a real linear multiplet, containing an antisymmetric tensor field, which transforms nontrivially under gauge and Lorentz transformations, as it comes from the Green-Schwarz anomaly cancellation mechanism in D = 10. It is found that local supersymmetry requires a third Chern-Simons form related to the axial gauge field of conformal supergravity.

Massive vector multiplets from superstrings

The four-dimensional Green-Schwarz anomaly cancellation mechanism with a surviving U(1) gauge group is described in the context of standard tensor calculus (superspace) techniques for local supersymmetry. This phenomenon is “dual” to the case in which a massless vector field is eaten up by an antisymmetric tensor which thereby describes a massive spin-one field. Both mechanisms are motivated by recent string-loop calculations. Unlike the case of some supergravity models, these mechanisms seem unable (order by order, at least) to break supersymmetry while keeping the cosmological constant vanishing.