arXiv subjects
Publications and source records attributed to Laurent Houart.
We find a purely gravitational classical solution of M-theory/eleven-dimensional supergravity which corresponds to a solution of the E10 brane sigma-model involving a null root. This solution is not supersymmetric and is regularly embedded into E11.
We revisit non-marginal half-BPS solutions of M-theory in the framework of the possible existence of an underlying E11 Kac-Moody symmetry. In this context, non-marginal BPS solutions of M-theory can be described as exact solutions of the brane sigma-model E10/K(E10), extending results obtained earlier for marginal BPS solutions. We uncover an elegant and simple algebraic structure underlying the bound states by looking at subalgebras embedded in E10. Furthermore, we show that the non-marginal BPS solutions can be obtained from the elementary marginal ones by the action of K(E10) transformations.
We study the symmetries of pure N=2 supergravity in D=4. As is known, this theory reduced on one Killing vector is characterised by a non-linearly realised symmetry SU(2,1) which is a non-split real form of SL(3,C). We consider the BPS brane solutions of the theory preserving half of the supersymmetry and the action of SU(2,1) on them. Furthermore we provide evidence that the theory exhibits an underlying algebraic structure described by the Lorentzian Kac-Moody group SU(2,1)^{+++}. This evidence arises both from the correspondence between the bosonic space-time fields of N=2 supergravity in D=4 and a one-parameter sigma-model based on the hyperbolic group SU(2,1)^{++}, as well as from the fact that the structure of BPS brane solutions is neatly encoded in SU(2,1)^{+++}. As a nice by-product of our analysis, we obtain a regular embedding of the Kac-Moody algebra su(2,1)^{+++} in e_{11} based on brane physics.
We study how the supersymmetry algebra copes with gravitational duality. As a playground, we consider a charged Taub-NUT solution of D=4, N=2 supergravity. We find explicitly its Killing spinors, and the projection they obey provides evidence that the dual magnetic momenta necessarily have to appear in the supersymmetry algebra. The existence of such a modification is further supported using an approach based on the Nester form. In the process, we find new expressions for the dual magnetic momenta, including the NUT charge. The same expressions are then rederived using gravitational duality.
The boosted Taub-NUT metric with zero ADM mass is shown to possess a dual momentum in the direction of the boost giving credit to the existence of another 4-vector K_μin linearized gravity associated to the NUT charge and dual to the usual P_μ. Taking the infinite boost limit we obtain a shock pp-wave with NUT charge. We show that the latter is the gravitational dual of the infinitely boosted Schwarzschild metric, also known as the Aichelburg-Sexl pp-wave. We review the fact that this new shock pp-wave is also an half-BPS solution of N=1 supergravity. It has a BPS bound equal to K_t=|K_z|.
Claudio's warm and endearing personality adds to our admiration for his achievements in physics a sense of friendliness. His constant interest in fundamental questions motivated the following presentation of our attempt to understand the nature of fermions. This problem is an essential element of the quantum world and might be related to the quest for quantum gravity. We shall review how space-time fermions can emerge out of bosons in string theory and how this fact affects the extended Kac-Moody approach to the M-theory project.
We construct an infinite E9 multiplet of BPS states for 11D supergravity. For each positive real root of E9 we obtain a BPS solution of 11D supergravity, or of its exotic counterparts, depending on two non-compact transverse space variables. All these solutions are related by U-dualities realised via E9 Weyl transformations in the regular embedding of E9 in E10, E10 in E11. In this way we recover the basic BPS solutions, namely the KK-wave, the M2 brane, the M5 brane and the KK6-monopole, as well as other solutions admitting eight longitudinal space dimensions. A novel technique of combining Weyl reflexions with compensating transformations allows the construction of many new BPS solutions, each of which can be mapped to a solution of a dual effective action of gravity coupled to a certain higher rank tensor field. For real roots of E10 which are not roots of E9, we obtain additional BPS solutions transcending 11D supergravity (as exemplified by the lowest level solution corresponding to the M9 brane). The relation between the dual formulation and the one in terms of the original 11D supergravity fields has significance beyond the realm of BPS solutions. We establish the link with the Geroch group of general relativity, and explain how the E9 duality transformations generalize the standard Hodge dualities to an infinite set of `non-closing dualities'.
The formulation of gravity and M-theories as very-extended Kac-Moody invariant theories is reviewed. Exact solutions describing intersecting extremal brane configurations smeared in all directions but one are presented. The intersection rules characterising these solutions are neatly encoded in the algebra. The existence of dualities for all G+++ and their group theoretical-origin are discussed.
The G++ content of the formulation of gravity and M-theories as very-extended Kac-Moody invariant theories is further analysed. The different exotic phases of all the G_B++ theories, which admit exact solutions describing intersecting branes smeared in all directions but one, are derived. This is achieved by analysing for all G++ the signatures which are related to the conventional one (1,D-1) by `dualities' generated by the Weyl reflections.
The formulation of gravity and M-theories as very-extended Kac-Moody invariant theories encompasses, for each very-extended algebra G+++, two distinct actions invariant under the overextended Kac-Moody subalgebra G++. The first carries a Euclidean signature and is the generalisation to G++ of the E10-invariant action proposed in the context of M-theory and cosmological billiards. The second action carries various Lorentzian signatures revealed through various equivalent formulations related by Weyl transformations of fields. It admits exact solutions, identical to those of the maximally oxidised field theories and of their exotic counterparts, which describe intersecting extremal branes smeared in all directions but one. The Weyl transformations of G++ relates these solutions by conventional and exotic dualities. These exact solutions, common to the Kac-Moody theories and to space-time covariant theories, provide a laboratory for analysing the significance of the infinite set of fields appearing in the Kac-Moody formulations.
The set of exact solutions of the non-linear realisations of the G+++ Kac-Moody algebras is further analysed. Intersection rules for extremal branes translate into orthogonality conditions on the positive real roots characterising each brane. It is proven that all the intersecting extremal brane solutions of the maximally oxidised theories have their algebraic counterparts as exact solutions in the G+++ invariant theories. The proof is extended to include the intersecting extremal brane solutions of the exotic phases of the maximally oxidised theories.
Theories of gravity coupled to forms and dilatons may admit as solutions zero binding energy configurations of intersecting closed extremal branes. In such configurations, some branes may open on host closed branes. Properties of extremal branes reveal symmetries of the underlying theory which are well known in M-theory but transcend supersymmetry. From these properties it is possible to reconstruct all actions, comprising in particular pure gravity in D dimensions, the bosonic effective actions of M-theory and of the bosonic string, which upon dimensional reduction to three dimensions are invariant under the maximally non-compact simple simply laced Lie groups G. Moreover the features of extremal branes suggest the existence of a much larger symmetry, namely the `very-extended' Kac-Moody algebras G+++. This motivates the construction of explicit non-linear realisations of all simple G+++, which hopefully contain new degrees of freedom such as those encountered in string theories. They are defined without a priori reference to space-time and are proposed as substitutes for original field theoretic models of gravity, forms and dilatons. From the G+++ invariant theories, all algebraic properties of extremal branes are recovered from exact solutions, and there are indications that space-time is hidden in the infinite symmetry structure. The transformation properties of the exact solutions, which possibly induce new solutions foreign to conventional theories, put into evidence the general group-theoretical origin of `dualities' for all G+++. These dualities apparently do not require an underlying string theory.
We consider theories containing gravity, at most one dilaton and form field strengths. We show that the existence of particular BPS solutions of intersecting extremal closed branes select the theories, which upon dimensional reduction to three dimensions possess a simple simply laced Lie group symmetry G. Furthermore these theories can be fully reconstructed from the dynamics of such branes and of their openings. Amongst such theories are the effective actions of the bosonic sector of M-theory and of the bosonic string. The BPS intersecting brane solutions form representations of a subgroup of the group of Weyl reflections and outer automorphisms of the triple Kac-Moody extension G+++ of the G algebra, which cannot be embedded in the overextended Kac-Moody subalgebra G++ characterising the cosmological Kasner solutions.
A universal symmetric truncation of the bosonic string Hilbert space yields all known closed fermionic string theories in ten dimensions, their D-branes and their open descendants. We highlight the crucial role played by group theory and two-dimensional conformal field theory in the construction and emphasize the predictive power of the truncation. Such circumstantial evidence points towards the existence of a mechanism which generates space-time fermions out of bosons dynamically within the framework of bosonic string theory.
We extend the search for fermionic subspaces of the bosonic string compactified on E8 X SO(16) lattices to include all fermionic D-branes. This extension constraints the truncation procedure previously proposed and relates the fermionic strings, supersymmetric or not, to the global structure of the SO(16) group. The specific properties of all the fermionic D-branes are found to be encoded in its universal covering, whose maximal toroid defines the configuration space torus of their mother bosonic theory.
We review the emergence of the ten-dimensional fermionic closed string theories from subspaces of the Hilbert space of the 26-dimensional bosonic closed string theory compactified on an $E_8\times SO(16)$ lattice. They arise from a consistent truncation procedure which generates space-time fermions out of bosons. This procedure is extended to open string sectors. We prove, from bosonic considerations alone, that truncation of the unique tadpole-free $SO(2^{13})$ bosonic string theory compactified on the above lattice determines the anomaly free Chan-Paton group of the Type I theory. It also yields the Chan-Paton groups making Type O theories tadpole-free. These results establish a link between all M-theory strings and the bosonic string within the framework of conformal field theory. Its significance is discussed.
The results conjectured here are based on tachyon condensation in compactified bosonic strings. They can in fact be proven from compactification alone, but this step was not treated consistently here. The proof is given in a new version of the paper: hep-th/0106235
We review the emergence of the ten-dimensional fermionic closed string theories from subspaces of the Hilbert space of the 26-dimensional bosonic closed string theory compactified on an $E_8\times SO(16)$ lattice. They arise from a consistent truncation procedure which generates space-time fermions out of bosons. This procedure is extended to open string sectors. We prove that truncation of the unique tadpole-free $SO(2^{13})$ bosonic string theory compactified on the above lattice determines the anomaly free Chan-Paton group of the Type I theory and the consistent Chan-Paton groups of Type O theories. It also predicts the tension of space-filling D-branes in these fermionic theories. The derivation of these fermionic string properties from bosonic considerations alone points towards a dynamical origin of the truncation process. Space-time fermions and supersymmetries would then arise from bosonic degrees of freedom and no fermionic degrees of freedom would be needed in a fundamental theory of quantum gravity.