arXiv subjects

C. Grojean

Publications and source records attributed to C. Grojean.

65 records · Page 4Linked to original sources

arXiv2000

Dynamical Instability of Brane Solutions with a Self-Tuning Cosmological Constant

A five-dimensional solution to Einstein's equations coupled to a scalar field has been proposed as a partial solution to the cosmological constant problem: the effect of arbitrary vacuum energy (tension) of a 3-brane is cancelled; however, the scalar field becomes singular at some finite proper distance in the extra dimension. We show that in the original model with a vanishing bulk potential for the scalar, the solution is a saddle point which is unstable to expansion or contraction of the brane world. We construct exact time-dependent solutions which generalize the static solution, and demonstrate that they do not conserve energy on the brane; thus they do not have an effective 4-D field theoretic description. When a bulk scalar field potential is added, the boundary conditions on the brane cannot be trivially satisfied, raising hope that the self-tuning mechanism may still give some insight into the cosmological constant problem in this case.

hep-th↗

arXiv2000

Supergravity Inspired Warped Compactifications and Effective Cosmological Constants

We propose a supergravity inspired derivation of a Randall-Sundrum's type action as an effective description of the dynamics of a brane coupled to the bulk through gravity only. The cosmological constants in the bulk and on the brane appear at the classical level when solving the equations of motion describing the bosonic sector of supergravities in ten and eleven dimensions coupled to the brane. They are related to physical quantities like the brane electric charge and thus inherit some of their physical properties. The most appealing property is their quantization: in d_\perp extra dimensions, Lambda_brane goes like N and Lambda_bulk like N^{2/(2-d_perp)}. This dynamical origin also explains the apparent fine-tuning required in the Randall-Sundrum scenario. In our approach, the cosmological constants are derived parameters and cannot be chosen arbitrarily; instead they are determined by the underlying Lagrangian. Some of the branes we construct that support cosmological constant in the bulk have supersymmetric properties: D3-branes of type IIB superstring theory provide an explicit example.

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arXiv2000

T Self-Dual Transverse Space and Gravity Trapping

We advocate that the orbifold Z_2 symmetry of the gravity trapping model proposed by Randall and Sundrum can be seen, in appropriate coordinates, as a symmetry that exchanges the short distances with the large ones. Using diffeomorphism invariance, we construct extensions defined by patch glued together. A singularity occurs at the junction and it is interpreted as a brane, the jump brane, of codimension one. We give explicit realization in ten and eleven dimensional supergravity and show that the lower dimensional Planck scale on the brane is finite. The standard model would be trapped on a supersymmetric brane located at the origin whereas the jump brane would surround it at a finite distance. The bulk interactions could transmit the supersymmetry breaking from the jump brane to the SM brane.

hep-th↗

arXiv1999

Inflating Intersecting Branes and Remarks on the Hierarchy Problem

We generalize solutions of Einstein's equations for intersecting branes in higher dimensional spacetimes to the nonstatic case, modeling an expanding universe. The relation between the Hubble rate, the brane tensions, and the bulk cosmological constant is similar to the case of a single 3-brane in a 5-dimensional spacetime. However, because the bulk inflates as well as the branes, this class of solutions suffers from Newton's constant tending toward zero on the TeV brane, where the Randall-Sundrum mechanism should solve the weak scale hierarchy problem. The strength of gravity remains constant on the Planck brane, however.

hep-ph↗

arXiv1999

Anomaly Matching and Syzygies in N=1 Gauge Theories

We investigate the connection between the moduli space of N=1 supersymmetric gauge theories and the set of polynomial gauge invariants constrained by classical/quantum relations called syzygies. We examine the existence of a superpotential reproducing these syzygies and the link with the 't Hooft anomaly matching between the fundamental fields at high energy and the gauge invariant degrees of freedom at low energy for the flavour symmetry group. We show that the anomaly matching is equivalent to the vanishing of the flavour anomaly on the normal space to the manifold defined by the syzygies. For normal spaces in a real representation of the flavour group we strengthen the connection between the 't Hooft anomaly matching and the existence of a superpotential by constructing a flavour invariant polynomial whose gradient vanishes at least on the solutions of the syzygies. This corroborates a recent definition of confining theories. We illustrate our general result by considering two examples based on the SU(Nc) and Spin(7) gauge theories. We also examine the role of syzygies in the context of non-Abelian duality. We emphasize the relevance of non-perturbative effects in the dual magnetic theories in proving the equivalence of the electric and magnetic syzygies.

hep-ph↗

arXiv1999

Super Fivebranes near the boundary of $AdS_7\times S^4$

We determine, to the first order in the radius of Anti-de-Sitter, the realisation of the $OSp(6,2|2)$ superconformal algebra on vector fields. We then calculate, to this order, the superspace metric describing the background of $AdS_7\times S^4$. The coordinates we work with are adapted to a 6+5 splitting of the eleven dimensional superspace. Finally, we deduce in a manifestly supersymmetric form the equations governing the dynamics of the fivebrane near the boundary of $AdS_7$.

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arXiv1998

Report of the GDR working group on the R-parity violation

This report summarizes the work of the "R-parity violation group" of the French Research Network (GDR) in Supersymmetry, concerning the physics of supersymmetric models without conservation of R-parity at HERA, LEP, Tevatron and LHC and limits on R-parity violating couplings from various processes. The report includes a discussion of the recent searches at the HERA experiment, prospects for new experiments, a review of the existing limits, and also theoretically motivated alternatives to R-parity and a brief discussion on the implications of R-parity violation on the neutrino masses.

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arXiv1998

Superconformal 6D (2,0) theories in superspace

A geometrical construction of superconformal transformations in six dimensional (2,0) superspace is proposed. Superconformal Killing vectors are determined. It is shown that the transformation of the tensor multiplet involves a zero curvature non-trivial cochain.

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arXiv1997

Geometrical approach to duality in N=1 supersymmetric theories

We investigate the geometry of the moduli spaces of dual electric and magnetic N=1 supersymmetric field theories. Using the SU(N_c) gauge group as a guideline we show that the electric and magnetic moduli spaces coincide for a suitable choice of the Kahler potential of the magnetic theory. We analyse the Kahler structure of the dual moduli spaces.

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arXiv1997

Four-dimensional M-theory and supersymmetry breaking

We investigate compactifications of M-theory from $11\to 5\to 4$ dimensions and discuss geometrical properties of 4-d moduli fields related to the structure of 5-d theory. We study supersymmetry breaking by compactification of the fifth dimension and find that an universal superpotential is generated for the axion-dilaton superfield $S$. The resulting theory has a vacuum with $ =1$, zero cosmological constant and a gravitino mass depending on the fifth radius as $m_{3/2} \sim R_5^{-2}/M_{Pl}$. We discuss phenomenological aspects of this scenario, mainly the string unification and the decompactification problem.

hep-th↗

arXiv1996

Abelian Flavour Symmetries in Supersymmetric Models

We propose a theory of flavour based on abelian horizontal gauge symmetries and modular invariances. We construct explicit supergravity models where the scale of the horizontal $U(1)$ symmetry breaking is fixed by the Green-Schwarz mechanism for anomaly cancellation. The supersymmetric spectrum is obtained in terms of the $U(1)$ charges which are determined by the Yukawa matrices.

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