Publications
112 results found
de Rham C, Tolley AJ, 2010, DBI and the Galileon reunited, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, ISSN: 1475-7516
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- Citations: 281
de Rham C, Khoury J, Tolley A, 2009, Flat 3-brane with Tension in Cascading Gravity, PHYSICAL REVIEW LETTERS, Vol: 103, ISSN: 0031-9007
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- Citations: 46
Burgess CP, Hoover D, de Rham C, et al., 2009, Effective field theories and matching for codimension-2 branes, JOURNAL OF HIGH ENERGY PHYSICS, ISSN: 1029-8479
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- Citations: 40
de Rham C, 2009, Cascading gravity and degravitation, CANADIAN JOURNAL OF PHYSICS, Vol: 87, Pages: 201-203, ISSN: 0008-4204
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- Citations: 18
Burgess CP, de Rham C, van Nierop L, 2008, The hierarchy problem and the self-localized Higgs, The Journal of High Energy Physics, Vol: 2008, Pages: 1-34, ISSN: 1029-8479
We examine brane-world scenarios in which all the observed Standard Model particles reside on a brane but the Higgs is an elementary extra-dimensional scalar in the bulk. We show that, for codimension 2 branes, often-neglected interactions between the bulk Higgs and the branes cause two novel effects. First, they cause langHrang to depend only logarithmically on the UV-sensitive coefficient, mB2, of the mass term, mB2 H*H, of the bulk potential, thus providing a new mechanism for tackling the hierarchy problem. Second, the Higgs brane couplings cause the lowest mass KK mode to localize near the brane without any need for geometrical effects like warping. We explore some preliminary implications such models have for the Higgs signature at the LHC, both in the case where the extra dimensions arise at the TeV scale, and in ADD models having Large Extra Dimensions. Novel Higgs features include couplings to fermions which can be different from Standard Model values, mf/v, despite the fermions acquiring their mass completely from the Higgs expectation value.
Tolley AJ, Burgess CP, de Rham C, et al., 2008, Exact wave solutions to 6D gauged chiral supergravity, The Journal of High Energy Physics, Vol: 2008, Pages: 1-20, ISSN: 1029-8479
We describe a broad class of time-dependent exact wave solutions to 6D gauged chiral supergravity with two compact dimensions. These 6D solutions are nontrivial warped generalizations of 4D pp-waves and Kundt class solutions and describe how a broad class of previously-static compactifications from 6D to 4D (sourced by two 3-branes) respond to waves moving along one of the uncompactified directions. Because our methods are generally applicable to any higher dimensional supergravity they are likely to be of use for finding the supergravity limit of time-dependent solutions in string theory. The 6D solutions are interesting in their own right, describing 6D shock waves induced by high energy particles on the branes, and as descriptions of the near-brane limit of the transient wavefront arising from a local bubble-nucleation event on one of the branes, such as might occur if a tension-changing phase transition were to occur.
de Rham C, Dvali G, Hofmann S, et al., 2008, Cascading gravity: extending the dvali-gabadadze-porrati model to higher dimension, Physical Review Letters, Vol: 100, Pages: 251603-1-251603-4, ISSN: 0031-9007
We present a generalization of the Dvali-Gabadadze-Porrati scenario to higher codimensions which, unlike previous attempts, is free of ghost instabilities. The 4D propagator is made regular by embedding our visible 3-brane within a 4-brane, each with their own induced gravity terms, in a flat 6D bulk. The model is ghost-free if the tension on the 3-brane is larger than a certain critical value, while the induced metric remains flat. The gravitational force law “cascades” from a 6D behavior at the largest distances followed by a 5D and finally a 4D regime at the shortest scales.
Kobayashi T, Shiromizu T, de Rham C, 2008, Curvature corrections to the low energy effective theory in 6D regularized braneworlds, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 77, Pages: 124012-1-124012-11, ISSN: 1550-2368
We study the effective gravitational theory on a brane in a six-dimensional Einstein-Maxwell model of flux compactification, regularizing a conical defect as a codimension-one brane. We employ the gradient expansion technique valid at low energies. A lowest order analysis showed that standard four-dimensional Einstein gravity is reproduced on the brane. We extend this study to include second order corrections in the effective equations, and show that the correction term is given by a quadratic energy-momentum tensor. Taking the thin-brane limit where the regularized brane shrinks to the pole, we find that the second order metric diverges logarithmically on the brane, giving rise to divergences in the brane effective action. Away from the branes, the effective action is, however, well defined.
de Rham C, Hofmann S, Khoury J, et al., 2008, Cascading gravity and degravitation, Journal of Cosmology and Astroparticle Physics, Vol: 2008, Pages: 1-28, ISSN: 1475-7516
We construct a cascading brane model of gravity in which the behavior of the gravitational force law interpolates from (n+4)-dimensional to (n+3)-dimensional all the way down to 4-dimensional from longer to shorter length scales. We show that, at the linearized level, this model exhibits the features necessary for degravitation of the cosmological constant. The model is shown to be ghost free with the addition of suitable brane kinetic operators, and we demonstrate this using a number of independent procedures. Consequently this is a consistent infrared (IR) modification of gravity, providing a promising framework for a dynamical, degravitating solution of the cosmological constant problem.
de Rham C, 2008, The effective field theory of codimension-two branes, The Journal of High Energy Physics, Vol: 2008, Pages: 1-33, ISSN: 1029-8479
Distributional sources of matter on codimension-two and higher branes are only well-defined as regularized objects. Nevertheless, intuition from effective field theory suggests that the low-energy physics on such branes should be independent of any high-energy regularization scheme. In this paper, we address this issue in the context of a scalar field model where matter fields (the standard model) living on such a brane interact with bulk fields (gravity). The low-energy effective theory is shown to be consistent and independent of the regularization scheme, provided the brane couplings are renormalized appropriately at the classical level. We perform explicit computations of the classical renormalization group flows at tree and one-loop level, demonstrate that the theory is renormalizable against codimension-two divergences, and extend the analysis to several physical applications such as electrodynamics and brane localized kinetic terms.
de Rham C, Watson S, 2007, Living on a dS brane: effects of KK modes on inflation, Classical and Quantum Gravity, Vol: 24, Pages: 4219-4234, ISSN: 0264-9381
We develop a formalism to study non-local higher dimensional effects in braneworld scenarios from a four-dimensional effective theory point of view and check it against the well-known Garriga–Tanaka result in the appropriate limit. We then use this formalism to study the spectrum of density perturbations during inflation as seen from the lower dimensional effective theory. In particular, we find that the gravitational potential is greatly enhanced at short wavelengths. The consequences to the curvature perturbations are nonetheless very weak and will lead to no characteristic signatures on the power spectrum.
de Rham C, 2007, Classical renormalization of codimension-two brane couplings, 13th International Symposium on Particles, Strings and Cosmology (PASCOS 2007), Publisher: AMER INST PHYSICS, Pages: 309-312, ISSN: 0094-243X
The curvature on codimension‐two and higher branes is not regular for arbitrary matter sources. Nevertheless, the low‐energy theory for an observer on such a brane should be well‐defined and independent to any regularization procedure. This is achieved via appropriate classical renormalization of the brane couplings, and leads to a natural hierarchy between standard model couplings and couplings to gravity.
Burgess CP, de Rham C, Hoover D, et al., 2007, Kicking the rugby ball: perturbations of 6D gauged chiral supergravity, Journal of Cosmology and Astroparticle Physics, Vol: 2007, Pages: 1-37, ISSN: 1475-7516
We analyse the axially symmetric scalar perturbations of 6D chiral gauged supergravity compactified on the general warped geometries in the presence of two source branes. We find that all of the conical geometries are marginally stable for normalizable perturbations (in disagreement with some recent calculations) and the non-conical ones for regular perturbations, even though none of them are supersymmetric (apart from the trivial Salam–Sezgin solution, for which there are no source branes). The marginal direction is the one whose presence is required by the classical scaling property of the field equations, and all other modes have positive squared mass. In the special case of the conical solutions, including (but not restricted to) the unwarped 'rugby-ball' solutions, we find closed-form expressions for the mode functions in terms of Legendre and hypergeometric functions. In so doing we show how to match the asymptotic near-brane form for the solution to the physics of the source branes, and thereby how to physically interpret perturbations which can be singular at the brane positions.
de Rham C, Rajantie A, Contaldi C, et al., 2007, Classical Renormalization of Codimension-two Brane Couplings, PARTICLES, STRINGS, AND COSMOLOGY, Publisher: AIP, ISSN: 0094-243X
Tolley AJ, Burgess CP, de Rham C, et al., 2006, Scaling solutions to 6D gauged chiral supergravity, New Journal of Physics, Vol: 8, Pages: 1-26, ISSN: 1367-2630
We construct explicitly time-dependent exact solutions to the field equations of six-dimensional (6D) gauged chiral supergravity, compactified to 4D in the presence of up to two three-branes situated within the extra dimensions. The solutions we find are scaling solutions, and are plausibly attractors which represent the late-time evolution of a broad class of initial conditions. By matching their near-brane boundary conditions to physical brane properties, we argue that these solutions (together with the known maximally symmetric solutions and a new class of non-Lorentz-invariant static solutions, which we also present here) describe the bulk geometry between a pair of three-branes with non-trivial on-brane equations of state.
de Rham C, Tolley AJ, 2006, Mimicking Lambda with a spin-two ghost condensate, Journal of Cosmology and Astroparticle Physics, Vol: 2006, Pages: 1-23, ISSN: 1475-7516
We propose a simple higher-derivative braneworld gravity model which contains a stable accelerating branch, in the absence of a cosmological constant or potential, that can be used to describe the late-time cosmic acceleration. This model has similar qualitative features to that of Dvali, Gabadadze and Porrati, such as the recovery of four-dimensional gravity at subhorizon scales, but unlike that case, the graviton zero mode is massless and there are no linearized instabilities. The acceleration rather is driven by bulk gravity in the form of a spin-two ghost condensate. We show that this model can be consistent with cosmological bounds and tests of gravity.
Shiromizu T, Fujii S, de Rham C, et al., 2006, High-energy effective theory for orbifold branes, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 73, Pages: 087301-1-087301-4, ISSN: 1550-2368
We derive an effective theory on the orbifold branes of the Randall-Sundrum 1 (RS1) braneworld scenario in the presence of a bulk brane. We concentrate on the regime where the three branes are close and consider a scenario where the bulk brane collides with one of the orbifold branes. This theory allows us to understand the corrections to a low-energy approach due to the presence of higher velocity terms, coming from the Kaluza-Klein modes. We consider the evolution of gravitational waves on a cosmological background and find that, within the large velocity limit, the boundary branes recover a purely four-dimensional behavior.
de Rham C, Tolley AJ, 2006, Gravitational waves in a codimension two braneworld, Journal of Cosmology and Astroparticle Physics, Vol: 3, Pages: 1-20, ISSN: 1475-7516
We consider the propagation of gravitational waves in six dimensions induced by sources living on 3-branes in the context of a recent exact solution (Mukohyama et al 2005 J. Cosmol. Astropart. Phys. JCAP07(2005)013). The brane geometries are de Sitter and the bulk is a warped geometry supported by a positive cosmological constant as well as a 2-form flux. We show that at low energies ordinary gravity is reproduced, and explicitly compute the leading corrections from six-dimensional effects. After regulating the brane we find a logarithmic dependence on the cut-off scale of brane physics even for modes whose frequency is much less than this energy scale. We discuss the possibility that this dependence can be renormalized into bulk or brane counterterms in line with effective field theory expectations. We discuss the inclusion of Gauss–Bonnet terms that have been used elsewhere to regulate codimension two branes. We find that such terms do not regulate codimension two branes for compact extra dimensions.
de Rham C, Fujii S, Shiromizu T, et al., 2005, High-energy effective theory for a bulk brane, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 72, Pages: 123522-1-123522-9, ISSN: 1550-2368
We derive an effective theory describing the physics of a bulk brane in the context of the RS1 model. This theory goes beyond the usual low-energy effective theory in that it describes the regime where the bulk brane has a large velocity and the radion can change rapidly. We achieve this by concentrating on the region where the distance between the orbifold planes is small in comparison to the AdS length scale. Consequently our effective theory will describe the physics shortly before a bulk/boundary or boundary/boundary brane collision. We study the cosmological solutions and find that at large velocities, the bulk brane decouples from the matter on the boundary branes, a result which remains true for cosmological perturbations.
de Rham C, Webster S, 2005, High-energy effective theory for matter on close Randall-Sundrum branes, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 72, Pages: 064013-1-064013-12, ISSN: 1550-2368
Extending the analysis of C. de Rham and S. Webster [Phys. Rev. D 71, 124025 (2005)], we obtain a formal expression for the coupling between brane matter and the radion in a Randall-Sundrum braneworld. This effective theory is correct to all orders in derivatives of the radion in the limit of small brane separation, and, in particular, contains no higher than second derivatives. In the case of cosmological symmetry the theory can be obtained in closed form and reproduces the five-dimensional behavior. Perturbations in the tensor and scalar sectors are then studied. When the branes are moving, the effective Newtonian constant on the brane is shown to depend both on the distance between the branes and on their velocity. In the small-distance limit, we compute the exact dependence between the four-dimensional and the five-dimensional Newtonian constants.
de Rham C, Webster S, 2005, High-energy theory for close Randall-Sundrum branes, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 71, Pages: 124025-1-124025-19, ISSN: 1550-2368
We obtain an effective theory for the radion dynamics of the two-brane Randall-Sundrum model, correct to all orders in brane velocity in the limit of close separation, which is of interest for studying brane collisions and early universe cosmology. Obtained via a recursive solution of the bulk equation of motion, the resulting theory represents a simple extension of the corresponding low-energy effective theory to the high-energy regime. The four-dimensional low-energy theory is indeed not valid when corrections at second order in velocity are considered. This extension has the remarkable property of including only second derivatives and powers of first order derivatives. This important feature makes the theory particularly easy to solve. We then extend the theory by introducing a potential and detuning the branes.
de Rham C, 2005, Beyond the low energy approximation in braneworld cosmology, Physical Review D: Particles, Fields, Gravitation and Cosmology, Vol: 71, Pages: 024015-1-024015-20, ISSN: 1550-2368
We develop a four-dimensional effective theory for Randall-Sundrum models which allows us to calculate long-wavelength adiabatic perturbations in a regime where the ρ2 terms characteristic of braneworld cosmology are significant. This extends previous work employing the moduli space approximation. We extend the treatment of the system to include higher derivative corrections present in the context of braneworld cosmology. The developed formalism allows us to study perturbations beyond the general long-wavelength, slow-velocity regime to which the usual moduli approximation is restricted. It enables us to extend the study to a wide range of braneworld cosmology models for which the extra terms play a significant role. As an example we discuss high-energy inflation on the brane and analyze the key observational features that distinguish braneworlds from ordinary inflation by considering scalar and tensor perturbations as well as non-Gaussianities. We also compare inflation and cyclic models and study how they can be distinguished in terms of these corrections.
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