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Braneworld gravity
 Living Rev. Rel
"... The observable universe could be a 1 + 3surface (the “brane”) embedded in a 1 + 3 + ddimensional spacetime (the “bulk”), with Standard Model particles and fields trapped on the brane while gravity is free to access the bulk. At least one of the d extra spatial dimensions could be very large relati ..."
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The observable universe could be a 1 + 3surface (the “brane”) embedded in a 1 + 3 + ddimensional spacetime (the “bulk”), with Standard Model particles and fields trapped on the brane while gravity is free to access the bulk. At least one of the d extra spatial dimensions could be very large relative to the Planck scale, which lowers the fundamental gravity scale, possibly even down to the electroweak ( ∼ TeV) level. This revolutionary picture arises in the framework of recent developments in M theory. The 1+10dimensional M theory encompasses the known 1 + 9dimensional superstring theories, and is widely considered to be a promising potential route to quantum gravity. General relativity cannot describe gravity at high enough energies and must be replaced by a quantum gravity theory, picking up significant corrections as the fundamental energy scale is approached. At low energies, gravity is localized at the brane and general relativity is recovered, but at high energies gravity “leaks ” into the bulk, behaving in a truly higherdimensional way. This introduces significant changes to gravitational dynamics and perturbations, with interesting and potentially testable implications for highenergy astrophysics, black holes, and cosmology. Braneworld models offer a phenomenological way to test some of the novel predictions and corrections to general relativity that are implied by M theory. This review discusses the geometry, dynamics and perturbations of simple braneworld models for cosmology and astrophysics, mainly focusing on warped 5dimensional braneworlds based on the Randall–Sundrum models. c©Max Planck Society and the authors. Further information on copyright is given at
Infrared effects in inflationary correlation functions, Class.Quant.Grav
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Decoding the bispectrum of singlefield inflation
 JCAP
"... Abstract. Galileon fields arise naturally from the decoupling limit of massive gravities, and possess special selfinteractions which are protected by a spacetime generalization of Galilean symmetry. We briefly revisit the inflationary phenomenology of Galileon theories. Working from recent computat ..."
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Abstract. Galileon fields arise naturally from the decoupling limit of massive gravities, and possess special selfinteractions which are protected by a spacetime generalization of Galilean symmetry. We briefly revisit the inflationary phenomenology of Galileon theories. Working from recent computations of the fluctuation Lagrangian to cubic order in the most general model with secondorder equations of motion, we show that a distinct shape is present but with suppressed amplitude. A similar shape has been found in other higherderivative models. It may be visible in a theory tuned to suppress the leadingorder shapes, or if the overall bispectrum has large amplitude. Using a partialwave expansion of the bispectrum, we suggest a possible origin for the frequent appearance of this shape. It follows that models with very disparate microphysics can produce very similar bispectra. We argue that it may be more profitable to distinguish these models by searching for relations between the amplitudes of these common shapes. We illustrate this method using the examples of DBI and kinflation.
Mixed nonGaussianity
 in multipleDBI inflation, JCAP 05 (2013) 021, [arXiv:1303.3975
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Equilateral NonGaussianity and New Physics on the Horizon
"... We examine the effective theory of singlefield inflation in the limit where the scalar perturbations propagate with a small speed of sound. In this case the nonlinearly realized timetranslation symmetry of the Lagrangian implies large interactions, giving rise to primordial nonGaussianities. Wh ..."
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We examine the effective theory of singlefield inflation in the limit where the scalar perturbations propagate with a small speed of sound. In this case the nonlinearly realized timetranslation symmetry of the Lagrangian implies large interactions, giving rise to primordial nonGaussianities. When the nonGaussianities are measurable, these interactions will become strongly coupled unless new physics appears close to the Hubble scale. Due to its proximity to the Hubble scale, the new physics is not necessarily decoupled from inflationary observables and can potentially affect the predictions of the model. To understand the types of corrections that may arise, we construct weaklycoupled completions of the theory and study their observational signatures. ar X iv
QuasiSingle Field Inflation with Large Mass
"... We study the effect of massive isocurvaton on density perturbations in quasisingle field inflation models, when the mass of the isocurvaton M becomes larger than the order of the Hubble parameter H. We analytically compute the correction to the power spectrum, leading order in coupling but exact fo ..."
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We study the effect of massive isocurvaton on density perturbations in quasisingle field inflation models, when the mass of the isocurvaton M becomes larger than the order of the Hubble parameter H. We analytically compute the correction to the power spectrum, leading order in coupling but exact for all values of mass. This verifies the previous numerical results for the range 0 < M < 3H/2 and shows that, in the large mass limit, the correction is of order H2/M2. ar X iv