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26
Monodromy in the CMB: Gravity waves and string inflation,” arXiv:0803.3085 [hepth]; – 71
 J. High Energy Phys
"... We present a simple mechanism for obtaining largefield inflation, and hence a gravitational wave signature, from string theory compactified on twisted tori. For Nil manifolds, we obtain a leading inflationary potential proportional to φ 2/3 in terms of the canonically normalized field φ, yielding p ..."
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Cited by 20 (1 self)
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We present a simple mechanism for obtaining largefield inflation, and hence a gravitational wave signature, from string theory compactified on twisted tori. For Nil manifolds, we obtain a leading inflationary potential proportional to φ 2/3 in terms of the canonically normalized field φ, yielding predictions for the tilt of the power spectrum and the tensortoscalar ratio, ns ≈ 0.98 and r ≈ 0.04 with 60 efoldings of inflation; we note also the possibility of a variant with a candidate inflaton potential proportional to φ 2/5. The basic mechanism involved in extending the field range – monodromy in Dbranes as they move in circles on the manifold – arises in a more general class of compactifications, though our methods for controlling the
Effects of ScaleDependent NonGaussianity on Cosmological Structures
, 2008
"... Abstract: The detection of primordial nonGaussianity could provide a powerful means to test various inflationary scenarios. Although scaleinvariant nonGaussianity (often described by the fNL formalism) is currently best constrained by the CMB, singlefield models with changing sound speed can hav ..."
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Abstract: The detection of primordial nonGaussianity could provide a powerful means to test various inflationary scenarios. Although scaleinvariant nonGaussianity (often described by the fNL formalism) is currently best constrained by the CMB, singlefield models with changing sound speed can have strongly scaledependent nonGaussianity. Such models could evade the CMB constraints but still have important effects at scales responsible for the formation of cosmological objects such as clusters and galaxies. We compute the effect of scaledependent primordial nonGaussianity on cluster number counts as a function of redshift, using a simple ansatz to model scaledependent features. We forecast constraints on these models achievable with forthcoming data sets. We also examine consequences for the galaxy bispectrum. Our results are relevant for the DiracBornInfeld model of brane inflation, where the scaledependence of the nonGaussianity is directly related to
Constraining Inflationary Scenarios with Braneworld Models and Second Order Cosmological Perturbations
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Perturbation Theory in kInflation Coupled to
"... Abstract. We consider kinflation models where the action is a nonlinear function of both the inflaton and the inflaton kinetic term. We focus on a scalartensor extension of kinflation coupled to matter for which we derive a modified MukhanovSasaki equation for the curvature perturbation. Signif ..."
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Abstract. We consider kinflation models where the action is a nonlinear function of both the inflaton and the inflaton kinetic term. We focus on a scalartensor extension of kinflation coupled to matter for which we derive a modified MukhanovSasaki equation for the curvature perturbation. Significant corrections to the power spectrum appear when the coupling function changes abruptly along the inflationary trajectory. This gives rise to a modification of Starobinsky’s model of perturbation features. We analyse the way the power spectrum is altered in the infrared when such features are present. 1.
Duality Cascade in Brane Inflation
, 2008
"... We show that brane inflation is very sensitive to tiny sharp features in extra dimensions, including those in the potential and in the warp factor. This can show up as observational signatures in the power spectrum and/or nonGaussianities of the cosmic microwave background radiation (CMBR). One ge ..."
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Cited by 1 (0 self)
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We show that brane inflation is very sensitive to tiny sharp features in extra dimensions, including those in the potential and in the warp factor. This can show up as observational signatures in the power spectrum and/or nonGaussianities of the cosmic microwave background radiation (CMBR). One general example of such sharp features is a succession of small steps in a warped throat, caused by Seiberg duality cascade using gauge/gravity duality. We study the cosmological observational consequences of these steps in brane inflation. Since the steps come in a series, the prediction of other steps and their properties can be tested by future data and analysis. It is also possible that the steps are too close to be resolved in the power spectrum, in which case they may show up only in the nonGaussianity of the CMB temperature fluctuations and/or EE polarization. We study two cases. In the slowroll scenario where steps appear in the inflaton potential, the sensitivity of brane inflation to the height and width of the steps is increased by several orders of magnitude comparing to that in previously studied large field models. In the IR DBI scenario where steps appear in the warp factor, we find that the glitches in the power spectrum caused by these sharp features are generally small or even unobservable,
DBI Realizations of the PseudoConformal Universe and Galilean Genesis Scenarios
, 2012
"... The pseudoconformal universe is an alternative to inflation in which the early universe is described by a conformal field theory on approximately flat spacetime. The fields develop timedependent expectation values, spontaneously breaking the conformal symmetries to a de Sitter subalgebra, and fi ..."
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The pseudoconformal universe is an alternative to inflation in which the early universe is described by a conformal field theory on approximately flat spacetime. The fields develop timedependent expectation values, spontaneously breaking the conformal symmetries to a de Sitter subalgebra, and fields of conformal weight zero acquire a scale invariant spectrum of perturbations. In this paper, we show that the pseudoconformal scenario can be naturally realized within theories that would ordinarily be of interest for DBI inflation, such as the worldvolume theory of a probe brane in an AdS bulk spacetime. In this approach, the weight zero spectator field can be associated with a geometric flat direction in the bulk, and its scale invariance is protected by a shift symmetry.
Inflation in DBI models with constant γ
, 711
"... Abstract: DiracBornInfeld scalar field theories which appear in the context of inflation in string theory in general have a field dependent speed of sound. It is however possible to write down DBI models which posess exact solutions characterized by a constant speed of sound different from unity. ..."
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Abstract: DiracBornInfeld scalar field theories which appear in the context of inflation in string theory in general have a field dependent speed of sound. It is however possible to write down DBI models which posess exact solutions characterized by a constant speed of sound different from unity. For this to be possible the potential and the “throat function ” appearing in a DBI action have to be related in a specific way. This paper describes such models in general and presents some examples with a constant speed of sound cs < 1 for which the spectrum of scalar perturbations can be found analytically without resorting to the slow roll approximation.
Reconstructing Single Field Inflationary Actions From CMBR Data. ∗
, 804
"... This paper describes a general program for deriving the action of single field inflation models with nonstandard kinetic energy terms using CMBR power spectrum data. This method assumes that an action depends on a set of undetermined functions, each of which is a function of either the inflaton wave ..."
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This paper describes a general program for deriving the action of single field inflation models with nonstandard kinetic energy terms using CMBR power spectrum data. This method assumes that an action depends on a set of undetermined functions, each of which is a function of either the inflaton wave function or its time derivative. The scalar, tensor and nongaussianity of the curvature perturbation spectrum are used to derive a set of reconstruction equations whose solution set can specify up to three of the undetermined functions. The method is then used to find the undetermined functions in various types of actions assuming power law type scalar and tensor spectra. In actions that contain only two unknown functions, the third reconstruction equation implies a consistency relation between the nongaussianty, sound speed and slow roll parameters. In particular we focus on reconstructing a generalized DBI action with an unknown potential and warp factor. We find that for realistic scalar and tensor spectra, the reconstructed warp factor and potential are very similar to the theoretically derived result. Furthermore, physical consistency of the reconstructed warp factor and potential imposes strict constraints on the scalar and tensor spectral indices. 1