Results 1  10
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153
String cosmology
"... Abstract: We derive the corrections to the Friedmann equation of order ρ 2 in the RandallSundrum (RS) model, where two 3branes bound a slice of fivedimensional AntideSitter space. The effects of radion stabilization by the GoldbergerWise mechanism are taken into account. Surprisingly, we find t ..."
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Cited by 48 (2 self)
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Abstract: We derive the corrections to the Friedmann equation of order ρ 2 in the RandallSundrum (RS) model, where two 3branes bound a slice of fivedimensional AntideSitter space. The effects of radion stabilization by the GoldbergerWise mechanism are taken into account. Surprisingly, we find that an inflaton on either brane will experience no order ρ 2 corrections in the Hubble rate H due to its own energy density, although an observer on the opposite brane does see such a correction. Thus there is no enhancement of the slowroll condition unless inflation is simultaneously driven by inflatons on both branes. Similarly, during radiation domination, the ρ 2 correction to H on a given brane vanish unless there is nonvanishing energy density on the opposite brane. During the electroweak phase transition the correction can be large, but is has the wrong sign for causing sphalerons to go out of thermal equilibrium, so it cannot help electroweak baryogenesis. We discuss the differences
Inflationary trispectrum from graviton exchange
"... Abstract. We compute the connected fourpoint correlation function of the primordial curvature perturbation generated during inflation with standard kinetic terms, where the correlation is established via exchange of a graviton between two pairs of scalar fluctuations. Any such correlation yields a ..."
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Cited by 40 (6 self)
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Abstract. We compute the connected fourpoint correlation function of the primordial curvature perturbation generated during inflation with standard kinetic terms, where the correlation is established via exchange of a graviton between two pairs of scalar fluctuations. Any such correlation yields a contribution to the scalar trispectrum of the order of the tensor to scalar ratio r. This contribution is numerically one order of magnitude larger than the one previously calculated on the basis of scalar perturbations interacting at a point and satisfies a simple relation in the limit where the momentum of the graviton which is exchanged becomes much smaller than the external momenta. We conclude that the total nonlinearity parameter generated by singlefield models of slowroll inflation is at maximum τNL  ∼ r. ‡ Permanent addressInflationary trispectrum from graviton exchange 2 1.
Comparing Infrared DiracBornInfeld Brane Inflation to Observations
, 2008
"... We compare the Infrared DiracBornInfeld (IR DBI) brane inflation model to observations using a Bayesian analysis. The current data cannot distinguish it from the ΛCDM model, but is able to give interesting constraints on various microscopic parameters including the mass of the brane moduli potenti ..."
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Cited by 26 (4 self)
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We compare the Infrared DiracBornInfeld (IR DBI) brane inflation model to observations using a Bayesian analysis. The current data cannot distinguish it from the ΛCDM model, but is able to give interesting constraints on various microscopic parameters including the mass of the brane moduli potential, the fundamental string scale, the charge or warp factor of throats, and the number of the mobile branes. We quantify some distinctive testable predictions with stringy signatures, such as the large nonGaussianity, and the large, but regional, running of the spectral index. These results illustrate how we may be able to probe aspects of string theory using cosmological observations.
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
Phenomenology of a PseudoScalar Inflaton
 Naturally Large Nongaussianity,” JCAP 1104 (2011) 009, arXiv:1102.4333
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Infrared effects in inflationary correlation functions, Class.Quant.Grav
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Large Nongaussianity from Nonlocal Inflation
 JCAP 0707, 017 (2007) [arXiv:0704.3426 [hepth]]; “Predictions for Nongaussianity from Nonlocal Inflation,” arXiv:0802.3218 [hepth
"... Abstract: We study the possibility of obtaining large nongaussian signatures in the Cosmic Microwave Background in a general class of singlefield nonlocal hilltop inflation models. We estimate the nonlinearity parameter fNL which characterizes nongaussianity in such models and show that large nong ..."
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Cited by 14 (3 self)
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Abstract: We study the possibility of obtaining large nongaussian signatures in the Cosmic Microwave Background in a general class of singlefield nonlocal hilltop inflation models. We estimate the nonlinearity parameter fNL which characterizes nongaussianity in such models and show that large nongaussianity is possible. For the recently proposed padic inflation model we find that fNL ∼ 120 when the string coupling is order unity. We show that large nongaussianity is also possible in a toy model with an action similar to
Quasisingle field inflation and nonGaussianities
 JCAP 1009, 027 (2010) [arXiv:0911.3380 [hepth
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Generating ScaleInvariant Perturbations from RapidlyEvolving Equation
 of State,” Phys.Rev. D83 (2011) 123502, arXiv:1101.3548 [hepth
"... Recently, we introduced an ekpyrotic model based on a single, canonical scalar field that generates nearly scale invariant curvature fluctuations through a purely “adiabatic mechanism ” in which the background evolution is a dynamical attractor. Despite the starkly different physical mechanism for ..."
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Recently, we introduced an ekpyrotic model based on a single, canonical scalar field that generates nearly scale invariant curvature fluctuations through a purely “adiabatic mechanism ” in which the background evolution is a dynamical attractor. Despite the starkly different physical mechanism for generating fluctuations, the twopoint function is identical to inflation. In this paper, we further explore this concept, focusing in particular on issues of nongaussianity and quantum corrections. We find that the degeneracy with inflation is broken at threepoint level: for the simplest case of an exponential potential, the threepoint amplitude is strongly scale dependent, resulting in a breakdown of perturbation theory on small scales. However, we show that the perturbative breakdown can be circumvented — and all issues raised in Linde et al. (arXiv:0912.0944) can be addressed — by altering the potential such that power is suppressed on small scales. The resulting range of nearly scale invariant, gaussian modes can be as much as twelve efolds, enough to span the scales probed by microwave background and large scale structure observations. On smaller scales, the spectrum is not scale invariant but is observationally acceptable. 1 ar