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163
Observational signatures and nongaussianities of general single field inflation
"... We perform a general study of primordial scalar nonGaussianities in single field inflationary models in Einstein gravity. We consider models where the inflaton Lagrangian is an arbitrary function of the scalar field and its first derivative, and the sound speed is arbitrary. We find that under reas ..."
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Cited by 157 (9 self)
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We perform a general study of primordial scalar nonGaussianities in single field inflationary models in Einstein gravity. We consider models where the inflaton Lagrangian is an arbitrary function of the scalar field and its first derivative, and the sound speed is arbitrary. We find that under reasonable assumptions, the nonGaussianity is completely determined by 5 parameters. In special limits of the parameter space, one finds distinctive “shapes ” of the nonGaussianity. In models with a small sound speed, several of these shapes would become potentially observable in the near future. Different limits of our formulae recover various previously known results. Contents
Inflationary scenarios from branes at angles
 JHEP 0207 (2002) 051 [arXiv:hepth/0203163
"... Abstract: We describe a simple mechanism that can lead to inflation within stringbased braneworld scenarios. The idea is to start from a supersymmetric configuration with two parallel static Dpbranes, and slightly break the supersymmetry conditions to produce a very flat potential for the field t ..."
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Cited by 50 (2 self)
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Abstract: We describe a simple mechanism that can lead to inflation within stringbased braneworld scenarios. The idea is to start from a supersymmetric configuration with two parallel static Dpbranes, and slightly break the supersymmetry conditions to produce a very flat potential for the field that parametrises the distance between the branes, i.e. the inflaton field. This breaking can be achieved in various ways: by slight relative rotations of the branes with small angles, by considering small relative velocities between the branes, etc. If the breaking parameter is sufficiently small, a large number of efolds can be produced within the Dbrane, for small changes of the configuration in the compactified directions. Such a process is local, i.e. it does not depend very strongly on the compactification space nor on the initial conditions. Moreover, the breaking induces a very small velocity and acceleration, which ensures very small slowroll parameters and thus an almost scale invariant spectrum of metric fluctuations, responsible for the observed temperature anisotropies in the microwave background. Inflation ends as in hybrid inflation, triggered by the negative curvature of the string tachyon potential. In this paper we elaborate on one of the simplest examples: two almost parallel D4branes in a flat compactified space. JHEP01(2002)036
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 49 (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
Gravitational Wave Experiments and Early Universe Cosmology
"... Gravitationalwave experiments with interferometers and with resonant masses can search for stochastic backgrounds of gravitational waves of cosmological origin. We review both experimental and theoretical aspects of the search for these backgrounds. We give a pedagogical derivation of the various r ..."
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Cited by 36 (0 self)
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Gravitationalwave experiments with interferometers and with resonant masses can search for stochastic backgrounds of gravitational waves of cosmological origin. We review both experimental and theoretical aspects of the search for these backgrounds. We give a pedagogical derivation of the various relations that characterize the response of a detector to a stochastic background. We discuss the sensitivities of the large interferometers under constructions (LIGO, VIRGO, GEO600, TAMA300, AIGO) or planned (Avdanced LIGO, LISA) and of the presently operating resonant bars, and we give the sensitivities for various twodetectors correlations. We examine the existing limits on the energy density in gravitational waves from nucleosynthesis, COBE and pulsars, and their effects on theoretical predictions. We discuss general theoretical principles for orderofmagnitude estimates of cosmological production mechanisms, and then we turn to specific theoretical predictions from inflation, string cosmology, phase transitions, cosmic strings and other mechanisms. We finally compare with the stochastic backgrounds of astrophysical origin.
Towards an explicit model of dbrane inflation
"... We present a detailed analysis of an explicit model of warped Dbrane inflation, incorporating the effects of moduli stabilization. We consider the potential for D3brane motion in a warped conifold background that includes fluxes and holomorphicallyembedded D7branes involved in moduli stabilizati ..."
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Cited by 35 (3 self)
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We present a detailed analysis of an explicit model of warped Dbrane inflation, incorporating the effects of moduli stabilization. We consider the potential for D3brane motion in a warped conifold background that includes fluxes and holomorphicallyembedded D7branes involved in moduli stabilization. Although the D7branes significantly modify the inflaton potential, they do not correct the quadratic term in the potential, and hence do not cause a uniform change in the slowroll parameter η. Nevertheless, we present a simple example based on the Kuperstein embedding of D7branes, z1 = constant, in which the potential can be finetuned to be sufficiently flat for inflation. To derive this result, it is essential to incorporate the fact that the compactification volume changes slightly as the D3brane moves. We stress that the compactification geometry dictates certain relationships among the parameters in the inflaton Lagrangian, and these microscopic constraints impose severe restrictions on the space of possible models. We note that the shape of the final inflaton potential differs from projections given in earlier studies: in configurations where inflation occurs, it does so near an inflection point. Finally, we comment on the difficulty of making precise cosmological predictions in this scenario. This is the companion paper to [1].
de Sitter holography and the cosmic microwave background
 JHEP
, 2002
"... Abstract: We interpret cosmological evolution holographically as a renormalisation group flow in a dual Euclidean field theory, as suggested by the conjectured dS/CFT correspondence. Inflation is described by perturbing around the infrared fixed point of the dual field theory. The spectrum of the c ..."
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Cited by 34 (8 self)
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Abstract: We interpret cosmological evolution holographically as a renormalisation group flow in a dual Euclidean field theory, as suggested by the conjectured dS/CFT correspondence. Inflation is described by perturbing around the infrared fixed point of the dual field theory. The spectrum of the cosmic microwave background radiation is determined in terms of scaling violations in the field theory. The dark energy allows similar, albeit less predictive, considerations. We discuss the cosmological finetuning
Inflation after wmap3: Confronting the slowroll and exact power spectra with cmb data, JCAP 0608
, 2006
"... year data for inflation are investigated using both the slowroll approximation and an exact numerical integration of the inflationary power spectra including a phenomenological modelling of the reheating era. At slowroll leading order, the constraints ǫ1 < 0.022 and −0.07 < ǫ2 < 0.07 are ..."
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Cited by 33 (7 self)
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year data for inflation are investigated using both the slowroll approximation and an exact numerical integration of the inflationary power spectra including a phenomenological modelling of the reheating era. At slowroll leading order, the constraints ǫ1 < 0.022 and −0.07 < ǫ2 < 0.07 are obtained at 95 % CL (Confidence Level) implying a tensortoscalar ratio r10 < 0.21 and a Hubble parameter during inflation H/mPl < 1.3 × 10−5. At nexttoleading order, a tendency for ǫ3> 0 is observed. With regards to the exact numerical integration, large field models, V (φ) ∝ φp, with p> 3.1 are now excluded at 95 % CL. Small field models, V (φ) ∝ 1 − (φ/µ) p, are still compatible with the data for all values of p. However, if µ/mPl < 10 is assumed, then the case p = 2 is slightly disfavoured. In addition, mild constraints on the reheating temperature for an extreme equation of state wreh � −1/3 are found, namely Treh> 2 TeV at 95 % CL. Hybrid models are disfavoured by the data, the best fit model having ∆χ2 ≃ +5 with two extra parameters in comparison with large field models. Running mass models remain compatible, but no prior independent constraints can be obtained. Finally, superimposed oscillations of transPlanckian origin are studied. The vanilla slowroll model is still the most probable one. However, the overall statistical weight in favour of superimposed oscillations has increased in comparison with the WMAP first year data, the amplitude of the oscillations satisfying 2xσ0 < 0.76 at 95 % CL. The best fit model leads to an improvement of ∆χ2 ≃ −12 for 3 extra parameters. Moreover, compared to other oscillatory patterns, the logarithmic shape is favoured. PACS numbers: 98.80.Cq, 98.70.VcInflation after WMAP3 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 27 (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.
Closed string tachyon condensation and worldsheet inflation,” Phys
 Rev. D
"... Closed string tachyon condensation in spacetime generates potentials on the worldsheet that model twodimensional inflationary cosmology. These models illustrate and elucidate a variety of aspects of inflation, in particular the generation of quantum fluctuations and their backreaction on geometry. ..."
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Cited by 23 (3 self)
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Closed string tachyon condensation in spacetime generates potentials on the worldsheet that model twodimensional inflationary cosmology. These models illustrate and elucidate a variety of aspects of inflation, in particular the generation of quantum fluctuations and their backreaction on geometry. We exhibit a class of Liouville gravity models coupled to matter that can exhibit, for example: (a) pure de Sitter gravity; (b) slowroll inflation; (c) topological inflation; and (d) graceful exit into an FRW phase. The models also provide a quantitative testing ground for ideas about the origin of inflation, such as the various ‘noboundary/tunnelling ’ proposals, and the ‘eternal/chaotic ’ inflationary scenario. We suggest an alternative mechanism for quantum creation of cosmological spacetimes which, in the context of the model, provides a natural explanation for why the typical FRW cosmology at large scales underwent a period of inflation at small scale.