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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
Towards inflation in string theory
 JCAP
, 2003
"... We investigate the embedding of brane inflation into stable compactifications of string theory. At first sight a warped compactification geometry seems to produce a naturally flat inflaton potential, evading one wellknown difficulty of braneantibrane scenarios. Careful consideration of the closed ..."
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Cited by 82 (8 self)
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We investigate the embedding of brane inflation into stable compactifications of string theory. At first sight a warped compactification geometry seems to produce a naturally flat inflaton potential, evading one wellknown difficulty of braneantibrane scenarios. Careful consideration of the closed string moduli reveals a further obstacle: superpotential stabilization of the compactification volume typically modifies the inflaton potential and renders it too steep for inflation. We discuss the nongeneric conditions under which this problem does not arise. We conclude that brane inflation models can only work if restrictive assumptions about the method of volume stabilization, the warping of the internal space, and the source of inflationary energy are satisfied. We argue that this may not be a real problem, given the large range of available fluxes and background geometries in string theory.
Beauty is attractive: Moduli trapping at enhanced symmetry points,” JHEP 0405, 030 (2004) [arXiv:hepth/0403001]; T. Mohaupt and F. Saueressig, “Effective supergravity actions for conifold transitions
 JCAP
, 2004
"... We study quantum effects on moduli dynamics arising from the production of particles which are light at points of enhanced symmetry in moduli space. The resulting forces trap the moduli at these points. Moduli trapping occurs in timedependent quantum field theory, as well as in systems of moving D ..."
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Cited by 63 (13 self)
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We study quantum effects on moduli dynamics arising from the production of particles which are light at points of enhanced symmetry in moduli space. The resulting forces trap the moduli at these points. Moduli trapping occurs in timedependent quantum field theory, as well as in systems of moving Dbranes, where it leads the branes to combine into stacks. Trapping also occurs in the presence of gravity, though the range over which the moduli can roll is limited by Hubble friction. We observe that a scalar field trapped on a steep potential can induce a stage of acceleration of the universe, which we call trapped inflation. Moduli trapping ameliorates the cosmological moduli problem and may affect vacuum selection. In particular, rolling moduli are most powerfully attracted to the points of greatest symmetry. Given suitable assumptions about the dynamics of the very early universe, this effect might help to explain why among the plethora of possible vacuum states of string theory, we appear to live in one with a large number of (spontaneously
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
Inflation from warped space
 JHEP
, 2005
"... A long period of inflation can be triggered when the inflaton is held up on the top of a steep potential by the infrared end of a warped space. We first study the field theory description of such a model. We then embed it in the flux stabilized string compactification. Some special effects in the th ..."
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Cited by 39 (8 self)
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A long period of inflation can be triggered when the inflaton is held up on the top of a steep potential by the infrared end of a warped space. We first study the field theory description of such a model. We then embed it in the flux stabilized string compactification. Some special effects in the throat reheating process by relativistic branes are discussed. We put all these ingredients into a multithroat brane inflationary scenario. The resulting cosmic string tension Inflation [1–3] provides a natural mechanism for creating the homogeneity and flatness of our observable universe. It also gives an elegant way of generating the perturbations [4–10] which seed the structure formation. In order for the inflation to last sufficiently long and then successfully exit to reheat the universe, the inflaton has to be held up on a potential for
The giant inflaton
, 2002
"... We investigate a new mechanism for realizing slow roll inflation in string theory, based on the dynamics of p antiD3 branes in a class of mildly warped flux compactifications. Attracted to the bottom of a warped conifold throat, the antibranes then cluster due to a novel mechanism wherein the back ..."
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Cited by 30 (4 self)
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We investigate a new mechanism for realizing slow roll inflation in string theory, based on the dynamics of p antiD3 branes in a class of mildly warped flux compactifications. Attracted to the bottom of a warped conifold throat, the antibranes then cluster due to a novel mechanism wherein the background flux polarizes in an attempt to screen them. Once they are sufficiently close, the M units of flux cause the antibranes to expand into a fuzzy NS5brane, which for rather generic choices of p/M will unwrap around the geometry, decaying into D3branes via a classical process. We find that the effective potential governing this evolution possesses several epochs that can potentially support slowroll inflation, provided the process can be arranged to take place at a high enough energy scale, of about one or two orders of magnitude below the Planck energy; this scale, however, lies just outside the bounds of our approximations
Brane Inflation and Cosmic String Tension in Superstring Theory,” arXiv:hepth/0501099
"... Abstract. In a simple reanalysis of the KKLMMT scenario, we argue that the slow roll condition in the D3D3brane inflationary scenario in superstring theory requires ..."
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Cited by 30 (11 self)
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Abstract. In a simple reanalysis of the KKLMMT scenario, we argue that the slow roll condition in the D3D3brane inflationary scenario in superstring theory requires
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.
Heating in brane inflation and hidden dark matter
, 2006
"... Towards the end of brane inflation, the brane pair annihilation produces massive closed strings. The transfer of this energy to Standard Model (SM) open string modes depends on where the SM branes and the brane annihilation are located: in the bulk, in the same throat or in different throats. We fi ..."
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Cited by 21 (6 self)
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Towards the end of brane inflation, the brane pair annihilation produces massive closed strings. The transfer of this energy to Standard Model (SM) open string modes depends on where the SM branes and the brane annihilation are located: in the bulk, in the same throat or in different throats. We find that, in all cases as long as the brane annihilation and the SM branes are not both in the bulk, the transfer of energy to start the hot big bang epoch can be efficient enough to be compatible with big bang nucleosynthesis. The suppression of the abundance of the graviton and its KaluzaKlein (KK) thermal relics follows from the warped geometry in flux compactification. This works out even in the scenarios where a long period of tunneling is expected. In the multithroat scenario, we find a dynamical mechnism of selecting a long throat as the SM throat. We establish three new dark matter candidates: KK modes with specific angular momentum in the SM throat, those in the brane annihilation throat, and different matters generated by KK modes tunneled to other throats. Since the latter two couple to the visible matter sector only through graviton mediation, they behave as hidden dark matter. Hidden dark matter has novel implications on the dark matter coincidence problem and the high energy cosmic rays.