Results 1  10
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12
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.
Rapid Tunneling and Percolation in the Landscape
, 708
"... Abstract: Motivated by the possibility of a string landscape, we reexamine tunneling of a scalar field across single/multiple barriers. Recent investigations have suggested modifications to the usual picture of false vacuum decay that lead to efficient and rapid tunneling in the landscape when certa ..."
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Cited by 6 (0 self)
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Abstract: Motivated by the possibility of a string landscape, we reexamine tunneling of a scalar field across single/multiple barriers. Recent investigations have suggested modifications to the usual picture of false vacuum decay that lead to efficient and rapid tunneling in the landscape when certain conditions are met. This can be due to stringy effects (e.g. tunneling via the DBI action), or by effects arising due to the presence of multiple vacua (e.g. resonance tunneling). In this paper we discuss both DBI tunneling and resonance tunneling. We provide a QFT treatment of resonance tunneling using the Schrödinger functional approach. We also show how DBI tunneling for supercritical barriers can naturally lead to conditions suitable for resonance tunneling. We argue using basic ideas from percolation theory that tunneling can be rapid in a landscape where a typical vacuum has multiple decay channels and discuss various cosmological implications. This rapidity vacuum decay can happen even if there are no resonance/DBI tunneling enhancements, solely due to the presence of a large number of decay channels. Finally, we consider various ways of circumventing a recent nogo theorem for resonance tunneling in quantum field theory.
A Renormalization Group Approach to the Cosmological Constant Problem,” arXiv:0708.4374 [hepth
"... Abstract: In an earlier paper, it is proposed that, due to resonance tunneling effect, tunneling from a large cosmological constant Λ site in the stringy comic landscape can be fast, while tunneling from a small Λ site may take exponentially long time. If there is a sharp transition at a small criti ..."
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Cited by 5 (2 self)
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Abstract: In an earlier paper, it is proposed that, due to resonance tunneling effect, tunneling from a large cosmological constant Λ site in the stringy comic landscape can be fast, while tunneling from a small Λ site may take exponentially long time. If there is a sharp transition at a small critical value Λc from fast tunneling for Λ> Λc to suppressed tunneling for Λc> Λ> 0, we may have a qualitative understanding why today’s dark energy is so small. Here, the arguments for fast tunneling and the subsequent sharp transition to exponentially slow tunneling are strengthened by directly borrowing the renormalization group analysis of the conductance in the Anderson localization transition. As an illustration, we
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,
Update of D3/D7Brane Inflation on K3 . . .
, 2008
"... We update the D3/D7brane inflation model on K3×T 2 /Z2 with branes and fluxes. For this purpose, we study the low energy theory including gs corrections to the gaugino condensate superpotential that stabilizes the K3 volume modulus. The gauge kinetic function is verified to become holomorphic when ..."
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We update the D3/D7brane inflation model on K3×T 2 /Z2 with branes and fluxes. For this purpose, we study the low energy theory including gs corrections to the gaugino condensate superpotential that stabilizes the K3 volume modulus. The gauge kinetic function is verified to become holomorphic when the original N = 2 supersymmetry is spontaneously broken to N = 1 by bulk fluxes. From the underlying classical N = 2 supergravity, the theory inherits a shift symmetry which provides the inflaton with a naturally flat potential. We analyze the fate of this shift symmetry after the inclusion of quantum corrections. The field range of the inflaton is found to depend significantly on the complex structure of the torus but is independent of its volume. This allows for a large kinematical field range for the inflaton. Furthermore, we show that the D3/D7 model may lead to a realization of the recent CMB fit by Hindmarsh et al. with an 11 % contribution from cosmic strings and a spectral index close to ns = 1. On the other hand, by a slight change of the parameters of the model one can strongly suppress the cosmic string contribution and reduce the spectral index ns to fit the WMAP5 data in the absence of cosmic strings. We also demonstrate that the inclusion of quantum corrections allows for a regime of eternal D3/D7 inflation.
Stochastic Inflation Revisited: NonSlow Roll Statistics and DBI Inflation
, 801
"... Abstract: Stochastic inflation describes the global structure of the inflationary universe by modeling the superHubble dynamics as a system of matter fields coupled to gravity where the subHubble field fluctuations induce a stochastic force into the equations of motion. The superHubble dynamics a ..."
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Abstract: Stochastic inflation describes the global structure of the inflationary universe by modeling the superHubble dynamics as a system of matter fields coupled to gravity where the subHubble field fluctuations induce a stochastic force into the equations of motion. The superHubble dynamics are ultralocal, allowing us to neglect spatial derivatives and treat each Hubble patch as a separate universe. This provides a natural framework in which to discuss probabilities on the space of solutions and initial conditions. In this article we derive an evolution equation for this probability for an arbitrary class of matter systems, including DBI and kinflationary models, and discover equilibrium solutions that satisfy detailed balance. Our results are more general than those derived assuming slow roll or a quaside Sitter geometry, and so are directly applicable to models that do not satisfy the usual slow roll conditions. We discuss in general terms the conditions for eternal inflation to set in, and we give explicit numerical solutions of highly stochastic, quasistationary trajectories in the relativistic DBI regime. Finally, we show that the probability for stochastic/thermal tunneling can be significantly enhanced relative to the HawkingMoss instanton result due to relativistic DBI effects. Contents
Seoul 130722, Korea
, 707
"... We investigate whether the eternal chaotic inflation can be achieved when the weak gravity conjecture is taken into account. We show that even the assisted chaotic inflation with potential λφ 4 or m 2 φ 2 can not be eternal. The effective field theory description for the inflaton field breaks down b ..."
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We investigate whether the eternal chaotic inflation can be achieved when the weak gravity conjecture is taken into account. We show that even the assisted chaotic inflation with potential λφ 4 or m 2 φ 2 can not be eternal. The effective field theory description for the inflaton field breaks down before inflation reaches the eternal regime. We also find that the total number of efolds is still bounded by the inflationary entropy for the assisted inflation. Inflation [1–3] is the leading theoretical paradigm for understanding the early universe and the origin of the primordial perturbations. In the new version of inflation, inflaton may begin either in the false vacuum, or in an unstable state at the top of the effective potential. Then the inflaton field slowly rolls down to the minimum of its effective potential. This picture relies on an application of lowenergy effective field theory to inflation. An interesting phenomenon in inflationary scenario is eternal inflation. There are actually two kinds of eternal inflation. One is driven by the quasiexponential expansion of the metastable vacua themselves. In our paper, we focus on the other version called slowroll eternal inflation [4,5]. In this scenario, during the period of inflation, the evolution