Fine-tuning in DBI inflationary mechanism

Chen, Xingang

doi:10.1088/1475-7516/2008/12/009

Cited by 29 publications

(25 citation statements)

References 39 publications

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“…Finally, we note that periodic features in the inflationary potential can excite the vacuum state, as well as perturbing the background inflation trajectory (Chen 2010a). Such models offer the intriguing possibility of combining the flattened non-Bunch-Davies shape with periodic oscillations:…”

Section: Multi-field Modelsmentioning

confidence: 85%

Planck2013 results. XXIV. Constraints on primordial non-Gaussianity

Ade

Aghanim

Armitage-Caplan

et al. 2014

A&A

388

293

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The Planck nominal mission cosmic microwave background (CMB) maps yield unprecedented constraints on primordial non-Gaussianity (NG). Using three optimal bispectrum estimators, separable template-fitting (KSW), binned, and modal, we obtain consistent values for the primordial local, equilateral, and orthogonal bispectrum amplitudes, quoting as our final result f local NL = 2.7 ± 5.8, f equil NL = −42 ± 75, and f ortho NL = −25 ± 39 (68% CL statistical). Non-Gaussianity is detected in the data; using skew-C statistics we find a nonzero bispectrum from residual point sources, and the integrated-Sachs-Wolfe-lensing bispectrum at a level expected in the ΛCDM scenario. The results are based on comprehensive crossvalidation of these estimators on Gaussian and non-Gaussian simulations, are stable across component separation techniques, pass an extensive suite of tests, and are confirmed by skew-C , wavelet bispectrum and Minkowski functional estimators. Beyond estimates of individual shape amplitudes, we present model-independent, three-dimensional reconstructions of the Planck CMB bispectrum and thus derive constraints on early-Universe scenarios that generate primordial NG, including general single-field models of inflation, excited initial states (non-Bunch-Davies vacua), and directionally-dependent vector models. We provide an initial survey of scale-dependent feature and resonance models. These results bound both general single-field and multi-field model parameter ranges, such as the speed of sound, c s ≥ 0.02 (95% CL), in an effective field theory parametrization, and the curvaton decay fraction r D ≥ 0.15 (95% CL). The Planck data significantly limit the viable parameter space of the ekpyrotic/cyclic scenarios. The amplitude of the four-point function in the local model τ NL < 2800 (95% CL). Taken together, these constraints represent the highest precision tests to date of physical mechanisms for the origin of cosmic structure.

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Section: Multi-field Modelsmentioning

confidence: 85%

Planck2013 results. XXIV. Constraints on primordial non-Gaussianity

Ade

Aghanim

Armitage-Caplan

et al. 2014

A&A

388

293

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“…Resonant single-field models with varying sound speed c s generate three leading-order bispectrum terms (Chen 2010a):…”

Section: Resonance and Axion Monodromy Modelsmentioning

confidence: 99%

“…(12), Non-BunchDavies (NBD; Chen et al 2007b), NBD1 and NBD2 models (Agullo & Parker 2011; now called "NBD1 cos" and "NBD2 cos") and NBD3 (Chen 2010b). We also introduce three new templates, NBD sin which is motivated by (Chen 2010a) and takes the form…”

Section: Non-gaussianity From Excited Initial Statesmentioning

confidence: 99%

Planck2015 results

Ade

Aghanim

Arnaud

et al. 2016

A&A

477

256

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The Planck full mission cosmic microwave background (CMB) temperature and E-mode polarization maps are analysed to obtain constraints on primordial non-Gaussianity (NG). Using three classes of optimal bispectrum estimators -separable template-fitting (KSW), binned, and modalwe obtain consistent values for the primordial local, equilateral, and orthogonal bispectrum amplitudes, quoting as our final result from temperature alone f local NL = 2.5 ± 5.7, f equil NL = −16 ± 70, and f ortho NL = −34 ± 33 (68% CL, statistical). Combining temperature and polarization data we obtain f local NL = 0.8 ± 5.0, f equil NL = −4 ± 43, and f ortho NL = −26 ± 21 (68% CL, statistical). The results are based on comprehensive cross-validation of these estimators on Gaussian and non-Gaussian simulations, are stable across component separation techniques, pass an extensive suite of tests, and are consistent with estimators based on measuring the Minkowski functionals of the CMB. The effect of time-domain de-glitching systematics on the bispectrum is negligible. In spite of these test outcomes we conservatively label the results including polarization data as preliminary, owing to a known mismatch of the noise model in simulations and the data. Beyond estimates of individual shape amplitudes, we present model-independent, three-dimensional reconstructions of the Planck CMB bispectrum and derive constraints on early universe scenarios that generate primordial NG, including general single-field models of inflation, axion inflation, initial state modifications, models producing parityviolating tensor bispectra, and directionally dependent vector models. We present a wide survey of scale-dependent feature and resonance models, accounting for the "look elsewhere" effect in estimating the statistical significance of features. We also look for isocurvature NG, and find no signal, but we obtain constraints that improve significantly with the inclusion of polarization. The primordial trispectrum amplitude in the local model is constrained to be g local NL = (−9.0 ± 7.7) × 10 4 (68% CL statistical), and we perform an analysis of trispectrum shapes beyond the local case. The global picture that emerges is one of consistency with the premises of the ΛCDM cosmology, namely that the structure we observe today was sourced by adiabatic, passive, Gaussian, and primordial seed perturbations.

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“…Inspired by these ideas, several workers, especially Bekenstein (2004), Sanders (2005), and Zlosnik et al (2007), proposed to extend the application to galaxy scale to use it to explain missing matter (i.e., dark matter). Many have constrained the theory using empirical astronomical data ( Famaey & Binney 2005;Zhao & Famaey 2006;Zhao 2006;Famaey et al 2007), including gravitational lensing Chen & Zhao 2006;Chen 2008;Angus et al 2007). Most recently Zhao (2007) found a simple Lagrangian within these frameworks to give rise to the DM-DE effects of the right amplitude, offering a possible explanation of coincidence of DE scale and DM scale in ÃCDM cosmology.…”

Section: Introducing a Framework For Vector Fieldsmentioning

confidence: 99%

A Nonuniform Dark Energy Fluid: Perturbation Equations

Halle¹,

Zhao²,

Li³

2008

ASTROPHYS J SUPPL S

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We propose that galactic dark matter can be described by a nonuniform dark energy fluid. The underlying field is a decaying vector field, which might corresponds to a photon-like but massive particle of 4 degrees of dynamical freedom. We propose a very general Lagrangian for this vector field. The model includes a continuous spectrum of plausible gravity theories, for example, quintessence, f (R), Einstein-Aether, MOND, TeVeS, BSTV, V-Ã theories, and the inflaton scalar field as special cases. We study in detail a special class of models with a fixed norm of the timelike vector field in the physical metric, which includes a nonlinear K 4 term and a Ricci scalar term. We derive the Einstein equations in the perturbed form, which are needed for simulating structure growth in an FRW universe to test such theories. A special case of the model V-Ã shows promise of resembling the ÃCDM cosmology. We show that the vector field has the effect of a nonuniform dark fluid, which resembles dark matter in galaxies and dark energy in the late universe. Subject headingg s: cosmology: theory -dark matter -gravitation INTRODUCING A FRAMEWORK FOR VECTOR FIELDSGeneral relativity (GR) is actually a special case and minimal construction of a range of theories describing the metric of a plausible universe. While completely adequate on small scales, GR by itself predicts a missing mass and missing energy compared to astronomical observations of the metric of the universe on the scale of kpc to Gpc (e.g., Spergel et al. 2007). While the missing mass is arguably explained by dark matter (DM) particle fields in supersymmetry particle physics, the missing energy almost certainly cannot be explained unless the present universe is immersed in an exotic dark energy (DE) field (White 2007). Since both the effects of DM and DE occur when the gravity is weak, one wonders if the underlying fields are tracking the metric field of the gravity (Zhao 2007).Quantum gravity and string theory often predict a nontrivial coupling of some vector field, which violates CPT symmetry satisfied by standard physics ( Kostelecky & Samuel 1989;Kostelecky 2004). It has been considered by Will & Nordvedt (1972) that a vector field can be coupled to the spacetime metric. This creates a ''preferred frame'' in gravitational physics. A global violation is undesirable, but a local violation is allowed. A four timelike vector field with a nonvanishing time component would select a preferred direction at a given spacetime coordinate. It is an aether-like fluid present everywhere, somewhat like a dark energy with some preferred direction. If such a vector coupling to matter is zero or small, then it can evade current experimental detection (e.g., the CPT violation experiments at Princeton). There has been an increase of interest about such vectors in recent years, especially in works by (to name a few) Kostelecky & Samuel (1989) Here we propose a very general Lagrangian of the vector field. We show its relation with existing theories. We isolate a simple case and gi...

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Fine-tuning in DBI inflationary mechanism

Cited by 29 publications

References 39 publications

Planck2013 results. XXIV. Constraints on primordial non-Gaussianity

Planck2013 results. XXIV. Constraints on primordial non-Gaussianity

Planck2015 results

A Nonuniform Dark Energy Fluid: Perturbation Equations

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