Constraints on Single-Field Inflation from the BOSS Galaxy Survey.

Nonlocal primordial non-Gaussianity (NLPNG) is a smoking gun of interactions in single-field inflationary models and can be written as a combination of the equilateral and orthogonal templates. We present the first constraints on these from the redshift-space galaxy power spectra and bispectra of the BOSS data. These are the first such measurements independent of the cosmic microwave background fluctuations. We perform a consistent analysis that includes all necessary nonlinear corrections generated by NLPNG and vary all relevant cosmological and nuisance parameters in a global fit to the data. Our conservative analysis yields joint limits on the amplitudes of the equilateral and orthogonal shapes, f_{NL}^{equil}=940±600 and f_{NL}^{ortho}=-170±170 (both at 68% CL). These can be used to derive constraints on coefficients of the effective single-field inflationary Lagrangian; in particular, we find that the sound speed of inflaton fluctuations has the bound c_{s}≥0.013 at 95% CL. Fixing the quadratic galaxy bias and cosmological parameters, the constraints can be tightened to f_{NL}^{equil}=260±300 and f_{NL}^{ortho}=-23±120 (68% CL).

ϕ(2) or not ϕ(2): testing the simplest inflationary potential.

The simplest inflationary model V=1/2m(2)ϕ(2) represents the benchmark for future constraints. For a quadratic potential, the quantity (n(s)-1)+r/4+11(n(s)-1)(2)/24 vanishes (up to corrections which are cubic in slow roll) and can be used to parametrize small deviations from the minimal scenario. Future constraints on this quantity will be able to distinguish a quadratic potential from a pseudo-Nambu-Goldstone boson with f≲30M(pl) and set limits on the deviation from unity of the speed of sound |c(s)-1|≲3×10(-2) (corresponding to an energy scale Λ≳2×10(16) GeV) and on the contribution of a second field to perturbations (≲6×10(-2)). The limiting factor for these bounds will be the uncertainty on the spectral index. The error on the number of e-folds will be ΔN≃0.4, corresponding to an error on the reheating temperature ΔT(rh)/T(rh)≃1.2. We comment on the relevance of non-Gaussianity after BICEP2 results.

New window on primordial non-gaussianity.

We know very little about primordial curvature perturbations on scales smaller than about a Mpc. Measurements of the µ distortion of the cosmic microwave background spectrum provide the unique opportunity to probe these scales over the unexplored range from 50 to 10(4) Mpc(-1). This is a very clean probe, in that it relies only on well understood linear evolution. Also, just the information about the low multipoles (l∼100) of µ is necessary. We point out that correlations between µ distortion and temperature anisotropies can be used to test gaussianity at these very small scales. In particular the µT two-point correlation is proportional to the very squeezed limit of the primordial bispectrum and hence measures f(NL)(loc), while µµ is proportional to the primordial trispectrum and measures τ(NL). We present a Fisher matrix forecast of the observational constraints on f(NL)(loc) and stress that a cosmic variance limited experiment could in principle reach Δf(NL)(loc)∼O(10(-3)).

Universal bound on N-point correlations from inflation.

Models of inflation in which non-Gaussianity is generated outside the horizon, such as curvaton models, generate distinctive higher-order correlation functions in the cosmic microwave background and other cosmological observables. Testing for violation of the Suyama-Yamaguchi inequality τ(NL) ≥ (6/5f (NL))(2), where f(NL) and f(NL) denote the amplitude of the three-point and four-point functions in certain limits, has been proposed as a way to distinguish qualitative classes of models. This inequality has been proved for a wide range of models, but only weaker versions have been proved in general. In this Letter, we give a proof that the Suyama-Yamaguchi inequality is always satisfied. We discuss scenarios in which the inequality may appear to be violated in an experiment such as Planck and how this apparent violation should be interpreted.

Measuring the small-scale power spectrum of cosmic density fluctuations through 21 cm tomography prior to the epoch of structure formation.

The thermal evolution of the cosmic gas decoupled from that of the cosmic microwave background (CMB) at a redshift z approximately 200. Afterwards and before the first stars had formed, the cosmic neutral hydrogen absorbed the CMB flux at its resonant 21 cm spin-flip transition. We calculate the evolution of the spin temperature for this transition and the resulting anisotropies that are imprinted on the CMB sky due to linear density fluctuations during this epoch. These anisotropies, at an observed wavelength of 10.56[(1+z)/50] m, contain an amount of information that is orders of magnitude larger than any other cosmological probe.

Changing alpha with time: implications for fifth-force-type experiments and quintessence.

If the recent observations suggesting a time variation of the fine structure constant are correct, they imply the existence of an ultralight scalar particle. This particle inevitably couples to nucleons through the alpha dependence of their masses and thus mediates an isotope-dependent long-range force. The strength of the coupling is within a couple of orders of magnitude of the existing experimental bounds for such forces. The new force can be potentially measured in precision experimental tests of the equivalence principle. Because of a coincidence of the required time scales, the scalar field can at the same time play the role of a quintessence field.