Tensors, non-Gaussianities, and the future of potential reconstruction

We present projections for reconstruction of the inflationary potential expected from ESA's upcoming Planck Surveyor CMB mission. We focus on the effects that tensor perturbations and the presence of non-Gaussianities have on reconstruction efforts in the context of non-canonical inflation models. We consider potential constraints for different combinations of detection/null-detection of tensors and non-Gaussianities. We perform Markov Chain Monte Carlo and flow analyses on a simulated Planck-precision data set to obtain constraints. We find that a failure to detect non-Gaussianities precludes a successful inversion of the primordial power spectrum, greatly affecting uncertainties, even in the presence of a tensor detection. In the absence of a tensor detection, while unable to determine the energy scale of inflation, an observable level of non-Gaussianities provides correlations between the errors of the potential parameters, suggesting that constraints might be improved for suitable combinations of parameters. Constraints are optimized for a positive detection of both tensors and non-Gaussianities.Comment: 12 pages, 5 figures, LaTeX; V2: version submitted to JCA

Constraints on the SZ Power Spectrum on Degree Angular Scales in WMAP Data

The Sunyaev-Zel'dovich (SZ) effect has a distinct spectral signature that allows its separation from fluctuations in the cosmic microwave background (CMB) and foregrounds. Using CMB anisotropies measured in Wilkinson Microwave Anisotropy Probe's five-year maps, we constrain the SZ fluctuations at large, degree angular scales corresponding to multipoles in the range from 10 to 400. We provide upper bounds on SZ fluctuations at multipoles greater than 50, and find evidence for a hemispherically asymmetric signal at ten degrees angular scales. The amplitude of the detected signal cannot be easily explained with the allowed number density and temperature of electrons in the Galactic halo. We have failed to explain the excess signal as a residual from known Galactic foregrounds or instrumental uncertainties such as 1/f-noise.Comment: 14 pages, 3 figures, 2 tables. Simple typos fixe

Non-Gaussianity from violation of slow-roll in multiple inflation

Multiple inflation is a model based on N=1 supergravity wherein there are sudden changes in the mass of the inflaton because it couples to 'flat direction' scalar fields which undergo symmetry breaking phase transitions as the universe cools. The resulting brief violations of slow-roll evolution generate a non-gaussian signal which we find to be oscillatory and yielding f_NL ~ 5-20. This is potentially detectable by e.g. Planck but would require new bispectrum estimators to do so. We also derive a model-independent result relating the period of oscillations of a phase transition during inflation to the period of oscillations in the primordial curvature perturbation generated by the inflaton.Comment: 21 pages, 6 figures; Clarifying comments and references added; Accepted for publication in JCA

Isocurvature modes and Baryon Acoustic Oscillations

The measurement of Baryonic Acoustic Oscillations from galaxy surveys is well known to be a robust and powerful tool to constrain dark energy. This method relies on the knowledge of the size of the acoustic horizon at radiation drag derived from Cosmic Microwave Background Anisotropy measurements. In this paper we quantify the effect of non-standard initial conditions in the form of an isocurvature component on the determination of dark energy parameters from future BAO surveys. In particular, if there is an isocurvature component (at a level still allowed by present data) but it is ignored in the CMB analysis, the sound horizon and cosmological parameters determination is biased, and, as a consequence, future surveys may incorrectly suggest deviations from a cosmological constant. In order to recover an unbiased determination of the sound horizon and dark energy parameters, a component of isocurvature perturbations must be included in the model when analyzing CMB data. Fortunately, doing so does not increase parameter errors significantly.Comment: 23 pages, 3 figure

The CMB Bispectrum

We use a separable mode expansion estimator with WMAP data to estimate the bispectrum for all the primary families of non-Gaussian models. We review the late-time mode expansion estimator methodology which can be applied to any non-separable primordial and CMB bispectrum model, and we demonstrate how the method can be used to reconstruct the CMB bispectrum from an observational map. We extend the previous validation of the general estimator using local map simulations. We apply the estimator to the coadded WMAP 5-year data, reconstructing the WMAP bispectrum using $l<500$ multipoles and $n=31$ orthonormal 3D eigenmodes. We constrain all popular nearly scale-invariant models, ensuring that the theoretical bispectrum is well-described by a convergent mode expansion. Constraints from the local model \fnl=54.4\pm 29.4 and the equilateral model \fnl=143.5\pm 151.2 (\Fnl = 25.1\pm 26.4) are consistent with previously published results. (Here, we use a nonlinearity parameter \Fnl normalised to the local case, to allow more direct comparison between different models.) Notable new constraints from our method include those for the constant model \Fnl = 35.1 \pm 27.4 , the flattened model \Fnl = 35.4\pm 29.2, and warm inflation \Fnl = 10.3\pm 27.2. We investigate feature models surveying a wide parameter range in both the scale and phase, and we find no significant evidence of non-Gaussianity in the models surveyed. We propose a measure \barFnl for the total integrated bispectrum and find that the measured value is consistent with the null hypothesis that CMB anisotropies obey Gaussian statistics. We argue that this general bispectrum survey with the WMAP data represents the best evidence for Gaussianity to date and we discuss future prospects, notably from the Planck satellite

Optimal limits on f_{NL}^{local} from WMAP 5-year data

We have applied the optimal estimator for f_{NL}^{local} to the 5 year WMAP data. Marginalizing over the amplitude of foreground templates we get -4 < f_{NL}^{local} < 80 at 95% CL. Error bars of previous (sub-optimal) analyses are roughly 40% larger than these. The probability that a Gaussian simulation, analyzed using our estimator, gives a result larger in magnitude than the one we find is 7%. Our pipeline gives consistent results when applied to the three and five year WMAP data releases and agrees well with the results from our own sub-optimal pipeline. We find no evidence of any residual foreground contamination.Comment: [v1] 21 pages, 7 figures. [v2] minor changes matching published versio

Probing the course of cosmic expansion with a combination of observational data

We study the cosmic expansion history by reconstructing the deceleration parameter $q(z)$ from the SDSS-II type Ia supernova sample (SNIa) with two different light curve fits (MLCS2k2 and SALT-II), the baryon acoustic oscillation (BAO) distance ratio, the cosmic microwave background (CMB) shift parameter, and the lookback time-redshift (LT) from the age of old passive galaxies. Three parametrization forms for the equation of state of dark energy (CPL, JBP, and UIS) are considered. Our results show that, for the CPL and the UIS forms, MLCS2k2 SDSS-II SNIa+BAO+CMB and MLCS2k2 SDSS-II SNIa+BAO+CMB+LT favor a currently slowing-down cosmic acceleration, but this does not occur for all other cases, where an increasing cosmic acceleration is still favored. Thus, the reconstructed evolutionary behaviors of dark energy and the course of the cosmic acceleration are highly dependent both on the light curve fitting method for the SNIa and the parametrization form for the equation of state of dark energy.Comment: 19 pages, 6 figures, accepted for publication in JCA

Cosmic Microwave Background Observables of Small Field Models of Inflation

We construct a class of single small field models of inflation that can predict, contrary to popular wisdom, an observable gravitational wave signal in the cosmic microwave background anisotropies. The spectral index, its running, the tensor to scalar ratio and the number of e-folds can cover all the parameter space currently allowed by cosmological observations. A unique feature of models in this class is their ability to predict a negative spectral index running in accordance with recent cosmic microwave background observations. We discuss the new class of models from an effective field theory perspective and show that if the dimensionless trilinear coupling is small, as required for consistency, then the observed spectral index running implies a high scale of inflation and hence an observable gravitational wave signal. All the models share a distinct prediction of higher power at smaller scales, making them easy targets for detection.Comment: 13 pages, 3 figures, added numerical analysis and discussion on the properties of the spectra. Version to be published in JCA

Update of axion CDM energy density

We improve the estimate of the axion CDM energy density by considering the new values of current quark masses, the QCD phase transition effect and a possible anharmonic effect.Comment: 7 pages, 6 figures. References are added. A factor is correcte

Single-field inflation constraints from CMB and SDSS data

We present constraints on canonical single-field inflation derived from WMAP five year, ACBAR, QUAD, BICEP data combined with the halo power spectrum from SDSS LRG7. Models with a non-scale-invariant spectrum and a red tilt n_s < 1 are now preferred over the Harrison-Zel'dovich model (n_s = 1, tensor-to-scalar ratio r = 0) at high significance. Assuming no running of the spectral indices, we derive constraints on the parameters (n_s, r) and compare our results with the predictions of simple inflationary models. The marginalised credible intervals read n_s = 0.962^{+0.028}_{-0.026} and r < 0.17 (at 95% confidence level). Interestingly, the 68% c.l. contours favour mainly models with a convex potential in the observable region, but the quadratic potential model remains inside the 95% c.l. contours. We demonstrate that these results are robust to changes in the datasets considered and in the theoretical assumptions made. We then consider a non-vanishing running of the spectral indices by employing different methods, non-parametric but approximate, or parametric but exact. With our combination of CMB and LSS data, running models are preferred over power-law models only by a Delta chi^2 ~ 5.8, allowing inflationary stages producing a sizable negative running -0.063^{+0.061}_{-0.049} and larger tensor-scalar ratio r < 0.33 at the 95% c.l. This requires large values of the third derivative of the inflaton potential within the observable range. We derive bounds on this derivative under the assumption that the inflaton potential can be approximated as a third order polynomial within the observable range.Comment: 32 pages, 7 figures. v2: additional references, some typos corrected, passed to JCAP style. v3: minor changes, matches published versio