arXiv subjects

D. J. Brooker

Publications and source records attributed to D. J. Brooker.

8 recordsLinked to original sources

arXiv2019

Non-Gaussianity from Features

The strongest non-Gaussianity in single-scalar potential models of inflation is associated with features in the power spectrum. We stress the importance of accurately modelling the expected signal in order for the standard estimator to minimize contamination by random noise. We present explicit formulae which improve on the approximation introduced by Adshead, Hu, Dvorkin and Peiris. We also compare with a simple, analytic model of the first feature, and quantify our results using the correlators of Hung, Fergusson and Shellard.

gr-qc↗

arXiv2017

From Non-trivial Geometries to Power Spectra and Vice Versa

We review a recent formalism which derives the functional forms of the primordial -- tensor and scalar -- power spectra of scalar potential inflationary models. The formalism incorporates the case of geometries with non-constant first slow-roll parameter. Analytic expressions for the power spectra are given that explicitly display the dependence on the geometric properties of the background. Moreover, we present the full algorithm for using our formalism, to reconstruct the model from the observed power spectra. Our techniques are applied to models possessing "features" in their potential with excellent agreement.

gr-qc↗

arXiv2017

Improving the Single Scalar Consistency Relation

We propose a test of single-scalar inflation based on using the well-measured scalar power spectrum to reconstruct the tensor power spectrum, up to a single integration constant. Our test is a sort of integrated version of the single-scalar consistency relation. This sort of test can be used effectively, even when the tensor power spectrum is measured too poorly to resolve the tensor spectral index. We give an example using simulated data based on a hypothetical detection with tensor-to-scalar ratio $r = 0.01$. Our test can also be employed for correlating scalar and tensor features in the far future when the data is good.

astro-ph.CO↗

arXiv2017

Precision Predictions for the Primordial Power Spectra of Scalar Potential Models of Inflation

We exploit a new numerical technique for evaluating the tree order contributions to the primordial scalar and tensor power spectra for scalar potential models of inflation. Among other things we use the formalism to develop a good analytic approximation which goes beyond generalized slow roll expansions in that (1) it is not contaminated by the physically irrelevant phase, (2) its 0th order term is exact for constant first slow roll parameter, and (3) the correction is multiplicative rather than additive. These features allow our formalism to capture at first order, effects which are higher order in other expansions. Although this accuracy is not necessary to compare current data with any specific model, our method has a number of applications owing to the simpler representation it provides for the connection between the power spectra and the expansion history of a general model.

astro-ph.CO↗

arXiv2017

Final Thoughts on the Power Spectra of Scalar Potential Models

We give final shape to a recent formalism for deriving the functional forms of the primordial power spectra of single-scalar potential models and theories which are related to them by conformal transformation. An excellent analytic approximation is derived for the nonlocal correction factors which are crucial to capture the "ringing" that can result from features in the potential. We also present the full algorithm for using our representation, including the nonlocal factors, to reconstruct the inflationary geometry from the power spectra.

gr-qc↗

arXiv2016

The Effect of Features on the Functional Form of the Scalar Power Spectrum

We study how the scalar power spectrum of single-scalar inflation depends functionally on models with features which have been proposed to explain anomalies in the data. We exploit a new formalism based on evolving the norm-squared of the scalar mode functions, rather than the mode functions themselves.

gr-qc↗

arXiv2016

Precision Predictions for the Primordial Power Spectra from f(R) Models of Inflation

We study the power spectra of f(R) inflation using a new technique in which the norm-squared of the mode functions is evolved. Our technique results in excellent analytic approximations for how the spectra depend upon the function $f(R)$. Although the spectra are numerically the same in the Jordan and Einstein frames for the same wave number $k$, they depend upon the geometries of these frames in quite different ways. For example, the power spectra in the two frames are different functions of the number of e-foldings until end of inflation. We discuss how future data on reheating can be used to distinguish f(R) inflation from scalar-driven inflation.

gr-qc↗

arXiv2016

Role of electron-electron interactions in the charge dynamics of rare-earth-doped CaFe2As2

We have investigated the charge dynamics and the nature of many-body interactions in La- and Pr- doped CaFe2As2. From the infrared part of the optical conductivity, we discover that the scattering rate of mobile carriers above 200 K exhibits saturation at the Mott-Ioffe-Regel limit of metallic transport. However, the dc resistivity continues to increase with temperature above 200 K due to the loss of Drude spectral weight. The loss of Drude spectral weight with increasing temperature is seen in a wide temperature range in the uncollapsed tetragonal phase, and this spectral weight is recovered at energy scales about one order of magnitude larger than the Fermi energy scale in these semimetals. The phenomena noted above have been observed previously in other correlated metals in which the dominant interactions are electronic in origin. Further evidence of significant electron-electron interactions is obtained from the presence of quadratic temperature and frequency-dependent terms in the scattering rate at low temperatures and frequencies in the uncollapsed tetragonal structures of La-doped and Pr-doped CaFe2As2. For temperatures below the structure collapse transition in Pr-doped CaFe2As2 at 70 K, the scattering rate decreases due to weakening of electronic correlations, and the Drude spectral weight decreases due to modification of the low-energy electronic structure.

cond-mat.supr-con↗