Scale dependence of fNLf_{NL} in N-flation

Adopting the horizon-crossing approximation, we derive the spectral index of $f_{NL}$ in general N-flation model. Axion N-flation model is taken as a typical model for generating a large $f_{NL}$ which characterizes the size of local form bispectrum. We find that its tilt $n_{f_{NL}}$ is negligibly small when all inflatons have the same potential, but a negative detectable $n_{f_{NL}}$ can be achieved in the axion N-flation with different decay constants for different inflatons. The measurement of $n_{f_{NL}}$ can be used to support or falsify the axion N-flation in the near future.Comment: 15 pages, 2 figures; a subsection with detectable scale dependence of f_NL added; more discussions added and version accepted for publication in JCA

Scale-dependent non-Gaussianity probes inflationary physics

We calculate the scale dependence of the bispectrum and trispectrum in (quasi) local models of non-Gaussian primordial density perturbations, and characterize this scale dependence in terms of new observable parameters. They can help to discriminate between models of inflation, since they are sensitive to properties of the inflationary physics that are not probed by the standard observables. We find consistency relations between these parameters in certain classes of models. We apply our results to a scenario of modulated reheating, showing that the scale dependence of non-Gaussianity can be significant. We also discuss the scale dependence of the bispectrum and trispectrum, in cases where one varies the shape as well as the overall scale of the figure under consideration. We conclude providing a formulation of the curvature perturbation in real space, which generalises the standard local form by dropping the assumption that f_NL and g_NL are constants.Comment: 27 pages, 2 figures. v2: Minor changes to match the published versio

Local non-Gaussianity from inflation

The non-Gaussian distribution of primordial perturbations has the potential to reveal the physical processes at work in the very early Universe. Local models provide a well-defined class of non-Gaussian distributions that arise naturally from the non-linear evolution of density perturbations on super-Hubble scales starting from Gaussian field fluctuations during inflation. I describe the delta-N formalism used to calculate the primordial density perturbation on large scales and then review several models for the origin of local primordial non-Gaussianity, including the cuvaton, modulated reheating and ekpyrotic scenarios. I include an appendix with a table of sign conventions used in specific papers.Comment: 21 pages, 1 figure, invited review to appear in Classical and Quantum Gravity special issue on non-linear and non-Gaussian cosmological perturbation

Local non-Gaussianity from rapidly varying sound speeds

We study the effect of non-trivial sound speeds on local-type non-Gaussianity during multiple-field inflation. To this end, we consider a model of multiple-field DBI and use the deltaN formalism to track the super-horizon evolution of perturbations. By adopting a sum separable Hubble parameter we derive analytic expressions for the relevant quantities in the two-field case, valid beyond slow variation. We find that non-trivial sound speeds can, in principle, curve the trajectory in such a way that significant local-type non-Gaussianity is produced. Deviations from slow variation, such as rapidly varying sound speeds, enhance this effect. To illustrate our results we consider two-field inflation in the tip regions of two warped throats and find large local-type non-Gaussianity produced towards the end of the inflationary process.Comment: 30 pages, 7 figures; typos corrected, references added, accepted for publication in JCA

Brief report: Using global positioning system (GPS) enabled cell phones to examine adolescent travel patterns and time in proximity to alcohol outlets

As adolescents gain freedom to explore new environments unsupervised, more time in proximity to alcohol outlets may increase risks for alcohol and marijuana use. This pilot study: 1) Describes variations in adolescents' proximity to outlets by time of day and day of the week, 2) Examines variations in outlet proximity by drinking and marijuana use status, and 3) Tests feasibility of obtaining real-time data to study adolescent proximity to outlets. U.S. adolescents (N = 18) aged 16–17 (50% female) carried GPS-enabled smartphones for one week with their locations tracked. The geographic areas where adolescents spend time, activity spaces, were created by connecting GPS points sequentially and adding spatial buffers around routes. Proximity to outlets was greater during after school and evening hours. Drinkers and marijuana users were in proximity to outlets 1½ to 2 times more than non-users. Findings provide information about where adolescents spend time and times of greatest risk, informing prevention efforts

A Meta-Analysis Of Resource Pulse-Consumer Interactions

Resource Pulses are infrequent, large-magnitude, and short-duration events of increased resource availability. They include a diverse set of extreme events in a wide range of ecosystems, but identifying general patterns among the diversity of pulsed resource phenomena in nature remains an important challenge. Here we present a meta-analysis of resource pulse-consumer interactions that addresses four key questions: (1) Which characteristics of pulsed resources best predict their effects on consumers? (2) Which characteristics of consumers best predict their responses to resource pulses? (3) How do the effects of resource Pulses differ in different ecosystems? (4) What are the indirect effects of resource pulses in communities\u27? To investigate these questions, we built a data set of diverse Pulsed resource-consumer interactions from around the world, developed metrics to compare the effects of resource pulses across disparate systems, and conducted multilevel regression analyses to examine the manner in which variation in the characteristics of resource pulse-consumer interactions affects important aspects Of Consumer responses. Resource pulse magnitude, resource trophic level, resource Pulse duration, ecosystem type and subtype, consumer response mechanisms, and consumer body mass were found to be key. explanatory factors predicting the magnitude, duration, and timing of consumer responses. Larger consumers showed more persistent responses to resource pulses, and reproductive responses were more persistent than aggregative responses. Aquatic systems showed shorter temporal lags between peaks of resource availability and consumer response compared to terrestrial systems, and temporal lags were also shorter for smaller consumers compared to larger consumers. The magnitude of consumer responses relative to their resource pulses was generally smaller for the direct consumers of primary resource pulses, compared to consumers at greater trophic distances from the initial resource pulse. In specific systems, this data set showed both attenuating and amplifying indirect effects. We consider the mechanistic processes behind these patterns and their implications for the ecology of resource pulses

The Berwald-type linearisation of generalised connections

We study the existence of a natural `linearisation' process for generalised connections on an affine bundle. It is shown that this leads to an affine generalised connection over a prolonged bundle, which is the analogue of what is called a connection of Berwald type in the standard theory of connections. Various new insights are being obtained in the fine structure of affine bundles over an anchored vector bundle and affineness of generalised connections on such bundles.Comment: 25 page

Trispectrum from Ghost Inflation

Ghost inflation predicts almost scale-invariant primordial cosmological perturbations with relatively large non-Gaussianity. The bispectrum is known to have a large contribution at the wavenumbers forming an equilateral triangle and the corresponding nonlinear parameter $f_{NL}^{equil}$ is typically of order $O(10^2)$. In this paper we calculate trispectrum from ghost inflation and show that the corresponding nonlinear parameter $\tau_{NL}$ is typically of order $O(10^4)$. We investigate the shape dependence of the trispectrum and see that it has some features different from DBI inflation. Therefore, our result may be useful as a template to distinguish ghost inflation from other models of inflation by future experiments.Comment: 25 pages, 10 figure