New Shapes of Primordial Non-Gaussianity from Quasi-Single Field Inflation with Multiple Isocurvatons

We study a simple extension of quasi-single field inflation in which the inflaton interacts with multiple extra massive scalars known as isocurvatons. Due to the breaking of time translational invariance by the inflaton background, the theory includes kinetic mixings among the inflaton and isocurvatons. These mixings give rise to novel new features in the primordial non-Gaussianities of the scalar curvature perturbation. A noteworthy feature is the amplitude of the squeezed bispectrum can grow nearly as $(k_s/k_l)^{-3}$ while oscillating as ${\rm \cos\gamma \log}(k_s/k_l)$, where $k_s/k_l$ is the ratio of the lengths of the short and long wavevectors. Observation of such a shape would provide evidence for the existence of multiple isocurvatons during inflation. In addition, we consider the effects of these non-Gaussianities on large-scale structure.Comment: 18 pages, 6 figure

Loop-Induced Stochastic Bias at Small Wavevectors

Primordial non-Gaussianities enhanced at small wavevectors can induce a power spectrum of the galaxy overdensity that differs greatly from that of the matter overdensity at large length scales. In previous work, it was shown that "squeezed" three-point and "collapsed" four-point functions of the curvature perturbation $\zeta$ can generate these non-Gaussianities and give rise to so-called scale-dependent and stochastic bias in the galaxy overdensity power spectrum. We explore a third way to generate non-Gaussianities enhanced at small wavevectors: the infrared behavior of quantum loop contributions to the four-point correlations of $\zeta$. We show that these loop effects lead to stochastic bias, which can be observable in the context of quasi-single field inflation.Comment: 10 pages, 4 figure

Aspects of Quasi-Single Field Inflation

A simple extension of single-field slow roll inflation is called quasi-single field inflation (QSFI). In quasi-single field inflation, the inflaton is coupled to one or more scalar fields with masses of order Hubble constant during inflation, H, called isocurvatons. Depending on the interactions between the inflaton and the isocurvatons, the observable consequences of such a theory can vary dramatically. This thesis is primarily concerned with analyzing how these interactions affect cosmological observables. We begin by discussing QSFI with one isocurvaton. In particular, we study the non-perturbative limit of a kinetic interaction coupling the inflaton to the isocurvaton. In this non-perturbative limit, the kinetic interaction results in isocurvaton mode functions that oscillate yet decay quickly after horizon crossing. This oscillatory, decaying behavior is reflected in the primordial non-Gaussianity and other observables. Then, we study the perturbative limit of the aforementioned kinetic interaction. Instead of quickly decaying, oscillating mode functions as in the non-perturbative limit, the mode functions in the perturbative limit decay slowly and do not oscillate. Due to this slow decay, the primordial bispectrum is enhanced in the squeezed limit. This enhanced squeezed limit can result in large contributions to galactic halo correlations at long wavelengths. We explore these long wavelength enhancements to galactic halo correlations in detail. We then discuss how quantum loops of isocurvatons in QSFI can significantly contribute to galactic halo correlations at long wavelengths. In fact, we show that loops can give the most important contributions at long wavelengths in certain models. Finally, we consider theories with multiple isocurvatons. Such theories may consist of interactions coupling the isocurvatons to eachother. These interactions can result in slowly decaying yet oscillating late-time behavior for the isocurvaton mode functions. This combines the two characteristic features from the non-perturbative (oscillating) and perturbative (slowly-decaying) single isocurvaton QSFI models discussed above. These features could result in an oscillatory bispectrum that is enhanced in the squeezed limit. Oscillations in the galactic halo power spectrum at long wavelengths may then be indicative of such multi-isocurvaton models.</p

Quasi-single field inflation in the non-perturbative regime

In quasi-single field inflation there are massive fields that interact with the inflaton field. If these other fields are not much heavier than the Hubble constant during inflation (H) these interactions can lead to important consequences for the cosmological energy density perturbations. The simplest model of this type has a real scalar inflaton field that interacts with another real scalar S (with mass m). In this model there is a mixing term of the form μπS, where π is the Goldstone fluctuation that is associated with the breaking of time translation invariance by the time evolution of the inflaton field during the inflationary era. In this paper we study this model in the region (μ/H)^2 + (m/H)^2 > 9/4 and m/H∼O(1) or less. For a large part of the parameter space in this region standard perturbative methods are not applicable. Using numerical and analytic methods we study how large μ/H has to be for the large μ/H effective field theory approach to be applicable

New shapes of primordial non-Gaussianity from quasi-single field inflation with multiple isocurvatons

We study a simple extension of quasi-single field inflation in which the inflaton interacts with multiple extra massive scalars known as isocurvatons. Due to the breaking of time translational invariance by the inflaton background, the theory includes kinetic mixings among the inflaton and isocurvatons. These mixings give rise to novel new features in the primordial non-Gaussianities of the scalar curvature perturbation. A noteworthy feature is that the amplitude of the squeezed bispectrum can grow nearly as (k_s/k_l)^(−3) while oscillating as cosγlog(k_s/k_l), where k_s/k_l is the ratio of the lengths of the short and long wave vectors. Observation of such a shape would provide evidence for the existence of multiple isocurvatons during inflation. In addition, we consider the effects of these non-Gaussianities on large-scale structure

Non-Gaussian Enhancements of Galactic Halo Correlations in Quasi-Single Field Inflation

We consider a quasi-single field inflation model in which the inflaton interacts with a massive scalar field called the isocurvaton. Due to the breaking of time translational invariance by the inflaton background, these interactions induce kinetic mixing between the inflaton and isocurvaton, which is parameterized by a constant μ . We derive analytic formulas for the curvature perturbation two-, three-, four-, five-, and six-point functions explicitly in terms of the external wave vectors in the limit where μ and the mass of the isocurvaton m are both much smaller than H . In previous work, it has been noted that when m / H and μ / H are small, the non-Gaussianities predicted by quasi-single field inflation give rise to long wavelength enhancements of the power spectrum for biased objects (e.g., galactic halos). We review this calculation, and calculate the analogous enhanced contribution to the bispectrum of biased objects. We determine the scale at which these enhanced terms are larger than the Gaussian piece. We also identify the scaling of these enhanced parts to the n-point function of biased objects

Stochastic Bias from Loops of Massive Particles During Inflation

Primordial non-Gaussianities enhanced at small wavevectors can induce a power spectrum of the galaxy overdensity that differs greatly from that of the matter overdensity at large length scales. In previous work, it was shown that “squeezed" three-point and “collapsed" four-point functions of the curvature perturbation ζ can generate these non-Gaussianities and give rise to so-called scale-dependent and stochastic bias in the galaxy overdensity power spectrum. We explore a third way to generate non-Gaussianities enhanced at small wavevectors: the infrared behavior of quantum loop contributions to the four-point correlations of ζ. We show that these loop effects can give the largest contributions to the four-point function of ζ in the collapsed limit and be observable in the context of quasi-single field inflation