Fluctuations in a Hořava-Lifshitz Bouncing Cosmology

title: Curvaton dynamics and the non-linearity parameters in the curvaton model
abstract: We investigate the curvaton dynamics and the non-linearity parameters in the curvaton model with a potential slightly deviating from the quadratic form in detail. The non-linearity parameter gNL will show up due to the curvaton self-interaction. We also point out that the leading order of the non-quadratic term in the curvaton potential can be negative, for example in the axion-type curvaton model. If a large positive gNL is detected, the axion-type curvaton model will be preferred.

title: Quasi-Single Field Inflation and Non-Gaussianities
abstract: In quasi-single field inflation models, massive isocurvature modes, that are coupled to the inflaton and have mass of order the Hubble parameter, can have nontrivial impacts on density perturbations, especially non-Gaussianities. We study a simple example of quasi-single field inflation in terms of turning inflaton trajectory. Large bispectra with a one-parameter family of novel shapes arise, lying between the well-known local and equilateral shape. The trispectra can also be very large and its magnitude tNL can be much larger than fNL2.

title: Quadra-Spectrum and Quint-Spectrum from Inflation and Curvaton Models
abstract: We calculate the quadra-spectrum and quint-spectrum, corresponding to five and six point correlation functions of the curvature perturbation. For single field inflation with standard kinetic term, the quadra-spectrum and quint-spectrum are small, which are suppressed by slow roll parameters. The calculation can be generalized to multiple fields. When there is no entropy perturbation, the quadra-spectrum and quint-spectrum are suppressed as well. With the presence of entropy perturbation, the quadra-spectrum and quint-spectrum can get boosted. We illustrate this boost in the multi-brid inflation model. For the curvaton scenario, the quadra-spectrum and quint-spectrum are also large in the small r limit. We also calculate representative terms of quadra-spectrum and quint-spectrum for inflation with generalized kinetic terms, and estimate their order of magnitude for quasi-single field inflation.

title: CMB statistical anisotropies of classical and quantum origins
abstract: We examine the impact of different anisotropic relics on inflation, in particular the predictions on the density perturbations. These relics can be the source of the large scale anomalies in the cosmic microwave background. There are two different types of background relics, one from the matter sector and the other purely from the metric. Although the angular-dependence of the statistical anisotropy in both cases are degenerate, the scale-dependence are observationally distinctive. In addition, we demonstrate that non-Bunch-Davies vacuum states can extend the statistical anisotropy to much shorter scales, and leave a scale-dependence that is insensitive to the different backgrounds but sensitive to the initial quantum state.

title: Non-Gaussianity, isocurvature perturbation, gravitational waves, and a no-go theorem for the isocurvaton
abstract: We investigate the isocurvaton model, in which the isocurvature perturbation plays a role in suppressing the curvature perturbation, and large non-Gaussianity and gravitational waves can be produced with no isocurvature perturbation for dark matter. We show that in the slow-roll noninteracting multifield theory, the isocurvaton mechanism cannot be realized. This result can also be generalized to most of the studied models with generalized kinetic terms. We also study the implications for the curvaton model. We show that there is a combined constraint for curvaton on non-Gaussianity, gravitational waves, and isocurvature perturbation. The technique used in this paper can also help to simplify some calculations in the mixed inflaton and curvaton models. We also investigate the possibility of producing large negative non-Gaussianity and nonlocal non-Gaussianity in the curvaton model.

title: BBN and CMB constraints on universal lepton asymmetry, quintessential inflation, and brane world cosmology
abstract: Recent progress in cosmological deep survey has clarified progressively the origin and distribution of matter and evolution of Galaxies in the Universe. The origin of the light elements in the Big-Bang nucleosynthesis (BBN) has been a topic of broad interest for its significance in constraining the dark matter component in the Universe, and also in seeking for the cosmological model which best fits the recent data of cosmic microwave background (CMB) fluctuations.

title: Constraints on neutrino degeneracy from the cosmic microwave background and primordial nucleosynthesis
abstract: We reanalyze the cosmological constraints on the existence of a net universal lepton asymmetry and neutrino degeneracy based upon the latest high resolution CMB sky maps from BOOMERANG, DASI, and MAXIMA-1. We generate likelihood functions by marginalizing over $(\omegab h^2,\xinumt, \xinue, \Omega_\Lambda,h,n)$ plus the calibaration uncertainties. We consider flat $\Omega_M + \Omega_\Lambda = 1$ cosmological models with two identical degenerate neutrino species, $\xinumt \equiv \vert \xinum \vert = \vert \xinut \vert$ and a small $\xinue$. We assign weak top-hat priors on the electron-neutrino degeneracy parameter $\xinue$ and $\Omega_b h^2$ based upon allowed values consistent with the nucleosynthesis constraints as a function of $\xinumt$. The change in the background neutrino temperature with degeneracy is also explicitly included, and Gaussian priors for $h = 0.72 \pm 0.08$ and the experimental calibration uncertainties are adopted. The marginalized likelihood functions show a slight (0.5$\sigma$) preference for neutrino degeneracy. Optimum values with two equally degenerate $\mu$ and $\tau$ neutrinos imply $\xinumt = 1.0^{+0.8 (1\sigma)}_{-1.0 (0.5\sigma)}$, from which we deduce $\xi_{\nu_e} = 0.09^{+0.15}_{-0.09}$, and $\Omega_b h^2 = 0.021^{+0.06}_{- 0.002}$. The $2\sigma$ upper limit becomes $ \xinumt \le 2.1$, which implies $\xi_{\nu_e} \le 0.30$, and $\Omega_b h^2 \le 0.030$. For only a single large-degeneracy species the optimal value is $\vert \xinum \vert$ or $\vert \xinut \vert = 1.4$ with a $2\sigma$ upper limit of $\vert \xinum \vert$ or $\vert \xinut \vert \le 2.5$

title: Observational approaches to understanding dark energy
abstract: Illuminating the nature of dark energy is one of the most important challenges in cosmology today. In this review I discuss several promising observational approaches to understanding dark energy, in the context of the recommendations by the U.S. Dark Energy Task Force and the ESA-ESO Working Group on Fundamental Cosmology.

title: Is the energy generation rate of nuclear reactions in hot accretion flows important
abstract: The temperature of hot accretion flows around black holes is sufficiently high for the ignition of nuclear reactions. This is potentially an important nucleosynthesis mechanism in the universe. As the first step in studying this problem, we need to measure physical quantities such as density and temperature of the accretion flow. In usual studies of the hot accretion flow, viscous dissipation is considered to be the only heating mechanism, while the heating caused by nuclear reactions is not considered. In this paper, we investigate whether the energy generation rate of nuclear reaction is important compared to the viscous heating. Our calculation indicates that the former is at most one percent of the latter and thus is not important. The dynamics of accretion flow can be therefore calculated in the usual way, without the need to consider heating due to nuclear reactions.

title: Study of alternative ILC final focus optical configurations
abstract: The current design of ILC final focus achieves perfect first order chromaticity correction in both horizontal and vertical planes. Based on RDR FFS optics a set of alternative optical configurations were studied in which the horizontal beam size at the lP is increased while at the same time the vertical one is decreased, with the goal of reducing beamsstrahlung emission. Luminosity reduction due to the hour glass effect most be considered because beta(y)*/sigma(z)* becomes much smaller in this case. The beam-beam interaction simulation by Guineapig+ + was used for evaluation. Reduced bunch lengths are used to make sure that the obtained luminosities are not lower than those of the ILC RDR configuration.