String Gas Cosmology and Non-Gaussianities
Recently it has been shown that string gas cosmology, an alternative model of the very early universe which does not involve a period of cosmological inflation, can give rise to an almost scale invariant spectrum of metric perturbations. Here we calculate the non-Gaussianities of the spectrum of cosmological fluctuations in string gas cosmology, and find that these non-Gaussianities depend linearly on the wave number and that their amplitude depends sensitively on the string scale. If the string scale is at the TeV scale, string gas cosmology could lead to observable non-Gaussianities, if it is close to the Planck scale, then the non-Gaussianities on current cosmological scales are negligible.

title: A no-go theorem for generalized vector Galileons on flat spacetime
abstract: A bstractWe explore the possibility for generalized electromagnetism on flat spacetime. For a single copy of U(1) gauge theory, we show that the Galileon-type generalization of electromagnetism is forbidden. Given that the equations of motion for the vector field are gauge invariant and Lorentz invariant, follow from an action and contain no more than second derivative on Aμ, the equations of motion are at most linear with respect to second derivative of Aμ.

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: 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: 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: Linear accelerator for radiation chemistry research at Notre Dame
abstract: An 8 MeV, S-band linear accelerator has been delivered to Notre Dame by Titan Beta Corporation. This accelerator utilizes a variety of techniques to provide uniform dose repeatability, very low dark current, and high beam current over a range of pulse widths from 2 ns to 1.5 s. This paper describes the design and results of tests.

title: A Measurement of the Primordial Power Spectrum from Maxima and Boomerang Data
abstract: Model-independent measurements of the primordial power spectrum of matter density fluctuations provide a unique probe of physics in the very early universe, and can provide powerful constraints on inflationary models. We parametrize the primordial power spectrum A2s(k) as an arbitrary function, and measure its binned amplitude from the cosmic microwave background radiation anisotropy (CMB) data from Maxima and Boomerang. We find that for a flat universe with A2s(k) = 1 (scale-invariant) for scales k < 0.001 h/Mpc, the primordial power spectrum deviates significantly from a scale-invariant HarrisonZeldovich spectrum. It has a drop in power at 0.001 h/Mpc < ∼ k < ∼ 0.01 h/Mpc, and a rise in power at 0.01 h/Mpc < ∼ k < ∼ 0.1 h/Mpc, with the general trend of less power on small scales compared to a scale-invariant power spectrum. Our results are consistent with large scale structure data, and seem to suggest that unusual physics may have occurred in the very early universe. At the dawn of the new millennium, the inflationary paradigm appears the most plausible solution to the problems of the standard cosmology, and consistent with all current observational data. However, we are still far from establishing a definitive model of inflation. There currently exists a broad range of inflationary models (Kolb 1997, Turner 1997), many of which appear consistent with observational data. Model-independent measurements of the primordial power spectrum of matter density fluctuations can provide unique and powerful constraints on inflationary models. Although it has been conventional to take the primordial power spectrum to be a featureless power law in analyzing cosmological data, there are both theoretical and observational reasons to allow the primordial power spectrum to be a free function.

title: Inhomogeneous and Interacting Vacuum Energy
abstract: Vacuum energy is a simple model for dark energy driving an accelerated expansion of the universe. If the vacuum energy is inhomogeneous in spacetime then it must be interacting. We present the general equations for a spacetime-dependent vacuum energy in cosmology, including inhomogeneous perturbations. We show how any dark energy cosmology can be described by an interacting vacuum+matter. Different models for the interaction can lead to different behaviour (e.g., sound speed for dark energy perturbations) and hence could be distinguished by cosmological observations. As an example we present the cosmic microwave microwave background anisotropies and the matter power spectrum for two different versions of a generalised Chaplygin gas cosmology.

title: A side-by-side comparison of Daya Bay antineutrino detectors
abstract: The Daya Bay Reactor Neutrino Experiment is designed to determine precisely the neutrino mixing angle θ_(13) with a sensitivity better than 0.01 in the parameter sin^22θ_(13) at the 90% confidence level. To achieve this goal, the collaboration will build eight functionally identical antineutrino detectors. The first two detectors have been constructed, installed and commissioned in Experimental Hall 1, with steady data-taking beginning September 23, 2011. A comparison of the data collected over the subsequent three months indicates that the detectors are functionally identical, and that detector-related systematic uncertainties are smaller than requirements.

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.