Nonminimal Couplings in the Early Universe: Multifield Models of Inflation and the Latest Observations

Models of cosmic inflation suggest that our universe underwent an early phase of accelerated expansion, driven by the dynamics of one or more scalar fields. Inflationary models make specific, quantitative predictions for several observable quantities, including particular patterns of temperature anistropies in the cosmic microwave background radiation. Realistic models of high-energy physics include many scalar fields at high energies. Moreover, we may expect these fields to have nonminimal couplings to the spacetime curvature. Such couplings are quite generic, arising as renormalization counterterms when quantizing scalar fields in curved spacetime. In this chapter I review recent research on a general class of multifield inflationary models with nonminimal couplings. Models in this class exhibit a strong attractor behavior: across a wide range of couplings and initial conditions, the fields evolve along a single-field trajectory for most of inflation. Across large regions of phase space and parameter space, therefore, models in this general class yield robust predictions for observable quantities that fall squarely within the "sweet spot" of recent observations.Comment: 17pp, 2 figs. References added to match the published version. Published in {\it At the Frontier of Spacetime: Scalar-Tensor Theory, Bell's Inequality, Mach's Principle, Exotic Smoothness}, ed. T. Asselmeyer-Maluga (Springer, 2016), pp. 41-57, in honor of Carl Brans's 80th birthda

Production of Sodium Bose--Einstein condensates in an optical dimple trap

We report on the realization of a sodium Bose--Einstein condensate (BEC) in a combined red-detuned optical dipole trap, formed by two beams crossing in a horizontal plane and a third, tightly focused dimple trap propagating vertically. We produce a BEC in three main steps: loading of the crossed dipole trap from laser-cooled atoms, an intermediate evaporative cooling stage which results in efficient loading of the auxiliary dimple trap, and a final evaporative cooling stage in the dimple trap. Our protocol is implemented in a compact setup and allows us to reach quantum degeneracy even with relatively modest initial atom numbers and available laser power

Galaxy Alignments in Very X-ray Luminous Clusters at z>0.5

We present the results of a search for galaxy alignments in 12 galaxy clusters at z>0.5, a statistically complete subset of the very X-ray luminous clusters from the MAssive Cluster Survey (MACS). Using high-quality images taken with the Hubble Space Telescope (HST) that render measurement errors negligible, we find no radial galaxy alignments within 500 kpc of the cluster centres for a sample of 545 spectroscopically confirmed cluster members. A mild, but statistically insignificant trend favouring radial alignments is observed within a radius of 200 kpc and traced to galaxies on the cluster red sequence. Our results for massive clusters at z>0.5 are in stark contrast to the findings of previous studies which find highly significant radial alignments of galaxies in nearby clusters at z~0.1 out to at least half the virial radius using imaging data from the SDSS. The discrepancy becomes even more startling if radial alignment becomes more prevalent at decreasing clustercentric distance, as suggested by both our and previous work. We investigate and discuss potential causes for the disparity between our findings based on HST images of clusters at z>0.5 and those obtained using groundbased images of systems at z~0.1. We conclude that the most likely explanation is either dramatic evolution with redshift (in the sense that radial alignments are less pronounced in dynamically younger systems) or the presence of systematic biases in the analysis of SDSS imaging data that cause at least partly spurious alignment signals.Comment: 10 pages, 11 figures, and 1 table. Accepted for publication in MNRA

Simulations of Wide-Field Weak Lensing Surveys I: Basic Statistics and Non-Gaussian Effects

We study the lensing convergence power spectrum and its covariance for a standard LCDM cosmology. We run 400 cosmological N-body simulations and use the outputs to perform a total of 1000 independent ray-tracing simulations. We compare the simulation results with analytic model predictions. The semi-analytic model based on Smith et al.(2003) fitting formula underestimates the convergence power by ~30% at arc-minute angular scales. For the convergence power spectrum covariance, the halo model reproduces the simulation results remarkably well over a wide range of angular scales and source redshifts. The dominant contribution at small angular scales comes from the sample variance due to the number fluctuations of halos in a finite survey volume. The signal-to-noise ratio for the convergence power spectrum is degraded by the non-Gaussian covariances by up to a factor 5 for a weak lensing survey to z_s ~1. The probability distribution of the convergence power spectrum estimators, among the realizations, is well approximated by a chi-square distribution with broadened variance given by the non-Gaussian covariance, but has a larger positive tail. The skewness and kurtosis have non-negligible values especially for a shallow survey. We argue that a prior knowledge on the full distribution may be needed to obtain an unbiased estimate on the ensemble averaged band power at each angular scale from a finite volume survey.Comment: 11 pages, 11 figures. Accepted for publication in the Astrophysical Journal. Corrected typo in the equation of survey window function below Equation (18). The results unchange

Embedding Heterostructured α‐MnS/MnO Nanoparticles in S‐Doped Carbonaceous Porous Framework as High‐Performance Anode for Lithium‐Ion Batteries

In this work, the synthesis of α-MnS/MnO/S-doped C micro-rod composites via a simple sulfidation process is demonstrated, starting from a Mn-based metal-organic framework. The resulting heterostructured α-MnS/MnO nanoparticles (8±2 nm) are uniformly embedded into the S-doped carbonaceous porous framework with hierarchical micro-/meso-porosity. The combination of structural and compositional characteristics results in the promising electrochemical performance of the as-obtained composites as anode materials for lithium-ion batteries, coupled with high reversible capacity (940 mAh $g^{−1}$ at 0.1 A $g^{−1}$), excellent rate capability as well as long cycling lifespan at high rate of 2.0 A $g^{−1}$ for 2000 cycles with the eventual capacity of ∼300 mAh $g^{−1}$. Importantly, in situ X-ray diffraction studies clearly reveal mechanistic details of the lithium storage mechanism, involving multistep conversion processes upon initial lithiation

Cosmological constraints from the capture of non-Gaussianity in Weak Lensing data

Weak gravitational lensing has become a common tool to constrain the cosmological model. The majority of the methods to derive constraints on cosmological parameters use second-order statistics of the cosmic shear. Despite their success, second-order statistics are not optimal and degeneracies between some parameters remain. Tighter constraints can be obtained if second-order statistics are combined with a statistic that is efficient to capture non-Gaussianity. In this paper, we search for such a statistical tool and we show that there is additional information to be extracted from statistical analysis of the convergence maps beyond what can be obtained from statistical analysis of the shear field. For this purpose, we have carried out a large number of cosmological simulations along the {\sigma}8-{\Omega}m degeneracy, and we have considered three different statistics commonly used for non-Gaussian features characterization: skewness, kurtosis and peak count. To be able to investigate non-Gaussianity directly in the shear field we have used the aperture mass definition of these three statistics for different scales. Then, the results have been compared with the results obtained with the same statistics estimated in the convergence maps at the same scales. First, we show that shear statistics give similar constraints to those given by convergence statistics, if the same scale is considered. In addition, we find that the peak count statistic is the best to capture non-Gaussianities in the weak lensing field and to break the {\sigma}8-{\Omega}m degeneracy. We show that this statistical analysis should be conducted in the convergence maps: first, because there exist fast algorithms to compute the convergence map for different scales, and secondly because it offers the opportunity to denoise the reconstructed convergence map, which improves non-Gaussian features extraction.Comment: Accepted for publication in MNRAS (11 pages, 5 figures, 9 tables

Relativistic nuclear model with point-couplings constrained by QCD and chiral symmetry

We derive a microscopic relativistic point-coupling model of nuclear many-body dynamics constrained by in-medium QCD sum rules and chiral symmetry. The effective Lagrangian is characterized by density dependent coupling strengths, determined by chiral one- and two-pion exchange and by QCD sum rule constraints for the large isoscalar nucleon self-energies that arise through changes of the quark condensate and the quark density at finite baryon density. This approach is tested in the analysis of the equations of state for symmetric and asymmetric nuclear matter, and of bulk and single-nucleon properties of finite nuclei. In comparison with purely phenomenological mean-field approaches, the built-in QCD constraints and the explicit treatment of pion exchange restrict the freedom in adjusting parameters and functional forms of density dependent couplings. It is shown that chiral (two-pion exchange) fluctuations play a prominent role for nuclear binding and saturation, whereas strong scalar and vector fields of about equal magnitude and opposite sign, induced by changes of the QCD vacuum in the presence of baryonic matter, generate the large effective spin-orbit potential in finite nuclei.Comment: 46 pages, 12 figures, uses elsart.cls, revised version, to appear in Nucl.Phys. A735 (2004) 449-48

Free-standing sulfur-polypyrrole cathode in conjunction with polypyrrole-coated separator for flexible Li-S batteries

A free-standing sulfur-polypyrrole cathode and a polypyrrole coated separator were designed for flexible Li-S batteries. The free-standing sulfur-polypyrrole cathode was prepared by directly pasting a sulfur-coated polypyrrole (S@PPy) nanofiber composite on a flexible and conductive polypyrrole (PPy) film. Compared with carbonaceous matrixes, PPy has a strong interaction with polysulfides to mitigate the dissolution of polysulfides due to its unique chain structure and the lone pair electrons in the nitrogen atoms in PPy. In addition, the as-prepared PPy film not only shows excellent mechanical elasticity, but also possesses a rough surface, which can accommodate volume expansion, enhance the adhesion of active materials, and further trap the dissolved polysulfides. Due to the synergistic effect provided by the PPy film, the free-standing sulfur-polypyrrole cathode shows better electrochemical performance than the traditional cathode with S@PPy composite coated on Al foil. In order to further improve the cycling stability of Li-S batteries, a PPy coated separator was prepared, which acts as a fishing net to capture polysulfides and alleviate the shuttle effect, leading to a stable cycling performance. Moreover, the PPy layer coated on commercial separator is much lighter than many other free-standing interlayers reported previously. Considering the flexibility of the free-standing sulfur cathode and PPy coated separator, a soft-packaged flexible Li-S battery based on them has been designed and fabricated to power a device consisting of 24 light emitting diode (LED) lights. After repeated bending, the flexible Li-S battery can still maintain good performance, indicating the excellent mechanical flexibility of the designed Li-S battery

Unveiling the Intricate Intercalation Mechanism in Manganese Sesquioxide as Positive Electrode in Aqueous Zn‐Metal Battery

In the family of Zn/manganese oxide batteries with mild aqueous electrolytes, cubic α-Mn$_{2}$O$_{3}$ with bixbyite structure is rarely considered, because of the lack of the tunnel and/or layered structure that are usually believed to be indispensable for the incorporation of Zn ions. In this work, the charge storage mechanism of α-Mn$_{2}$O$_{3}$ is systematically and comprehensively investigated. It is demonstrated that the electrochemically induced irreversible phase transition from α-Mn$_{2}$O$_{3}$ to layered-typed L-Zn$_{x}$MnO$_{2}$, coupled with the dissolution of Mn$^{2+}$ and OH$^{-}$ into the electrolyte, allows for the subsequent reversible de-/intercalation of Zn$^{2+}$. Moreover, it is proven that α-Mn$_{2}$O$_{3}$ is not a host for H$^{+}$. Instead, the MnO$_{2}$ formed from L-Zn$_{x}$MnO$_{2}$ and the Mn^{2+ in the electrolyte upon the initial charge is the host for H$^{+}$. Based on this electrode mechanism, combined with fabricating hierarchically structured mesoporous α-Mn$_{2}$O$_{3}$ microrod array material, an unprecedented rate capability with 103 mAh g−1 at 5.0 A g−1 as well as an appealing stability of 2000 cycles (at 2.0 A g$^{-1}$) with a capacity decay of only ≈0.009% per-cycle are obtained