6,048 research outputs found
Effect of the length of inflation on angular TT and TE power spectra in power-law inflation
The effect of the length of inflation on the power spectra of scalar and
tensor perturbations is estimated using the power-law inflation model with a
scale factor of a(t) = t^q. Considering various pre-inflation models with
radiation-dominated or scalar matter-dominated periods before inflation in
combination with two matching conditions, the temperature angular power
spectrum (TT) and temperature-polarization cross-power spectrum (TE) are
calculated and a likelihood analysis is performed. It is shown that the
discrepancies between the Wilkinson Microwave Anisotropy Probe (WMAP) data and
the LCDM model, such as suppression of the spectrum at l = 2,3 and oscillatory
behavior, may be explained by the finite length of inflation model if the
length of inflation is near 60 e-folds and q > 300. The proposed models retain
similar values of chi^2 to that achieved by the LCDM model with respect to fit
to the WMAP data, but display different characteristics of the angular TE power
spectra at l < 20.Comment: 41 pages, 11 figure
Superconductivity in WO2.6F0.4 synthesized by reaction of WO3 with Teflon
WO3-xFx (x < 0.45) perovskite-like oxyfluorides were prepared by a chemically
reducing fluorination route using the polymer polytetrafluoroethylene (Teflon).
The symmetry of the crystal structures of WO3-xFx changes from monoclinic to
tetragonal to cubic as the fluorine content increases. Fluorine doping changes
insulating WO3 to a metallic conductor, and superconductivity (Tc = 0.4 K) was
discovered in the samples with fluorine contents of 0.41 < x < 0.45. This easy
fluorination method may be applicable to other systems and presents an
opportunity for finding new oxyfluoride superconductors.Comment: 9 pages, 3 figures, 2 tables. To be published in Phys Rev
The emergence of superconductivity in BaNi2(Ge1-xPx)2 at a structural instability
The physical properties and structural evolution of the 122-type solid
solution BaNi2(Ge1-xPx)2 are reported. The in-plane X-X (X = Ge1-xPx) dimer
formation present in the end member BaNi2Ge2, which results in a structural
transition to orthorhombic symmetry, is completely suppressed to zero
temperature on P substitution near x = 0.7, and a dome-shape superconducting
phase with a maximum Tc = 2.9 K emerges. Clear indications of phonon softening
and enhanced electron-phonon coupling are observed at the composition of the
structural instability. Our findings show that dimer breaking offers new
possibilities as a tuning parameter of superconductivity.Comment: 14 pages, 4 figure
Angular Power Spectrum in Modular Invariant Inflation Model
We propose a scalar potential of inflation, motivated by modular invariant
supergravity, and compute the angular power spectra of the adiabatic density
perturbations that result from this model. The potential consists of three
scalar fields, S, Y and T, together with two free parameters. By fitting the
parameters to cosmological data at the fixed point T=1, we find that the
potential behaves like the single-field potential of S, which slowly rolls down
along the minimized trajectory in Y. We further show that the inflation
predictions corresponding to this potential provide a good fit to the recent
three-year WMAP data, e.g. the spectral index n_s = 0.951. The TT and TE
angular power spectra obtained from our model almost completely coincide with
the corresponding results obtained from the \LambdaCDM model. We conclude that
our model is considered to be an adequate theory of inflation that explains the
present data, although the theoretical basis of this model should be further
explicated.Comment: 8 pages, 8 figures and 1 tabl
Initial condition of scalar perturbation in inflation
A formula for the power spectrum of curvature perturbations having any
initial conditions in inflation is obtained. Based on the physical conditions
before inflation, the possibility exists that the initial state of scalar
perturbations is not only the Bunch-Davies state, but also a more general state
(a squeezed state). For example, the derived formula for the power spectrum is
calculated using simple toy cosmological models. When there exists a
radiation-dominated period before inflation, the behavior of the scalar
perturbation is revealed not to vary greatly; however, from large scales to
small scales the power spectrum of the curvature perturbations oscillates
around the normal value. In addition, when inflation has a large break and the
breaking time is a radiation- dominated period, a large enhancement is revealed
to occur which depends on the length of the breaking time.Comment: 24 pages,3 figue
Nuclear parton distribution functions and their uncertainties
We analyze experimental data of nuclear structure-function ratios
F_2^A/F_2^{A'} and Drell-Yan cross section ratios for obtaining optimum parton
distribution functions (PDFs) in nuclei. Then, uncertainties of the nuclear
PDFs are estimated by the Hessian method. Valence-quark distributions are
determined by the F_2 data at large x; however, the small-x part is not obvious
from the data. On the other hand, the antiquark distributions are determined
well at x~0.01 from the F_2 data and at x~0.1 by the Drell-Yan data; however,
the large-x behavior is not clear. Gluon distributions cannot be fixed by the
present data and they have large uncertainties in the whole x region.
Parametrization results are shown in comparison with the data. We provide a
useful code for calculating nuclear PDFs at given x and Q^2.Comment: 9 pages, REVTeX, 23 eps files, Phys. Rev. C in press. Nuclear PDF
library is available at http://hs.phys.saga-u.ac.jp/nuclp.htm
Heavy quark & direct photon production and heavy quark parton densities
Direct photon production in association with a heavy quark can serve as an
excellent tool for the study of the heavy quark distributions. Currently it is
believed that heavy quarks are produced radiatively inside the nucleon, and so
there is no need to take into account heavy quark parameters inside global PDF
analyses. Certain models taking into account the possibility of an intrinsic
charm component exist. Here we present how these affect the \gamma + c cross
section. While at pA collisions the potential of this process to constrain the
gluon nuclear PDF which is currently largely unconstrained is presented.Comment: Quarkonium 2010 Proceeding
Discrete Convex Functions on Graphs and Their Algorithmic Applications
The present article is an exposition of a theory of discrete convex functions
on certain graph structures, developed by the author in recent years. This
theory is a spin-off of discrete convex analysis by Murota, and is motivated by
combinatorial dualities in multiflow problems and the complexity classification
of facility location problems on graphs. We outline the theory and algorithmic
applications in combinatorial optimization problems
- …