118580858
High-resolution search for the Theta(+) pentaquark via a pion-induced reaction at J-PARC
The pentaquark Theta(+) has been searched for via the pi(-) p --> K- X reaction with beam momenta of 1.92 and 2.01 GeV/c at J-PARC. A missing mass resolution of 2 MeV (FWHM) was achieved but no sharp peak structure was observed. The upper limits on the production cross section averaged over the scattering angle from 2 degrees to 15 degrees in the laboratory frame were found to be less than 0.28 mu b/sr at the 90% confidence level for both the 1.92- and 2.01- GeV/c data. The systematic uncertainty of the upper limits was controlled within 10%. Constraints on the Theta(+) decay width were also evaluated with a theoretical calculation using an effective Lagrangian. The present result implies that the width should be less than 0.36 and 1.9 MeV for the spin-parity of 1/2(+) and 1/2(-), respectively
118888696
Search for $^6_\Lambda$H hypernucleus by the $^6$Li$(\pi^-,K^+)$ reaction at $p_{\pi^-}$ = 1.2 GeV/$c$
We have carried out an experiment to search for a neutron-ric h hypernucleus, 6 Λ H, by the6Li(π−,K+) reaction atpπ− =1.2 GeV/c. The obtained missing-mass spectrum with an estimated energy re solution of 3.2 MeV (FWHM) showed no peak structure correspo nding to the6 Λ H hypernucleus neither below nor above the 4 Λ H+2n particle decay threshold. An upper limit of the production c ross section for the bound6 Λ H hypernucleus was estimated to be 1.2 nb /sr at 90% confidence level.
14311314
Implications of dark energy parametrizations for the determination of the curvature of the universe
We investigate how the nature of dark energy affects the determination of the curvature of the universe, using recent observations. For this purpose, we consider the constraints on the matter and dark energy density using observations of type Ia supernovae, the baryon acoustic oscillation peak and the cosmic microwave background with dark energy equations of state of several types. Although it is usually said that the combination of current observations favours a flat universe, we found that a relatively large parameter space allows the universe to be open for a particular model of dark energy. We also discuss what kind of dark energy model or prior allows a non-flat universe.
118525697
Studying Inflation with Future Space-Based Gravitational Wave Detectors
Motivated by recent progress in our understanding of the B-mode polarization of cosmic microwave background (CMB), which provides important information about the inflationary gravitational waves (IGWs), we study the possibility to acquire information about the early universe using future space-based gravitational wave (GW) detectors. We perform a detailed statistical analysis to estimate how well we can determine the reheating temperature after inflation as well as the amplitude, the tensor spectral index, and the running of the inflationary gravitational waves. We discuss how the accuracies depend on noise parameters of the detector and the minimum frequency available in the analysis. Implication of such a study on the test of inflation models is also discussed.
2581930
Non-Gaussianity and baryonic isocurvature fluctuations in the curvaton scenario
Abstract We discuss non-Gaussianity and baryonic isocurvature fluctuations in the curvaton scenario, assuming that the baryon asymmetry of the universe originates only from the decay products of the inflaton. When large non-Gaussianity is realized in such a scenario, non-vanishing baryonic isocurvature fluctuations can also be generated unless the baryogenesis occurs after the decay of the curvaton. We calculate the non-linearity parameter f NL and the baryonic isocurvature fluctuations, taking account of the primordial fluctuations of both the inflaton and the curvaton. We show that, although current constraints on isocurvature fluctuations are severe, the non-linearity parameter can be large as f NL ∼ O ( 10 – 100 ) without conflicting with the constraints.
118475719
Primordial trispectrum from isocurvature fluctuations
We study non-Gaussianity generated by adiabatic and isocurvature primordial perturbations. We first obtain, in a very general setting, the non-linear perturbations, up to third order, for an arbitrary number of cosmological fluids, going through one or several decay transitions. We then apply this formalism to the mixed curvaton and inflaton model, allowing for several decay channels. We compute the various contributions to the bispectrum and trispectrum resulting from adiabatic and isocurvature perturbations, which are correlated in general. By investigating some hybrid decay scenario, we show that significant non-Gaussianity of adiabatic and isocurvature types can be generated without conflicting with the present isocurvature constraints from the power spectrum. In particular, we find cases where non-Gaussianity of isocurvature origin can dominate its adiabatic counterpart, both in the bispectrum and in the trispectrum.
118361349
Probing quintessence potential with future cosmological surveys
Quintessence, a scalar field model, has been proposed to account for the acceleration of the Universe at present. We discuss how accurately quintessence models are discriminated by future cosmological surveys, which include experiments of CMB, galaxy clustering, weak lensing, and the type Ia SNe surveys, by making use of the conventional parameterized dark energy models. We can see clear differences between the thawing and the freezing quintessence models at more than 1σ (2σ) confidence level as long as the present equation of state for quintessence is away from -1 as wX−0.95(−0.90). However, it is found to be difficult to probe the effective mass squared for the potential in thawing models, whose signs are different between the quadratic and the cosine-type potentials. This fact may require us to invent a new estimator to distinguish quintessence models beyond the thawing and the freezing ones.