17896390
PRODUCTION OF NEUTRON-RICH LAMBDA HYPERNUCLEI AT J-PARC
We discuss the usefulness of the double charge-exchange reactions (DCX) for the production of the neutron-rich Λ-hypernuclei. We believe the (π-, K+) reaction is one of the most promising DCX reactions, and propose to produce the neutron-rich Λ-hypernuclei, and , at the J-PARC 50 GeV PS by the reaction (J-PARC E10 experiment). The design of the experiment is presented.
122452235
Beam and SKS spectrometers at the K1.8 beam line
High-resolution spectrometers for both incident beams and scattered particles have been constructed at the K1.8 beam line of the Hadron Experimental Facility at J-PARC. A point-to-point optics is realized between the entrance and exit of QQDQQ magnets for the beam spectrometer. Fine-pitch wire chamber trackers and hodoscope counters are installed in the beam spectrometer to accept a high rate beam up to 107 Hz. The superconducting kaon spectrometer for scattered particles was transferred from KEK with modifications to the cryogenic system and detectors. A missing-mass resolution of 1.9 ± 0.1 MeV/c2 (FWHM) was achieved for the Σ peaks of (π±,K+) reactions on a proton target in the first physics run of E19 in 2010
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.
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
104175735
Xi hypernuclear spectroscopy with SKS+ spectrometer at J-PARC
14553754
The fate of dark energy
Abstract By studying the present cosmological data, particularly on CMB, SNeIA and LSS, we find that the future fate of the universe, for simple linear models of the dark energy equation-of-state, can vary between the extremes of (I) a divergence of the scale factor in as little as 7 Gyr; (II) an infinite lifetime of the universe with dark energy dominant for all future time; (III) a disappearing dark energy where the universe asymptotes as t →∞ to a ( t )∼ t 2/3 , i.e., matter domination. Our dreadful conclusion is that no amount of data from our past light-cone can select between these future scenarios.
3907251
Large tensor-to-scalar ratio in small-field inflation.
We show that density perturbations seeded by the inflaton can be suppressed when having additional light degrees of freedom contributing to the production of perturbations. The inflaton fluctuations affect the light field dynamics by modulating the length of the inflationary period and, hence, produce additional density perturbations in the postinflationary era. Such perturbations can cancel those generated during inflation as both originate from the same inflaton fluctuations. This allows production of large gravitational waves from small-field inflation, which is normally forbidden by the Lyth bound on the inflaton field excursion. We also find that the field bound is taken over by the light scalar when the inflaton-induced perturbations are suppressed and, thus, present a generalized form of the Lyth bound that applies to the total field space. The novel mechanism allows violation of the usual consistency relation r≤-8n(T) for the tensor spectral index.
2226144
Cosmic Microwave Background Anisotropy with Late Time Entropy Production
We discuss effects of cosmological moduli fields on the cosmic microwave background (CMB). If a modulus field \phi once dominates the universe, the CMB we observe today is from the decay of \phi and its anisotropy is affected by the primordial fluctuation in the amplitude of the modulus field. As a result, constraints on the inflaton potential from the CMB anisotropy can be relaxed. In addition, with the cosmological moduli fields, correlated mixture of adiabatic and isocurvature fluctuations may be generated, which results in enhanced CMB angular power spectrum at higher multipoles relative to that of lower ones. Such an enhancement can be an evidence of late time entropy production due to the cosmological moduli fields, and may be observed at on-going and future experiments.
15108045
Adiabatic fluctuations from cosmic strings in a contracting universe
We show that adiabatic, super-Hubble, and almost scale invariant density fluctuations are produced by cosmic strings in a contracting universe. An essential point is that isocurvature perturbations produced by topological defects such as cosmic strings on super-Hubble scales lead to a source term which seeds the growth of curvature fluctuations on these scales. Once the symmetry has been restored at high temperatures, the isocurvature seeds disappear, and the fluctuations evolve as adiabatic ones in the expanding phase. Thus, cosmic strings may be resurrected as a mechanism for generating the primordial density fluctuations observed today.
118625411
Density fluctuations in thermal inflation and non-Gaussianity
We consider primordial fluctuations in thermal inflation scenario. Since the thermal inflation drives about 10 e-folds after the standard inflation, the time of horizon-exit during inflation corresponding to the present observational scale shifts toward the end of inflation. It generally makes the primordial power spectrum more deviated from a scale-invariant one and hence renders some models inconsistent with observations. We present a mechanism of generating the primordial curvature perturbation at the end of thermal inflation utilizing a fluctuating coupling of a flaton field with the fields in thermal bath. We show that, by adopting the mechanism, some inflation models can be liberated even in the presence of the thermal inflation. We also discuss non-Gaussianity in the mechanism and show that large non-Gaussianity can be generated in this scenario.