T. Kajino

Constraints on the Evolution of the Primordial Magnetic Field from the Small-Scale Cosmic Microwave Background Angular Anisotropy

Recent observations of the cosmic microwave background (CMB) have extended the measured power spectrum to higher multipoles l 1000, and there appears to be possible evidence for excess power on small angular scales. The primordial magnetic field (PMF) can strongly affect the CMB power spectrum and the formation of large-scale structure. In this paper, we calculate the CMB temperature anisotropies generated by including a power-law magnetic field at the photon last-scattering surface (PLSS). We then deduce an upper limit on the PMF based on our theoretical analysis of the power excess on small angular scales. We have taken into account several important effects such as the modified matter sound speed in the presence of a magnetic field. An upper limit to the field strength of |Bλ| 4.7 nG at the present scale of 1 Mpc is deduced. This is obtained by comparing the calculated theoretical result including the Sunyaev-Zeldovich (SZ) effect with recent observed data on the small-scale CMB anisotropies from the Wilkinson Microwave Anisotropy Probe (WMAP), the Cosmic Background Imager (CBI), and the Arcminute Cosmology Bolometer Array Receiver (ACBAR). We discuss several possible mechanisms for the generation and evolution of the PMF.

Constraints on resonant particle production during inflation from the matter and CMB power spectra

We analyze the limits on resonant particle production during inflation based upon the power spectrum of fluctuations in matter and the cosmic microwave background. We show that such a model is consistent with features observed in the matter power spectrum deduced from galaxy surveys and damped Lyman-{alpha} systems at high redshift. It also provides an alternative explanation for the excess power observed in the power spectrum of the cosmic microwave background fluctuations in the range of 1000<l<3500. For our best-fit models, epochs of resonant particle creation reenter the horizon at wave numbers of k{sub *}{approx}0.4 and/or 0.2 (h Mpc{sup -1}). The amplitude and location of these features correspond to the creation of fermion species of mass {approx}1-2 M{sub pl} during inflation with a coupling constant between the inflaton field and the created fermion species of near unity. Although the evidence is marginal, if this interpretation is correct, this could be one of the first observational hints of new physics at the Planck-scale.

Constraining the primordial magnetic field from cosmic microwave background anisotropies at higher multipoles

The cosmological magnetic field is one of the important physical quantities that strongly affect the cosmic microwave background (CMB) power spectrum. Recent CMB observations have been extended to higher multipoles (l 1000), and they resultantly exhibit an excess power that is more than the standard model prediction in cosmological theory that best fits the Wilkinson Microwave Anisotropy Probe (WMAP) data at lower multipoles (l 900). We calculate the CMB temperature anisotropies generated by the power-law magnetic field at the last scattering surface in order to remove the tension between theory and observation at higher multipoles and also to place an upper limit on the primordial magnetic field. In our present calculation we take account of the effect of the ionization ratio, without approximation. This effect is very crucial to precisely estimating the effect of the magnetic field on the CMB power spectrum. We consider effects of both the scalar and vector modes of the magnetic field on the CMB anisotropies, for which current data are known to be insensitive to the tensor mode, which we ignore in the present study. In order to constrain the primordial magnetic field, we evaluate the likelihood function of the WMAP data in a wide range of parameters of the magnetic field strength ||λ and the power-law spectral index nB, along with six cosmological parameters in flat universe models, using the technique of the Markov chain Monte Carlo method. We find that the upper limit at the 2 σ confidence level turns out to be |λ| 3.9 nG at 1 Mpc for any nB-values, which is obtained by comparing the calculated result, including the Sunyaev-Zeldovich effect, with recent WMAP data of the CMB anisotropies.

THE NEW DETECTIONS OF 7Li/6Li ISOTOPIC RATIO IN THE INTERSTELLAR MEDIA*

We have determined the isotopic abundance ratio of 7Li/6Li in the interstellar media (ISMs) along lines of sight to HD169454 and HD250290 using the High-Dispersion Spectrograph on the Subaru Telescope. We also observed ζ Oph for comparison with previous data. The observed abundance ratios were 7Li/6Li = 8.1+3.6 –1.8 and 6.3+3.0 –1.7 for HD169454 and HD250290, respectively. These values are in reasonable agreement with those observed previously in the solar neighborhood ISMs within ±2σ error bars and are also consistent with our measurement of 7Li/6Li = 7.1+2.9 –1.6 for a cloud along the line of sight to ζ Oph. This is good evidence for homogeneous mixing and instantaneous recycling of the gas component in the Galactic disk. We also discuss several source compositions of 7Li, Galactic cosmic-ray interactions, stellar nucleosynthesis, and big bang nucleosynthesis.

New s-process path and its implications for a 187Re-187Os nucleo-cosmochronometer

We study a new s-process path through an isomer of 186Re to improve a 187Re-187Os nucleo-cosmochronometer. The nucleus 187Re is produced by this new path of 185Re(n, γ)186Rem(n, γ)187Re. We measure a ratio of neutron-capture cross sections for the 185Re(n, γ)186Rem and 185Re(n, γ)186Reg reactions at thermal neutron energy because the ratio with the experimental uncertainty has not been reported. Using an activation method with reactor neutrons, we obtain the ratio of Rth = 0.54% ± 0.11%. From this ratio we estimate the ratio of Maxwellian-averaged cross sections in a typical s-process environment at kT = 30 keV with the help of the temperature dependence given in a statistical-model calculation because the energy dependence of the isomer/ground ratio is smaller than the absolute neutron-capture cross section. The ratio at kT = 30 keV is estimated to be Rst = 1.3% ± 0.8%. We calculate the s-process contribution from the new path in a steady-flow model. The additional abundance of 187Re through this path is estimated to be Ns = 0.56% ± 0.35% relative to the abundance of 186Os. This additional increase of 187Re does not make any remarkable change in the 187Re-187Os chronometer for an age estimate of a primitive meteorite, which has recently been found to be affected strongly by a single supernova r-process episode.

Exploring the neutrino mass hierarchy probability with meteoritic supernova material, ν -process nucleosynthesis, and θ 13 mixing

There is recent evidence that some SiC X grains from the Murchison meteorite may contain supernova-produced {\nu}-process 11B and or 7Li encapsulated in the grains. The synthesis of 11B and 7Li via neutrino-induced nucleon emission (the {\nu} -process) in supernovae is sensitive to the neutrino mass hierarchy for finite sin^2(2{\theta}13) > 0.001}. This sensitivity arises because, when there is 13 mixing, the average electron neutrino energy for charged-current neutrino reactions is larger for a normal mass hierarchy than for an inverted hierarchy. Recent constraints on {\theta}13 from the Daya Bay, Double Chooz, MINOS, RENO and T2K collaborations all suggest that indeed sin^2(2{\theta}13) > 0.001}. We examine the possible implications of these new results based upon a Bayesian analysis of the uncertainties in the measured meteoritic material and the associated supernova nucleosynthesis models. We show that although the uncertainties are large, they hint at a marginal preference for an inverted neutrino mass hierarchy. We discuss the possibility that an analysis of more X grains enriched in Li and B along with a better understanding of the relevant stellar nuclear and neutrino reactions could eventually reveal the neutrino mass hierarchy.

Reanalysis of the (J=5) state at592keV inTa180and its role in theν-process nucleosynthesis ofTa180in supernovae

We analyze the production and freeze-out of the isomer 180Tam in the neutrino-process. We consider the influence of a possible low-lying intermediate (J = 5) state at 592 keV using a transition width estimated from the measured half-life. This more realistic width is much smaller than the previous estimate.We find that the 592-keV state leads only to a small reduction of the residual isomer population ratio from the previous result; that is, considering this better estimate for the transition width, the isomer population ratio changes from R = 0.39 to R = 0.38, whereas previously it was estimated that this transition could reduce the ratio to R = 0.18. This finding strengthens the evidence that 138La and 180Ta are coproduced by neutrino nucleosynthesis with an electron neutrino temperature of kT~4 MeV.

Light-element nucleosynthesis from jet-cloud interactions in active galactic nuclei

The production of light nuclei via the interactions of jets from the central engines of active galactic nuclei and the surrounding medium is studied. Several environments ranging from hot, dense knots of gas near the central engine to the cold broad-line region clouds are simulated by a nuclear reaction network that couples the thermonuclear processes in the cloud to the reactions between the jet particles and the cloud. Reaction products from the jet-cloud interactions are followed until they react or are thermalized, which may involve several subsequent reactions. The effects of nucleosynthesis from the introduction of a jet into the cloud can result in enhanced production of light nuclei well above their primordial abundances, and enhancement of CNO nuclei is also predicted above thermally produced abundances. In these scenarios, the jets can enhance abundances of CNO nuclei by first producing excess amounts of nuclei with A < 8, then by increasing the cloud density to the point at which the thermonuclear reaction rates become important. The comparison to observed abundances in quasars leads to the conclusion that the interactions of ejected matter from AGNs may be responsible for large observed abundances of light nuclei in addition to significant abundances of nuclei in the CNO region.

Production of 2H, 3He, and 7Li from Interactions between Jets and Clouds

The interactions between jets of high-energy nuclei and nuclei of the surrounding medium are studied. Such interactions could be initiated by jets from active galactic nuclei interacting with surrounding cool clouds. The resulting nuclear interactions are found to produce copious amounts of 2H and 3He from the 4He nuclei. These results suggest that jets of particles from quasars could have produced anomalously high abundances in surrounding clouds of some of the nuclides usually thought to characterize big bang nucleosynthesis, specifically, the 2H seen in absorption spectra.

Neutron Capture Cross Section to 113Cd Isomer and s-Process Contribution to Rare p-Nuclide 115Sn

A neutron capture cross section for the 112Cd(n, γ)113Cdm reaction has been measured with neutrons provided from a nuclear reactor in order to study the astrophysical origin of a rare p-process isotope 115Sn, which may be produced by a nucleosynthesis flow through 113Cdm in the s-process. We have obtained the thermal neutron capture cross section of 0.028 ± 0.009 [b] and the resonance integral of 1.1 ± 0.3 [b] using a cadmium difference method. The cross section ratio of the isomer to the ground state has been calculated as a function of the incident neutron energy, E, by using a statistical model. The calculated ratios are almost constant over a wide range of E < 100 keV. We have evaluated the s-process contribution to the solar abundance of 115Sn using the classical steady-flow model with various astrophysical parameters. This calculated result has shown that the production through 113Cdm may give minor contribution to 115Sn.