Development of portable NMR polarimeter system for polarized HD target

A portable NMR polarimeter system has been developed to measure the polarization of a polarized Hydrogen-Deuteride (HD) target for hadron photoproduction experiments at SPring-8. The polarized HD target is produced at the Research Center for Nuclear Physics (RCNP), Osaka university and is transported to SPring-8. The HD polarization should be monitored at both places. We have constructed the portable NMR polarimeter system by replacing the devices in the conventional system with the software system with PCI eXtensions for Instrumentation (PXI). The weight of the NMR system is downsized from 80 kg to 7 kg, and the cost is reduced to 25%. We check the performance of the portable NMR polarimeter system. The signal-to-noise (S/N) ratio of the NMR signal for the portable system is about 50% of that for the conventional NMR system. This performance of the portable NMR system is proved to be compatible with the conventional NMR system for the polarization measurement.Comment: 6 page, 8 figures, 2011/Mar/9 Replace Author

Cosmological constraints on dark matter models with velocity-dependent annihilation cross section

We derive cosmological constraints on the annihilation cross section of dark matter with velocity-dependent structure, motivated by annihilating dark matter models through Sommerfeld or Breit-Wigner enhancement mechanisms. In models with annihilation cross section increasing with decreasing dark matter velocity, big-bang nucleosynthesis and cosmic microwave background give stringent constraints.Comment: 23 pages, 9 figures; Added reference

Bounds on long-lived charged massive particles from Big Bang nucleosynthesis

The Big Bang nucleosynthesis (BBN) in the presence of charged massive particles (CHAMPs) is studied in detail. All currently known effects due to the existence of bound states between CHAMPs and nuclei, including possible late-time destruction of Li6 and Li7 are included. The study sets conservative bounds on CHAMP abundances in the decay time range 3x10^2 sec - 10^12 sec. It is stressed that the production of Li6 at early times T ~ 10keV is overestimated by a factor ~ 10 when the approximation of the Saha equation for the He4 bound state fraction is utilised. To obtain conservative limits on the abundance of CHAMPs, a Monte-Carlo analysis with ~ 3x10^6 independent BBN runs, varying reaction rates of nineteen different reactions, is performed (see attached erratum, however). The analysis yields the surprising result that except for small areas in the particle parameter space conservative constraints on the abundance of decaying charged particles are currently very close to those of neutral particles. It is shown that, in case a number of heretofore unconsidered reactions may be determined reliably in future, it is conceivable that the limit on CHAMPs in the early Universe could be tightened by orders of magnitude. An ERRATUM gives limits on primordial CHAMP densities when the by Ref. Kamimura et al. recently more accurately determined CHAMP reaction rates are employed.Comment: includes Erratum showing most up to date limits after determination of the most important reaction rate

A Pair Polarimeter for Linearly Polarized High Energy Photons

A high quality beam of linearly polarized photons of several GeV will become available with the coherent bremsstrahlung technique at JLab. We have developed a polarimeter which requires about two meters of the beam line, has an analyzing power of 20% and an efficiency of 0.02%. The layout and first results of a polarimeter test on the laser back-scattering photon beam at SPring-8/LEPS are presented

Revisiting vertical structure of neutrino-dominated accretion disks: Bernoulli parameter, neutrino trapping and other distributions

We revisit the vertical structure of neutrino dominated accretion flows (NDAFs) in spherical coordinates with a new boundary condition based on the mechanical equilibrium. The solutions show that NDAF is significantly thick. The Bernoulli parameter and neutrino trapping are determined by the mass accretion rate and the viscosity parameter. According to the distribution of the Bernoulli parameter, the possible outflow may appear in the outer region of the disk. The neutrino trapping can essentially affect the neutrino radiation luminosity. The vertical structure of NDAF is like a "sandwich", and the multilayer accretion may account for the flares in gamma-ray bursts.Comment: 7 pages, 2 figures, Accepted for publication in Astrophysics & Space Scienc

Primordial nucleosynthesis and hadronic decay of a massive particle with a relatively short lifetime

In this paper we consider the effects on big bang nucleosynthesis (BBN) of the hadronic decay of a long-lived massive particle. If high-energy hadrons are emitted near the BBN epoch ($t \sim 10^{-2}$ -- $10^2 \sec$), they extraordinarily inter-convert the background nucleons each other even after the freeze-out time of the neutron to proton ratio. Then, produced light element abundances are changed, and that may result in a significant discrepancy between standard BBN and observations. Especially on the theoretical side, now we can obtain a lot of experimental data of hadrons and simulate the hadronic decay process executing the numerical code of the hadron fragmentation even in the high energy region where we have no experimental data. Using the light element abundances computed in the hadron-injection scenario, we derive a constraint on properties of such a particle by comparing our theoretical results with observations.Comment: 33 pages, 14 postscript figures, reference added, typo corrected, to appear in Phys. Rev.