17,679 research outputs found

    Exchange and spin Jahn-Teller distortions for a triangular cluster of spin-1/2

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    We study the effects of magnetoelastic coupling on the degenerate ground state of the spin-1/2 antiferromagnetic Heisenberg model for the regular triangular spin cluster. Static displacement of spins spontaneously lifts the degeneracy of the ground state through the distance dependence of exchange coupling, i.e., a spin Jahn-Teller mechanism takes place. On the other hand, dynamical displacement does not lift the degeneracy, though the cluster distorts spontaneously. The energy decrease obtained by dynamical theory is twice as large as that obtained by static theory because of quantum fluctuation.Comment: 4 pages, 1 figure. Accepted by JPSJ. Clarified some setences. Corrected typo

    Effective Theory Approach to the Skyrme model and Application to Pentaquarks

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    The Skyrme model is reconsidered from an effective theory point of view. From the most general chiral Lagrangian up to including terms of order p4p^4, NcN_c and δm2\delta m^2 (δmmsm\delta m\equiv m_s-m), new interactions, which have never been considered before, appear upon collective coordinate quantization. We obtain the parameter set best fitted to the observed low-lying baryon masses, by performing the second order perturbative calculations with respect to δm\delta m. We calculate the masses and the decay widths of the other members of (mainly) anti-decuplet pentaquark states. The formula for the decay widths is reconsidered and its baryon mass dependence is clarified.Comment: 65 pages, 1 figure. Revised version:the complete second order perturbative calculations performed and two appendices adde

    Two loop finiteness of Higgs mass and potential in the gauge-Higgs unification

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    The zero mode of an extra-dimensional component of gauge potentials serves as a 4D Higgs field in the gauge-Higgs unification. We examine QED on M4×S1M^4 \times S^1 and determine the mass and potential of a 4D Higgs field (the A5A_5 component) at the two loop level with gauge invariant reguralization. It is seen that the mass is free from divergences and independent of the renormalization scheme.Comment: 18 pages, 1 figur

    Charge 4/3 leptons in cosmic rays

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    A cosmic ray counter telescope has been operated at zenith angles of 0, 40, 44, and 60 degs in order to look for charge 4/3 particles. A few million clean single cosmic rays of each zenith angle are analyzed

    Preparation of Neutron-activated Xenon for Liquid Xenon Detector Calibration

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    We report the preparation of neutron-activated xenon for the calibration of liquid xenon (LXe) detectors. Gamma rays from the decay of xenon metastable states, produced by fast neutron activation, were detected and their activities measured in a LXe scintillation detector. Following a five-day activation of natural xenon gas with a Cf-252 (4 x 10^5 n/s) source, the activities of two gamma ray lines at 164 keV and 236 keV, from Xe-131m and Xe-129m metastable states, were measured at about 95 and 130 Bq/kg, respectively. We also observed three additional lines at 35 keV, 100 keV and 275 keV, which decay away within a few days. No long-lifetime activity was observed after the neutron activation.Comment: to be published in NIM A, corrected typos in Table 1 and Fig.6 of the previous versio

    Biomass Gasification for the Co-Production of Fischer-Tropsch Liquids and Electricity

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    This report examines the co-production of Fischer-Tropsch (F-T) liquids and electricity using biomass gasification. F-T liquids and electricity derived from biomass gasification appear as attractive alternatives for meeting energy needs in the medium-term. Biomassbased electricity generation constitutes an attractive option for the introduction of renewable energy resources and the gasification technology could offer an efficient, flexible and clean option for electricity production, as compared to conventional combustion-based plants. On the other hand, F-T liquids could have applications in the transportation sector, enabling the use of advanced internal combustion engines while being compatible with today's fuel delivery infrastructure. However, they still have to undergo substantial cost reductions in order to become competitive in the energy markets. Our analysis illustrates that a sales strategy for the co-product electricity could substantially contribute to improve the economics of F-T liquids. The biomass gasification could act as a facilitating technology for the development of integrated and flexible bioenergy strategies, since it allows the production or coproduction of, among others, electricity, hydrogen and clean liquid fuels. Biomassbased "energyplexes" would have an inherent flexibility that could be an important asset in liberalized energy markets. We also illustrate the costs and energy consumption associated with long-distance bioenergy transport to Japan using two scenarios where forest residues produced in North America and energy crops produced in Latin America are transported to Japan via ship. A variety of supply chains were compared, including transport in the forms of logs, bales, chips, pellets and F-T liquids. Early conversion of biomass to F-T liquids in advance of long-distance transport via ship appears as a favorable option on economic and energy-consumption grounds