28,526 research outputs found

    Induced top Yukawa coupling and suppressed Higgs mass parameters

    Get PDF
    In the scenarios with heavy top squarks, mass parameters of the Higgs field must be fine-tuned due to a large logarithmic correction to the soft scalar mass. We consider a new possibility that the top Yukawa coupling is small above TeV scale. The large top mass is induced from strong Yukawa interaction of the Higgs with another gauge sector, in which supersymmetry breaking parameters are given to be small. Then it is found that the logarithmic correction to the Higgs soft scalar mass is suppressed in spite of the strong coupling and the fine-tuning is ameliorated. We propose an explicit model coupled to a superconformal gauge theory which realizes the above situation.Comment: RevTeX4 style, 10 pages, 3 figure

    Kamland Results

    Full text link
    The LMA solution of the solar neutrino problem has been explored with the 1,000 ton liquid scinatillator detector, KamLAND. It utilizes nuclear power reactors distributing effectively 180km from the experimental site. Comparing observed neutrino rate with the calculation of reactor operation histories, an evidence for reactor neutrino disapearance has been obtained from 162 ton-year exposure data. This deficit is only compatible with the LMA solution and the other solutions in the two neutrino oscillation hypotheisis are excluded at 99.95% confidence level.Comment: 8 pages, 5 figures, proceeding of the Moriond Conference "Electroweak Interactions and Unified Thories

    A possible signature of primordial stellar populations in z=3z=3 Lyman α\alpha emitters

    Full text link
    Observations with Subaru telescope have detected surprisingly strong Lyman continuum (LyC; 900\sim900 \AA\ in the rest-frame) from some Lyman α\alpha emitters (LAEs) at z=3.1z=3.1. We have examined the stellar population which simultaneously accounts for the strength of the LyC and the spectral slope of non-ionizing ultraviolet of the LAEs. As a result, we have found that stellar populations with metallicity Z1/50ZZ\geq1/50 Z_\odot can explain the observed LyC strength only with a very top-heavy initial mass function (IMF; 50M \sim 50 M_\odot). However, the critical metallicity for such an IMF is expected to be much lower. A very young (1\sim1 Myr) and massive (100\sim100 MM_\odot) extremely metal-poor (Z5×104ZZ\leq5\times10^{-4}Z_\odot) or metal-free (so-called Population III) stellar population can also reproduce the observed LyC strength if the mass fraction of such 'primordial' stellar population is 1\sim1% in total stellar mass of the LAEs.Comment: 4 pages, 2 figures, First Stars IV in Kyoto conference (May 2012) proceedin

    Evolution of Dust-to-Metal Ratio in Galaxies

    Full text link
    This paper investigates the evolution of the dust-to-metal ratio in galaxies based on a simple evolution model for the amount of metal and dust with infall. We take into account grain formation in stellar mass-loss gas, grain growth by the accretion of metallic atoms in a cold dense cloud, and grain destruction by SNe shocks. Especially, we propose that the accretion efficiency is independent of the star-formation history. This predicts various evolutionary tracks in the metallicity (ZZ)--dust-to-gas ratio (D\cal D) plane depending on the star-formation history. In this framework, the observed linear ZZ--D\cal D relation of nearby spiral galaxies can be interpreted as a sequence of a constant galactic age. We emphasize that an observational study of the ZZ--D\cal D relation of galaxies at z1z\sim 1 is very useful to constrain the efficiencies of dust growth and destruction. We also suggest that the Lyman break galaxies at z3z\sim 3 have a very low dust-to-metal ratio, typically \ltsim 0.1. Although the effect of infall on the evolutionary tracks in the ZZ--D\cal D plane is quite small, the dispersion of the infall rate can disturb the ZZ--D\cal D relation with a constant galactic age.Comment: 9 pages, accepted to appear in PASJ October issu

    Method of manufacturing ceramic shaped articles

    Get PDF
    A method of manufacturing ceramic shaped articles, wherein tapes of ceramic powder material in mixture with a binder material and special additives are shaped and then articles are stamped out from said tapes and sintered in a sintering furnace is described

    Structure and Stability of Magnetic Fields in Solar Active Region12192 Based on Nonlinear Force-Free Field Modeling

    Full text link
    We analyze a three-dimensional (3D) magnetic structure and its stability in large solar active region(AR) 12192, using the 3D coronal magnetic field constructed under a nonlinear force-free field (NLFFF) approximation. In particular, we focus on the magnetic structure that produced an X3.1-class flare which is one of the X-class flares observed in AR 12192. According to our analysis, the AR contains multiple-flux-tube system, {\it e.g.}, a large flux tube, both of whose footpoints are anchored to the large bipole field, under which other tubes exist close to a polarity inversion line (PIL). These various flux tubes of different sizes and shapes coexist there. In particular, the later are embedded along the PIL, which produces a favorable shape for the tether-cutting reconnection and is related to the X-class solar flare. We further found that most of magnetic twists are not released even after the flare, which is consistent with the fact that no observational evidence for major eruptions was found. On the other hand, the upper part of the flux tube is beyond a critical decay index, essential for the excitation of torus instability before the flare, even though no coronal mass ejections (CMEs) were observed. We discuss the stability of the complicated flux tube system and suggest the reason for the existence of the stable flux tube. In addition, we further point out a possibility for tracing the shape of flare ribbons, on the basis of a detailed structural analysis of the NLFFF before a flare.Comment: 24 pages, 9 figures, accepted for publication in The Astrophysical Journa

    Constraint on intergalactic dust from thermal history of intergalactic medium

    Get PDF
    This Letter investigates the amount of dust in the intergalactic medium (IGM). The dust photoelectric heating can be the most efficient heating mechanism in the IGM where the density is very small and there are a lot of hard ultraviolet photons. Comparing the observational thermal history of IGM with a theoretical one taking into account the dust photoelectric heating, we can put an upper limit on the dust-to-gas ratio, D{\cal D}, in the IGM. Since the rate of the dust photoelectric heating depends on the size of dust, we find the following results: If the grain size is \ga 100 \AA, D{\cal D} at z3z \sim 3 is \la 1/100 Galactic value corresponding to \Omega_{\rm dust}^{\rm IGM}\la 10^{-5}. On the other hand, if the grain size is as small as 10\sim 10 \AA, D{\cal D} is \la 1/1000 Galactic value corresponding to \Omega_{\rm dust}^{\rm IGM}\la 10^{-6}.Comment: 5 pages, 2 figures; accepted for publication in MNRAS pink page
    corecore