27,943 research outputs found

    Induced top Yukawa coupling and suppressed Higgs mass parameters

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    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

    K2πK \to 2 \pi Decay in the Nambu-Jona-Lasinio Model

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    We study the K2πK \to 2 \pi decays using the UL(3)×UR(3)U_L(3) \times U_R(3) version of the Nambu-Jona-Lasinio model with the effective ΔS=1\Delta S = 1 nonleptonic weak interaction. The ΔI=3/2\Delta I = {3/2} amplitude is in reasonable agreement with experimental data. On the other hand, the calculated ΔI=1/2\Delta I = {1/2} amplitudes strongly depend on the mass of the low-lying scalar-isoscalar σ\sigma meson, and therefore give a strong constraint on the parameters of the model.Comment: 10 pages, 3 Postscript figures, Talk given at YITP Workshp: From Hadronic Matter to Quark Matter: Evolving View of Hadronic Matter, Kyoto, Japan, Oct. 30-Nov. 1, 1994, to be published in Prog. Theor. Phys. Supp

    Doubly magic nuclei from Lattice QCD forces at MPS=M_{PS}=469 MeV/c2^2

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    We perform ab initio self-consistent Green's function calculations of the closed shell nuclei 4^{\rm 4}He, 16^{\rm 16}O and 40^{\rm 40}Ca, based on two-nucleon potentials derived from Lattice QCD simulations, in the flavor SU(3) limit and at the pseudo-scalar meson mass of 469~MeV/c2^{\rm 2}. The nucleon-nucleon interaction is obtained using the HAL QCD method and its short-distance repulsion is treated by means of ladder resummations outside the model space. Our results show that this approach diagonalises ultraviolet degrees of freedom correctly. Therefore, ground state energies can be obtained from infrared extrapolations even for the relatively hard potentials of HAL QCD. Comparing to previous Brueckner Hartree-Fock calculations, the total binding energies are sensibly improved by the full account of many-body correlations. The results suggest an interesting possible behaviour in which nuclei are unbound at very large pion masses and islands of stability appear at first around the traditional doubly-magic numbers when the pion mass is lowered toward its physical value. The calculated one-nucleon spectral distributions are qualitatively close to those of real nuclei even for the pseudo-scalar meson mass considered here.Comment: 7 pages, 4 figures, RIKEN-QHP-286, RIKEN-iTHEMS-Report-1

    X-ray and Radio Follow-up Observations of High-Redshift Blazar Candidates in the Fermi-LAT Unassociated Source Population

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    We report on the results of X-ray and radio follow-up observations of two GeV gamma-ray sources 2FGL J0923.5+1508 and 2FGL J1502.1+5548, selected as candidates for high-redshift blazars from unassociated sources in the {\it Fermi} Large Area Telescope Second Source Catalog. We utilize the Suzaku satellite and the VLBI Exploration of Radio Astrometry (VERA) telescopes for X-ray and radio observations, respectively. For 2FGL J0923.5+1508, a possible radio counterpart NVSS J092357+150518 is found at 1.4 GHz from an existing catalog, but we do not detect any X-ray emission from it and derive a flux upper limit F28keV<F_{\rm 2-8 keV} < 1.37 ×\times 1014^{-14} erg cm2^{-2} s1^{-1}. Radio observations at 6.7 GHz also result in an upper limit of S6.7GHzS_{\rm 6.7 GHz} << 19 mJy, implying a steep radio spectrum that is not expected for a blazar. On the other hand, we detect X-rays from NVSS J150229+555204, the potential 1.4 GHz radio counterpart of 2FGL J1502.1+5548. The X-ray spectrum can be fitted with an absorbed power-law model with a photon index γ\gamma=1.80.2+0.3^{+0.3}_{-0.2} and the unabsorbed flux is F28keVF_{\rm 2-8 keV}=4.31.0+1.1^{+1.1}_{-1.0} ×\times 1014^{-14} erg cm2^{-2} s1^{-1}. Moreover, we detect unresolved radio emission at 6.7 GHz with flux S6.7GHzS_{\rm 6.7 GHz}=30.1 mJy, indicating a compact, flat-spectrum radio source. If NVSS J150229+555204 is indeed associated with 2FGL J1502.1+5548, we find that its multiwavelength spectrum is consistent with a blazar at redshift z34z \sim 3-4.Comment: 24 pages, 7 figures, 6 tables, accepted for publication in Ap
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