6,003 research outputs found

    Ratios of heavy hadron semileptonic decay rates

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    Ratios of charmed meson and baryon semileptonic decay rates appear to be satisfactorily described by considering only the lowest-lying (S-wave) hadronic final states and assuming the kinematic factor describing phase space suppression is the same as that for free quarks. For example, the rate for DsD_s semileptonic decay is known to be (17.0±5.3)(17.0 \pm 5.3)% lower than those for D0D^0 or D+D^+, and the model accounts for this difference. When applied to hadrons containing bb quarks, this method implies that the BsB_s semileptonic decay rate is about 1% higher than that of the nonstrange BB mesons. This small difference thus suggests surprisingly good local quark-hadron duality for BB semileptonic decays, complementing the expectation based on inclusive quark-hadron duality that these differences in rates should not exceed a few tenths of a percent. For Λb\Lambda_b semileptonic decay, however, the inclusive rate is predicted to be about 13% greater than that of the nonstrange BB mesons. This value, representing a considerable departure from a calculation using a heavy quark expansion, is close to the corresponding experimental ratio Γ(Λb)/Γˉ(B)=1.13±0.03\Gamma(\Lambda_b)/ \bar \Gamma(B) = 1.13 \pm 0.03 of total decay rates.Comment: 12 pages, no figures. References adde

    Extracting the Omega- electric quadrupole moment from lattice QCD data

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    The Omega- has an extremely long lifetime, and is the most stable of the baryons with spin 3/2. Therefore the Omega- magnetic moment is very accurately known. Nevertheless, its electric quadrupole moment was never measured, although estimates exist in different formalisms. In principle, lattice QCD simulations provide at present the most appropriate way to estimate the Omega- form factors, as function of the square of the transferred four-momentum, Q2, since it describes baryon systems at the physical mass for the strange quark. However, lattice QCD form factors, and in particular GE2, are determined at finite Q2 only, and the extraction of the electric quadrupole moment, Q_Omega= GE2(0) e/(2 M_Omega), involves an extrapolation of the numerical lattice results. In this work we reproduce the lattice QCD data with a covariant spectator quark model for Omega- which includes a mixture of S and two D states for the relative quark-diquark motion. Once the model is calibrated, it is used to determine Q_Omega. Our prediction is Q_Omega= (0.96 +/- 0.02)*10^(-2) efm2 [GE2(0)=0.680 +/- 0.012].Comment: To appear in Phys. Rev. D. Version with small modifications. 8 pages, 1 figur

    Repulsive force in the field theory of gravitation

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    It is shown that the slowing down of the rate of time referencing to the inertial time leads in the field theory of gravitation to arising of repulsive forces which remove the cosmological singularity in the evolution of a homogeneous and isotropic universe and stop the collapse of large masses.Comment: 22 pages, Plenary talk presented at Workshop on High Energy Physics&Field Theory (Protvino, Russia, 2005

    Chiral Lagrangian with Heavy Quark-Diquark Symmetry

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    We construct a chiral Lagrangian for doubly heavy baryons and heavy mesons that is invariant under heavy quark-diquark symmetry at leading order and includes the leading O(1/m_Q) symmetry violating operators. The theory is used to predict the electromagnetic decay width of the J=3/2 member of the ground state doubly heavy baryon doublet. Numerical estimates are provided for doubly charm baryons. We also calculate chiral corrections to doubly heavy baryon masses and strong decay widths of low lying excited doubly heavy baryons.Comment: 20 pages, no figure

    The Graviton Production in a Hot Homogeneous Isotropic Universe

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    It is shown that the RTG predicts an opportunity of the intensive production of gravitons at the early stage of evolution of the homogeneous isotropic Universe. A hypothesis is suggested that the produced gas of gravitons could be just the ``dark matter'' which presently manifests itself as a ``missing mass'' in our Universe.Comment: 6 pages, latex fil