5,553 research outputs found

    Comment on "On the TST_S-Anomaly in Betaine Calcium Chloride Dihydrate"

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    Recently, Hlinka and Ishibashi [J. Phys. Soc. Jpn. 67, 495 (1998)] discussed the TST_S-anomaly in betaine calcium chloride dihydrate (BCCD) in a Landau-type approach. We comment on the shortcomings of this approach and discuss the TST_S-anomaly in the framework of a microscopical pseudo spin model based on a realistic description of BCCD in terms of symmetry-adapted local modes.Comment: 2 pages, RevTex, submitted to J. Phys. Soc. Jp

    Renormalization of Velocity-Changing Dimension-Five Operators in the Heavy-Quark Effective Theory

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    We study the renormalization of operators of the type hˉvΓGμνhv{\bar h_{v'}} \Gamma G^{\mu\nu} h_v in the heavy-quark effective theory (HQET). We construct the combinations of such operators that are renormalized multiplicatively, and calculate their velocity-dependent anomalous dimensions at the one-loop order. We then show that the virial theorem of the HQET is not renormalized, and that in the limit of equal velocities the anomalous dimension of the chromo-electric operator vanishes to all orders in perturbation theory. This implies an exact relation between renormalization constants, which may help in a future calculation of the two-loop anomalous dimension of the chromo-magnetic operator.Comment: 9 pages, 1 figur

    Impact of Four-Quark Shape Functions on Inclusive B Decay Spectra

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    It has recently been pointed out that a new class of subleading shape functions involving B-meson matrix elements of non-local four-quark operators contributes at order Lambda_{QCD}/m_b to B->X_u+l+nu decay distributions in the endpoint region. The corresponding functions f_u(omega) and f_v(omega) are estimated using the vacuum-insertion approximation. A numerical analysis of various B->X_u+l+nu decay spectra suggests that these power corrections are very small, below present theoretical uncertainties due to other subleading shape-function contributions.Comment: 8 pages, 2 figures; minor revisions and figure added; version to appear in Eur. Phys. J.

    Note on Tests of the Factorization Hypothesis and the Determination of Meson Decay Constants

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    We discuss various tests of the factorization hypothesis making use of the close relationship between semi-leptonic and factorized nonleptonic decay amplitudes. It is pointed out that factorization leads to truely model-independent predictions for the ratio of nonleptonic to semi-leptonic decay rates, if in the nonleptonic decay a spin one meson of arbitrary mass or a pion take the place of the lepton pair. Where the decay constants of those mesons are known, these predictions represent ideal tests of the factorization hypothesis. In other cases they may be used to extract the decay constants. Currently available data on the decays Bˉ0D+π,D+π,D+ϱ,D+ϱ\bar B^0 \to D^+\pi^-,\, D^{*+}\pi^-,\, D^+\varrho^-,\, D^{*+}\varrho^- are shown to be in excellent agreement with the factorization results. A weighted average of the four independent values for the QCD coefficient a1a_1 extracted from the data gives a1=1.15±0.06a_1=1.15\pm 0.06 suggesting that it may be equal to the Wilson coefficient c1(μ)c_1(\mu) evaluated at the scale μ=mb\mu = m_b.Comment: (9 pages, ReVTeX, no figures), HD-THEP-92-3

    Infrared effects and the asymptotics of perturbation theory in weak decays of heavy particles

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    I discuss the interplay of infrared sensitivity in large order perturbative expansions with the presence of explicit nonperturbative corrections in the context of heavy quark expansions. The main focus is on inclusive decays and the status of the kinetic energy of the heavy quark. This talk summarizes work done with Braun and Zakharov.Comment: LATEX, world_sci.sty (appended to the file), UM-TH-94-30 (Invited talk presented at the conference ``QCD'94'', Montpellier, France, July 7 - 13, 1994) [Typo in ref. 6 corrected, pardon.

    Simply Modeling Meson HQET

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    A simple relativistic model of heavy-quark-light-quark mesons is proposed. In an expansion in inverse powers of the heavy quark mass we find that all zeroth and first order heavy quark symmetry relations are satisfied. The main results are: - the difference between the meson mass and the heavy quark mass plays a significant role even at zeroth order; - the slope of the Isgur-Wise function at the zero recoil point is typically less than 1-1; - the first order correction to the pseudoscalar decay constant is large and negative; - the four universal functions describing the first order corrections to the semileptonic decay form factors are small; - these latter corrections are quite insensitive to the choice of model parameters, and in particular to the effects of hyperfine mass splitting.Comment: 17 pages, LaTeX, 3 LaTeX figures in separate file, UTPT-92-16. This is the version published long ago but not previously archive

    Higher-order estimates of the chromomagnetic moment of a heavy quark

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    The leading beta_0^(n-1) alpha_s^n terms in the Wilson coefficient and anomalous dimension of the chromomagnetic operator in the heavy-quark effective Lagrangian are summed to all orders of perturbation theory. The perturbation series for the anomalous dimension is well behaved, while that for the Wilson coefficient exhibits a divergent behaviour already in low orders, caused by a nearby infrared renormalon singularity. The resulting ambiguity is commensurate with terms of order 1/m^2 in the effective Lagrangian, whose corresponding ultraviolet renormalons are identified. An excellent approximation for the scheme-invariant Wilson coefficient at next-to-next-to-leading order in renormalization-group improved perturbation theory is obtained.Comment: 16 pages, 3 figures embedde

    B -> X_u l nu decay distributions to order alpha_s

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    An analytic result for the O(alpha_s corrections to the triple differential B -> X_u l nu decay rate is presented, to leading order in the heavy-quark expansion. This is relevant for computing partially integrated decay distributions with arbitrary cuts on kinematic variables. Several double and single differential distributions are derived, most of which generalize known results. In particular, an analytic result for the O(alpha_s) corrections to the hadronic invariant mass spectrum is presented. The effects of Fermi motion, which are important for the description of decay spectra close to infrared sensitive regions, are included. The behaviour of perturbation theory in the region of time-like momenta is also investigatedComment: 24 pages, 11 figures, 1 typo in eq.(5.4) corrected; version published in JHEP06(1999)01

    Nonleptonic Weak Decays of B to D_s and D mesons

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    Branching ratios and polarization amplitudes for B decaying to all allowed pseudoscalar, vector, axial-vector, scalar and tensor combinations of D_s and D mesons are calculated in the Isgur Scora Grinstein Wise (ISGW) quark model after assuming factorization. We find good agreement with other models in the literature and the limited experimental data and make predictions for as yet unseen decay modes. Lattice QCD results in this area are very limited. We make phenomenological observations on decays in to D_s(2317) and D_s(2460) and propose tests for determining the status and mixings of the axial mesons. We use the same approach to calculate branching ratios and polarization fraction for decays in to two D type mesons.Comment: 21 pages, 9 figures. v3: updated to reflect changes in published paper, conclusions unchanged (see source file for details). Added comments on factorization. v2: experimental data updated, references added, tables of results added, more on axial D_s mixing, added section on D D decay modes and typos correcte

    Decay constants and radiative decays of heavy mesons in light-front quark model

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    We investigate the magnetic dipole decays VPγV\to P\gamma of various heavy-flavored mesons such as (D,D,Ds,Ds,ηc,J/ψ)(D,D^*,D_s,D^{*}_s,\eta_c, J/\psi) and (B,B,Bs,Bs,ηb,Υ)(B,B^*,B_s,B^*_s,\eta_b,\Upsilon) using the light-front quark model constrained by the variational principle for the QCD-motivated effective Hamiltonian. The momentum dependent form factors FVP(q2)F_{VP}(q^2) for VPγV\to P\gamma^* decays are obtained in the q+=0q^+=0 frame and then analytically continued to the timelike region by changing q{\bf q}_\perp to iqi{\bf q}_\perp in the form factors. The coupling constant gVPγg_{VP\gamma} for real photon case is then obtained in the limit as q20q^2\to 0, i.e. gVPγ=FVP(q2=0)g_{VP\gamma}=F_{VP}(q^2=0). The weak decay constants of heavy pseudoscalar and vector mesons are also calculated. Our numerical results for the decay constants and radiative decay widths for the heavy-flavored mesons are overall in good agreement with the available experimental data as well as other theoretical model calculations.Comment: 9 pages, 3figures, added few more references, typos correcte
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