Chiral Lagrangian with Heavy Quark-Diquark Symmetry

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

Two-particle decays of B_c meson into charmonium states

The factorization of hard and soft contributions into the hadronic decays of B_c meson at large recoils is explored in order to evaluate the decay rates into the S, P and D-wave charmonia associated with rho and pi. The constraints of approach applicability and uncertainties of numerical estimates are discussed. The mode with the J/psi in the final state is evaluated taking into account the cascade radiative electromagnetic decays of excited P-wave states, that enlarges the branching ratio by 20-25%.Comment: 13 pages, LaTeX axodraw-style, 1 figure, 2 table

Semileptonic Bc−→D∗0ℓνB_{c}^{-}\to D^{*0}\ell\nu transition in three--point QCD sum rules and HQET with gluon condensate corrections

Taking into account the gluon condensate contributions, the form factors of the semileptonic $B_c^- \to D^{*0}\ell\nu$ transition with $l=\tau, e$ are calculated in the framework of the three point QCD sum rules. The heavy quark effective theory limit of the form factors are also computed. The relevant total decay width as well as the branching ratio are evaluated and compared with the predictions of the other non-perturbative approaches.Comment: 27 Pages, 4 Figures and 4 Table

Light-cone sum rules for the NγΔN\gamma\Delta transitions for real photons

We examine the radiative $\Delta \to \gamma N$ transition at the real photon point $Q^2=0$ using the framework of light-cone QCD sum rules. In particular, the sum rules for the transition form factors $G_M(0)$ and $R_{EM}$ are determined up to twist 4. The result for $G_M(0)$ agrees with experiment within 10% accuracy. The agreement for $R_{EM}$ is also reasonable. In addition, we derive new light-cone sum rules for the magnetic moments of nucleons, with a complete account of twist-4 corrections based on a recent reanalysis of photon distribution amplitudes.Comment: 34 pages, 9 figures, revised version, published in Phys. Rev. D, one misplaced reference correcte

Observations on the radiative corrections to pion beta-decay

We find that, in the local V-A theory, the radiative corrections to pion beta-decay involving the weak vector current, when evaluated in the current algebra (CA) formulation in which quarks are the fundamental underlying fields, show a small difference with the more elementary calculations based directly on the pion fields. We show that this difference arises from a specific short-distance effect that depends on the algebra satisfied by the weak and electromagnetic currents. On the other hand, we present a simple theoretical argument that concludes that this difference does not occur when the CA formulation is compared with the chiral perturbation theory (chiPT) approach. Comparisons with previous studies, and with a more recent calculation based on chiPT, are included. We also briefly review the important differences between the results in the local V-A theory and the Standard Model.Comment: 5 pages, 1 figure. V2: two paragraphs have been added in Section III. Final version on PR

Spectroscopy of doubly charmed baryons: Ξcc+\Xi_{cc}^{+} and Ξcc++\Xi_{cc}^{++}

Using the quark-diquark approximation in the framework of Buchm\" uller-Tye potential model, we investigate the spectroscopy of doubly charmed baryons: $\Xi_{cc}^{++}$ and $\Xi_{cc}^{+}$. Our results include the masses, parameters of radial wave functions of states with the different excitations of both diquark and light quark-diquark system. We calculate the values of fine and hyperfine splittings of these levels and discuss some new features, connected to the identity of heavy quarks, in the dynamics of hadronic and radiative transitions between the states of these baryons.Comment: 10 pages, Latex file, 1 fig, corrected some typo

Elastic scattering theory and transport in graphene

Electron properties of graphene are described in terms of Dirac fermions. Here we thoroughly outline the elastic scattering theory for the two-dimensional massive Dirac fermions in the presence of an axially symmetric potential. While the massless limit is relevant for pristine graphene, keeping finite mass allows for generalizations onto situations with broken symmetry between the two sublattices, and provides a link to the scattering theory of electrons in a parabolic band. We demonstrate that the Dirac theory requires short-distance regularization for potentials which are more singular than 1/r. The formalism is then applied to scattering off a smooth short-ranged potential. Next we consider the Coulomb potential scattering, where the Dirac theory is consistent for a point scatterer only for the effective impurity strength below 1/2. From the scattering phase shifts we obtain the exact Coulomb transport cross-section in terms of the impurity strength. The results are relevant for transport in graphene in the presence of impurities that do not induce scattering between the Dirac points in the Brillouin zone.Comment: 17 pages, 4 figures. Published versio

Analysis of the rare semileptonic B_c \rar P(D,D_s) l^{+}l^{-}/\nu\bar{\nu} decays within QCD sum rules

Considering the gluon condensate corrections, the form factors relevant to the semileptonic rare B_c \rar D,D_s(J^{P}=0^{-}) l^{+}l^{-} with $l=\tau,\mu,e$ and B_c \rar D,D_s(J^{P}=0^{-})\nu\bar{\nu} transitions are calculated in the framework of the three point QCD sum rules. The heavy quark effective theory limit of the form factors are computed. The branching fraction of these decays are also evaluated and compared with the predictions of the relativistic constituent quark model. Analyzing of such type transitions could give useful information about the strong interactions inside the pseudoscalar $D_{s}$ meson and its structure.Comment: 32 Pages, 8 Figures and 6 Table

A relativistic quark model for the Omega- electromagnetic form factors

We compute the Omega- electromagnetic form factors and the decuplet baryon magnetic moments using a quark model application of the Covariant Spectator Theory. Our predictions for the Omega- electromagnetic form factors can be tested in the future by lattice QCD simulations at the physical strange quark mass.Comment: 13 pages, 5 figure

SU(3) symmetry breaking in decay constants and electromagnetic properties of pseudoscalar heavy mesons

In this paper, the decay constants and mean square radii of pseudoscalar heavy mesons are studied in the SU(3) symmetry breaking. Within the light-front framework, the ratios $f_{D_s}/f_D$ and $f_{B_s}/f_B$ are individually estimated using the hyperfine splittings in the $D_{(s)}^*-D_{(s)}$ and $B_{(s)}^*-B_{(s)}$ states and the light quark masses, $m_{s,q}$ ($q=u,d$), to extract the wave function parameter $\beta$. The values $f_{D_s}/f_D= 1.29\pm0.07$ and $f_{B_s}/f_B= 1.32\pm 0.08$ are obtained, which are not only chiefly determined by the ratio of light quark masses $m_s/m_q$, but also insensitive to the heavy quark masses $m_{c,b}$ and the decay constants $f_{D,B}$. The dependence of $f_{B_c}/f_B$ on $\Delta M_{B_cB^*_c}$ with the varied charm quark masses is also shown. In addition, the mean square radii are estimated as well. The values $\sqrt{} =0.740^{-0.041}_{+0.050}$ and $\sqrt{} =0.711^{-0.049}_{+0.058}$ are obtained, and the sensitivities of $$ on the heavy and light quark masses are similar to those of the decay constants.Comment: 21 pages, 5 figures, 4 tables, some typos are corrected, version to be published in Phys. Rev.