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In this paper we construct a covariant light-front model of heavy mesons within the framework of heavy quark effective theory (HQET). The covariant model consists of the light-front heavy meson bound states constructed in the heavy quark limit with heavy quark symmetry and heavy quark effective theory as its basis. Within this model, the Isgur-Wise function and decay constants in the infinite quark mass limit can be evaluated in a very simple and the most general way. The results are ensured to be consistent with heavy quark symmetry. From the heavy-quark-limit bound states, we can further develop a systematic approach to calculate 1/mQ corrections from the 1/mQ expansion of QCD. This covariant model can serve as a quasi-first-principles description of heavy meson dynamics, namely, a phenomenological covariant bound state in the heavy quark limit which is consistent with heavy quark symmetry, plus a reliable first-principles computation of the 1/mQ corrections in HQET in terms of the 1/mQ expansion of the fundamental QCD theory.

Within the light-front framework, form factors for $P\to P$ and $P\to V$ transitions ($P$: pseudoscalar meson, $V$: vector meson) due to the valence-quark configuration are calculated directly in the entire physical range of momentum transfer. The behavior of form factors in the infinite quark mass limit are examined to see if the requirements of heavy-quark symmetry are fulfilled. We find that the Bauer-Stech-Wirbel type of light-front wave function fails to give a correct normalization for the Isgur-Wise function at zero recoil in $P\to V$ transition. Some of the $P\to V$ form factors are found to depend on the recoiling direction of the daughter mesons relative to their parents. Thus, the inclusion of the non-valence configuration arising from quark-pair creation is mandatory in order to ensure that the physical form factors are independent of the recoiling direction. The main feature of the non-valence contribution is discussed., Comment: 49 pages, 11 figures

In this paper, a study of light-cone distribution amplitudes for p-wave heavy mesons is presented in both general and heavy quark frameworks. Within the light-front approach, the leading twist light-cone distribution amplitudes, \phi_M(u) and their relevant decay constants of heavy scalar, axial-vector and tensor mesons, f_M, are formulated. The relations of some decay constants can be simplified when the heavy quark limit is taken into account. After fixing the parameters which appear in a Gaussian wave function, the corresponding decay constants are calculated and compared with those of other theoretical approaches. The curves and the first six \xi moments of \phi_M(u) are plotted and estimated. These results all endorse the requirements of heavy quark symmetry., Comment: 27 pages, 7 figures, 6 tables, version to appear in Phys. Rev. D. arXiv admin note: substantial text overlap with arXiv:1003.0972, arXiv:0906.4412

In this paper, a study of light-cone distribution amplitudes (LCDAs) for $s$-wave heavy meson are presented in both general and heavy quark frameworks. Within the light-front approach, the leading twist light-cone distribution amplitudes, $\phi_M(u)$, and their relevant decay constants of heavy pseudoscalar and vector mesons, $f_M$, have simple relations. These relations can be further simplified when the heavy quark limit is taken into consideration. After fixing the parameters that appear in both Gaussian and power-law wave functions, the corresponding decay constants are calculated and compared with those of other theoretical approaches. The curves and the first six $\xi$-moments of $\phi_M(u)$ are plotted and estimated. A conclusion is drawn from these results: Even though the values of the decay constants of the distinct mesons are almost equal, the curves of their LCDAs may have quite large differences, and vice versa. Additionally, in the heavy quark limit, the leading twist LCDAs, $\Phi_{Qq}(\omega)$ and $\Phi_{Qq}(\omega)$, are compared with the $B$-meson LCDAs, $\psi_+(\omega)$, suggested by the other theoretical groups., Comment: 25 pages, 3 figures, 4 tables, some typos are corrected, version to be published in Phys. Rev. D

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 ${D}_{(s)}^{*}\ensuremath{-}{D}_{(s)}$ and ${B}_{(s)}^{*}\ensuremath{-}{B}_{(s)}$ states and the light quark masses, ${m}_{s,q}$ ($q=u$, $d$), to extract the wave function parameter $\ensuremath{\beta}$. The values ${f}_{{D}_{s}}/{f}_{D}=1.29\ifmmode\pm\else\textpm\fi{}0.07$ and ${f}_{{B}_{s}}/{f}_{B}=1.32\ifmmode\pm\else\textpm\fi{}0.08$ 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 $\ensuremath{\Delta}{M}_{{B}_{c}{B}_{c}^{*}}$ with the varied charm quark masses is also shown. In addition, the mean square radii are estimated as well. The values $\sqrt{⟨{r}_{{D}_{s}^{+}}^{2}⟩/⟨{r}_{{D}^{+}}^{2}⟩}={0.740}_{+0.050}^{\ensuremath{-}0.041}$ and $\sqrt{⟨{r}_{{B}_{s}^{0}}^{2}⟩/⟨{r}_{{B}^{0}}^{2}⟩}={0.711}_{+0.058}^{\ensuremath{-}0.049}$ are obtained, and the sensitivities of $⟨{r}_{P}^{2}⟩$ on the heavy and light quark masses are similar to those of the decay constants.

In this paper, the electromagnetic mass differences of heavy hadrons are discussed, while the relevant hyperfine interactions are ignored. The effects of one-photon exchange interaction and up-down quark mass difference are parametrized. Two mass difference equations 2{sigma}{sub c}{sup +}-({sigma}{sub c}{sup ++}+{sigma}{sub c}{sup 0})=2{sigma}{sub b}{sup 0}-({sigma}{sub b}{sup +}+{sigma}{sub b}{sup -}) and ({xi}{sub cc}{sup +}-{xi}{sub cc}{sup ++})+({xi}{sub bb}{sup -}-{xi}{sub bb}{sup 0})=2({xi}{sub bc}{sup 0}-{xi}{sub bc}{sup +}) for the heavy baryons are obtained. In addition, the masses of {sigma}{sub b}{sup 0}, {xi}{sub b}{sup 0}, and {xi}{sub cc}{sup ++} are predicted based on the known experimental data.

Assuming the two diquark structure for the pentaquark state as advocated in the Jaffe-Wilczek model, there exist exotic parity-even anti-sextet and parity-odd triplet heavy pentaquark baryons. The theoretical estimate of charmed and bottom pentaquark masses is quite controversial and it is not clear whether the ground-state heavy pentaquark lies above or below the strong-decay threshold. We study the weak transitions of heavy pentaquark states using the light-front quark model. In the heavy quark limit, heavy-to-heavy pentaquark transition form factors can be expressed in terms of three Isgur-Wise functions: two of them are found to be normalized to unity at zero recoil, while the third one is equal to 1/2 at the maximum momentum transfer, in accordance with the prediction of the large-Nc approach or the quark model. Therefore, the light-front model calculations are consistent with the requirement of heavy quark symmetry. Numerical results for form factors and Isgur-Wise functions are presented. Decay rates of the weak decays Theta_b+ to Theta_c0 pi+ (rho+), Theta_c0 to Theta+ pi- (rho-), Sigma'_{5b}+ to Sigma'_{5c}0 pi+ (rho+) and Sigma'_{5c}0 to N_8+ pi- (rho-) with Theta_Q, Sigma'_{5Q} and N_8 being the heavy anti-sextet, heavy triplet and light octet pentaquarks, respectively, are obtained. For weakly decaying Theta_b+ and Theta_c0, the branching ratios of Theta_b+ to Theta_c0 pi+, Theta_c0 to Theta+ pi- are estimated to be at the level of 10^{-3} and a few percents, respectively., 33 pages, 3 figures, version to be published in Phys. Rev. D

We study the rare decays of ${B}_{c}^{+}\ensuremath{\rightarrow}{D}_{q}^{(*)+}l\overline{l}$ $(q=d,s$ and $l={\ensuremath{\nu}}_{l},e,\ensuremath{\mu},\ensuremath{\tau})$ in the standard model. The form factors are evaluated in the light front and constituent quark models, respectively. We find that the decay branching ratios calculated in the two models for ${B}_{c}^{+}\ensuremath{\rightarrow}{D}_{q}^{+}l\overline{l}$ agree well with each other, whereas those for ${B}_{c}^{+}\ensuremath{\rightarrow}{D}_{q}^{*+}l\overline{l}$ are different.