33 research outputs found
The B_c Meson Lifetime in the Light--Front Constituent Quark Model
We present an investigation of the total decay rate of the (ground state) B_c
meson within the framework of the relativistic constituent quark model
formulated on the light-front (LF). The exclusive semileptonic (SL) and
nonleptonic (NL) beauty and charm decays of the B_c meson are described through
vector and axial hadronic form factors, which are calculated in terms of a
constituent quark model LF wave functions. The latter ones are derived via the
Hamiltonian LF formalism using as input the update versions of the constituent
quark model. The inclusive SL and NL partial rates are calculated within a
convolution approach inspired by the partonic model and involving the same B_c
wave function which is used for evaluation of the exclusive modes. The
framework incorporates systematically 84 exclusive and 44 inclusive partial
rates corresponding to the underlying \bar{b}\to\bar{c} and c\to s quark
decays. Based on our approach we find\tau_{B_c}=0.59 \pm 0.06 ps where the
theoretical uncertainty is dominated by the uncertainty in the choice of LF
wave functions and the threshold values for the hadron continuum. For the
branching fractions of the B^+_c \to J/\psi\mu^+\nu_{\mu} and B_c^+\to
J/\psi\pi^+ decays we obtain 1.6 % and 0.1 %, respectively.Comment: 10 pages, LaTeX, 1 ps figur
Weak decays of the B_c meson to charmonium and D mesons in the relativistic quark model
Semileptonic and nonleptonic decays of the B_c meson to charmonium and D
mesons are studied in the framework of the relativistic quark model. The decay
form factors are explicitly expressed through the overlap integrals of the
meson wave functions in the whole accessible kinematical range. The
relativistic meson wave functions are used for the calculation of the decay
rates. The obtained results are compared with the predictions of other
approaches.Comment: 27 pages, 17 figures, 1 figure and 1 reference added, version to
appear in Phys. Rev.
The semileptonic decays of the B_c meson
We study the semileptonic transitions B_c to \eta_c, J/\psi, D, D^*, B, B^*,
B_s, B_s^* in the framework of a relativistic constituent quark model. We use
experimental data on leptonic J/\psi decay, lattice and QCD sum rule results on
leptonic B_c decay, and on radiative \eta_c transitions to adjust the quark
model parameters. We compute all form factors of the above semileptonic
B_c-transitions and give predictions for various semileptonic B_c decay modes
including their \tau-modes when they are kinematically accessible. The
implications of heavy quark symmetry for the semileptonic decays are discussed
and are shown to be manifest in our explicit relativistic quark model
calculation. A comparison of our results with the results of other calculations
is performed.Comment: 31 pages Latex (uses epsf, revtex). Section II expanded, typos
corrected. This version will appear in Phys. Rev.
Mass spectra of doubly heavy Omega_QQ' baryons
We evaluate the masses of baryons composed of two heavy quarks and a strange
quark with account for spin-dependent splittings in the framework of potential
model with the KKO potential motivated by QCD with a three-loop beta-function
for the effective charge consistent with both the perturbative limit at short
distances and linear confinement term at long distances between the quarks. The
factorization of dynamics is supposed and explored in the nonrelativistic
Schroedinger equation for the motion in the system of two heavy quarks
constituting the doubly heavy diquark and the strange quark interaction with
the diquark. The limits of approach, its justification and uncertainties are
discussed. Excited quasistable states are classified by the quantum numbers of
heavy diquark composed by the heavy quarks of the same flavor.Comment: 14 pages, revtex4-file, 3 eps-figures, 5 tables, typos correcte
Prognosis of complicated clinical course of varicose veins of lower extremities on the basis of analysis of phenotypic characteristics of connective tissue dysplasia
Aim: to identify the phenotypic characteristics of indeterminate connective tissue dysplasia, which help to predict the progression of varicose veins of lower extremities and disease recurrence after surgery. Material and Methods. The long-term results of surgical treatment of 60 patients with varicose veins of lower extremities in a 5-year period after phlebectomy were analyzed. The phenotypic characteristics of indeterminate connective tissue dysplasia were researched. 24 patients had recurrence of varicose veins of lower extremities associated with disease progression; 36 patients did not have recurrence of varicose veins of lower extremities. Results. All the patients demonstrated the signs of indeterminate connective tissue dysplasia, whereas their frequency was different. There were specified nine phenotypic characteristics of indeterminate connective tissue dysplasia, which were significantly more frequent for patients with recurrence of varicose vein disease of lower extremities: 1) postural abnormality, 2) flat foot, 3) skin pallor, 4) hyperextension of skin, 5) positive "wrist test", 6) positive "pollex test", 7) diastasis recti abdominis, 8) myopia, 9) hematomas which form quickly. Conclusion. The determined sum of phenotypic characters of indeterminate connective tissue dysplasia allows to predict progression of varicose vein disease of lower extremities, and offers new opportunities for improving the results of surgical treatment via developing special therapeutic measures aimed at improving lifestyle and dysplasia treatment
Surgical approach to patients with varicothrombophlebitis with undifferentiated dysplasia of connective tissue
Aim: to study the peculiar features of clinical course of acute varicothrombophlebitis and surgical approach to patients with undifferentiated dysplasia of connective tissue. Material and Methods. The features of undifferentiated dysplasia of connective tissue, character of clinical course of acute varicothrombophlebitis, remote results for 94 patients, who had had Troyanov — Trendelenburg's operation, were studied. Results. 70 patients (74,5%) with acute varicothrombophlebitis demonstrated more than four phenotypic characters which showed the presence of undifferentiated dysplasia of connective tissue. 22 patients (31,4%) with acute varicothrombophlebitis with undifferentiated dysplasia of connective tissue were proved to have the discrepancy between localization of acute varicothrombophlebitis clinical evidences and level of proximal part of thrombus in the lumen of great saphenous vein. During the remote observation period, 66 patients (94,3%) with acute varicothrombophlebitis with undifferentiated dysplasia of connective tissue had pheblectomy, as there was vertical and horizontal pathological venous reflux. Out of 24 patients (25,5%) with acute varicothrombophlebitis without undifferentiated dysplasia of connective tissue, only four patients (16,7%) needed thesecond stage of surgical treatment, because 20 patients (83,3%), in 6 months after Troyanov — Trendelenburg's operation, demonstrated the restoration of functional consistency of valves of great saphenous and perforating veins. Conclusion. When determining the indications for urgent disconnection of saphenofemoral junction for patients with acute varicothrombophlebitis and also when choosing surgical treatment approach during remote observation period, it is reasonable to examine the phenotypic characters of undifferentiated dysplasia of connective tissue.</p