1,193 research outputs found
Gauge Invariant Summation of All QCD Virtual Gluon Exchanges
The interpretation of virtual gluons as ghosts in the non-linear gluonic
structure of QCD permits the formulation and realization of a manifestly
gauge-invariant and Lorentz covariant theory of interacting quarks/anti-quarks,
for all values of coupling. The simplest example of quark/anti-quark scattering
in a high-energy, quenched, eikonal model at large coupling is shown to be
expressible as a set of finite, local integrals which may be evaluated
numerically; and before evaluation, it is clear that the result will be
dependent only on, and is damped by increasing momentum transfer, while
displaying physically-reasonable color dependence in a manner underlying the
MIT Bag Model and an effective, asymptotic freedom. A similar but more
complicated integral will result from all possible gluonic-radiative
corrections to this simplest eikonal model. Our results are compatible with an
earlier, field-strength analysis of Reinhardt et al.Comment: 35 pages, no figure
Dynamic modeling and tracking control of a nonholonomic wheeled mobile manipulator with dual arms
This paper presents methodologies for dynamic modeling and trajectory tracking of a nonholonomic wheeled mobile manipulator (WMM) with dual arms. The complete dynamic model of such a manipulator is easily established using the Lagrange's equation and MATHEMATICA. The structural properties of the overall system along with its subsystems are also well investigated and then exploited in further controller synthesis. The derived model is shown valid by reducing it to agree well with the mobile platform model. In order to solve the path tracking control problem of the wheeled mobile manipulator, a novel kinematic control scheme is proposed to deal with the nonholonomic constraints. With the backstepping technique and the filtered-error method, the nonlinear tracking control laws for the mobile manipulator system are constructed based on the Lyapunov stability theory. The proposed control scheme not only achieves simultaneous trajectory and velocity tracking, but also compensates for the dynamic interactions caused by the motions of the mobile platform and the two onboard manipulators. Simulation results are performed to illustrate the efficacy of the proposed control strategy
Relations between inclusive decay rates of heavy baryons
The dependence of inclusive weak decay rates of heavy hadrons on the flavors
of spectator light quarks is revisited with application to decays of charmed
and b hyperons. It is pointed out that the differences in the semileptonic
decay rates, the differences in the Cabibbo suppressed decay rates of the
charmed hyperons, and the splitting of the total decay rates of the b hyperons
are all related to the differences in the lifetimes of the charmed hyperons
independently of poor knowledge of hadronic matrix elements. The approximations
used in these relations are the applicability of the expansion in the inverse
of the charmed quark mass and the flavor SU(3) symmetry.Comment: 12 pages, LaTeX, minor typos corrected, one reference adde
Effective Hamiltonian for non-minimally coupled scalar fields
Performing a relativistic approximation as the generalization to a curved
spacetime of the flat space Klein-Gordon equation, an effective Hamiltonian
which includes non-minimial coupling between gravity and scalar field and also
quartic self-interaction of scalar field term is obtained.Comment: 4 page
CKM Favored Semileptonic Decays of Heavy Hadrons at Zero Recoil
We study the properties of Cabibbo-Kobayashi-Maskawa (CKM) favored
semileptonic decays of mesons and baryons containing a heavy quark at the point
of no recoil. We first use a diagrammatic analysis to rederive the result
observed by earlier authors that at this kinematic point the meson decays
via transitions can only produce a or meson. The result is
generalized to include photon emissions which violate heavy quark flavor
symmetry. We show that photons emitted by the heavy quarks and the charged
lepton are the only light particles that can decorate the decays at zero recoil, and the similar processes of heavy baryons.
Implications for the determinations of the CKM parameter are
discussed. Also studied in this paper is the connection between our
diagrammatic analysis of suppression of particle emission and the formal
observation based on weak currents at zero recoil being generators of heavy
quark symmetry. We show that the two approaches can be unified by considering
the Isgur-Wise function in the presence of an external source.Comment: 27 pages, including 11 figures using macros FEYNMAN.te
Two-Body Cabibbo-Suppressed Charmed Meson Decays
Singly-Cabibbo-suppressed decays of charmed particles governed by the quark
subprocesses and are analyzed using a
flavor-topology approach, based on a previous analysis of the Cabibbo-favored
decays governed by . Decays to and , where is a
pseudoscalar meson and is a vector meson, are considered. We include
processes in which and are produced.Comment: 18 pages, latex, 2 figures, to be submitted to Phys. Rev.
Light-Front Approach for Pentaquark Strong Decays
Assuming the two diquark structure for the pentaquark state as advocated in
the Jaffe-Wilczek model, we study the strong decays of light and heavy
parity-even pentaquark states using the light-front quark model in conjunction
with the spectator approximation. The narrowness of the Theta width is ascribed
to the p-wave configuration of the diquark pair. Taking the Theta width as a
benchmark, we estimate the rates of the strong decays Xi_{3/2}-- to Xi- pi-,
Sigma- K-, Sigma_{5c}0 to D_s- p, D_{s0}*- p and Xi_{5c}0 to D_s- Sigma+,
D_{s0}^{*-} Sigma+ with Sigma_{5c} Xi_{5c} being antisextet charmed pentaquarks
and D_{s0}* a scalar strange charmed meson. The ratio of Gamma(P_c to Baryon
D_{s0}*)/Gamma(P_c to Baryon D_s) is very useful for verifying the parity of
the antisextet charmed pentaquark P_c. It is expected to be of order unity for
an even parity P_c and much less than one for an odd parity pentaquark.Comment: 24 pages, 2 figure
The evolution of cosmic string loops in Kerr-de Sitter spacetimes
The equation of cosmic string loops in Kerr-de Sitter spacetimes is derived.
Having solved the equation numerically, we find that the loops can expand and
exist except for too small ones.Comment: 8 page
Light-Front Approach for Heavy Pentaquark Transitions
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.Comment: 33 pages, 3 figures, version to be published in Phys. Rev.
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