6,003 research outputs found

### Ratios of heavy hadron semileptonic decay rates

Ratios of charmed meson and baryon semileptonic decay rates appear to be
satisfactorily described by considering only the lowest-lying (S-wave) hadronic
final states and assuming the kinematic factor describing phase space
suppression is the same as that for free quarks. For example, the rate for
$D_s$ semileptonic decay is known to be $(17.0 \pm 5.3)%$ lower than those for
$D^0$ or $D^+$, and the model accounts for this difference. When applied to
hadrons containing $b$ quarks, this method implies that the $B_s$ semileptonic
decay rate is about 1% higher than that of the nonstrange $B$ mesons. This
small difference thus suggests surprisingly good local quark-hadron duality for
$B$ semileptonic decays, complementing the expectation based on inclusive
quark-hadron duality that these differences in rates should not exceed a few
tenths of a percent. For $\Lambda_b$ semileptonic decay, however, the inclusive
rate is predicted to be about 13% greater than that of the nonstrange $B$
mesons. This value, representing a considerable departure from a calculation
using a heavy quark expansion, is close to the corresponding experimental ratio
$\Gamma(\Lambda_b)/ \bar \Gamma(B) = 1.13 \pm 0.03$ of total decay rates.Comment: 12 pages, no figures. References adde

### Extracting the Omega- electric quadrupole moment from lattice QCD data

The Omega- has an extremely long lifetime, and is the most stable of the
baryons with spin 3/2. Therefore the Omega- magnetic moment is very accurately
known. Nevertheless, its electric quadrupole moment was never measured,
although estimates exist in different formalisms. In principle, lattice QCD
simulations provide at present the most appropriate way to estimate the Omega-
form factors, as function of the square of the transferred four-momentum, Q2,
since it describes baryon systems at the physical mass for the strange quark.
However, lattice QCD form factors, and in particular GE2, are determined at
finite Q2 only, and the extraction of the electric quadrupole moment, Q_Omega=
GE2(0) e/(2 M_Omega), involves an extrapolation of the numerical lattice
results. In this work we reproduce the lattice QCD data with a covariant
spectator quark model for Omega- which includes a mixture of S and two D states
for the relative quark-diquark motion. Once the model is calibrated, it is used
to determine Q_Omega. Our prediction is Q_Omega= (0.96 +/- 0.02)*10^(-2) efm2
[GE2(0)=0.680 +/- 0.012].Comment: To appear in Phys. Rev. D. Version with small modifications. 8 pages,
1 figur

### Repulsive force in the field theory of gravitation

It is shown that the slowing down of the rate of time referencing to the
inertial time leads in the field theory of gravitation to arising of repulsive
forces which remove the cosmological singularity in the evolution of a
homogeneous and isotropic universe and stop the collapse of large masses.Comment: 22 pages, Plenary talk presented at Workshop on High Energy
Physics&Field Theory (Protvino, Russia, 2005

### 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

### The Graviton Production in a Hot Homogeneous Isotropic Universe

It is shown that the RTG predicts an opportunity of the intensive production
of gravitons at the early stage of evolution of the homogeneous isotropic
Universe. A hypothesis is suggested that the produced gas of gravitons could be
just the ``dark matter'' which presently manifests itself as a ``missing mass''
in our Universe.Comment: 6 pages, latex fil

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