27 research outputs found
Perturbative QCD estimation of the branching ratio
Working in a perturbative QCD model approach, we obtain the essential form
factor of the radiative transition and estimate
the branching ratio . The results are
determined by a parameter expressing the momentum distribution in the -
meson wave function. Our estimations are compared to other theoretical
predictions as well as to experimental data.Comment: 8 pages, Figure is not include
A Toy Model Approach to the Canonical Non-perturbative Quantization of the Spatially Flat Robertson-Walker Spacetimes with Cosmological Constant
We present a toy model approach to the canonical non-perturbative
quantization of the spatially-flat Robertson-Walker Universes with cosmological
constant, based on the fact that such models are exactly solvable within the
framework of a simple Lagrangian formulation. The essential quantum dynamical
metric-field and the corresponding Hamiltonian, explicitly derived in terms of
annihilation and creation operators, point out that the Wheeler - DeWitt
equation is a natural (quantum) generalization of the - Einstein
equation for the classical De Sitter spacetime and selects the physical states
of the quantum De Sitter Universe. As a result of the exponential universal
expansion, the usual Fock states (defined as the eigenstates of the
number-operator) are no longer invariant under the derived Hamiltonian. They
exhibit quantum fluctuation of the energy and of the metric field which lead to
a (geometrical) volume quantization.Comment: 22 pages, LaTe
Alternative Approach to Branching Ratio Calculation
Since the calculation of in the framework of
QCD improved factorization method, developed by Beneke et al., leads to
numerical values much below the experimental data, we include two different
contributions, in an alternative way. First, we find out that the spectator
hard-scattering mechanism increases the value with almost 50%, but the
predictions depend on the combined singularities in the amplitude convolution.
Secondly, by adding SUSY contributions to the Wilson coefficients, we come to a
depending on three parameters, whose values are constrained by the
experimental data.Comment: 17 pages, 2 Postscript figure
Approximative Analytic Study of Fermions in Magnetar's Crust; Ultra-relativistic Plane Waves, Heun and Mathieu Solutions and Beyond
Working with a magnetic field periodic along and decaying in time, we
deal with the Dirac-type equation characterizing the fermions evolving in
magnetar's crust. For ultra-relativistic particles, one can employ the
perturbative approach, to compute the conserved current density components. If
the magnetic field is frozen and the magnetar is treated as a stationary
object, the fermion's wave function is expressed in terms of the Heun's
Confluent functions. Finally, we are extending some previous investigations on
the linearly independent fermionic modes solutions to the Mathieu's equation
and we discuss the energy spectrum and the Mathieu Characteristic Exponent.Comment: Accepted for publication in Astrophysics & Space Science, 15 pages,
No figure
Planary Symmetric Static Worlds with Massless Scalar Sources
Motivated by the recent wave of investigations on plane domain wall
spacetimes with nontrivial topologies, the present paper deals with (probably)
the most simple source field configuration which can generate a spatially
planary symmetric static spacetime, namely a minimally coupled massless scalar
field that depends only upon a spacelike coordinate, . It is shown that the
corresponding exact solutions are
algebraically special, type , and represent globally
pathologic spacetimes with a - group of motion acting on orbits. In spite of the model simplicity, these
- generated worlds possess naked timelike singularities (reached within
a finite universal time by normal non-spacelike geodesics), are completely free
of Cauchy surfaces and contain into the - leveled sections points which can
not be jointed by - trajectories images of oblique non-spacelike
geodesics. Finally, we comment on the possibility of deriving from two other physically interesting ^^ ^^ -
generated'' spacetimes, by appropiate jonction conditions in the -
plane.Comment: 14 pages, LaTeX format, figures not include
Fermion confinement induced by geometry
We consider a five-dimensional model in which fermions are confined in a
hypersurface due to an interaction with a purely geometric field. Inspired by
the Rubakov-Shaposhnikov field-theoretical model, in which massless fermions
can be localized in a domain wall through the interaction of a scalar field, we
show that particle confinement may also take place if we endow the
five-dimensional bulk with a Weyl integrable geometric structure, or if we
assume the existence of a torsion field acting in the bulk. In this picture,
the kind of interaction considered in the Rubakov-Shaposhnikov model is
replaced by the interaction of fermions with a geometric field, namely a Weyl
scalar field or a torsion field. We show that in both cases the confinement is
independent of the energy and the mass of the fermionic particle. We generalize
these results to the case in which the bulk is an arbitrary n-dimensional
curved space.Comment: 8 page
Flavor SU(3) symmetry and QCD factorization in and decays
Using flavor SU(3) symmetry, we perform a model-independent analysis of
charmless decays. All the relevant
topological diagrams, including the presumably subleading diagrams, such as the
QCD- and EW-penguin exchange diagrams and flavor-singlet weak annihilation
ones, are introduced. Indeed, the QCD-penguin exchange diagram turns out to be
important in understanding the data for penguin-dominated decay modes. In this
work we make efforts to bridge the (model-independent but less quantitative)
topological diagram or flavor SU(3) approach and the (quantitative but somewhat
model-dependent) QCD factorization (QCDF) approach in these decays, by
explicitly showing how to translate each flavor SU(3) amplitude into the
corresponding terms in the QCDF framework. After estimating each flavor SU(3)
amplitude numerically using QCDF, we discuss various physical consequences,
including SU(3) breaking effects and some useful SU(3) relations among decay
amplitudes of and .Comment: 47 pages, 3 figures, 28 table
Dynamical Boson Stars
The idea of stable, localized bundles of energy has strong appeal as a model
for particles. In the 1950s John Wheeler envisioned such bundles as smooth
configurations of electromagnetic energy that he called {\em geons}, but none
were found. Instead, particle-like solutions were found in the late 1960s with
the addition of a scalar field, and these were given the name {\em boson
stars}. Since then, boson stars find use in a wide variety of models as sources
of dark matter, as black hole mimickers, in simple models of binary systems,
and as a tool in finding black holes in higher dimensions with only a single
killing vector. We discuss important varieties of boson stars, their dynamic
properties, and some of their uses, concentrating on recent efforts.Comment: 79 pages, 25 figures, invited review for Living Reviews in
Relativity; major revision in 201
Measurement of the ratio of branching fractions BR(B0 -> K*0 gamma)/BR(Bs0 -> phi gamma) and the direct CP asymmetry in B0 -> K*0 gamma
The ratio of branching fractions of the radiative B decays B0 -> K*0 gamma
and Bs0 phi gamma has been measured using an integrated luminosity of 1.0 fb-1
of pp collision data collected by the LHCb experiment at a centre-of-mass
energy of sqrt(s)=7 TeV. The value obtained is BR(B0 -> K*0 gamma)/BR(Bs0 ->
phi gamma) = 1.23 +/- 0.06(stat.) +/- 0.04(syst.) +/- 0.10(fs/fd), where the
first uncertainty is statistical, the second is the experimental systematic
uncertainty and the third is associated with the ratio of fragmentation
fractions fs/fd. Using the world average value for BR(B0 -> K*0 gamma), the
branching fraction BR(Bs0 -> phi gamma) is measured to be (3.5 +/- 0.4) x
10^{-5}.
The direct CP asymmetry in B0 -> K*0 gamma decays has also been measured with
the same data and found to be A(CP)(B0 -> K*0 gamma) = (0.8 +/- 1.7(stat.) +/-
0.9(syst.))%.
Both measurements are the most precise to date and are in agreement with the
previous experimental results and theoretical expectations.Comment: 21 pages, 3 figues, 4 table