297 research outputs found
Multipath propagation model for high altitude platform (HAP) based on circular straigh cone geometry
A geometric model that describes a multipath
propagation for a fixed wireless communication system between a
High Altitude Platform and a fixed terrestrial user is presented.
The model describes the propagation of the reflected signals that
are able to reach the receiver as a consequence of all the
scatterers located inside the system coverage area. The
establishment of a particular geometry characterizing the system
coverage area allows the behavior of the multipath phenomenon
effects to be modeled accurately.Postprint (published version
Isospin Breaking in B -> K^* gamma Decays
A calculation of the leading isospin-breaking contributions to the B -> K^*
gamma decay amplitudes based on the QCD factorization approach is presented.
They arise at order Lambda/m_b in the heavy-quark expansion and are due to
annihilation contributions from 4-quark operators, the chromo-magnetic dipole
operator, and charm penguins. In the Standard Model the decay rate for B^0 ->
K^{*0} gamma is predicted to be about 10-20 % larger than that for B^- ->
K^{*-} gamma. Isospin-breaking effects are a sensitive probe of the penguin
sector of the effective weak Hamiltonian. New Physics models in which the
hierarchy of B -> K^* gamma decay rates is either flipped or greatly enhanced
could be ruled out with more precise data.Comment: 11 pages, 2 figures. Extended version to appear in Physics Letters B.
Includes an additional section with a discussion of New Physics effect
NRQCD Analysis of Bottomonium Production at the Tevatron
Recent data from the CDF collaboration on the production of spin-triplet
bottomonium states at the Tevatron p \bar p collider are analyzed within the
NRQCD factorization formalism. The color-singlet matrix elements are determined
from electromagnetic decays and from potential models. The color-octet matrix
elements are determined by fitting the CDF data on the cross sections for
Upsilon(1S), Upsilon(2S), and Upsilon(3S) at large p_T and the fractions of
Upsilon(1S) coming from chi_b(1P) and chi_b(2P). We use the resulting matrix
elements to predict the cross sections at the Tevatron for the spin-singlet
states eta_b(nS) and h_b(nP). We argue that eta_b(1S) should be observable in
Run II through the decay eta_b -> J/psi + J/psi.Comment: 20 pages, 3 figure
Heavy-Light Meson Decay Constant from QCD Sum Rules in Three-Loop Approximation
In this paper we compute the decay constant of the pseudo-scalar heavy-light
mesons in the heavy quark effective theory framework of QCD sum rules. In our
analysis we include the recently evaluated three-loop result of order
for the heavy-light current correlator. The value of the bottom
quark mass, which essentially limits the accuracy of the sum rules for
meson, is extracted from the nonrelativistic sum rules for
resonances in the next-to-next-to-leading approximation. We find stability of
our result with respect to all types of corrections and the specific form of
the sum rule which reduces the uncertainty. Our results MeV and
MeV for the and meson decay constants are in impressive
agreement with recent lattice calculations.Comment: minor editorial changes, references added, to appear in PR
Statistical Reconstruction of Qutrits
We discuss a procedure of measurement followed by the reproduction of the
quantum state of a three-level optical system - a frequency- and spatially
degenerate two-photon field. The method of statistical estimation of the
quantum state based on solving the likelihood equation and analyzing the
statistical properties of the obtained estimates is developed. Using the root
approach of estimating quantum states, the initial two-photon state vector is
reproduced from the measured fourth moments in the field . The developed
approach applied to quantum states reconstruction is based on the amplitudes of
mutually complementary processes. Classical algorithm of statistical estimation
based on the Fisher information matrix is generalized to the case of quantum
systems obeying Bohr's complementarity principle. It has been experimentally
proved that biphoton-qutrit states can be reconstructed with the fidelity of
0.995-0.999 and higher.Comment: Submitted to Physical Review
Analytic Perturbation Theory for Practitioners and Upsilon Decay
Within the ghost-free Analytic Perturbation Theory (APT), devised in the last
decade for low energy QCD, simple approximations are proposed for 3-loop
analytic couplings and their effective powers, in both the space-like
(Euclidean) and time-like (Minkowskian) regions, accurate enough in the large
range (1--100 GeV) of current physical interest.\par Effectiveness of the new
Model is illustrated by the example of decay where the
standard analysis gives value that is
inconsistent with the bulk of data for .
Instead, we obtain that
corresponds to that is close to the world
average.\par The issue of scale uncertainty for decay is also
discussed.Comment: 12 pages, 0 figures. Model slightly modified to increase its
accuracy. Numerical results upgraded, references added. The issue of scale
uncertainty is discusse
APPLICATION DE LA METHODE PROCUSTE A L'ANALYSE QUANTITATIVE DE LA « POULAINE » : INFLUENCE DE LA SPECIALITE ATHLETIQUE
National audienceLa méthode morphométrique Procuste, jusqu'alors destinée à l'étude quantitative de la forme géométrique des pièces osseuses en anthropologie, est appliquée, pour la première fois, à une forme spécifique extraite d'un mouvement cyclique. La forme choisie ici est la « poulaine », caractéristique du mouvement relatif de la cheville par rapport à l'articulation de la hanche au cours d'un cycle complet de course chez l'humain. L'objectif de cette étude est de quantifier les changements de forme de la poulaine en fonction de la spécialité athlétique du coureur
Quark-hadron duality for mixing
Long distance contribution to the mixing is taken into account
consistently and the corrections to the naive duality result represented by the
famous box diagram are found to be small. Estimates are given in the leading
order of the chiral perturbation theory.Comment: 11 pages, Late
Optimized Perturbation Theory for Wave Functions of Quantum Systems
The notion of the optimized perturbation, which has been successfully applied
to energy eigenvalues, is generalized to treat wave functions of quantum
systems. The key ingredient is to construct an envelope of a set of
perturbative wave functions. This leads to a condition similar to that obtained
from the principle of minimal sensitivity. Applications of the method to
quantum anharmonic oscillator and the double well potential show that uniformly
valid wave functions with correct asymptotic behavior are obtained in the
first-order optimized perturbation even for strong couplings.Comment: 11 pages, RevTeX, three ps figure
World-sheet Stability of (0,2) Linear Sigma Models
We argue that two-dimensional (0,2) gauged linear sigma models are not
destabilized by instanton generated world-sheet superpotentials. We construct
several examples where we show this to be true. The general proof is based on
the Konishi anomaly for (0,2) theories.Comment: 18 pages, LaTe
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