242 research outputs found
Theory Summary and Future Directions
Summary talk at the Lepton-Photon Symposium, Cornell University, Aug. 10-15,
1993.Comment: (Talk presented at the Lepton-Photon Symposium, Cornell University,
Aug. 10-15, 1993.) 19 page
Radiative Leptonic Decays
We analyze the radiative leptonic decay mode:
() using a QCD-inspired constituent quark model. The prediction:
makes this channel
experimentally promising in view of the large number of mesons which are
expected to be produced at the future hadron facilities.Comment: LaTex, 12 pages, 2 figures. A discussion on gauge invariance added.
Numerical results update
Study of Radiative Leptonic D Meson Decays
We study the radiative leptonic meson decays of D^+_{(s)}\to
\l^+\nu_{\l}\gamma (\l=e,\mu,\tau), and D^0\to
\l^+\l^-\gamma () within the light front quark model. In the standard
model, we find that the decay branching ratios of , and
are (), (), and
(), and that of D^0\to\l^+\l^-\gamma (\l=e,\mu) and
are and ,
respectively.Comment: 23 pages, 6 Figures, LaTex file, a reference added, to be published
in Mod. Phys. Lett.
Photoproduction and Radiative Decay of Spin 1/2 and 3/2 Pentaquarks
We study photoproduction and radiative decays of pentauqarks paying
particular attention to the differences between spin-1/2 and spin-3/2, positive
and negative parities of pentaquarks. Detailed study of these processes can not
only give crucial information about the spin, but also the parity of
pentaquarks.Comment: 14 pages, 7 figure
in the Light Front Model
We study the CP conserving and violating contributions to the decay of
\knng in the standard model. In our analysis, we use the form factors for
transitions calculated directly in the entire physical range of
momentum transfer within the light front model. We find that the branching
ratios for the CP conserving and violating parts are about
and , respectively.Comment: 11 pages, 2 Figures, LaTex file, accepted for Phys. Rev.
A Unified Approach to Distance-Two Colouring of Graphs on Surfaces
In this paper we introduce the notion of -colouring of a graph :
For given subsets of neighbours of , for every , this
is a proper colouring of the vertices of such that, in addition, vertices
that appear together in some receive different colours. This
concept generalises the notion of colouring the square of graphs and of cyclic
colouring of graphs embedded in a surface. We prove a general result for graphs
embeddable in a fixed surface, which implies asymptotic versions of Wegner's
and Borodin's Conjecture on the planar version of these two colourings. Using a
recent approach of Havet et al., we reduce the problem to edge-colouring of
multigraphs, and then use Kahn's result that the list chromatic index is close
to the fractional chromatic index.
Our results are based on a strong structural lemma for graphs embeddable in a
fixed surface, which also implies that the size of a clique in the square of a
graph of maximum degree embeddable in some fixed surface is at most
plus a constant.Comment: 36 page
Nanoscale waveguiding methods
While 32 nm lithography technology is on the horizon for integrated circuit (IC) fabrication, matching the pace for miniaturization with optics has been hampered by the diffraction limit. However, development of nanoscale components and guiding methods is burgeoning through advances in fabrication techniques and materials processing. As waveguiding presents the fundamental issue and cornerstone for ultra-high density photonic ICs, we examine the current state of methods in the field. Namely, plasmonic, metal slot and negative dielectric based waveguides as well as a few sub-micrometer techniques such as nanoribbons, high-index contrast and photonic crystals waveguides are investigated in terms of construction, transmission, and limitations. Furthermore, we discuss in detail quantum dot (QD) arrays as a gain-enabled and flexible means to transmit energy through straight paths and sharp bends. Modeling, fabrication and test results are provided and show that the QD waveguide may be effective as an alternate means to transfer light on sub-diffraction dimensions
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