24,159 research outputs found
Bethe-Salpeter study of radially excited vector quarkonia
We solve the Bethe-Salpeter equation (BSE) for a system of a heavy
quark-antiquark pair interacting with a Poincare invariant generalization of
screened linear confining potential. In order to get reliable description the
Lorentz scalar confining interaction is complemented by the effective one gluon
exchange. Within presented model we reasonably reproduce all known radial
excitations of the vector charmonia. We have found that is the only
charmonium left bellow naive quark-antiquark threshold , while the all
excited states are situated above this threshold. We develop a method which is
enable to provide solution of full four dimensional BSE for the all excited
states. We discuss the consequences of the use of the free propagators for
calculation of excited states above the threshold. The Bethe-Salpeter string
breaking scale appears to be relatively larger then the one
defined in various potential models .Comment: typos and grammar correcte
Exclusive Lambda_b -> Lambda l^+ l^- decay in two Higgs doublet model
Rare Lambda_b -> Lambda l^+ l^- decay is investigated in framework of general
two Higgs doublet model, in which a new source of CP violation exists (model
III). The polarization parameter, CP asymmetry and decay width are calculated.
It is shown that CP asymmetry is a very sensitive tool for establishing model
III.Comment: 16 pages, 3 figures, LaTeX formatte
The meson annihilation to leptons and inclusive light hadrons
The annihilation of the meson to leptons and inclusive light hadrons is
analyzed in the framework of nonrelativistic QCD (NRQCD) factorization. We find
that the decay mode, which escapes from the helicity suppression, contributes a
sizable fraction width. According to the analysis, the branching ratio due to
the contribution from the color-singlet component of the meson can be of
order (10^{-2}). We also estimate the contributions from the color-octet
components. With the velocity scaling rule of NRQCD, we find that the
color-octet contributions are sizable too, especially, in certain phase space
of the annihilation they are greater than (or comparative to) the color-singlet
component. A few observables relevant to the spectrum of charged lepton are
suggested, that may be used as measurements on the color-octet and
color-singlet components in the future experiments. A typical long
distance contribution in the annihilation is estimated too.Comment: 26 pages, 5 figures (6 eps-files), submitted to Phys. Rev.
The effects of compressible and incompressible states on the FIR-absorption of quantum wires and dots in a magnetic field
We investigate the effects of compressible and incompressible states on the
FIR-absorption of quantum wires and dots in a homogeneous perpendicular
magnetic field. The electron-electron interaction is treated in the Hartree
approximation at a finite low temperature. The calculated dispersion of the
collective excitations reproduces several experimental results.Comment: To be published by Physica Scripta in the proceedings of the 17NSM. 6
pages in LaTeX + 6 postscript figure
Lepton flavor violation in SUSY left-right symmetric theories
The seesaw mechanism is the most popular explanation for the smallness of
neutrino masses. However, its high scale makes direct tests impossible and only
indirect signals at low energies are reachable for collider experiments. One of
these indirect links with the high scale is lepton flavor violation (LFV). We
discuss LFV decays of sleptons in the context of a SUSY left-right symmetric
model that naturally incorporates the seesaw mechanism. This non-minimal
embedding of the seesaw leads to observable LFV effects in the right-handed
sleptons sector, contrary to minimal models where these are found to be totally
negligible. Therefore, LFV observables can be used as a powerful tool to study
physics right below the GUT scale.Comment: To appear in the proceedings of PASCOS 2010, the 16th International
Symposium on Particles, Strings and Cosmology, Valencia, Spai
Exploring the Atmosphere of Neoproterozoic Earth: The Effect of O on Haze Formation and Composition
Previous studies of haze formation in the atmosphere of the Early Earth have
focused on N/CO/CH atmospheres. Here, we experimentally
investigate the effect of O on the formation and composition of aerosols
to improve our understanding of haze formation on the Neoproterozoic Earth. We
obtained in situ size, particle density, and composition measurements of
aerosol particles produced from N/CO/CH/O gas mixtures
subjected to FUV radiation (115-400 nm) for a range of initial
CO/CH/O mixing ratios (O ranging from 2 ppm to 0.2\%).
At the lowest O concentration (2 ppm), the addition increased particle
production for all but one gas mixture. At higher oxygen concentrations (20 ppm
and greater) particles are still produced, but the addition of O
decreases the production rate. Both the particle size and number density
decrease with increasing O, indicating that O affects particle
nucleation and growth. The particle density increases with increasing O.
The addition of CO and O not only increases the amount of oxygen in
the aerosol, but it also increases the degree of nitrogen incorporation. In
particular, the addition of O results in the formation of nitrate bearing
molecules. The fact that the presence of oxygen bearing molecules increases the
efficiency of nitrogen fixation has implications for the role of haze as a
source of molecules required for the origin and evolution of life. The
composition changes also likely affect the absorption and scattering behavior
of these particles but optical properties measurements are required to fully
understand the implications for the effect on the planetary radiative energy
balance and climate.Comment: 15 pages, 3 tables, 8 figures, accepted in Astrophysical Journa
Charges On Jet Drops Produced By Bursting Bubbles
The sizes and charges of jet drops produced by bursting air bubbles are examined experimentally. The variation in charge for bubble lifetimes of up to 200 sec in NaCl and KCl solutions is reported. Jet drops refer to drops produced by a jet rising from a cavity left in a liquid surface by a bursting bubble; bubble lifetime is the interval during which a bubble is in motion between generation and rupture. With other variables held constant, drop charge shows a characteristic variation of a rise to a maximum followed by a decrease to an asymptotic value, as bubble lifetime is increased. The influences of various parameters on the characteristic behavior are discussed. © 1971
Simulation and analysis of in vitro DNA evolution
We study theoretically the in vitro evolution of a DNA sequence by binding to
a transcription factor. Using a simple model of protein-DNA binding and
available binding constants for the Mnt protein, we perform large-scale,
realistic simulations of evolution starting from a single DNA sequence. We
identify different parameter regimes characterized by distinct evolutionary
behaviors. For each regime we find analytical estimates which agree well with
simulation results. For small population sizes, the DNA evolutional path is a
random walk on a smooth landscape. While for large population sizes, the
evolution dynamics can be well described by a mean-field theory. We also study
how the details of the DNA-protein interaction affect the evolution.Comment: 11 pages, 11 figures. Submitted to PNA
SNX 9 interacts with dynamin 2 and N-wasp to regulate focal adhesion disassembly and cell migration
The turnover of focal adhesions is essential for normal cell migration and tumor
invasion, but the underlying mechanisms are poorly understood. We have previously shown that the
disassembly of focal adhesions occurs by endocytosis of activated integrins from adhesion sites (1). We
have further identified new components that mediate integrin endocytosis. Here, we provide the initial
characterization of one of these components, sorting nexin 9 (Snx9), an endocytic adaptor protein not
previously implicated in cell adhesion and migration
Neutrino Masses and A TeV Scale Seesaw Mechanism
A simple extension of the Standard Model providing TeV scale seesaw mechanism
is presented. Beside the Standard Model particles and right-handed Majorana
neutrinos, the model contains a singly charged scalar, an extra Higgs doublet
and three vector like singly charged fermions. In our model, Dirac neutrino
mass matrix raises only at the loop level. Small but non-zero Majorana neutrino
masses come from integrating out heavy Majorana neutrinos, which can be at the
TeV scale. The phenomenologies of the model are investigated, including scalar
mass spectrum, neutrino masses and mixings, lepton flavor violations, heavy
neutrino magnetic moments as well as possible collider signatures of the model
at the LHC.Comment: 13 pages, 4 figures. references adde
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