9,756 research outputs found
Isoscalar meson spectroscopy from lattice QCD
We extract to high statistical precision an excited spectrum of
single-particle isoscalar mesons using lattice QCD, including states of high
spin and, for the first time, light exotic JPC isoscalars. The use of a novel
quark field construction has enabled us to overcome the long-standing challenge
of efficiently including quark-annihilation contributions. Hidden-flavor mixing
angles are extracted and while most states are found to be close to ideally
flavor mixed, there are examples of large mixing in the pseudoscalar and axial
sectors in line with experiment. The exotic JPC isoscalar states appear at a
mass scale comparable to the exotic isovector states.Comment: 4 pages, 4 figure
Generation of two-photon EPR and Wstates
In this paper we present a scheme for generation of two-photon EPR and W
states in the cavity QED context. The scheme requires only one three-level
Rydberg atom and two or three cavities. The atom is sent to interact with
cavities previously prepared in vacuum states, via two-photon process. An
appropriate choice of the interaction times one obtains the mentioned state
with maximized fidelities. These specific times and the values of success
probability and fidelity are discussed.Comment: 4 pages, 5 figure
A New Era in High-energy Physics
In TeV-scale gravity, scattering of particles with center-of-mass energy of
the order of a few TeV can lead to the creation of nonperturbative, extended,
higher-dimensional gravitational objects: Branes. Neutral or charged, spinning
or spinless, Einsteinian or supersymmetric, low-energy branes could
dramatically change our picture of high-energy physics. Will we create branes
in future particle colliders, observe them from ultra high energy cosmic rays,
and discover them to be dark matter?Comment: 8 pages, 2 figures. Essay submitted on Mar 26, 2002 to the Gravity
Research Foundation. Awarded the third prize in the 2002 GRF competitio
Stochastic theory of spin-transfer oscillator linewidths
We present a stochastic theory of linewidths for magnetization oscillations
in spin-valve structures driven by spin-polarized currents. Starting from a
nonlinear oscillator model derived from spin-wave theory, we derive Langevin
equations for amplitude and phase fluctuations due to the presence of thermal
noise. We find that the spectral linewidths are inversely proportional to the
spin-wave intensities with a lower bound that is determined purely by
modulations in the oscillation frequencies. Reasonable quantitative agreement
with recent experimental results from spin-valve nanopillars is demonstrated.Comment: Submitted to Physical Review
Electroexcitation of the P33(1232), P11(1440), D13(1520), S11(1535) at Q^2=0.4 and 0.65(GeV/c)^2
Using two approaches: dispersion relations and isobar model, we have analyzed
recent high precision CLAS data on cross sections of \pi^0, \pi^+, and \eta
electroproduction on protons, and the longitudinally polarized electron beam
asymmetry for p(\vec{e},e'p)\pi^0 and p(\vec{e},e'n)\pi^+. The contributions of
the resonances P33(1232), P11(1440), D13(1520), S11(1535) to \pi
electroproduction and S11(1535) to \eta electroproduction are found. The
results obtained in the two approaches are in good agreement with each other.
There is also good agreement between amplitudes of the \gamma^* N \to S11(1535)
transition found in \pi and \eta electroproduction. For the first time accurate
results are obtained for the longitudinal amplitudes of the P11(1440),
D13(1520) and S11(1535) electroexcitation on protons.Comment: 9 pages, 9 figure
Effects of Noise on Ecological Invasion Processes: Bacteriophage-mediated Competition in Bacteria
Pathogen-mediated competition, through which an invasive species carrying and
transmitting a pathogen can be a superior competitor to a more vulnerable
resident species, is one of the principle driving forces influencing
biodiversity in nature. Using an experimental system of bacteriophage-mediated
competition in bacterial populations and a deterministic model, we have shown
in [Joo et al 2005] that the competitive advantage conferred by the phage
depends only on the relative phage pathology and is independent of the initial
phage concentration and other phage and host parameters such as the
infection-causing contact rate, the spontaneous and infection-induced lysis
rates, and the phage burst size. Here we investigate the effects of stochastic
fluctuations on bacterial invasion facilitated by bacteriophage, and examine
the validity of the deterministic approach. We use both numerical and
analytical methods of stochastic processes to identify the source of noise and
assess its magnitude. We show that the conclusions obtained from the
deterministic model are robust against stochastic fluctuations, yet deviations
become prominently large when the phage are more pathological to the invading
bacterial strain.Comment: 39 pages, 7 figure
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