9,314 research outputs found
Low-lying even parity meson resonances and spin-flavor symmetry
A study is presented of the wave meson-meson interactions involving
members of the nonet and of the octet. The starting point is an
SU(6) spin-flavor extension of the SU(3) flavor Weinberg-Tomozawa Lagrangian.
SU(6) symmetry breaking terms are then included to account for the physical
meson masses and decay constants, while preserving partial conservation of the
axial current in the light pseudoscalar sector. Next, the matrix amplitudes
are obtained by solving the Bethe Salpeter equation in coupled-channel with the
kernel built from the above interactions. The poles found on the first and
second Riemann sheets of the amplitudes are identified with their possible
Particle Data Group (PDG) counterparts. It is shown that most of the low-lying
even parity PDG meson resonances, specially in the and sectors,
can be classified according to multiplets of the spin-flavor symmetry group
SU(6). The , and some resonances cannot be
accommodated within this SU(6) scheme and thus they would be clear candidates
to be glueballs or hybrids. Finally, we predict the existence of five exotic
resonances ( and/or ) with masses in the range 1.4--1.6 GeV,
which would complete the , , and multiplets of
SU(3)SU(2).Comment: 43 pages, 2 figures, 61 tables. Improved discussion of Section II. To
appear in Physical Review
Study of Long Distance Contributions to
We calculate long distance contributions to $K\to\pi\nu\bar{\nu}\,,\
\pi\pi\nu\bar{\nu}\pi\pi\pi\nu\bar{\nu}K\to \pi\nu\bar{\nu}K\to \pi\pi\nu\bar{\nu}$ in the chiral logarithmic
approximation are at least seven orders of magnitude suppressed relative to
those from the short distance parts. The long distance effects in this class of
decays are therefore negligible.Comment: 13 pages, LaTeX fil
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GENOME WIDE DNA METHYLATION PROFILING IS PREDICTIVE OF OUTCOME IN JUVENILE MYELOMONOCYTIC LEUKEMIA
The CP-violating asymmetry in \eta\to\pi^+ \pi^- e^+e^-
We study the CP-violating asymmetry {\cal A}_{\rm CP}, which arises, in
\eta\to\pi^+\pi^- e^+e^-, from the angular correlation of the e^+ e^- and
\pi^+\pi^- planes due to the interference between the magnetic and electric
decay amplitudes. With the phenomenologically determined magnetic amplitude and
branching ratio as input, the asymmetry, induced by the electric bremsstrahlung
amplitude through the CP-violating decay \eta\to\pi^+\pi^-, and by an
unconventional tensor type operator, has been estimated respectively. The upper
bound of {\cal A}_{\rm CP} from the former is about 10^{-3}, and the asymmetry
from the latter might be up to O(10^{-2}). One can therefore expect that this
CP asymmetry would be an interesting CP-violating observable for the future
precise measurements in the \eta factories.Comment: LaTeX, 6 pages. One reference corrected, and some new references
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Design of multihundredwatt DIPS for robotic space missions
Design of a dynamic isotope power system (DIPS) general purpose heat source (GPHS) and small free piston Stirling engine (FPSE) is being pursued as a potential lower cost alternative to radioisotope thermoelectric generators (RTG's). The design is targeted at the power needs of future unmanned deep space and planetary surface exploration missions ranging from scientific probes to SEI precursor missions. These are multihundredwatt missions. The incentive for any dynamic system is that it can save fuel which reduces cost and radiological hazard. However, unlike a conventional DIPS based on turbomachinery converions, the small Stirling DIPS can be advantageously scaled to multihundred watt unit size while preserving size and weight competitiveness with RTG's. Stirling conversion extends the range where dynamic systems are competitive to hundreds of watts (a power range not previously considered for dynamic systems). The challenge of course is to demonstrate reliability similar to RTG experience. Since the competative potential of FPSE as an isotope converter was first identified, work has focused on the feasibility of directly integrating GPHS with the Stirling heater head. Extensive thermal modeling of various radiatively coupled heat source/heater head geometries were performed using data furnished by the developers of FPSE and GPHS. The analysis indicates that, for the 1050 K heater head configurations considered, GPHS fuel clad temperatures remain within safe operating limits under all conditions including shutdown of one engine. Based on these results, preliminary characterizations of multihundred watt units were established
Generation of spatially-separated spin entanglement in a triple quantum dot system
We propose a novel method for the creation of spatially-separated spin
entanglement by means of adiabatic passage of an external gate voltage in a
triple quantum dot system.Comment: 10 pages, 6 figure
Long distance contribution to decay and terms in CHPT
The long distance contribution to is
calculated using chiral perturbation theory. The leading contribution comes
from tree terms. The branching ratio of the long distance
contribution is found to be of order smaller than the short distance
contributions.Comment: 12 pages, 1 figure (available upon request
Saccades to a remembered location elicit spatially specific activation in human retinotopic visual cortex
The possible impact upon human visual cortex from saccades to remembered target locations was investigated using functional magnetic resonance imaging (fMRI). A specific location in the upper-right or upper-left visual quadrant served as the saccadic target. After a delay of 2,400 msec, an auditory signal indicated whether to execute a saccade to that location (go trial) or to cancel the saccade and remain centrally fixated (no-go). Group fMRI analysis revealed activation specific to the remembered target location for executed saccades, in the contralateral lingual gyrus. No-go trials produced similar, albeit significantly reduced, effects. Individual retinotopic mapping confirmed that on go trials, quadrant-specific activations arose in those parts of ventral V1, V2, and V3 that coded the target location for the saccade, whereas on no-go trials, only the corresponding parts of V2 and V3 were significantly activated. These results indicate that a spatial-motor saccadic task (i.e., making an eye movement to a remembered location) is sufficient to activate retinotopic visual cortex spatially corresponding to the target location, and that this activation is also present (though reduced) when no saccade is executed. We discuss the implications of finding that saccades to remembered locations can affect early visual cortex, not just those structures conventionally associated with eye movements, in relation to recent ideas about attention, spatial working memory, and the notion that recently activated representations can be "refreshed" when needed
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