519 research outputs found
1/N Expansion for Exotic Baryons
The 1/N expansion for exotic baryons is developed, and applied to the masses,
meson couplings and decay widths. Masses and widths of the 27 and 35 pentaquark
states in the same tower as the Theta+ are related by spin-flavor symmetry. The
27 and 35 states can decay within the pentaquark tower, as well as to normal
baryons, and so have larger decay widths than the lightest pentaquark Theta.
The 1/N expansion also is applied to baryon exotics containing a single heavy
antiquark. The decay widths of heavy pentaquarks via pion emission, and to
normal baryons plus heavy D^(*),B^(*) mesons are studied, and relations
following from large-N spin-flavor symmetry and from heavy quark symmetry are
derived.Comment: Major additions: plots of widths and branching ratios, discussion of
strong decays of heavy pentaquarks, including consequences of heavy quark
symmetr
Spin-Flavor Structure of Large N Baryons
The spin-flavor structure of large N baryons is described in the 1/N
expansion of QCD using quark operators. The complete set of quark operator
identities is obtained, and used to derive an operator reduction rule which
simplifies the 1/N expansion. The operator reduction rule is applied to the
axial currents, masses, magnetic moments and hyperon non-leptonic decay
amplitudes in the limit, to first order in breaking, and
without assuming symmetry. The connection between the Skyrme and quark
representations is discussed. An explicit formula is given for the quark model
operators in terms of the Skyrme model operators to all orders in for
the two flavor case.Comment: 36 pages, 2 eps figures, uses revte
Bosonic Operator Methods for the Quark Model
Quark model matrix elements can be computed using bosonic operators and the
holomorphic representation for the harmonic oscillator. The technique is
illustrated for normal and exotic baryons for an arbitrary number of colors.
The computations are much simpler than those using conventional quark model
wavefunctions
Multiple roles for UV RESISTANCE LOCUS8 in regulating gene expression and metabolite accumulation in arabidopsis under solar ultraviolet radiation
Photomorphogenic responses triggered by low fluence rates of ultraviolet B radiation (UV-B; 280–315 nm) are mediated by the UV-B photoreceptor UV RESISTANCE LOCUS8 (UVR8). Beyond our understanding of the molecular mechanisms of UV-B perception by UVR8, there is still limited information on how the UVR8 pathway functions under natural sunlight. Here, wild-type Arabidopsis (Arabidopsis thaliana) and the uvr8-2 mutant were used in an experiment outdoors where UV-A (315–400 nm) and UV-B irradiances were attenuated using plastic films. Gene expression, PYRIDOXINE BIOSYNTHESIS1 (PDX1) accumulation, and leaf metabolite signatures were analyzed. The results show that UVR8 is required for transcript accumulation of genes involved in UV protection, oxidative stress, hormone signal transduction, and defense against herbivores under solar UV. Under natural UV-A irradiance, UVR8 is likely to interact with UV-A/blue light signaling pathways to moderate UV-B-driven transcript and PDX1 accumulation. UVR8 both positively and negatively affects UV-A-regulated gene expression and metabolite accumulation but is required for the UV-B induction of phenolics. Moreover, UVR8-dependent UV-B acclimation during the early stages of plant development may enhance normal growth under long-term exposure to solar UV
The Chiral Soliton Model for Arbitrary Colors and Flavors
The quantum numbers of the chiral soliton are derived for an arbitrary number
of colors and flavors
Chiral structure of nucleon gravitational form factors
We study the low momentum behavior of nucleon gravitational form factors in
the framework of the heavy baryon chiral perturbation theory. At zero recoil
they determine the momentum and spin apportion between nucleon constituents.
Our result provides an insight into the response of the nucleon's pion cloud to
an external weak gravitational field and establishes a theoretical framework
for extrapolation of experimental and lattice data on the nucleon form factors
to zero momentum transfer. We also discuss form factors corresponding to
higher-rank tensor currents related to the moments of generalized parton
distributions.Comment: 10 pages, LaTeX, 1 figur
Unified description of long-time tails and long-range correlation functions for sheared granular liquids
Unified description on the long-time tail of velocity autocorrelation
function and the long-range correlation for the equal-time spatial correlation
functions is developed based on the generalized fluctuating hydrodynamics. The
cross-over of the long-time tail from to is predicted
independent of the density, and the equal-time spatial density correlation
function and the equal-time spatial velocity correlation function respectively
satisfy and for large limit.Comment: 10 pages. to be published in Euro. Phys. J.
On chiral corrections to nucleon GPD
Within the pion-nucleon chiral perturbation theory we derive the leading
chiral correction to the nucleon GPD at . We discuss the difficulties of
consideration of nonlocal light-cone operators within the theory with a heavy
particle and the methods to solve the difficulties. The consideration of the
chiral corrections directly for nonlocal operators allows to resolve the
ambiguity of the inverse Mellin transformation. In particular, we show that the
mixing between axial and vector GPDs are of order , which is two
orders of magnitude less that it follows from the Mellin moments calculation.Comment: 17 pages, 1 figure; minor corrections in the tex
The distribution of transit durations for Kepler planet candidates and implications for their orbital eccentricities
‘In these times, during the rise in the popularity of institutional repositories, the Society does not forbid authors from depositing their work in such repositories. However, the AAS regards the deposit of scholarly work in such repositories to be a decision of the individual scholar, as long as the individual's actions respect the diligence of the journals and their reviewers.’ Original article can be found at : http://iopscience.iop.org/ Copyright American Astronomical SocietyDoppler planet searches have discovered that giant planets follow orbits with a wide range of orbital eccentricities, revolutionizing theories of planet formation. The discovery of hundreds of exoplanet candidates by NASA's Kepler mission enables astronomers to characterize the eccentricity distribution of small exoplanets. Measuring the eccentricity of individual planets is only practical in favorable cases that are amenable to complementary techniques (e.g., radial velocities, transit timing variations, occultation photometry). Yet even in the absence of individual eccentricities, it is possible to study the distribution of eccentricities based on the distribution of transit durations (relative to the maximum transit duration for a circular orbit). We analyze the transit duration distribution of Kepler planet candidates. We find that for host stars with T > 5100 K we cannot invert this to infer the eccentricity distribution at this time due to uncertainties and possible systematics in the host star densities. With this limitation in mind, we compare the observed transit duration distribution with models to rule out extreme distributions. If we assume a Rayleigh eccentricity distribution for Kepler planet candidates, then we find best fits with a mean eccentricity of 0.1-0.25 for host stars with T ≤ 5100 K. We compare the transit duration distribution for different subsets of Kepler planet candidates and discuss tentative trends with planetary radius and multiplicity. High-precision spectroscopic follow-up observations for a large sample of host stars will be required to confirm which trends are real and which are the results of systematic errors in stellar radii. Finally, we identify planet candidates that must be eccentric or have a significantly underestimated stellar radius.Peer reviewedFinal Accepted Versio
Hyperbolic chaos in self-oscillating systems based on mechanical triple linkage: Testing absence of tangencies of stable and unstable manifolds for phase trajectories
Dynamical equations are formulated and a numerical study is provided for
self-oscillatory model systems based on the triple linkage hinge mechanism of
Thurston -- Weeks -- Hunt -- MacKay. We consider systems with holonomic
mechanical constraint of three rotators as well as systems, where three
rotators interact by potential forces. We present and discuss some quantitative
characteristics of the chaotic regimes (Lyapunov exponents, power spectrum).
Chaotic dynamics of the models we consider are associated with hyperbolic
attractors, at least, at relatively small supercriticality of the
self-oscillating modes; that follows from numerical analysis of the
distribution for angles of intersection of stable and unstable manifolds of
phase trajectories on the attractors. In systems based on rotators with
interacting potential the hyperbolicity is violated starting from a certain
level of excitation.Comment: 30 pages, 18 figure
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