6,764 research outputs found
Predicting the Configuration of Planetary System: KOI-152 Observed by Kepler
The recent Kepler discovery of KOI-152 reveals a system of three hot
super-Earth candidates that are in or near a 4:2:1 mean motion resonance. It is
unlikely that they formed in situ, the planets probably underwent orbital
migration during the formation and evolution process. The small semimajor axes
of the three planets suggest that migration stopped at the inner edge of the
primordial gas disk. In this paper we focus on the influence of migration
halting mechanisms, including migration "dead zones", and inner truncation by
the stellar magnetic field. We show that the stellar accretion rate, stellar
magnetic field and the speed of migration in the proto-planetary disk are the
main factors affecting the final configuration of KOI-152. Our simulations
suggest that three planets may be around a star with low star accretion rate or
with high magnetic field. On the other hand, slow type I migration, which
decreases to one tenth of the linear analysis results, favors forming the
configuration of KOI-152. Under such formation scenario, the planets in the
system are not massive enough to open gaps in the gas disk. The upper limit of
the planetary masses are estimated to be about , and ,
respectively. Our results are also indicative of the near Laplacian
configurations that are quite common in planetary systems.Comment: 11 pages, 8 figures, accepted for publication in Ap
Master Formula for Twist-3 Soft-Gluon-Pole Mechanism to Single Transverse-Spin Asymmetry
Perturbative QCD relates the single transverse-spin asymmetries (SSAs) for
hard processes at large transverse-momentum of produced particle to partonic
matrix elements that describe interference between scattering from a coherent
quark-gluon pair and from a single quark, generated through twist-3 quark-gluon
correlations inside a hadron. When the coherent gluon is soft at the gluonic
poles, its coupling to partonic subprocess can be systematically disentangled,
so that the relevant interfering amplitude can be derived entirely from the
Born diagrams for the scattering from a single quark. We establish a new
formula that represents the exact rules to derive the SSA due to soft-gluon
poles from the knowledge of the twist-2 cross section formula for unpolarized
processes. This single master formula is applicable to a range of processes
like Drell-Yan and direct-photon production, and semi-inclusive deep inelastic
scattering, and is also useful to manifest the gauge invariance of the results.Comment: 20 pages, 6 figures; [v2] a paragraph with new Eq. (30) added, minor
modifications, typos corrected; [v3] Erratum added, and minor change
Spin densities in the transverse plane and generalized transversity distributions
We show how generalized quark distributions in the nucleon describe the
density of polarized quarks in the impact parameter plane, both for
longitudinal and transverse polarization of the quark and the nucleon. This
density representation entails positivity bounds including chiral-odd
distributions, which tighten the known bounds in the chiral-even sector. Using
the quark equations of motion, we derive relations between the moments of
chiral-odd generalized parton distributions of twist two and twist three. We
exhibit the analogy between polarized quark distributions in impact parameter
space and transverse momentum dependent distribution functions.Comment: 23 pages, 6 eps-figure
Single Transverse Spin Asymmetry for Large-p_T Pion Production in Semi-Inclusive Deep Inelastic Scattering
We study the single spin asymmetry (SSA) for the pion production with large
transverse momentum p_T in semi-inclusive deep inelastic scattering
. We derive the twist-3 cross section formula for SSA,
focussing on the soft-gluon-pole contributions associated with the twist-3
distribution for the nucleon and with the twist-3 fragmentation function for
the pion. We present a simple estimate of the asymmetries due to each twist-3
effect from nucleon and pion, respectively, by fixing the overall strength of
the relevant nonperturbative quantities by the data on the SSA A_N in
collision.Comment: 19 pages in LaTex. Some discussions added. To appear in Nucl. Phys.
Photosynthetic recovery of desiccated intertidal seaweeds after rehydration
Intertidal seaweeds experience periodical desiccation and rehydration to different extents due to the tidal cycles and their vertical distributions. Their photosynthetic recovery process during the rehydration may show different patterns among the seaweeds from different zonations or depths at intertidal zone. In this study 12 species of seaweeds collected from the upper, middle, lower and sublittoral zones were examined. The relationship of the photosynthetic recovery to vertical distribution was assessed by comparing their patterns of photosynthetic and respiratory performances after rehydration following desiccation. Both the photosynthesis and dark respiration declined during emersion, showing certain degrees of recovery after re-immersion into seawater for most species, but the extents were markedly different from one species to the other. The species from upper intertidal zone after being rehydrated for 1 hour, following 2 hours of desiccation, achieved 100 % recovery of their initial physiological activity, while most of the lower or sublittoral species did not achieve full recovery. It is the ability to withstand desiccation stress (fast recovery during rehydration), but not that to avoid desiccation (water retaining ability) that determines the distribution of intertidal seaweeds. Such physiological behavior during rehydration after desiccation reflects the adaptive strategy of intertidal seaweeds against desiccation and their capability of primary production in the process of rehydration
Twist-3 Formalism for Single Transverse Spin Asymmetry Reexamined: Semi-Inclusive Deep Inelastic Scattering
We study the single spin asymmetry (SSA) for the pion production in
semi-inclusive deep inelastic scattering, , in the
framework of the collinear factorization. We derive the complete cross section
formula associated with the twist-3 quark-gluon correlation functions for the
transversely polarized nucleon, including all types of pole (hard-pole,
soft-fermion-pole and soft-gluon-pole) contributions which produce the strong
interaction phase necessary for SSA. We prove that the partonic hard part from
each pole contribution satisfies certain constraints from Ward identities for
color gauge invariance. We demonstrate that the use of these new constraints is
crucial to reorganize the collinear expansion of the Feynman diagrams into
manifestly gauge-invariant form so as to obtain the factorization formula for
the cross section in terms of a complete set of the twist-3 distributions
without any double counting. It also provides a simpler method for the actual
calculation. We also present a simple estimate of SSA based on our cross
section formula, using a model for the ``soft-gluon-pole function'' that
represents the relevant twist-3 quark-gluon correlation, and compare the
magnitude of the terms involving the derivative of the soft-gluon-pole function
with that of the ``non-derivative'' terms.Comment: 38 pages, 11 figures. Final version, to appear in Nucl. Phys.
Forming Habitable Planets around Dwarf Stars: Application to OGLE-06-109L
Dwarf stars are believed to have small protostar disk where planets may grow
up. During the planet formation stage, embryos undergoing type I migration are
expected to be stalled at inner edge of magnetic inactive disk (AU). This mechanism makes the location around a
sweet spot of forming planets. Especially, of dwarf stars with
masses is roughly inside the habitable zone of the system.
In this paper we study the formation of habitable planets due to this mechanism
with a model system OGLE-06-109L. It has a dwarf star with two
giant planets in 2.3 and 4.6 AU observed by microlensing. We model the embryos
undergoing type I migration in the gas disk with a constant disk accretion rate
(). Giant planets in outside orbits affect the formation of habitable
planets through secular perturbations at the early stage and secular resonance
at the later stage. We find that the existence and the masses of the habitable
planets in OGLE-06-10L system depend on both and the speed of type I
migration. If planets formed earlier so that is larger ( yr), terrestrial planet can not be survived unless the type I
migration rate is an order of magnitude less. If planets formed later so that
is smaller ( yr), single and high mass
terrestrial planets with high water contents () will be formed by
inward migration of outer planet cores. A slower speed migration will result in
several planets by collisions of embryos, thus their water contents are low
(). Mean motion resonances or apsidal resonances among planets may be
observed if multiple planets survived in the inner system.Comment: 10 pages, 9 figures, accepted by Ap
QCD Corrections to the nucleon's spin structure function
We investigate the renormalization of the twist-3 operators which are
relevant for the spin-dependent structure function . We derive
the anomalous dimension for the non-singlet part by calculating the off-shell
Green's functions of the twist-3 operators including the operators which are
proportional to the equation of motion.Comment: 10 pages, LaTeX, 1 Postscript figur
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