333 research outputs found
Orbital Evolution of Planets around Intermediate-Mass Giants
Around low- and intermediate-mass (1.5-3 M_sun) red giants, no planets have
been found inside 0.6 AU. Such a paucity is not seen in the case of 1 M_sun
main sequence stars. In this study, we examine the possibility that
short-period planets were engulfed by their host star evolving off the main
sequence. To do so, we have simulated the orbital evolution of planets,
including the effects of stellar tide and mass loss, to determine the critical
semimajor axis, a_crit, beyond which planets survive the RGB expansion of their
host star. We have found that a_crit changes drastically around 2 M_sun: In the
lower-mass range, a_crit is more than 1 AU, while a_crit is as small as about
0.2 AU in the higher-mass range. Comparison with measured semimajor axes of
known planets suggests that there is a lack of planets that only planet
engulfment never accounts for in the higher-mass range. Whether the lack is
real affects our understanding of planet formation. Therefore, increasing the
number of planet samples around evolved intermediate-mass stars is quite
meaningful to confirm robustness of the lack of planets.Comment: 4 pages, 3 figures, Part of PlanetsbeyondMS/2010 proceedings
http://arxiv.org/html/1011.660
On the Formation Age of the First Planetary System
Recently, it has been observed the extreme metal-poor stars in the Galactic
halo, which must be formed just after Pop III objects. On the other hand, the
first gas clouds of mass are supposed to be formed at 10, 20, and 30 for the , and , where the
density perturbations are assumed of the standard CDM cosmology. If we
could apply this gaussian distribution to the extreme small probability, the
gas clouds would be formed at 40, 60, and 80 for the ,
, and . The first gas clouds within our galaxy must be formed
around . Even if the gas cloud is metal poor, there is a lot of
possibility to form the planets around such stars. The first planetary systems
could be formed within years after the Big Bang in the
universe. Even in our galaxies, it could be formed within
years. It is interesting to wait the observations of planets around metal-poor
stars. For the panspermia theory, the origin of life could be expected in such
systems.Comment: 5 pages,Proceedings IAU Symposium No. 249, 2007, Exoplanets:Y-S. Sun,
S. Ferraz-Mello and J.-L, Zhou, eds. (p325
Construction of N = 2 Chiral Supergravity Compatible with the Reality Condition
We construct N = 2 chiral supergravity (SUGRA) which leads to Ashtekar's
canonical formulation. The supersymmetry (SUSY) transformation parameters are
not constrained at all and auxiliary fields are not required in contrast with
the method of the two-form gravity. We also show that our formulation is
compatible with the reality condition, and that its real section is reduced to
the usual N = 2 SUGRA up to an imaginary boundary term.Comment: 16 pages, late
Light-cone Gauge NSR Strings in Noncritical Dimensions II -- Ramond Sector
Light-cone gauge superstring theory in noncritical dimensions corresponds to
a worldsheet theory with nonstandard longitudinal part in the conformal gauge.
The longitudinal part of the worldsheet theory is a superconformal field theory
called X^{\pm} CFT. We show that the X^{\pm} CFT combined with the
super-reparametrization ghost system can be described by free variables. It is
possible to express the correlation functions in terms of these free variables.
Bosonizing the free variables, we construct the spin fields and BRST invariant
vertex operators for the Ramond sector in the conformal gauge formulation. By
using these vertex operators, we can rewrite the tree amplitudes of the
noncritical light-cone gauge string field theory, with external lines in the
(R,R) sector as well as those in the (NS,NS) sector, in a BRST invariant way.Comment: 33 pages; v2: minor modification
N = 3 chiral supergravity compatible with the reality condition and higher N chiral Lagrangian density
We obtain N = 3 chiral supergravity (SUGRA) compatible with the reality
condition by applying the prescription of constructing the chiral Lagrangian
density from the usual SUGRA. The chiral Lagrangian density in
first-order form, which leads to the Ashtekar's canonical formulation, is
determined so that it reproduces the second-order Lagrangian density of the
usual SUGRA especially by adding appropriate four-fermion contact terms. We
show that the four-fermion contact terms added in the first-order chiral
Lagrangian density are the non-minimal terms required from the invariance under
first-order supersymmetry transformations. We also discuss the case of higher N
theories, especially for N = 4 and N = 8.Comment: 20 pages, Latex, some more discussions and new references added, some
typos corrected, accepted for publication in Physical Review
Supersymmetry algebra in N = 1 chiral supergravity
We consider the supersymmetry (SUSY) transformations in the chiral Lagrangian
for supergravity (SUGRA) with the complex tetrad following the method
used in the usual SUGRA, and present the explicit form of the SUSY
trasformations in the first-order form. The SUSY transformations are generated
by two independent Majorana spinor parameters, which are apparently different
from the constrained parameters employed in the method of the 2-form gravity.
We also calculate the commutator algebra of the SUSY transformations on-shell.Comment: 10 pages, late
Minimal Off-Shell Version of N = 1 Chiral Supergravity
We construct the minimal off-shell formulation of N = 1 chiral supergravity
(SUGRA) introducing a complex antisymmetric tensor field and a
complex axial-vector field as auxiliary fields. The resulting algebra
of the right- and left-handed supersymmetry (SUSY) transformations closes off
shell and generates chiral gauge transforamtions and vector gauge
transformations in addition to the transformations which appear in the case
without auxiliary fields.Comment: 9 pages, late
Multiphoton Transitions in a Spin System Driven by Strong Bichromatic Field
EPR transient nutation spectroscopy is used to measure the effective field
(Rabi frequency) for multiphoton transitions in a two-level spin system
bichromatically driven by a transverse microwave (MW) field and a longitudinal
radio-frequency (RF) field. The behavior of the effective field amplitude is
examined in the case of a relatively strong MW field, when the derivation of
the effective Hamiltonian cannot be reduced to first-order perturbation theory
in w_{1} / w_{rf} (w_{1} is the microwave Rabi frequency, w_{rf} is the RF
frequency). Experimental results are consistently interpreted by taking into
account the contributions of second and third order in w_{1} / w_{rf} evaluated
by Krylov-Bogolyubov-Mitropolsky averaging. In the case of inhomogeneously
broadened EPR line, the third-order correction modifies the nutation frequency,
while the second-order correction gives rise to a change in the nutation
amplitude due to a Bloch-Siegert shift.Comment: 7 pages, 6 figure
Canonical formulation of N = 2 supergravity in terms of the Ashtekar variable
We reconstruct the Ashtekar's canonical formulation of N = 2 supergravity
(SUGRA) starting from the N = 2 chiral Lagrangian derived by closely following
the method employed in the usual SUGRA. In order to get the full graded algebra
of the Gauss, U(1) gauge and right-handed supersymmetry (SUSY) constraints, we
extend the internal, global O(2) invariance to local one by introducing a
cosmological constant to the chiral Lagrangian. The resultant Lagrangian does
not contain any auxiliary fields in contrast with the 2-form SUGRA and the SUSY
transformation parameters are not constrained at all. We derive the canonical
formulation of the N = 2 theory in such a manner as the relation with the usual
SUGRA be explicit at least in classical level, and show that the algebra of the
Gauss, U(1) gauge and right-handed SUSY constraints form the graded algebra,
G^2SU(2)(Osp(2,2)). Furthermore, we introduce the graded variables associated
with the G^2SU(2)(Osp(2,2)) algebra and we rewrite the canonical constraints in
a simple form in terms of these variables. We quantize the theory in the
graded-connection representation and discuss the solutions of quantum
constraints.Comment: 19 pages, Latex, corrected some typos and added a referenc
Insights on the Sun birth environment in the context of star-cluster formation in hub-filament systems
Cylindrical molecular filaments are observed to be the main sites of Sun-like
star formation, while massive stars form in dense hubs, at the junction of
multiple filaments. The role of hub-filament configurations has not been
discussed yet in relation to the birth environment of the solar system and to
infer the origin of isotopic ratios of Short-Lived Radionuclides (SLR, such as
Al) of Calcium-Aluminum-rich Inclusions (CAIs) observed in meteorites.
In this work, we present simple analytical estimates of the impact of stellar
feedback on the young solar system forming along a filament of a hub-filament
system. We find that the host filament can shield the young solar system from
the stellar feedback, both during the formation and evolution of stars (stellar
outflow, wind, and radiation) and at the end of their life (supernovae). We
show that the young solar system formed along a dense filament can be enriched
with supernova ejecta (e.g., Al) during the formation timescale of CAIs.
We also propose that the streamers recently observed around protostars may be
channeling the SLR-rich material onto the young solar system. We conclude that
considering hub-filament configurations as the birth environment of the Sun is
important when deriving theoretical models explaining the observed properties
of the solar system.Comment: Accepted for publication in The Astrophysical Journal Letter
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