304 research outputs found
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
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
Quasinormal modes prefer supersymmetry ?
One ambiguity in loop quantum gravity is the appearance of a free parameter
which is called Immirzi parameter. Recently Dreyer has argued that this
parameter may be fixed by considering the quasinormal mode spectrum of black
holes, while at the price of changing the gauge group to SO(3) rather than the
original one SU(2). Physically such a replacement is not quite natural or
desirable. In this paper we study the relationship between the black hole
entropy and the quasi normal mode spectrum in the loop quantization of N=1
supergravity. We find that a single value of the Immirzi parameter agrees with
the semiclassical expectations as well. But in this case the lowest
supersymmetric representation dominates, fitting well with the result based on
statistical consideration. This suggests that, so long as fermions are included
in the theory, supersymemtry may be favored for the consistency of the low
energy limit of loop quantum gravity.Comment: 3 page
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
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
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
Anti-self-dual Maxwell solutions on hyperk\"ahler manifold and N=2 supersymmetric Ashtekar gravity
Anti-self-dual (ASD) Maxwell solutions on 4-dimensional hyperk\"ahler
manifolds are constructed. The N=2 supersymmetric half-flat equations are
derived in the context of the Ashtekar formulation of N=2 supergravity. These
equations show that the ASD Maxwell solutions have a direct connection with the
solutions of the reduced N=2 supersymmetric ASD Yang-Mills equations with a
special choice of gauge group. Two examples of the Maxwell solutions are
presented.Comment: 9 page
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
- …