7,581 research outputs found
The Peak Brightness and Spatial Distribution of AGB Stars Near the Nucleus of M32
The bright stellar content near the center of the Local Group elliptical
galaxy M32 is investigated with 0.12 arcsec FWHM H and K images obtained with
the Gemini Mauna Kea telescope. Stars with K = 15.5, which are likely evolving
near the tip of the asymptotic giant branch (AGB), are resolved to within 2
arcsec of the nucleus, and it is concluded that the peak stellar brightness
near the center of M32 is similar to that in the outer regions of the galaxy.
Moreover, the projected density of bright AGB stars follows the visible light
profile to within 2 arcsec of the nucleus, indicating that the brightest stars
are well mixed throughout the galaxy. Thus, there is no evidence for an age
gradient, and the radial variations in spectroscopic indices and ultraviolet
colors that have been detected previously must be due to metallicity and/or
some other parameter. We suggest that either the bright AGB stars formed as
part of a highly uniform and coherent galaxy-wide episode of star formation, or
they originated in a separate system that merged with M32.Comment: 9 pages of text, 3 figures. ApJ (Letters) in pres
Fermion Masses and Mixing and CP-Violation in SO(10) Models with Family Symmetries
Several ideas for solving the problem of fermion mass hierarchy and mixing
and specific supersymmetric models that realize it are reviewed. In particular,
we discuss many models based on SO(10) in four dimensions combined with a
family symmetry to accommodate fermion mass hierarchy and mixing, including the
case of neutrinos. These models are compared and various tests that can be used
to distinguish these models are suggested. We also include a discussion of a
few SO(10) models in higher space-time dimensions.Comment: 66 pages; 5 figures; Submitted to International Journal of Modern
Physics A; v2: a few references added; some changes in tex
Quasiparticles in the Pseudogap Phase of Underdoped Cuprate
Recent angle resolved photoemission \cite{yang-nature-08} and scanning
tunneling microscopy \cite{kohsaka-nature-08} measurements on underdoped
cuprates have yielded new spectroscopic information on quasiparticles in the
pseudogap phase. New features of the normal state such as particle-hole
asymmetry, maxima in the energy dispersion and accompanying drops in the
spectral weight of quasiparticles agree with the ansatz of Yang \textit{et al.}
for the single particle propagator in the pseudogap phase. The coherent
quasiparticle dispersion and reduced asymmetry in the tunneling density of
states in the superconducting state can also be described by this propagator.Comment: updated version, 6 pages, 7 figures, 1 table, EPL 86 (2009) 37002
(https://www.epletters.net
The lack of carbon stars in the Galactic bulge
In order to explain the lack of carbon stars in the Galactic bulge, we have
made a detailed study of thermal pulse - asymptotic giant branch stars by using
a population synthesis code. The effects of the oxygen overabundance and the
mass loss rate on the ratio of the number of carbon stars to that of oxygen
stars in the Galactic bulge are discussed. We find that the oxygen
overabundance which is about twice as large as that in the solar neighbourhood
(close to the present observations) is insufficient to explain the rareness of
carbon stars in the bulge. We suggest that the large mass loss rate may serve
as a controlling factor in the ratio of the number of carbon stars to that of
oxygen stars.Comment: 16 pages, 5 figure
Evidence of metallic clustering in annealed Ga1-xMnxAs from atypical scaling behavior of the anomalous Hall coefficient
We report on the anomalous Hall coefficient and longitudinal resistivity
scaling relationships on a series of annealed Ga1-xMnxAs epilayers (x~0.055).
As-grown samples exhibit scaling parameter n of ~ 1. Near the optimal annealing
temperature, we find n ~ 2 to be consistent with recent theories on the
intrinsic origins of anomalous Hall Effect in Ga1-xMnxAs. For annealing
temperatures far above the optimum, we note n > 3, similar behavior to certain
inhomogeneous systems. This observation of atypical behavior agrees well with
characteristic features attributable to spherical resonance from metallic
inclusions from optical spectroscopy measurements.Comment: 3 pages, 3 figure
Molecular dynamics study of the fragmentation of silicon doped fullerenes
Tight binding molecular dynamics simulations, with a non orthogonal basis
set, are performed to study the fragmentation of carbon fullerenes doped with
up to six silicon atoms. Both substitutional and adsorbed cases are considered.
The fragmentation process is simulated starting from the equilibrium
configuration in each case and imposing a high initial temperature to the
atoms. Kinetic energy quickly converts into potential energy, so that the
system oscillates for some picoseconds and eventually breaks up. The most
probable first event for substituted fullerenes is the ejection of a C2
molecule, another very frequent event being that one Si atom goes to an
adsorbed position. Adsorbed Si clusters tend to desorb as a whole when they
have four or more atoms, while the smaller ones tend to dissociate and
sometimes interchange positions with the C atoms. These results are compared
with experimental information from mass abundance spectroscopy and the products
of photofragmentation.Comment: Seven two-column pages, six postscript figures. To be published in
Physical Review
The Phase Diagram and Spectrum of Gauge-Fixed Abelian Lattice Gauge Theory
We consider a lattice discretization of a covariantly gauge-fixed abelian
gauge theory. The gauge fixing is part of the action defining the theory, and
we study the phase diagram in detail. As there is no BRST symmetry on the
lattice, counterterms are needed, and we construct those explicitly. We show
that the proper adjustment of these counterterms drives the theory to a new
type of phase transition, at which we recover a continuum theory of (free)
photons. We present both numerical and (one-loop) perturbative results, and
show that they are in good agreement near this phase transition. Since
perturbation theory plays an important role, it is important to choose a
discretization of the gauge-fixing action such that lattice perturbation theory
is valid. Indeed, we find numerical evidence that lattice actions not
satisfying this requirement do not lead to the desired continuum limit. While
we do not consider fermions here, we argue that our results, in combination
with previous work, provide very strong evidence that this new phase transition
can be used to define abelian lattice chiral gauge theories.Comment: 42 pages, 30 figure
Identification of the Beutler-Fano formula in eigenphase shifts and eigentime delays near a resonance
Eigenphase shifts and eigentime delays near a resonance for a system of one
discrete state and two continua are shown to be functionals of the Beutler-
Fano formulas using appropriate dimensionless energy units and line profile
indices. Parameters responsible for the avoided crossing of eigenphase shifts
and eigentime delays are identified. Similarly, parameters responsible for the
eigentime delays due to a frame change are identified. With the help of new
parameters, an analogy with the spin model is pursued for the S matrix and time
delay matrix. The time delay matrix is shown to comprise three terms, one due
to resonance, one due to a avoided crossing interaction, and one due to a frame
change. It is found that the squared sum of time delays due to the avoided
crossing interaction and frame change is unity.Comment: 17 pages, 3 figures, RevTe
Relaxation of the Dynamical Gluino Phase and Unambiguous Electric Dipole Moments
We propose a new axionic solution of the strong CP problem with a
Peccei-Quinn mechanism using the gluino rather than quarks. The spontaneous
breaking of this new global U(1) at 10^{11} GeV also generates the
supersymmetry breaking scale of 1 TeV (solving the so-called \mu problem at the
same time) and results in the MSSM (Minimal Supersymmetric Standard Model) with
R parity conservation. In this framework, electric dipole moments become
calculable without ambiguity.Comment: Typos corrected and a footnote added, 10 p
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