5,830 research outputs found
Detection of the Red Giant Branch Stars in M82 Using the Hubble Space Telescope
We present color-magnitude diagrams and luminosity functions of stars in two
halo regions of the irregular galaxy in M82, based on F555W and F814W
photometry taken with the Hubble Space Telescope and Wide Field Planetary
Camera 2. The I-band luminosity function shows a sudden jump at I~23.95 mag,
which is identified as the tip of the red giant branch (TRGB). Adopting the Lee
et al. (1993) calibration of the TRGB based on the RR Lyrae distances to
Galactic globular clusters, we obtain the distance modulus of (m-M)_0=27.95 +-
0.14 (random) +- 0.16 (systematic) mag. This corresponds to a linear distance
of 3.9 +- 0.3 (random) +- 0.3 (systematicf) Mpc, which agrees well with the
distance of M81 deteremined from the HST observations of the Cepheid variable
stars. In addition, we observe a significant number of stars apparently
brighter than the TRGB. However, with the current data, we cannot rule out
whether these stars are blends of fainter stars, or are indeed intermediate-age
asymptotic giant branch stars.Comment: 8 figure
Conformality and Gauge Coupling Unification
It has been recently proposed to embed the standard model in a conformal
gauge theory to resolve the hierarchy problem, and to avoid assuming either
grand unification or low-energy supersymmetry. By model building based on
string-field duality we show how to maintain the successful prediction of an
electroweak mixing angle with in conformal gauge
theories with three chiral families.Comment: 8 pages LaTe
Properties of global monopoles with an event horizon
We investigate the properties of global monopoles with an event horizon. We
find that there is an unstable circular orbit even if a particle does not have
an angular momentum when the core mass is negative. We also obtain the
asymptotic form of solutions when the event horizon is much larger than the
core radius of the monopole, and discuss if they could be a model of galactic
halos.Comment: 5 pages, 7 figure
Cepheid and Tip of the Red Giant Branch Distances To the Dwarf Irregular Galaxy IC10
We present color-magnitude diagrams and luminosity functions of stars in the
nearby galaxy IC 10, based on VI CCD photometry acquired with the COSMIC
prime-focus camera on the Palomar 5m telescope. The apparent I-band luminosity
function of stars in the halo of IC 10 shows an identifiable rise at I~21.7
mag. This is interpreted as being the tip of the red giant branch (TRGB) at
M_V~-4 mag. Since IC 10 is at a very low Galactic latitude, its foreground
extinction is expected to be high and the uncertainty associated with that
correction is the largest contributor to the error associated with its distance
determination. Multi-wavelength observations of Cepheid variable stars in IC 10
give a Population I distance modulus of 24.1 +- 0.2 mag, which corresponds to a
linear distance of 660 +- 66 kpc for a total line-of-sight reddening of E(B-V)
= 1.16 +- 0.08 mag, derived self-consistently from the Cepheid data alone.
Applying this Population I reddening to the Population II halo stars gives a
TRGB distance modulus of 23.5 +- 0.2 mag, corresponding to 500 +- 50 kpc. We
consider this to be a lower limit on the TRGB distance. Reconciling the Cepheid
and TRGB distances would require that the reddening to the halo is
E(B-V) = 0.31 mag lower than that into the main body of the galaxy.
This then suggests that the Galactic extinction in the direction of IC10 is
(B-V) ~ 0.85
Modelling the dynamics of global monopoles
A thin wall approximation is exploited to describe a global monopole coupled
to gravity. The core is modelled by de Sitter space; its boundary by a thin
wall with a constant energy density; its exterior by the asymptotic
Schwarzschild solution with negative gravitational mass and solid angle
deficit, , where is the symmetry
breaking scale. The deficit angle equals when . We find that: (1) if , there exists a unique globally
static non-singular solution with a well defined mass, . provides
a lower bound on . If , the solution oscillates. There are no
inflating solutions in this symmetry breaking regime. (2) if ,
non-singular solutions with an inflating core and an asymptotically
cosmological exterior will exist for all . (3) if is not too large,
there exists a finite range of values of where a non-inflating monopole
will also exist. These solutions appear to be metastable towards inflation. If
is positive all solutions are singular. We provide a detailed description
of the configuration space of the model for each point in the space of
parameters, and trace the wall trajectories on both the interior
and the exterior spacetimes. Our results support the proposal that topological
defects can undergo inflation.Comment: 44 pages, REVTeX, 11 PostScript figures, submitted to the Physical
Review D. Abstract's correcte
Description of even-even triaxial Nuclei within the Coherent State and the Triaxial Rotation-Vibration Models
The coherent state model (CSM) and the triaxial rotation-vibration model
(TRVM) are alternatively used to describe the ground, gamma and beta bands of
228Th. CSM is also applied to the nuclei 126Xe and 130Ba, which were recently
considered in TRVM. The two models are compared with respect to both their
underlying assumptions and to their predicted results for energy levels and E2
branching ratios. Both models describe energies and quadrupole transitions of
228Th equally well and in good agreement with experiment, if the 0 level
at 1120 keV is interpreted as the head of the beta band. The other two 0
levels at 832 and 939 keV are most likely not of a pure quadrupole vibration
nature as has already been pointed out in the literature.Comment: 31 pages, RevTeX, 6 figure
How to distinguish the Haldane/Large-D state and the intermediate-D state in an S=2 quantum spin chain with the XXZ and on-site anisotropies
We numerically investigate the ground-state phase diagram of an S=2 quantum
spin chain with the and on-site anisotropies described by , where denotes the XXZ anisotropy parameter of the
nearest-neighbor interactions and the on-site anisotropy parameter. We
restrict ourselves to the and case for simplicity. Our main
purpose is to obtain the definite conclusion whether there exists or not the
intermediate- (ID) phase, which was proposed by Oshikawa in 1992 and has
been believed to be absent since the DMRG studies in the latter half of 1990's.
In the phase diagram with and there appear the XY state, the
Haldane state, the ID state, the large- (LD) state and the N\'eel state. In
the analysis of the numerical data it is important to distinguish three gapped
states; the Haldane state, the ID state and the LD state. We give a physical
and intuitive explanation for our level spectroscopy method how to distinguish
these three phases.Comment: Proceedings of "International Conference on Frustration in Condensed
Matter (ICFCM)" (Jan. 11-14, 2011, Sendai, Japan
Spin-Reorientation Transition of Field-Induced Magnetic Ordering Phases in the Anisotropic Haldane System
A possible spin-reorientation transition in field-induced magnetic ordering
phases of the S=1 Haldane system with large easy-plane anisotropy is proposed,
using an effective Lagrangian formalism as well as the density matrix
renormalization group method. Such a spin-reorientation transition is predicted
in the case where the applied magnetic field is inclined from the easy axis of
the anisotropy. We point out that this transition has a close connection with a
variation of the order parameter even at zero temperature, although it is
different from a quantum analog of the so-called spin-flop transition proposed
for the system having a strong easy axis anisotropy. In connection with a novel
phase observed recently in the Haldane system at high fields, we discuss
possible implications for the field-induced magnetic ordering.Comment: 14 pages, 7 figure
Comment On ``Grand Unification and Supersymmetric Threshold"
Barbieri and Hall have argued that threshold effects at the scale of
grand-unification wipe out predictions on the SUSY scale, M_S. Using triviality
arguments we give upper bounds on ultraheavy particles, while proton stability
gives lower bounds on the mass of the higgs color-triplet. We find no useful
lower bound on the supermultiplet, but if the strong coupling constant
is as large as recent experiments suggest, unification in the minimal SUSY
SU(5) model requires that the masses be and that the
color octet and weak triplet be split in mass by a factor of 100.Comment: 6 pages (revised
Quantum spin chains in a magnetic field
We demonstrate that the ``worm'' algorithm allows very effective and precise
quantum Monte Carlo (QMC) simulations of spin systems in a magnetic field, and
its auto-correlation time is rather insensitive to the value of H at low
temperature. Magnetization curves for the and chains are
presented and compared with existing Bethe ansatz and exact diagonalization
results. From the Green function analysis we deduce the magnon spectra in the
s=1 system, and directly establish the "relativistic" form E(p)=(\Delta ^2 +v^2
p^2)^{1/2} of the dispersion law.Comment: 6 pages, 8 figures; removed discussion of spin-2 case - will be
published later in a separate pape
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