2,373 research outputs found
iTIMP: isotriplet Technicolor Interacting Massive Particle as Dark Matter
We suggest that a weak isotriplet composite scalar possessing an unbroken
U(1) global symmetry naturally arises in technicolor models leading to an
interesting type of dark matter candidate: the iTIMP. We propose explicit
models of the iTIMP, study earth based constraints and suggest possible
collider signals.Comment: 4 pages, 4 Figures, added content, added reference
Quantitative characterization of short-range orthorhombic fluctuations in FeSe through pair distribution function analysis
Neutron and x-ray total scattering measurements have been performed on powder
samples of the iron chalcogenide superconductor FeSe. Using pair distribution
function (PDF) analysis of the total scattering data to investigate short-range
atomic correlations, we establish the existence of an instantaneous, local
orthorhombic structural distortion attributable to nematic fluctuations that
persists well into the high-temperature tetragonal phase, at least up to 300 K
and likely to significantly higher temperatures. This short-range orthorhombic
distortion is correlated over a length scale of about 1 nm at 300 K and grows
to several nm as the temperature is lowered toward the long-range structural
transition temperature. In the low-temperature nematic state, the local
instantaneous structure exhibits an enhanced orthorhombic distortion relative
to the average structure with a typical relaxation length of 3 nm. The
quantitative characterization of these orthorhombic fluctuations sheds light on
nematicity in this canonical iron-based superconductor
WASP-1: A lithium- and metal-rich star with an oversized planet
In this paper we present our results of a comprehensive spectroscopicanalysis
of WASP-1, the host star to the exoplanet WASP-1b. We derive T_eff = 6110 +/-
45 K, log g = 4.28 +/- 0.15, and [M/H] = 0.23 +/- 0.08, and also a high
abundance of lithium, log n(Li) = 2.91 +/- 0.05. These parameters suggests an
age for the system of 1-3 Gyr and a stellar mass of 1.25-1.35 M_sun. This means
that WASP-1 has properties very similar to those of HD 149026, the host star
for the highest density planet yet detected. Moreover, their planets orbit at
comparable distances and receive comparable irradiating fluxes from their host
stars. However, despite the similarity of WASP-1 with HD 149026, their planets
have strongly different densities. This suggests that gas-giant planet density
is not a simple function of host-star metallicity or of radiation environment
at ages of ~2 Gyr.Comment: Accepted for publication in MNRAS. 6 pages, 4 figure
Emergent phases in iron pnictides: Double-Q antiferromagnetism, charge order and enhanced nematic correlations
Electron correlations produce a rich phase diagram in the iron pnictides.
Earlier theoretical studies on the correlation effect demonstrated how quantum
fluctuations weaken and concurrently suppress a -symmetric single-Q
antiferromagnetic order and a nematic order. Here we examine the emergent
phases near the quantum phase transition. For a -symmetric collinear
double-Q antiferromagnetic order, we show that it is accompanied by both a
charge order and an enhanced nematic susceptibility. Our results provide
understanding for several intriguing recent experiments in hole-doped iron
arsenides, and bring out common physics that underlies the different magnetic
phases of various iron-based superconductors.Comment: 5+6 pages, 2 figures; (v2) issues with cross-referencing between the
main text and supplementary material are fixe
Looking for a charge asymmetry in cosmic rays
We combine the data from PAMELA and FERMI-LAT cosmic ray experiments by
introducing a simple sum rule. This allows to investigate whether the lepton
excess observed by these experiments is charge symmetric or not. We also show
how the data can be used to predict the positron fraction at energies yet to be
explored by the AMS-02 experiment.Comment: Contribution to the proceedings of DISCRETE 2010, 5 pages, 2 figure
Minimal Walking Technicolor: Set Up for Collider Physics
Different theoretical and phenomenological aspects of the Minimal and
Nonminimal Walking Technicolor theories have recently been studied. The goal
here is to make the models ready for collider phenomenology. We do this by
constructing the low energy effective theory containing scalars, pseudoscalars,
vector mesons and other fields predicted by the minimal walking theory. We
construct their self-interactions and interactions with standard model fields.
Using the Weinberg sum rules, opportunely modified to take into account the
walking behavior of the underlying gauge theory, we find interesting relations
for the spin-one spectrum. We derive the electroweak parameters using the newly
constructed effective theory and compare the results with the underlying gauge
theory. Our analysis is sufficiently general such that the resulting model can
be used to represent a generic walking technicolor theory not at odds with
precision data.Comment: 42 pages, 3 figures. RevTex forma
Age and helium content of the open cluster NGC 6791 from multiple eclipsing binary members. I. Measurements, methods, and first results
Earlier measurements of the masses and radii of the detached eclipsing binary
V20 in the open cluster NGC 6791 were accurate enough to demonstrate that there
are significant differences between current stellar models. Here we improve on
those results and add measurements of two additional detached eclipsing
binaries, the cluster members V18 and V80. The enlarged sample sets much
tighter constraints on the properties of stellar models than has hitherto been
possible, thereby improving both the accuracy and precision of the cluster age.
We employed (i) high-resolution UVES spectroscopy of V18, V20 and V80 to
determine their spectroscopic effective temperatures, [Fe/H] values, and
spectroscopic orbital elements, and (ii) time-series photometry from the Nordic
Optical Telescope to obtain the photometric elements. The masses and radii of
the V18 and V20 components are found to high accuracy, with errors on the
masses in the range 0.27-0.36% and errors on the radii in the range 0.61-0.92%.
V80 is found to be magnetically active, and more observations are needed to
determine its parameters accurately. The metallicity of NGC 6791 is measured
from disentangled spectra of the binaries and a few single stars to be [Fe/H]=
+0.29 \pm 0.03 (random) \pm 0.07 (systematic). The cluster reddening and
apparent distance modulus are found to be E(B - V) = 0.160 \pm 0.025 and (m -
M)V = 13.51 \pm 0.06 . A first model comparison shows that we can constrain the
helium content of the NGC 6791 stars, and thus reach a more accurate age than
previously possible. It may be possible to constrain additional parameters, in
particular the C, N, and O abundances. This will be investigated in paper II.Comment: Accepted for publication in A&
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High-temperature magnetic anomaly in the Kitaev hyperhoneycomb compound β-Li2IrO3
We report the existence of a high-temperature magnetic anomaly in the three-dimensional Kitaev candidate material, β-Li2IrO3. Signatures of the anomaly appear in magnetization, heat capacity, and muon spin relaxation measurements. The onset coincides with a reordering of the principal axes of magnetization, which is thought to be connected to the onset of Kitaev-like correlations in the system. The anomaly also shows magnetic hysteresis with a spatially anisotropic magnitude that follows the spin-anisotropic exchange anisotropy of the underlying Kitaev Hamiltonian. We discuss possible scenarios for a bulk and impurity origin
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