2,673 research outputs found
LHC Benchmarks from Flavored Gauge Mediation
We present benchmark points for LHC searches from flavored gauge mediation
models, in which messenger-matter couplings give flavor-dependent squark
masses. Our examples include spectra in which a single squark - stop, scharm,
or sup - is much lighter than all other colored superpartners, motivating
improved quark flavor tagging at the LHC. Many examples feature flavor mixing;
in particular, large stop-scharm mixing is possible. The correct Higgs mass is
obtained in some examples by virtue of the large stop A-term. We also revisit
the general flavor and CP structure of the models. Even though the A-terms can
be substantial, their contributions to EDM's are very suppressed, because of
the particular dependence of the A-terms on the messenger coupling. This holds
regardless of the messenger-coupling texture. More generally, the special
structure of the soft terms often leads to stronger suppression of flavor- and
CP-violating processes, compared to naive estimates.Comment: 32 pages, 11 figures. Updated to published versio
Development of an EROD Assay to Characterize the Induction of CYP1A Activity in Xenopus laevis Cells
First-principles accurate total-energy surfaces for polar structural distortions of BaTiO3, PbTiO3, and SrTiO3: consequences to structural transition temperatures
Specific forms of the exchange correlation energy functionals in
first-principles density functional theory-based calculations, such as the
local density approximation (LDA) and generalized-gradient approximations
(GGA), give rise to structural lattice parameters with typical errors of -2%
and 2%. Due to a strong coupling between structure and polarization, the order
parameter of ferroelectric transitions, they result in large errors in
estimation of temperature dependent ferroelectric structural transition
properties. Here, we employ a recently developed GGA functional of Wu and Cohen
[Phys. Rev. B 73, 235116 (2006)] and determine total-energy surfaces for
zone-center distortions of BaTiO3, PbTiO3, and SrTiO3, and compare them with
the ones obtained with calculations based on standard LDA and GGA. Confirming
that the Wu and Cohen functional allows better estimation of structural
properties at 0 K, we determine a new set of parameters defining the effective
Hamiltonian for ferroelectric transition in BaTiO3. Using the new set of
parameters, we perform molecular-dynamics (MD) simulations under effective
pressures p=0.0 GPa, p=-2.0 GPa, and p=-0.005T GPa. The simulations under
p=-0.005T GPa, which is for simulating thermal expansion, show a clear
improvement in the cubic to tetragonal transition temperature and c/a parameter
of its ferroelectric tetragonal phase, while the description of transitions at
lower temperatures to orthorhombic and rhombohedral phases is marginally
improved. Our findings augur well for use of Wu-Cohen functional in studies of
ferroelectrics at nano-scale, particularly in the form of epitaxial films where
the properties depend crucially on the lattice mismatch.Comment: 10 pages, 7 figures, 3 tables, resubmitted to PR
Thermal Evolution and Light Curves of Young Bare Strange Stars
The cooling of a young bare strange star is studied numerically by solving
the equations of energy conservation and heat transport for both normal and
superconducting strange quark matter inside the star. We show that the thermal
luminosity from the strange star surface, due to both photon emission and e+e-
pair production, may be orders of magnitude higher than the Eddington limit,
for about one day for normal quark matter but possibly for up to a hundred
years for superconducting quark matter, while the maximum of the photon
spectrum is in hard X-rays with a mean energy of ~ 100 keV or even more. This
differs both qualitatively and quantitatively from the photon emission from
young neutron stars and provides a definite observational signature for bare
strange stars. It is shown that the energy gap of superconducting strange quark
matter may be estimated from the light curves if it is in the range from ~ 0.5
MeV to a few MeV.Comment: Ref [10] added and abstract shortened. 4 pages, 3 figures, revtex4.
To be published in Phys. Rev. Letter
Functional analysis of human mutations in homeodomain transcription factor PITX3
<p>Abstract</p> <p>Background</p> <p>The homeodomain-containing transcription factor <it>PITX3 </it>was shown to be essential for normal eye development in vertebrates. Human patients with point mutations in <it>PITX3 </it>demonstrate congenital cataracts along with anterior segment defects in some cases when one allele is affected and microphthalmia with brain malformations when both copies are mutated. The functional consequences of these human mutations remain unknown.</p> <p>Results</p> <p>We studied the PITX3 mutant proteins S13N and G219fs to determine the type and severity of functional defects. Our results demonstrate alterations in DNA-binding profiles and/or transactivation activities and suggest a partial loss-of-function in both mutants with the G219fs form being more severely affected. No anomalies in cellular distribution and no dominant-negative effects were discovered for these mutants. Interestingly, the impairment of the G219fs activity varied between different ocular cell lines.</p> <p>Conclusion</p> <p>The G219fs mutation was found in multiple families affected with congenital cataracts along with anterior segment malformations in many members. Our data suggest that the presence/severity of anterior segment defects in families affected with G219fs may be determined by secondary factors that are expressed in the developing anterior segment structures and may modify the effect(s) of this mutation. The S13N mutant showed only minor alteration of transactivation ability and DNA binding pattern and may represent a rare polymorphism in the <it>PITX3 </it>gene. A possible contribution of this mutation to human disease needs to be further investigated.</p
The contrasting fission potential-energy structure of actinides and mercury isotopes
Fission-fragment mass distributions are asymmetric in fission of typical
actinide nuclei for nucleon number in the range
and proton number in the range . For somewhat
lighter systems it has been observed that fission mass distributions are
usually symmetric. However, a recent experiment showed that fission of
Hg following electron capture on Tl is asymmetric. We calculate
potential-energy surfaces for a typical actinide nucleus and for 12 even
isotopes in the range Hg--Hg, to investigate the similarities
and differences of actinide compared to mercury potential surfaces and to what
extent fission-fragment properties, in particular shell structure, relate to
the structure of the static potential-energy surfaces. Potential-energy
surfaces are calculated in the macroscopic-microscopic approach as functions of
fiveshape coordinates for more than five million shapes. The structure of the
surfaces are investigated by use of an immersion technique. We determine
properties of minima, saddle points, valleys, and ridges between valleys in the
5D shape-coordinate space. Along the mercury isotope chain the barrier heights
and the ridge heights and persistence with elongation vary significantly and
show no obvious connection to possible fragment shell structure, in contrast to
the actinide region, where there is a deep asymmetric valley extending from the
saddle point to scission. The mechanism of asymmetric fission must be very
different in the lighter proton-rich mercury isotopes compared to the actinide
region and is apparently unrelated to fragment shell structure. Isotopes
lighter than Hg have the saddle point blocked from a deep symmetric
valley by a significant ridge. The ridge vanishes for the heavier Hg isotopes,
for which we would expect a qualitatively different asymmetry of the fragments.Comment: 8 pages, 9 figure
Pair Excitations and Vertex Corrections in Fermi Fluids
Based on an equations--of--motion approach for time--dependent pair
correlations in strongly interacting Fermi liquids, we have developed a theory
for describing the excitation spectrum of these systems. Compared to the known
``correlated'' random--phase approximation (CRPA), our approach has the
following properties: i) The CRPA is reproduced when pair fluctuations are
neglected. ii) The first two energy--weighted sumrules are fulfilled implying a
correct static structure. iii) No ad--hoc assumptions for the effective mass
are needed to reproduce the experimental dispersion of the roton in 3He. iv)
The density response function displays a novel form, arising from vertex
corrections in the proper polarisation. Our theory is presented here with
special emphasis on this latter point. We have also extended the approach to
the single particle self-energy and included pair fluctuations in the same way.
The theory provides a diagrammatic superset of the familiar GW approximation.
It aims at a consistent calculation of single particle excitations with an
accuracy that has previously only been achieved for impurities in Bose liquids.Comment: to be published in: JLTP (2007) Proc. Int. Symp. QFS2006, 1-6 Aug.
2006, Kyoto, Japa
Hypernova Nucleosynthesis and Galactic Chemical Evolution
We study nucleosynthesis in 'hypernovae', i.e., supernovae with very large
explosion energies ( \gsim 10^{52} ergs) for both spherical and aspherical
explosions. The hypernova yields compared to those of ordinary core-collapse
supernovae show the following characteristics: 1) Complete Si-burning takes
place in more extended region, so that the mass ratio between the complete and
incomplete Si burning regions is generally larger in hypernovae than normal
supernovae. As a result, higher energy explosions tend to produce larger [(Zn,
Co)/Fe], small [(Mn, Cr)/Fe], and larger [Fe/O], which could explain the trend
observed in very metal-poor stars. 2) Si-burning takes place in lower density
regions, so that the effects of -rich freezeout is enhanced. Thus
Ca, Ti, and Zn are produced more abundantly than in normal
supernovae. The large [(Ti, Zn)/Fe] ratios observed in very metal poor stars
strongly suggest a significant contribution of hypernovae. 3) Oxygen burning
also takes place in more extended regions for the larger explosion energy. Then
a larger amount of Si, S, Ar, and Ca ("Si") are synthesized, which makes the
"Si"/O ratio larger. The abundance pattern of the starburst galaxy M82 may be
attributed to hypernova explosions. Asphericity in the explosions strengthens
the nucleosynthesis properties of hypernovae except for "Si"/O. We thus suggest
that hypernovae make important contribution to the early Galactic (and cosmic)
chemical evolution.Comment: To be published in "The Influence of Binaries on Stellar Population
Studies", ed. D. Vanbeveren (Kluwer), 200
Superconductivity in correlated disordered two-dimensional electron gas
We calculate the dynamic effective electron-electron interaction potential
for a low density disordered two-dimensional electron gas. The disordered
response function is used to calculate the effective potential where the
scattering rate is taken from typical mobilities from recent experiments. We
investigate the development of an effective attractive pair potential for both
disordered and disorder free systems with correlations determined from existing
numerical simulation data. The effect of disorder and correlations on the
superconducting critical temperature Tc is discussed.Comment: 4 pages, RevTeX + epsf, 4 figure
Search for broad absorption lines in spectra of stars in the field of supernova remnant RX J0852.0-4622 (Vela Jr.)
Supernova remnant (SNR) RX J0852.0-4622 is one of the youngest and is most
likely the closest among known galactic supernova remnants (SNRs). It was
detected in X-rays, the 44Ti gamma-line, and radio. We obtain and analyze
medium-resolution spectra of 14 stars in the direction towards the SNR RX
J0852.0-4622 in an attempt to detect broad absorption lines of unshocked ejecta
against background stars. Spectral synthesis is performed for all the stars in
the wavelength range of 3740-4020AA to extract the broad absorption lines of Ca
II related to the SNR RX J0852.0-4622. We do not detect any broad absorption
line and place a 3-sigma upper limit on the relative depths of <0.04 for the
broad Ca II absorption produced by the SNR. We detect narrow low and high
velocity absorption components of Ca II. High velocity |V(LSR)|=100-140 km/s
components are attributed to radiative shocks in clouds engulfed by the old
Vela SNR. The upper limit to the absorption line strength combined with the
width and flux of the 44Ti gamma-ray line 1.16 MeV lead us to conclude that SNR
RX J0852.0-4622 was probably produced by an energetic SN Ic explosion.Comment: 9 pages, 8 figures, accepted in A&
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