1,302 research outputs found
Phase Diagram of the quadrumerized Shastry-Sutherland Model
We determine the phase diagram of a generalized Shastry-Sutherland model,
using a combination of dimer- and quadrumer-boson methods and numerical exact
diagonalization techniques. Along special lines in the parameter space the
model reduces to the standard Shastry-Sutherland model, the 1/5-th depleted
square lattice and the two-dimensional plaquette square lattice model. We study
the evolution of the ordered phases found in the latter two unfrustrated models
under the effect of frustration. Furthermore we present new exact
diagonalization results for the Shastry-Sutherland model on clusters with up to
32 sites, supporting the existence of an intermediate gapped valence bond
crystal phase with plaquette long-ranged order.Comment: Replaced with final version, added journal-re
Recent Efforts in the Computation of String Couplings:
We review recent advances towards the computation of string couplings.
Duality symmetry, mirror symmetry, Picard-Fuchs equations, etc. are some of the
tools.Comment: Talk hold at the `International Conference on Modern Problems in
Quantum Field Theorie, Strings and Quantum Gravity', Kiev, June 1992, 18
page
Phenomenology of Hybrid Scenarios of Neutrino Dark Energy
We study the phenomenology of hybrid scenarios of neutrino dark energy, where
in addition to a so-called Mass Varying Neutrino (MaVaN) sector a cosmological
constant (from a false vacuum) is driving the accelerated expansion of the
universe today. For general power law potentials we calculate the effective
equation of state parameter w_{eff}(z) in terms of the neutrino mass scale. Due
to the interaction of the dark energy field (acceleron) with the neutrino
sector, w_{eff}(z) is predicted to become smaller than -1 for z>0, which could
be tested in future cosmological observations. For the considered scenarios,
the neutrino mass scale additionally determines which fraction of the dark
energy is dynamical, and which originates from the cosmological constant like
vacuum energy of the false vacuum. On the other hand, the field value of the
acceleron field today as well as the masses of the right-handed neutrinos,
which appear in the seesaw-type mechanism for small neutrino masses, are not
fixed. This, in principle, allows to realise hybrid scenarios of neutrino dark
energy with a high-scale seesaw where the right-handed neutrino masses are
close to the GUT scale. We also comment on how MaVaN Hybrid Scenarios with
high-scale seesaw might help to resolve stability problems of dark energy
models with non-relativistic neutrinos.Comment: 22 pages, 5 figures; references and comments added; version to be
published in JCA
Molecular basis of telaprevir resistance due to V36 and T54 mutations in the NS3-4A protease of the hepatitis C virus
Structural analysis of the inhibitor Telaprevir (VX-950) of the hepatitis C virus (HCV) protease NS3-4A shows that mutations at V36 and/or T54 result in impaired interaction with VX-950, explaining the development of viral breakthrough variants
Gravitational corrections in supersymmetric gauge theory and matrix models
Gravitational corrections in N=1 and N=2 supersymmetric gauge theories are
obtained from topological string amplitudes. We show how they are recovered in
matrix model computations. This provides a test of the proposal by Dijkgraaf
and Vafa beyond the planar limit. Both, matrix model and topological string
theory, are used to check a conjecture of Nekrasov concerning these
gravitational couplings in Seiberg-Witten theory. Our analysis is performed for
those gauge theories which are related to the cubic matrix model, i.e. pure
SU(2) Seiberg-Witten theory and N=2 U(N) SYM broken to N=1 via a cubic
superpotential. We outline the computation of the topological amplitudes for
the local Calabi-Yau manifolds which are relevant for these two cases.Comment: 27 pages, one eps figur
The Large Scale Bias of Dark Matter Halos: Numerical Calibration and Model Tests
We measure the clustering of dark matter halos in a large set of
collisionless cosmological simulations of the flat LCDM cosmology. Halos are
identified using the spherical overdensity algorithm, which finds the mass
around isolated peaks in the density field such that the mean density is Delta
times the background. We calibrate fitting functions for the large scale bias
that are adaptable to any value of Delta we examine. We find a ~6% scatter
about our best fit bias relation. Our fitting functions couple to the halo mass
functions of Tinker et. al. (2008) such that bias of all dark matter is
normalized to unity. We demonstrate that the bias of massive, rare halos is
higher than that predicted in the modified ellipsoidal collapse model of Sheth,
Mo, & Tormen (2001), and approaches the predictions of the spherical collapse
model for the rarest halos. Halo bias results based on friends-of-friends halos
identified with linking length 0.2 are systematically lower than for halos with
the canonical Delta=200 overdensity by ~10%. In contrast to our previous
results on the mass function, we find that the universal bias function evolves
very weakly with redshift, if at all. We use our numerical results, both for
the mass function and the bias relation, to test the peak-background split
model for halo bias. We find that the peak-background split achieves a
reasonable agreement with the numerical results, but ~20% residuals remain,
both at high and low masses.Comment: 11 pages, submitted to ApJ, revised to include referee's coment
Kinematic Effects in Radiative Quarkonia Decays
Non-relativistic QCD (NRQCD) predicts colour octet contributions to be
significant not only in many production processes of heavy quarkonia but also
in their radiative decays. We investigate the photon energy distributions in
these processes in the endpoint region. There the velocity expansion of NRQCD
breaks down which requires a resummation of an infinite class of colour octet
operators to so-called shape functions. We model these non-perturbative
functions by the emission of a soft gluon cluster in the initial state. We
found that the spectrum in the endpoint region is poorly understood if the
values for the colour octet matrix elements are taken as large as indicated
from NRQCD scaling rules. Therefore the endpoint region should not be taken
into account for a fit of the strong coupling constant at the scale of the
heavy quark mass.Comment: LaTeX, 17 pages, 5 figures. The complete paper is also available via
the www at http://www-ttp.physik.uni-karlsruhe.de/Preprints
The transiting multi-planet system HD3167: a 5.7 MEarth Super-Earth and a 8.3 MEarth mini-Neptune
HD3167 is a bright (V=8.9 mag) K0V star observed by the NASA's K2 space
mission during its Campaign 8. It has been recently found to host two small
transiting planets, namely, HD3167b, an ultra short period (0.96 d)
super-Earth, and HD3167c, a mini-Neptune on a relatively long-period orbit
(29.85 d). Here we present an intensive radial velocity follow-up of HD3167
performed with the FIES@NOT, [email protected], and HARPS-N@TNG spectrographs. We
revise the system parameters and determine radii, masses, and densities of the
two transiting planets by combining the K2 photometry with our spectroscopic
data. With a mass of 5.69+/-0.44 MEarth, radius of 1.574+/-0.054 REarth, and
mean density of 8.00(+1.0)(-0.98) g/cm^3, HD3167b joins the small group of
ultra-short period planets known to have a rocky terrestrial composition.
HD3167c has a mass of 8.33 (+1.79)(-1.85) MEarth and a radius of
2.740(+0.106)(-0.100) REarth, yielding a mean density of 2.21(+0.56)(-0.53)
g/cm^3, indicative of a planet with a composition comprising a solid core
surrounded by a thick atmospheric envelope. The rather large pressure scale
height (about 350 km) and the brightness of the host star make HD3167c an ideal
target for atmospheric characterization via transmission spectroscopy across a
broad range of wavelengths. We found evidence of additional signals in the
radial velocity measurements but the currently available data set does not
allow us to draw any firm conclusion on the origin of the observed variation.Comment: 18 pages, 11 figures, 5 table
Falsification Of The Atmospheric CO2 Greenhouse Effects Within The Frame Of Physics
The atmospheric greenhouse effect, an idea that many authors trace back to
the traditional works of Fourier (1824), Tyndall (1861), and Arrhenius (1896),
and which is still supported in global climatology, essentially describes a
fictitious mechanism, in which a planetary atmosphere acts as a heat pump
driven by an environment that is radiatively interacting with but radiatively
equilibrated to the atmospheric system. According to the second law of
thermodynamics such a planetary machine can never exist. Nevertheless, in
almost all texts of global climatology and in a widespread secondary literature
it is taken for granted that such mechanism is real and stands on a firm
scientific foundation. In this paper the popular conjecture is analyzed and the
underlying physical principles are clarified. By showing that (a) there are no
common physical laws between the warming phenomenon in glass houses and the
fictitious atmospheric greenhouse effects, (b) there are no calculations to
determine an average surface temperature of a planet, (c) the frequently
mentioned difference of 33 degrees Celsius is a meaningless number calculated
wrongly, (d) the formulas of cavity radiation are used inappropriately, (e) the
assumption of a radiative balance is unphysical, (f) thermal conductivity and
friction must not be set to zero, the atmospheric greenhouse conjecture is
falsified.Comment: 115 pages, 32 figures, 13 tables (some typos corrected
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