31,196 research outputs found
Insights into the quark-gluon vertex from lattice QCD and meson spectroscopy
By comparing successful quark-gluon vertex interaction models with the
corresponding interaction extracted from lattice-QCD data on the quark's
propagator, we identify common qualitative features which could be important to
tune future interaction models beyond the rainbow ladder approximation.
Clearly, a quantitative comparison is conceptually not simple, but
qualitatively the results suggest that a realistic interaction should be
relatively broad with a strong support at about ~GeV and
infrared-finite
Reversible Superconductivity in Electrochromic Indium-Tin Oxide Films
Transparent conductive indium tin oxide (ITO) thin films, electrochemically
intercalated with sodium or other cations, show tunable superconducting
transitions with a maximum at 5 K. The transition temperature and the
density of states, (extracted from the measured Pauli susceptibility
exhibit the same dome shaped behavior as a function of electron
density. Optimally intercalated samples have an upper critical field T and . Accompanying the development of
superconductivity, the films show a reversible electrochromic change from
transparent to colored and are partially transparent (orange) at the peak of
the superconducting dome. This reversible intercalation of alkali and alkali
earth ions into thin ITO films opens diverse opportunities for tunable,
optically transparent superconductors
Nonlinear Realization of the Local Conform-Affine Symmetry Group for Gravity in the Composite Fiber Bundle Formalism
A gauge theory of gravity based on a nonlinear realization (NLR) of the local
Conform-Affine (CA) group of symmetry transformations is presented. The coframe
fields and gauge connections of the theory are obtained. The tetrads and
Lorentz group metric are used to induce a spacetime metric. The inhomogenously
transforming (under the Lorentz group) connection coefficients serve as
gravitational gauge potentials used to define covariant derivatives
accommodating minimal coupling of matter and gauge fields. On the other hand,
the tensor valued connection forms serve as auxillary dynamical fields
associated with the dilation, special conformal and deformational (shear)
degrees of freedom inherent in the bundle manifold. The bundle curvature of the
theory is determined. Boundary topological invariants are constructed. They
serve as a prototype (source free) gravitational Lagrangian. The Bianchi
identities, covariant field equations and gauge currents are obtained.Comment: 24 pages. to appear in IJGMM
HyRec: A fast and highly accurate primordial hydrogen and helium recombination code
We present a state-of-the-art primordial recombination code, HyRec, including
all the physical effects that have been shown to significantly affect
recombination. The computation of helium recombination includes simple analytic
treatments of hydrogen continuum opacity in the He I 2 1P - 1 1S line, the He
I] 2 3P - 1 1S line, and treats feedback between these lines within the
on-the-spot approximation. Hydrogen recombination is computed using the
effective multilevel atom method, virtually accounting for an infinite number
of excited states. We account for two-photon transitions from 2s and higher
levels as well as frequency diffusion in Lyman-alpha with a full radiative
transfer calculation. We present a new method to evolve the radiation field
simultaneously with the level populations and the free electron fraction. These
computations are sped up by taking advantage of the particular sparseness
pattern of the equations describing the radiative transfer. The computation
time for a full recombination history is ~2 seconds. This makes our code well
suited for inclusion in Monte Carlo Markov chains for cosmological parameter
estimation from upcoming high-precision cosmic microwave background anisotropy
measurements.Comment: Version accepted by PRD. Numerical integration switches adapted to be
well behaved for a wide range of cosmologies (Sec. V E). HyRec is available
at http://www.tapir.caltech.edu/~yacine/hyrec/hyrec.htm
Investigating the Effect of Stratospheric Radiation on Seed Germination and Growth
Three seed types: bean (Phaseolus vulgaris), corn (Zea mays) and radish (Raphanus sativus) were flown in a high altitude weather balloon into the mid-stratosphere to investigate the effects of high altitude radiation on germination success and seedling growth. After recovering and planting the seeds, the bean seeds showed lower germination success with exposure to high altitude radiation, and consequently stunted seedling growth. Cord and radish seeds experienced a statistically significant positive effect on germination success form radiation exposure compared to control seeds, but negative effect on seedling growth. Overall, the field experiments presented here support laboratory studies that show radiation exposure on vegetable seeds has a mixed effect on the germination success and negative effect on seedling growth on investigated seed types
Towards environmental sustainability in Russia: evidence from green universities
Environmental analysis; Environmental economics; Environmental management; Environmental pollution; Education; Sustainability; Environment; Universities; GM ranking; Fixed-effects, Random-effects; Russia © 2020Universities all over the world are increasingly recognizing the need for the attainment of environmental sustainability on campuses resulting in the adoption of several environmental sustainable initiatives by university management. This article, therefore, seeks to investigate the impact of campus-base management practices on environmental quality among Russian Universities. The study also explores the strengths and weaknesses against the best practices for campus sustainability as defined by the UI greenMetric world university ranking as well as the awareness of students about pro-environmental behaviours on campuses. Secondary data from the 2015 to 2019 world university ranking was sourced for the impact assessment as well as the strengths and weaknesses. The study also sourced primary data with the help of a structured questionnaire from student respondents to assess their awareness of pro-environmental behaviours. Fixed-effects, and random-effects models were used to assess the management impact on environmental quality. The result from the empirical models indicate that education and research, transportation and waste influence environmental quality on university campuses. The strengths and weaknesses of universities were assessed based on six (6) categories (setting and infrastructure, energy and climate change, waste, water, transport, and education and research). The study also assessed the perception of students on pro-environmental activities. While the results show an increasing trend of awareness among Russian universities (Management) in campus sustainability initiatives, most students appear to be unaware of environmental initiatives undertaken by their universities. The study, therefore, made some recommendations that can help improve campus sustainability levels while at the same time increase student participation. © 202
Matrix Gravity and Massive Colored Gravitons
We formulate a theory of gravity with a matrix-valued complex vierbein based
on the SL(2N,C)xSL(2N,C) gauge symmetry. The theory is metric independent, and
before symmetry breaking all fields are massless. The symmetry is broken
spontaneously and all gravitons corresponding to the broken generators acquire
masses. If the symmetry is broken to SL(2,C) then the spectrum would correspond
to one massless graviton coupled to massive gravitons. A novel
feature is the way the fields corresponding to non-compact generators acquire
kinetic energies with correct signs. Equally surprising is the way Yang-Mills
gauge fields acquire their correct kinetic energies through the coupling to the
non-dynamical antisymmetric components of the vierbeins.Comment: One reference adde
Supersymmetric Effects on Isospin Symmetry Breaking and Direct CP Violation in
We argue that one can search for physics beyond the standard model through
measurements of the isospin-violating quantity , its charge conjugate
, and direct CP violation in the partial decay rates of . We illustrate this by working out theoretical profiles of the
charge-conjugate averaged ratio and the CP asymmetry in the
standard model and in some variants of the minimal supersymmetric standard
model. We find that chargino contributions in the large region may
modify the magnitudes and flip the signs of and compared to their standard-model values, providing an
unmistakeable signature of supersymmetry.Comment: 10 pages, 7 figures (requires graphicx
- …