24,856 research outputs found
Constraints On Dark Energy Models From Galaxy Clusters and Gravitational Lensing Data
The Sunyaev--Zel'dovich (SZ) effect is a global distortion of the Cosmic
Microwave Background (CMB) spectrum as a result of its interaction with a hot
electron plasma in the intracluster medium of large structures gravitationally
viralized such as galaxy clusters (GC). Furthermore, this~hot gas of electrons
emits X-rays due to its fall in the gravitational potential well of the GC.
The~analysis of SZ and X-ray data provides a method for calculating distances
to GC at high redshifts. On the other hand, many galaxies and GC produce a
Strong Gravitational Lens (SGL) effect, which has become a useful astrophysical
tool for cosmology. We use these cosmological tests in addition to more
traditional ones to constrain some alternative dark energy (DE) models,
including the study of the history of cosmological expansion through the
cosmographic parameters. Using Akaike and Bayesian Information Criterion, we
find that the and models are the most favoured by the
observational data. In addition, we found at low redshift a peculiar behavior
of slowdown of the universe, which occurs in dynamical DE models when we use
data from GC.Comment: 21 page, 5 figures, 8 tables. Published: 22 January 2018, Universe,
MDPI, Special Issue "Progress in Cosmology in the Centenary of the 1917
Einstein Paper
On the exact continuous mapping of fermions
We derive a rigorous, quantum mechanical map of fermionic creation and
annihilation operators to continuous Cartesian variables that exactly
reproduces the matrix structure of the many-fermion problem. We show how our
scheme can be used to map a general many-fermion Hamiltonian and then consider
two specific models that encode the fundamental physics of many fermionic
systems, the Anderson impurity and Hubbard models. We use these models to
demonstrate how efficient mappings of these Hamiltonians can be constructed
using a judicious choice of index ordering of the fermions. This development
provides an alternative exact route to calculate the static and dynamical
properties of fermionic systems and sets the stage to exploit the
quantum-classical and semiclassical hierarchies to systematically derive
methods offering a range of accuracies, thus enabling the study of problems
where the fermionic degrees of freedom are coupled to complex anharmonic
nuclear motion and spins which lie beyond the reach of most currently available
methods.Comment: 7-page manuscript (2 figures) with 11-page supplemental materia
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