5,310 research outputs found
Dark spinor inflation -- theory primer and dynamics
Inflation driven by a single dark spinor field is discussed. We define the
notion of a dark spinor field and derive the cosmological field equations for
such a matter source. The conditions for inflation are determined and an
exactly solvable model is presented. We find the power spectrum of the quantum
fluctuation of this field and compare the results with scalar field inflation.Comment: 13 pages; typo in Eq. (12) corrected, minor improvement
Electronic nematic susceptibility of iron-based superconductors
We review our recent experimental results on the electronic nematic phase in
electron- and hole-doped BaFeAs and FeSe. The nematic susceptibility is
extracted from shear-modulus data (obtained using a three-point-bending method
in a capacitance dilatometer) using Landau theory and is compared to the
nematic susceptibility obtained from elastoresistivity and Raman data. FeSe is
particularly interesting in this context, because of a large nematic, i.e., a
structurally distorted but paramagnetic, region in its phase diagram. Scaling
of the nematic susceptibility with the spin lattice relaxation rate from NMR,
as predicted by the spin-nematic theory, is found in both electron- and
hole-doped BaFeAs, but not in FeSe. The intricate relationship of the
nematic susceptibility to spin and orbital degrees of freedom is discussed.Comment: Invited review article for a special issue on Fe-based
superconductors in Comptes Rendus Physiqu
Stable splitting of bivariate spline spaces by Bernstein-Bézier methods
We develop stable splitting of the minimal determining sets for the spaces of bivariate C1 splines on triangulations, including a modified Argyris space, Clough-Tocher, Powell-Sabin and quadrilateral macro-element spaces. This leads to the stable splitting of the corresponding bases as required in Böhmer's method for solving fully nonlinear elliptic PDEs on polygonal domains
Physics of dark energy particles
We consider the astrophysical and cosmological implications of the existence
of a minimum density and mass due to the presence of the cosmological constant.
If there is a minimum length in nature, then there is an absolute minimum mass
corresponding to a hypothetical particle with radius of the order of the Planck
length. On the other hand, quantum mechanical considerations suggest a
different minimum mass. These particles associated with the dark energy can be
interpreted as the ``quanta'' of the cosmological constant. We study the
possibility that these particles can form stable stellar-type configurations
through gravitational condensation, and their Jeans and Chandrasekhar masses
are estimated. From the requirement of the energetic stability of the minimum
density configuration on a macroscopic scale one obtains a mass of the order of
10^55 g, of the same order of magnitude as the mass of the universe. This mass
can also be interpreted as the Jeans mass of the dark energy fluid. Furthermore
we present a representation of the cosmological constant and of the total mass
of the universe in terms of `classical' fundamental constants.Comment: 10 pages, no figures; typos corrected, 4 references added; 1
reference added; reference added; entirely revised version, contains new
parts, now 14 page
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