7,505 research outputs found
Axionic extension of the Einstein-aether theory: How does dynamic aether regulate the state of axionic dark matter?
In the framework of axionic extension of the Einstein-aether theory we
establish the model, which describes a stiff regulation of the behavior of
axionic dark matter by the dynamic aether. The aether realizes this procedure
via the modified Higgs potential, designed for modeling of nonlinear
self-interaction of pseudoscalar (axion) field; the modification of this
potential is that its minima are not fixed, and their positions and depths
depend now on the square of the covariant derivative of the aether velocity
four-vector. Exact solutions to the master equations, modified correspondingly,
are obtained in the framework of homogeneous isotropic cosmological model. The
effective equation of state for axionic dark matter is of the stiff type.
Homogeneous perturbations of the pseudoscalar (axion) field, of the Hubble
function and of the scale factor are shown to fade out with cosmological time,
there are no growing modes, the model of stiff regulation is stable.Comment: 12 pages, 0 figures, revised version published in Physics of the Dark
Univers
Incremental and Transitive Discrete Rotations
A discrete rotation algorithm can be apprehended as a parametric application
from \ZZ[i] to \ZZ[i], whose resulting permutation ``looks
like'' the map induced by an Euclidean rotation. For this kind of algorithm, to
be incremental means to compute successively all the intermediate rotate d
copies of an image for angles in-between 0 and a destination angle. The di
scretized rotation consists in the composition of an Euclidean rotation with a
discretization; the aim of this article is to describe an algorithm whic h
computes incrementally a discretized rotation. The suggested method uses o nly
integer arithmetic and does not compute any sine nor any cosine. More pr
ecisely, its design relies on the analysis of the discretized rotation as a
step function: the precise description of the discontinuities turns to be th e
key ingredient that will make the resulting procedure optimally fast and e
xact. A complete description of the incremental rotation process is provided,
also this result may be useful in the specification of a consistent set of
defin itions for discrete geometry
Macroscopic loop formation in circular DNA denaturation
The statistical mechanics of DNA denaturation under fixed linking number is
qualitatively different from that of the unconstrained DNA. Quantitatively
different melting scenarios are reached from two alternative assumptions,
namely, that the denatured loops are formed in expense of 1) overtwist, 2)
supercoils. Recent work has shown that the supercoiling mechanism results in a
BEC-like picture where a macroscopic loop appears at Tc and grows steadily with
temperature, while the nature of the denatured phase for the overtwisting case
has not been studied. By extending an earlier result, we show here that a
macroscopic loop appears in the overtwisting scenario as well. We calculate its
size as a function of temperature and show that the fraction of the total sum
of microscopic loops decreases above Tc, with a cusp at the critical point.Comment: 5 pages, 3 figures, submitted for publicatio
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