29 research outputs found
The multi-measure cosmological model and its peculiar effective potential
The multi-measures model applied to cosmology has been recently shown to
reproduce qualitatively the expected stages of the Universe evolution, along
with some unexpected features. In this article, we continue its exploration
with a detailed study of the effective potential of the model. An analysis of
the limits of applicability of the effective potential show that during most of
the Universe evolution, the effective potential is a very good approximation of
the actual potential term. There is, however, a deviation between the two
occurring in the earliest moments of the evolution, which has an important role
on the behavior of the inflaton scalar field. In the studied cases, during this
initial time, the inflaton is increasing in absolute value, which seems
consistent with "climbing up" the effective potential. To investigate this
behavior, we use numerical integration to find the numerical potential and we
show that during the early stage of the evolution, the shape of the numerical
potential is very different from that of the effective one and instead of a
left plateau followed by steep slope, one observes only a slope with additional
local maximum and minimum. This result demonstrates that for complicated
equations of motion of the inflaton, one should not rely only on the notion of
kinetic and effective potential terms to describe the problem as they may not
be accurate in the entire numerical domain.Comment: 9 pages, 5 figure
Special cases of the Multi-Measure Model -- understanding the prolonged inflation
The multi-measure model (MMM), in which one modifies the action to include
both the Riemannian measure and a non-Riemannian one, has proven to be able to
produce viable Universe evolution scenarios. In this article we consider two
special cases of the multi-measure model, in which we remove some of the
non-linearity of the Lagrangian or we decouple the two kinetic terms entirely.
We show numerically that one can still get the needed evolutionary stages, but
furthermore, one can obtain a sufficient number of e-folds of the early
inflation in both cases. Furthermore, we connect the model with
hyperinflationary models and investigate how the different epochs are born from
the interplay between the two scalar fields. We also demonstrate that there is
a dynamically induces slow-roll epoch, which is prolonged by the complicated
movement of the two scalars in the field space. Finally, we show that while the
adiabatic speed of sound can become imaginary, the phase speed of sound is
equal to one.Comment: 9 pages, 4 figure
Solving systems of transcendental equations involving the Heun functions
The Heun functions have wide application in modern physics and are expected
to succeed the hypergeometrical functions in the physical problems of the 21st
century. The numerical work with those functions, however, is complicated and
requires filling the gaps in the theory of the Heun functions and also,
creating new algorithms able to work with them efficiently.
We propose a new algorithm for solving a system of two nonlinear
transcendental equations with two complex variables based on the M\"uller
algorithm. The new algorithm is particularly useful in systems featuring the
Heun functions and for them, the new algorithm gives distinctly better results
than Newton's and Broyden's methods.
As an example for its application in physics, the new algorithm was used to
find the quasi-normal modes (QNM) of Schwarzschild black hole described by the
Regge-Wheeler equation. The numerical results obtained by our method are
compared with the already published QNM frequencies and are found to coincide
to a great extent with them. Also discussed are the QNM of the Kerr black hole,
described by the Teukolsky Master equation.Comment: 17 pages, 4 figures. Typos corrected, one figure added, some sections
revised. The article is a rework of the internal report arXiv:1005.537
Cosmological solutions from models with unified dark energy and dark matter and with inflaton field
Recently, few cosmological models with additional non-Riemannian volume
form(s) have been proposed. In this article we use Supernovae type Ia
experimental data to test one of these models which provides a unified
description of both dark energy via dynamically generated cosmological constant
and dark matter as a "dust" fluid due to a hidden nonlinear Noether symmetry.
It turns out that the model allows various scenarios of the future Universe
evolution and in the same time perfectly fits contemporary observational data.
Further, we investigate the influence of an additional inflaton field with a
step like potential. With its help we can reproduce the Universe inflation
epoch, matter dominated epoch and present accelerating expansion in a seamless
way. Interesting feature is that inflaton undergoes a finite change during its
evolution. It can be speculated that the inflaton asymptotic value is connected
to the vacuum expectation value of the Higgs field.Comment: 10 pages, 4 figures, prepared for the Proceedings of the XII.
International Workshop Lie Theory And Its Applications In Physics (2017