893 research outputs found
Polynomial Palatini cosmology -- dynamical system approach
We investigate cosmological dynamics based on gravity in the Palatini
formulation. In this study we use the dynamical system methods. We show that
the evolution of the Friedmann equation reduces to the form of the piece-wise
smooth dynamical system. This system is is reduced to a 2D dynamical system of
the Newtonian type. We demonstrate how the trajectories can be sewn to
guarantee extendibility of the metric similarly as `Milne-like' FLRW
spacetimes are -extendible. We point out that importance of dynamical
system of Newtonian type with non-smooth right-hand sides in the context of
Palatini cosmology. In this framework we can investigate singularities which
appear in the past and future of the cosmic evolution. We consider cosmological
systems in both Einstein and Jordan frames. We show that at each frame the
topological structures of phase space are different.Comment: RevTeX 4-1, 30 pages, 19 figure
Does the diffusion DM-DE interaction model solve cosmological puzzles?
We study dynamics of cosmological models with diffusion effects modeling dark
matter and dark energy interactions. We show the simple model with diffusion
between the cosmological constant sector and dark matter, where the canonical
scaling law of dark matter is modified by an additive
to the form
. We reduced this model to the
autonomous dynamical system and investigate it using dynamical system methods.
This system possesses a two-dimensional invariant submanifold on which the
DM-DE interaction can be analyzed on the phase plane. The state variables are
density parameter for matter (dark and visible) and parameter
characterizing the rate of growth of energy transfer between the dark sectors.
A corresponding dynamical system belongs to a general class of jungle type of
cosmologies represented by coupled cosmological models in a Lotka-Volterra
framework. We demonstrate that the de Sitter solution is a global attractor for
all trajectories in the phase space and there are two repellers: the
Einstein-de Sitter universe and the de Sitter universe state dominating by the
diffusion effects. We distinguish in the phase space trajectories, which become
in good agreement with the data. They should intersect a rectangle with sides
of , at the
95\% CL. Our model could solve some of the puzzles of the CDM model,
such as the coincidence and fine-tuning problems. In the context of the
coincidence problem, our model can explain the present ratio of to
, which is equal at a 2
confidence level.Comment: 27 pages, 17 figure
Possibly Oriental elements in Slavonic folklore : kłobuk
The paper discusses a mythical creature known in Polish folklore as kłobuk, how it got its name, the Slavonic background of the word, and its relation to Turkic kalbuk. Usually, the Slavonic word is derived from Turkic; phonetic problems are sometimes mentioned but they do not tend to be viewed as critical. The present paper approaches this established etymology with more reservation and concludes that both Slavistic and Turkological work is necessary in order to connect the two words with an acceptable degree of probability.Bu yazıda Polonya folkloründe kłobuk olarak bilinen mitolojik bir varlık tart şılmakta, bu ismin nasıl alındığı, sözcüğün Slav dillerindeki tabanı ve Türkçe kalbuk ile bağı değerlendirilmektedir. Esasen Slav dillerindeki sözcük Türkçeden kaynaklanmaktadır.
Bazen fonetik sorunlardan bahsedilirse de bu eleştirel olarak görülme eğiliminde değildir. Mevcut makale varolan etimolojiye kuşku ile yaklaşır ve hem Slavistiğe hem de Türkolojiye ait çalışmaların kabul edilebilir derecede bir olasılıkla iki kelimenin ilişkilendirilmesi için gerekli olduğu sonucuna varır
Cosmology with decaying cosmological constant -- exact solutions and model testing
We study dynamics of cosmological models which are a natural
generalization of the standard cosmological model (the CDM model). We
consider a class of models: the ones with a prescribed form of
. This type of a
parametrization is motivated by different cosmological approaches.
We interpret the model with running Lambda () as a special model of
an interacting cosmology with the interaction term in which
energy transfer is between dark matter and dark energy sectors. For the
cosmology with a prescribed form of we have found the
exact solution in the form of Bessel functions. Our model shows that fractional
density of dark energy is constant and close to zero during the
early evolution of the universe.
We have also constrained the model parameters for this class of models using
the astronomical data such as SNIa data, BAO, CMB, measurements of and
the Alcock-Paczy{\'n}ski test. In this context we formulate a simple criterion
of variability of with respect to in terms of variability of the
jerk or sign of estimator . The
case study of our model enable us to find an upper limit
( C.L.) describing the variation from the cosmological constant while
the LCDM model seems to be consistent with various data.Comment: 24 pages, 15 figures; We pointed out that most stringent limit on
parameter \alpha^2 can be obtained if we apply Starobinsky argument and use
constraint of Ade et al. (arXiv:1502.01590). Let us note that while the
corresponding limit on the parameter \alpha^2 parameter is about twice less
than the limit obtained from our estimation, but it is obtained independently
of Starobinsky's argumen
Possibly Oriental elements in Slavonic folklore : "mamuna" [part 2]
A specialist in Middle Eastern languages will likely be quick to associate Pol. mamuna ‘an ape-like mythological creature’ with Ar./Pers./Tkc. majmun ‘ape’. It is possible and indeed probable that this name is an Oriental borrowing applied to an ancient native belief, but a closer inspection reveals at least several other possibilities tangled in an ethnolinguistic web of potential conflations and contaminations. This paper presents the ethnographic background and some etymological ideas, though without as yet a definite answer
Simple cosmological model with inflation and late times acceleration
In the framework of polynomial Palatini cosmology, we investigate a simple
cosmological homogeneous and isotropic model with matter in the Einstein frame.
We show that in this model during cosmic evolution, it appears the early
inflation and the accelerating phase of the expansion for the late times. In
this frame we obtain the Friedmann equation with matter and dark energy in the
form of a scalar field with the potential whose form is determined in a
covariant way by the Ricci scalar of the FRW metric. The energy density of
matter and dark energy are also parametrized through the Ricci scalar. The
early inflation is obtained only for an infinitesimally small fraction of
energy density of matter. Between the matter and dark energy, there exists
interaction because the dark energy is decaying. For characterization of
inflation we calculate the slow roll parameters and the constant roll parameter
in terms of the Ricci scalar. We have found a characteristic behaviour of the
time dependence of density of dark energy on the cosmic time following the
logistic-like curve which interpolates two almost constant value phases. From
the required numbers of -folds we have found a bound on model parameter.Comment: 8 pages, 10 figure
Is a pole type singularity an alternative to inflation?
In this paper, we apply a method of reducing the dynamics of FRW cosmological
models with the barotropic form of the equation of state to the dynamical
system of the Newtonian type to detect the finite scale factor singularities
and the finite-time singularities. In this approach all information concerning
the dynamics of the system is contained in a diagram of the potential function
of the scale factor. Singularities of the finite scale factor manifest
by poles of the potential function. In our approach the different types of
singularities are represented by critical exponents in the power-law
approximation of the potential. The classification can be given in terms of
these exponents. We have found that the pole singularity can mimick an
inflation epoch. We demonstrate that the cosmological singularities can be
investigated in terms of the critical exponents of the potential function of
the cosmological dynamical systems. We assume the general form of the model
contains matter and some kind of dark energy which is parameterized by the
potential. We distinguish singularities (by ansatz about the Lagrangian) of the
pole type with the inflation and demonstrate that such a singularity can appear
in the past.Comment: RevTeX 4.1; 33 pages, 9 figures; ver. 2: new title, new part on the
pole type singularities with inflatio
Possibly Oriental elements in Slavonic folklore : "mamuna" [part 1]
A specialist in Middle Eastern languages will likely be quick to associate Pol. mamuna ‘an ape-like mythological creature’ with Ar./Pers./Tkc. majmun ‘ape’. It is possible and indeed probable that this name is an Oriental borrowing applied to an ancient native belief, but a closer inspection reveals at least several other possibilities tangled in an ethnolinguistic web of potential conflations and contaminations. This paper presents the ethnographic background and some etymological ideas, though without as yet a definite answer
Cosmology with a Decaying Vacuum Energy Parametrization Derived from Quantum Mechanics
Within the quantum mechanical treatment of the decay problem one finds that
at late times the survival probability of an unstable state cannot have the
form of an exponentially decreasing function of time but it has an inverse
power-like form. This is a general property of unstable states following from
basic principles of quantum theory. The consequence of this property is that in
the case of false vacuum states the cosmological constant becomes dependent on
time: . We construct the cosmological model with decaying vacuum energy
density and matter for solving the cosmological constant problem and the
coincidence problem. We show the equivalence of the proposed decaying false
vacuum cosmology with the cosmologies (the CDM
models). The cosmological implications of the model of decaying vacuum energy
(dark energy) are discussed. We constrain the parameters of the model with
decaying vacuum using astronomical data. For this aim we use the observation of
distant supernovae of type Ia, measurements of , BAO, CMB and others. The
model analyzed is in good agreement with observation data and explain a small
value of the cosmological constant today.Comment: 9 pages, 4 figures. Talk given at Seventh International Workshop DICE
2014: Spacetime -- Matter -- Quantum Mechanics ... news on missing links,
Castiglioncello (Tuscany, Italy), September 15--19, 201
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