No Arabic abstract
It was recently shown that gravitons with a very small mass should have formed a Bose-Einstein condensate in the very early Universe, whose density and quantum potential can account for the dark matter and dark energy in the Universe respectively. Here we show that the condensation can also naturally explain the observed large scale homogeneity and isotropy of the Universe. Furthermore gravitons continue to fall into their ground state within the condensate at every epoch, accounting for the observed flatness of space at cosmological distances scales. Finally, we argue that the density perturbations due to quantum fluctuations within the condensate give rise to a scale invariant spectrum. This therefore provides a viable alternative to inflation, which is not associated with the well-known problems associated with the latter.
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 $V(a)$ 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.
In this paper, we study the effects of rainbow gravity on relativistic Bose-Einstein condensation and thermodynamics parameters. We initially discussed some formal aspects of the model to only then compute the corrections to the Bose-Einstein condensation. The calculations were carried out by computing the generating functional, from which we extract the thermodynamics parameters. The corrected critical temperature $T_c$ that sets the Bose-Einstein Condensation was also computed for the three mostly adopted cases for the rainbow functions. We have also obtained a phenomenological upper bound for a combination of the quantities involved in the model, besides showing the possibility of occurrence of the Bose-Einstein condensation in two spatial dimensions under appropriate conditions on those functions. Finally, we have discussed how harder is for the particles at an arbitrary temperature $T<T_c$ to enter the condensed state when compared with the usual scenario.
Applying the seminal work of Bose in 1924 on what was later known as Bose-Einstein statistics, Einstein predicted in 1925 that at sufficiently low temperatures, a macroscopic fraction of constituents of a gas of bosons will drop down to the lowest available energy state, forming a `giant molecule or a Bose-Einstein condensate (BEC), described by a `macroscopic wavefunction. In this article we show that when the BEC of ultralight bosons extends over cosmological length scales, it can potentially explain the origins of both dark matter and dark energy. We speculate on the nature of these bosons.
In this paper we investigate the inflationary phenomenology of an Einstein-Gauss-Bonnet theory with the extension of a logarithmic modified $f(R)$ gravity, compatible with the GW170817 event. The main idea of our work is to study different results for an almost linear Ricci scalar through logarithmic corrections and examine whether such model is viable. First of all, the theoretical framework under slow-roll evolution of the scalar field is presented and also developed the formalism of the constant-roll evolution making predictions for the non- Gaussianities of the models is developed , since the constant-roll evolution is known to enhance non-Gaussianities. As shown, the non-Gaussianities are of the order $mathcal{O}sim(10^{-1})$. Furthermore, the slow-roll indices and the observational indices of inflation, are calculated for several models of interest. As demonstrated, the phenomenological viability of the models at hand is achieved for a wide range of the free parameters and the logarithmic term has a minor contribution to numerical calculations, as expected.
We report the observation of a Bose Einstein condensate in a bosonic isotope of ytterbium (170Yb). More than 10^6 atoms are trapped in a crossed optical dipole trap and cooled by evaporation. Condensates of approximately 10^4 atoms have been obtained. From an expansion of the condensate, we have extracted the scattering length a=3.6(9) nm.