Masahiro Morikawa

Cosmic structures via Bose–Einstein condensation and its collapse

We develop our novel model of cosmology based on Bose–Einstein condensation. This model unifies the dark energy and the dark matter, and predicts the multiple collapse of condensation, followed by the final acceleration regime of cosmic expansion. We first explore the generality of this model, especially the constraints on the boson mass and condensation conditions. We further argue the robustness of this model over a wide range of parameters of mass, self-coupling constant and the condensation rate. Then the dynamics of BEC collapse and the preferred scale of the collapse are studied. Finally, we describe possible observational tests of our model, especially the periodicity of the collapses and the gravitational wave associated with them.

Stagflation: Bose-Einstein condensation in the early universe

Our universe experienced the accelerated expansion at least twice; an extreme inflationary acceleration in the early universe and the recent mild acceleration. By introducing the Bose-Einstein condensation (BEC) phase of a boson field, we have been developing a unified model of dark energy (DE) and dark matter (DM) for the later mild acceleration. In this scenario, two phases of BEC (=DE) and normal gas (=DM) transform with each other through BEC phase transition. This unified model has successfully explained the mild acceleration as an attractor. We extend this BEC cosmology to the early universe without introducing new ingredients. In this scenario, the inflation is naturally initiated by the condensation of the bosons in the huge vacuum energy. This inflation and even the cosmic expansion eventually terminates exactly at zero energy density. We call this stage as stagflation. At this stagflation era, particle production and the decay of BEC take place. The former makes the universe turn into the standard hot big bang stage and the latter makes the cosmological constant vanishingly small after the inflation. Furthermore, we calculate the density fluctuations produced in this model, which turns out to be in the range allowed by the present observational data. We also show that the stagflation is quite robust and easily appears when one allows negative region of the potential. Further, we comment on the possibility that BEC generation/decay series might have continued all the time in the cosmic history from the inflation to present.

Accuracy of Nonlinear Approximations in Spheroidal Collapse: Why Are Zeldovich-Type Approximations Good?

Among various analytic approximations for the growth of density fluctuations in the expanding universe, the Zeldovich approximation and its extensions in a Lagrangian scheme are known to be better than other approximations, even in mildly nonlinear regimes. We compare analytic approximations with true density evolution in the presence of spheroidal symmetry. We consider Eulerian and Lagrangian perturbation theories up to third order, and frozen-flow and linear potential approximation. We also introduce the Pade approximation in the Eulerian scheme which improves usual perturbation theories. In the course of comparison, we clarify the reason why these Zeldovich-type approximations effectively work beyond the linear regime, with reference to the two following aspects of the problem: (1) the dimensionality of the system and (2) the Lagrangian scheme on which the Zeldovich approximation is grounded. We mention which of these two aspects supports the validity of the Zeldovich-type approximations. We also give a suggestion for a better approximation method beyond the Zeldovich type.

Scaling analysis of galaxy distribution in the Las Campanas Redshift Survey data

The Las Campanas Redshift Survey data are used to investigate structures ofthe galaxy number distribution. We construct two volume-limited samples with sizes of

Universe with oscillating expansion rate

113 \times 113

The Relativistic Gross-Pitaevskii Equation and Cosmological Bose-Einstein Condensation: Quantum Structure in the Universe

and

X-Ray Spectra of Comets

126 \times 126

Origin of scaling structure and non-Gaussian velocity distribution in a self-gravitating ring model

h -1 Mpc, and calculate the second- to ninth-order moments with the count-in-cell method. The galaxy distribution at ≥ 30 h -1 Mpc is found to be statistically homogeneous. On the other hand, we find a multifractal scaling at h -1 Mpc. From the scaling exponent, we obtain the generalized dimension, which decreases from 2 toward 1 as the order is increased from 2 to 9. Galaxies are known to lie, around voids, in planar structures with filamentary dense regions. The present result indicates that these void-filament structures are predominant up to 30 h -1 Mpc. Statistically, they appear to be the largest-scale significant structures in the Universe.

Non-extensive galaxy distributions – Tsallis statistical mechanics

A model of the universe with oscillating Hubble parameter is proposed. This oscillation distorts the ordinary distance-redshift relation and induces various apparent effects in all cosmological observations which assume this relation. A massive nonconformal scalar field model is used, which is designed to explain the recently observed periodicity in the redshift distribution of galaxies with a characteristic scale of 128 h -1 Mpc (where h ∼ 0.5-1 is the present Hubble parameter in units of 100 km s -1 Mpc -1 ). A new method is also proposed to determine the present Hubble parameter by measuring time, rather than distance as in the traditional method.

Coupled spin models for magnetic variation of planets and stars

We do not know the identity of 96% of the total matter in the universe at present. In this paper, a cosmological model is proposed in which dark energy (DE) is identified with the Bose-Einstein condensation (BEC) of some boson fi eld. The global cosmic acceleration caused by this BEC and multiple rapid collapses of BEC into black holes and other forms of localized matter [= dark matter (DM)] are examined on the basis of the relativistic version of the Gross-Pitaevskii equation. We propose (a) a novel mechanism of inflation, free from the slow-rolling condition, (b) a natural solution to the cosmic coincidence (‘Why now?’) problem through the transition from DE to DM, (c) very early formation of highly nonlinear objects, such as black holes, which might have triggered the first light as a form of quasars, and (d) log-z periodicity in the subsequent BEC collapsing time. All of these are based on a steady, slow BEC process. It is amazing that recent cosmological observations provide us with a wide range of knowledge and mysteries. It is also amazing that the standard ΛCDM cosmological model works perfectly without specifying most of the matter content of the universe. In this model, the basic concepts and the structure of matter and space are both very simple, and the basic assumptions are clear. Moreover, within this model, the temperature fluctuations, δT, in the sky and the large scale power spectrum, P (k) , of density fluctuations can be calculated precisely from the primordial density fluctuations; 1) they correctly describe most observations. However as a theory of physics, there are at least two unsatisfactory points in this standard model. One is that the theory lacks identification of matter. Although significant amount of unknown matter plays an important role in the theory, this is simply called dark matter and dark energy, and the specification of them has been postponed. Thus we still do not know 96% of the cosmic matter contents, dark energy (DE) and dark matter (DM). Moreover, we do not know the relation between them. The second point is that the successful description of and the harmony with the cosmological observations are limited to the linear regime. There are many peculiarities in the non-linear regime: the too early formation of objects and reionization at around z ≈ 20, the physical details of the biasing for galaxy formation, and a natural mechanism of how the first stars formed, etc. These facts force us to consider some other source of instability, in addition to ordinary gravity, in order to form clearly localized structures.