Ordinary Matter Density Research Articles

Non-minimally coupled scalar field and scaling symmetry in a cosmological background

We study Noether symmetries of a class of non-minimally coupled scalar field in a background spatially flat Friedmann-Robertson-Walker (FRW) spacetime. We explore the model symmetries and its conserved currents and charges. Especially, the scaling symmetry, its possible break down and outcomes of such a symmetry breaking are treated in details. A suitable potential of the non-minimally coupled scalar field is adopted which is necessary to get a symmetric Lagrangian of the system including gravity, scalar field and ordinary matter density. We use the obtained charge and the adopted potential in the equations of motions to see the role of the non-minimal coupling (NMC) on the cosmic expansion. We study evolution of the scalar field in the phase space of the model and explore the stability of the obtained critical point. In this manner we derive a relation that relates the cosmological constant and gravitational constant via a unique identity which reflects the scaling symmetry breaking in the space (a, φ).

Unexpected LIGO events and the mirror world

ABSTRACT We consider the possibility that LIGO events GW190521, GW190425, and GW190814 may have emerged from the mirror world binaries. Theories of star evolution predict so-called upper and lower mass gaps and masses of these merger components lie in that gaps. In order to explain these challenging events very specific assumptions are required and we argue that such scenarios are order of magnitude more probable in mirror world, where star formation begins earlier and matter density can exceed five times the ordinary matter density.

A new unified model of dark matter and dark energy in 5-dimensional f(R,ϕ) gravity

We propose a new unified model that describes dark energy and dark matter in the context of [Formula: see text] gravity using a massive scalar field in five dimensions. The scalar field is considered in the bulk that surrounds the 3-brane in branworld model. We show that for a specific choice of the [Formula: see text] function, we can describe the Einstein gravitation in 4-dimensional space-time. We obtain a relationship between the speed of the Universe’s expansion and the speed of the bulk’s expansion. We also propose that the dark matter is represented by the scalar field mass and that the dark energy is a kinetic energy of this field. Finally, we show that, according to conditions, one can obtain the percentages of density of dark matter and the density of ordinary matter.

A first step in evolving quantum cosmology

Implementing Mach’s principle and Planck scale simultaneously in entire cosmic evolution can be considered as a first step in quantum cosmology. In this context, we propose a simple model of quantum cosmology without dark energy. Our assumptions are: 1) Universe is a quantum gravitational object. 2) Planck scale and Mach’s principle play a combined role in entire cosmic evolution. 3) Cosmic thermal wavelength is inversely proportional to ordinary matter density ratio. 4) Ordinary matter density ratio and dark matter density ratio play a combined role in estimating cosmic expansion velocity. 5) Critical energy density and dark energy density are equal in magnitude and physically there exists no dark energy.

LIGO signals from the mirror world

We want to explain non-observation of electromagnetic counterpart of currently confirmed ten gravitational wave signals from the black hole mergers assuming their existence in the hidden mirror universe. Mirror matter, which interacts with our world only through gravity, is a candidate of dark matter and its density can exceed ordinary matter density five times. Since mirror world is considered to be colder, star formation there started earlier and mirror black holes had more time to pick up the mass and to create more binary systems within the LIGO reachable zone. Totally we estimate a factor 10 amplification of black holes merging rate in mirror world with respect to our world, which is consistent with the LIGO observations.

An Outline Picture of a Growing and Rotating Planck Universe with Emerging Dark Foam

With reference to Planck scale, Mach’s relation, increasing support for large scale cosmic anisotropy and preferred directions and by introducing two new parameters Gamma and Beta, right from the beginning of Planck scale, we make an attempt to estimate ordinary matter density ratio, dark matter density ratio, mass, radius, temperature, age and expansion velocity (from and about the bay universe in all directions). We would like suggest that, from the beginning of Planck scale, 1) Dark matter can be considered as a kind of cosmic foam responsible for formation of galaxies. 2) Cosmic angular velocity is directly proportional to squared cosmic temperature. 3) Cosmic expansion velocity increases with decreasing total matter density ratio. 4) There is no need to consider dark energy for understanding cosmic acceleration.

Gravitational Waves from Mirror World

In this paper we consider the properties of the 10 confirmed by the LIGO (Laser Interferometer Gravitational-Wave Observatory) Collaboration gravitational wave signals from the black hole mergers. We want to explain non-observation of electromagnetic counterpart and higher then expected merging rates of these events, assuming the existence of their sources in the hidden mirror universe. Mirror matter, which interacts with our world only through gravity, is a candidate of dark matter and its density can exceed ordinary matter density five times. Since mirror world is considered to be colder, star formation there started earlier and mirror black holes had more time to pick up the mass and to create more binary systems within the LIGO reachable zone. In total, we estimate factor of 15 amplification of black holes merging rate in mirror world with respect to our world, which is consistent with the LIGO observations.

Accelerated universe with inflation and a divergence-free Big Bang

We consider a two-component universe consisting of ordinary matter and vacuum energy quantitatively described by the cosmological term L c = (l/a)ρ c , where l is a quantity having the dimension of length, ρ c is the density of ordinary matter, and a is the scale factor. To justify the form of L c , we use the Maxwell-like approach to gravitation in which it is supposed that the gravitational field energy gravitates. The total energy conservation law for both cosmic components determines the mass density and the vacuum energy density as a function of the scale factor. Applying this two-component cosmic model to the present universe, the important cosmic parameters get values consistent with observations. The ratio of density parameters of ordinary matter and vacuum mass-energy, Ω m /Ω l , in today’s universe is 1/2. Interesting features of our model are (i) the existence of an inflationary phase just at the earliest era of the universe follows directly from the modified Friedmann equations, and (ii) the beginning of cosmic expansion, the Big-Bang, is singularity-free, i.e., both the mass and vacuum energy contents assume finite values at the very origin of the universe.

Suppression of the multi-azimuthal-angle instability in dense neutrino gas during supernova accretion phase

It has been recently pointed out that by removing the axial symmetry in the ``multi-angle effects'' associated with the neutrino-neutrino interactions for supernova (SN) neutrinos a new multi-azimuthal-angle (MAA) instability would arise. In particular, for a flux ordering ${F}_{{\ensuremath{\nu}}_{e}}>{F}_{{\overline{\ensuremath{\nu}}}_{e}}>{F}_{{\ensuremath{\nu}}_{x}}$, as expected during the SN accretion phase, this instability occurs in the normal neutrino mass hierarchy. However, during this phase, the ordinary matter density can be larger than the neutrino one, suppressing the self-induced conversions. In this regard, we investigate the matter suppression of the MAA effects, performing a linearized stability analysis of the neutrino equations of motion, in the presence of realistic SN density profiles. We compare these results with the numerical solution of the SN neutrino nonlinear evolution equations. Assuming axially symmetric distributions of neutrino momenta, we find that the large matter term strongly inhibits the MAA effects. In particular, the hindrance becomes stronger including realistic forward-peaked neutrino angular distributions. As a result, in our model for a $10.8\text{ }{M}_{\ensuremath{\bigodot}}$ iron-core SNe, MAA instability does not trigger any flavor conversion during the accretion phase. Instead, for a $8.8\text{ }{M}_{\ensuremath{\bigodot}}$ O-Ne-Mg core SN model, with lower matter density profile and less forward-peaked angular distributions, flavor conversions are possible also at early times.

Evolution of homogeneous and isotropic scalar-tensor cosmological models

Homogeneous and isotropic cosmological models are considered in the framework of general scalar-tensor theories of gravity with arbitrary coupling function and scalar potential. Nonlinear approximate equations are derived for the regime close to the so-called limit of general relativity where the local observational constraints are satisfied. Approximate solutions in cosmological time are presented for the potential dominated era and for the era when the energy density of ordinary matter dominates over the energy density of scalar potential.

Scalar-tensor cosmologies with a potential in the general relativity limit

We consider Friedmann-Lemaître-Robertson-Walker flat cosmological models in the framework of general Jordan frame scalar-tensor theories of gravity with arbitrary coupling functions, in the era when the energy density of the scalar potential dominates over the energy density of ordinary matter. To study the regime suggested by the local weak field tests (i.e. close to the so-called limit of general relativity) we propose a nonlinear approximation scheme, solve for the phase trajectories, and provide a complete classification of possible solutions. We argue that the topology of phase trajectories in the nonlinear approximation is representative of those of the full system, and thus can tell for which scalar-tensor models general relativity functions as an attractor. To the classes of models which asymptotically approach general relativity we give the solutions also in cosmological time and conclude with some observational implications.

Scalar-tensor cosmologies with a potential in the general relativity limit: Time evolution

We consider Friedmann–Lemaître–Robertson–Walker flat cosmological models in the framework of general Jordan frame scalar-tensor theories of gravity with arbitrary coupling function and potential. For the era when the cosmological energy density of the scalar potential dominates over the energy density of ordinary matter, we use a nonlinear approximation of the decoupled scalar field equation for the regime close to the so-called limit of general relativity where the local weak field constraints are satisfied. We give the solutions in cosmological time with a particular attention to the classes of models asymptotically approaching general relativity. The latter can be subsumed under two types: (i) exponential convergence, and (ii) damped oscillations around general relativity. As an illustration we present an example of oscillating dark energy.

IS COSMOLOGICAL ACCELERATION DRIVEN BY CLASSICAL SPACE–TIME GEOMETRY?

The homogeneous expansion history H(z) of our universe (Hubble diagram) measures only kinematic variables, it cannot fix the underlying dynamics driving the recent acceleration: cosmographic measurements of the homogeneous universe are consistent with either a static fine-tuned cosmological constant or a dynamic "dark energy" mechanism, which itself may be either material dark energy or low-curvature modifications of Einstein gravity (dark gravity). This dark energy/dark gravity degeneracy in the homogeneous expansion observations can only be resolved by observing the growth of the cosmological fluctuations. However, because the "dark energy" evolution is now quasi-static at most, any dynamical effects on the fluctuation growth function g(z) will be minimal. Projected observations may potentially distinguish static from dynamic "dark energy", but distinguishing dynamic dark energy from dark gravity will require a weak lensing shear survey more ambitious than any now projected. Dark gravity is also, in principle, observable in the solar system or in isolated galaxy clusters. The cosmological constant problem — that quantum material vacuum fluctuations apparently do not gravitate — suggests identifying gravitational "vacuum energy" with classical intrinsic space–time curvature, divorcing it from any quantum material property. This empty space–time curvature appears cosmologically and about isolated sources and can only be fine-tuned, at present. The cosmological coincidence problem — that we live when the ordinary matter density approximates the "gravitational vacuum energy" — on the other hand, is a material problem, calling for an understanding of the observers' role in cosmology. A particularly restrictive weak anthropic principle, that dark energy and dark gravity be indistinguishable, selects static "dark energy" (ΛCDM) and rejects any dynamical effects in the growth of fluctuations.

Search for matter-dependent atmospheric neutrino oscillations in Super-Kamiokande

We consider {nu}{sub {mu}}{yields}{nu}{sub {tau}} oscillations in the context of the mass varying neutrino (MaVaN) model, where the neutrino mass can vary depending on the electron density along the flight path of the neutrino. Our analysis assumes a mechanism with dependence only upon the electron density, hence ordinary matter density, of the medium through which the neutrino travels. Fully-contained, partially-contained and upward-going muon atmospheric neutrino data from the Super-Kamiokande detector, taken from the entire SK-I period of 1489 live days, are compared to MaVaN model predictions. We find that, for the case of 2-flavor oscillations, and for the specific models tested, oscillation independent of electron density is favored over density dependence. Assuming maximal mixing, the best-fit case and the density-independent case do not differ significantly.

Classical cancellation of the cosmological constant reconsidered

We revisit a scenario in which the cosmological constant is cancelled by the potential energy of a slowly evolving scalar field, or "cosmon". The cosmon's evolution is tied to the cosmological constant by a feedback mechanism. This feedback is achieved by an unconventional coupling of the cosmon field to the Ricci curvature scalar. The solutions show that the effective cosmological constant evolves approximately as $t^{-2}$ and remains always of the same order as the density of ordinary matter and radiation. Newton's constant varies on cosmological time scales, with $\dot{G}_N/G_N \ll 1/t$. $G_N$ could have been somewhat different, and possibly smaller, at the time of Big Bang nucleosynthesis.

Transition from decelerated to accelerated cosmic expansion in braneworld universes

Braneworld theory provides a natural setting to treat, at a classical level, the cosmological effects of vacuum energy. Non-static extra dimensions can generally lead to a variable vacuum energy, which in turn may explain the present accelerated cosmic expansion. We concentrate our attention in models where the vacuum energy decreases as an inverse power law of the scale factor. These models agree with the observed accelerating universe, while fitting simultaneously the observational data for the density and deceleration parameter. The redshift at which the vacuum energy can start to dominate depends on the mass density of ordinary matter. For Omega = 0.3, the transition from decelerated to accelerated cosmic expansion occurs at z approx 0.48 +/- 0.20, which is compatible with SNe data. We set a lower bound on the deceleration parameter today, namely q > - 1 + 3 Omega/2, i.e., q > - 0.55 for Omega = 0.3. The future evolution of the universe crucially depends on the time when vacuum starts to dominate over ordinary matter. If it dominates only recently, at an epoch z < 0.64, then the universe is accelerating today and will continue that way forever. If vacuum dominates earlier, at z > 0.64, then the deceleration comes back and the universe recollapses at some point in the distant future. In the first case, quintessence and Cardassian expansion can be formally interpreted as the low energy limit of our model, although they are entirely different in philosophy. In the second case there is no correspondence between these models and ours.

Two-scalar model for a small but nonzero cosmological constant

We reexamine a model of the two-scalar system proposed previously for understanding a small but nonzero cosmological constant. The model provides solutions of the scalar-field energy ${\ensuremath{\rho}}_{s}$ which behaves as a true constant for a limited time interval rather than in the way of tracker- or scaling-type variations. This causes mini-inflation, as indicated by recent observations. As another novel feature, ${\ensuremath{\rho}}_{s}$ and the ordinary matter density ${\ensuremath{\rho}}_{m}$ always fall off side by side, but interlacing, also as $(\mathrm{time}{)}^{\ensuremath{-}2}$ as an overall behavior in conformity with the scenario of a decaying cosmological constant. Mini-inflation occurs whenever ${\ensuremath{\rho}}_{s}$ overtakes ${\ensuremath{\rho}}_{m},$ which may happen more than once, shedding new light on the coincidence problem. We present a new example of the solution, and offer an intuitive interpretation of the mechanism of the nonlinear dynamics. We also discuss the chaoslike nature of the solution.

Evolution of the cosmological constant

Supernova observations have indicated that the Universe is expanding faster than the theory of inflation predicts. Some theoretical cosmologists suggest that an exotic form of energy density called quintessence may be responsible. Quintessence began as Einstein's cosmological constant, but if it is not, in fact, constant it may explain why we appeared just when it had the same value as the density of ordinary matter.

Deuteronomy and numbers

Four light isotopes - D, ^3He, ^4He and ^7Li - were produced by nuclear reactions a few seconds after the big bang. New measurements of ^3He in the ISM by Gloeckler and Geiss and of deuterium in high redshift hydrogen clouds by Tytler and his collaborators provide further confirmation of big-bang nucleosynthesis and new insight about the density of ordinary matter (baryons).

Correlated stopping of Coulomb clusters in a dense jellium target.

The strongly correlated stopping of [ital N] pointlike charges organized in clusters with a regular geometry is thoroughly investigated at high velocity as a linear and binary superposition of the stopping of a dicluster polarized with respect to the overall drift velocity. For [ital N][ge]3, [ital a] priori unexpected [ital N]-body and collective behaviors are identified in terms of variations for the target electron density, cluster topology, charge distribution, and projectile velocity. The target is featured as a homogeneous and dense electron jellium quantified with the Wigner coupling parameters [ital r][sub [ital S]]. A corresponding dielectric function is taken in a plasmon pole approximation, allowing for a quasianalytic and transparent analysis. A recurring trend of this study is an enhanced stopping due to charge correlation, increasing rapidly with [ital N]. A noticeable counterexample is afforded by a regular [ital N] chain of charges flowing parallel to its velocity. As a rule, in most practical cases of interest, correlated charges within a few atomic interdistances can experience a stopping that is enhanced by orders of magnitudes relative to the isolated charge case, when stopped in a target at ordinary matter density, with initial kinetic energy in the tens of keV/amu range.