CYCLIC MAGNETIC UNIVERSE

Recent works have shown the important role nonlinear electrodynamics (NLED) can have in two crucial questions of cosmology, concerning particular moments of its evolution for very large and for low-curvature regimes, that is for very condensed phase and at the present period of acceleration. We present here a toy model of a complete cosmological scenario in which the main factor responsible for the geometry is a nonlinear magnetic field which produces a Friedmann–Robertson–Walker homogeneous and isotropic geometry. In this scenario we distinguish four distinct phases: a bouncing period, a radiation era, an acceleration era, and a re-bouncing period. It has already been shown that in NLED a strong magnetic field can overcome the inevitability of a singular region typical of linear Maxwell theory; on the other extreme situation, that is for very weak magnetic field it can accelerate the expansion. The present model goes one step further: after the acceleration phase the universe re-bounces and enters into a collapse era. This behavior is a manifestation of the invariance under the dual map of the scale factor a(t) → 1/a(t), a consequence of the corresponding inverse symmetry of the electromagnetic field (F → 1/F, where F ≡ FμνFμν) of the NLED theory presented here. Such sequence collapse–bouncing–expansion–acceleration–re-bouncing–collapse constitutes a basic unitary element for the structure of the universe that can be repeated indefinitely yielding what we call a cyclic magnetic universe.

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Magnetism in the Early Universe

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319004447 ◽

2018 ◽

Vol 14 (A30) ◽

pp. 295-298

Author(s):

Tina Kahniashvili ◽

Axel Brandenburg ◽

Arthur Kosowsky ◽

Sayan Mandal ◽

Alberto Roper Pol

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Gravitational Waves ◽

Early Universe ◽

Large Scale ◽

Direct Detection ◽

Correlation Lengths ◽

Cosmological Scenario ◽

Expansion Of The Universe ◽

The Universe

AbstractBlazar observations point toward the possible presence of magnetic fields over intergalactic scales of the order of up to ∼1 Mpc, with strengths of at least ∼10−16 G. Understanding the origin of these large-scale magnetic fields is a challenge for modern astrophysics. Here we discuss the cosmological scenario, focussing on the following questions: (i) How and when was this magnetic field generated? (ii) How does it evolve during the expansion of the universe? (iii) Are the amplitude and statistical properties of this field such that they can explain the strengths and correlation lengths of observed magnetic fields? We also discuss the possibility of observing primordial turbulence through direct detection of stochastic gravitational waves in the mHz range accessible to LISA.

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REALISTIC CYCLIC MAGNETIC UNIVERSE

International Journal of Modern Physics D ◽

10.1142/s0218271812500733 ◽

2012 ◽

Vol 21 (09) ◽

pp. 1250073 ◽

Cited By ~ 11

Author(s):

L. G. MEDEIROS

Keyword(s):

Magnetic Field ◽

Big Bang ◽

Nonlinear Electrodynamics ◽

Baryonic Matter ◽

Big Rip ◽

Cosmological Scenario ◽

Free Parameters ◽

Big Bang Model ◽

Theoretical Considerations ◽

The Magnetic Field

This work presents a complete cyclic cosmological scenario based on nonlinear magnetic field. It is constructed from a model composed of five fluids, namely baryonic matter, dark matter, radiation, neutrinos and a cosmological magnetic field. The first four fluids are treated in the standard way and the fifth fluid, the magnetic field, is described by a nonlinear electrodynamics. The free parameters are fitted by observational data (SNIa, CMB, extragalactic magnetic fields, etc.) and by simple theoretical considerations. As a result arises a cyclic cosmological model that preserves the main successes of the standard Big Bang model and solves some other problems such as the initial singularity, the present acceleration and the Big Rip.

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Noncommutativity in the early universe

International Journal of Modern Physics D ◽

10.1142/s0218271817500110 ◽

2017 ◽

Vol 26 (02) ◽

pp. 1750011 ◽

Cited By ~ 6

Author(s):

G. Oliveira-Neto ◽

M. Silva de Oliveira ◽

G. A. Monerat ◽

E. V. Corrêa Silva

Keyword(s):

Energy Spectrum ◽

Present Model ◽

Scale Factor ◽

Matter Content ◽

Quantum Level ◽

Discrete Energy ◽

Noncommutative Version ◽

The Universe ◽

Friedmann Robertson Walker ◽

Noncommutative Parameter

In the present work, we study the noncommutative version of a quantum cosmology model. The model has a Friedmann–Robertson–Walker (FRW) geometry, the matter content is a radiative perfect fluid and the spatial sections have zero constant curvature. In this model, the scale factor takes values in a bounded domain. Therefore, its quantum mechanical version has a discrete energy spectrum. We compute the discrete energy spectrum and the corresponding eigenfunctions. The energies depend on a noncommutative parameter [Formula: see text]. We compute the scale factor expected value ([Formula: see text]) for several values of [Formula: see text]. For all of them, [Formula: see text] oscillates between maxima and minima values and never vanishes. It gives an initial indication that those models are free from singularities, at the quantum level. We improve this result by showing that if we subtract a quantity proportional to the standard deviation of [Formula: see text] from [Formula: see text], this quantity is still positive. The [Formula: see text] behavior, for the present model, is a drastic modification of the [Formula: see text] behavior in the corresponding commutative version of the present model. There, [Formula: see text] grows without limits with the time variable. Therefore, if the present model may represent the early stages of the universe, the results of the present paper give an indication that [Formula: see text] may have been, initially, bounded due to noncommutativity. We also compute the Bohmian trajectories for [Formula: see text], which are in accordance with [Formula: see text], and the quantum potential [Formula: see text]. From [Formula: see text], we may understand why that model is free from singularities, at the quantum level.

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On the pinning force in high density MgB2 samples

Scientific Reports ◽

10.1038/s41598-021-85209-2 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

V. Sandu ◽

A. M. Ionescu ◽

G. Aldica ◽

M. A. Grigoroscuta ◽

M. Burdusel ◽

...

Keyword(s):

Magnetic Field ◽

Field Dependence ◽

Scaling Law ◽

Critical Force ◽

High Density ◽

Pinning Force ◽

Pinning Mechanism ◽

Grain Boundary Pinning ◽

Peaked Function ◽

Main Factor

AbstractAn analysis of the field dependence of the pinning force in different, high density sintered samples of MgB2 is presented. The samples were chosen to be representative for pure MgB2, MgB2 with additives, and partially oriented massive samples. In some cases, the curves of pinning force versus magnetic field of the selected samples present peculiar profiles and application of the typical scaling procedures fails. Based on the percolation model, we show that most features of the field dependence of the critical force that generate dissipation comply with the Dew-Hughes scaling law predictions within the grain boundary pinning mechanism if a connecting factor related to the superconducting connection of the grains is used. The field dependence of the connecting function, which is dependent on the superconducting anisotropy, is the main factor that controls the boundary between dissipative and non-dissipative current transport in high magnetic field. Experimental data indicate that the connecting function is also dependent on the particular properties (e.g., the presence of slightly non-stoichiometric phases, defects, homogeneity, and others) of each sample and it has the form of a single or double peaked function in all investigated samples.

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Signature change in p-adic and noncommutative FRW cosmology

International Journal of Modern Physics A ◽

10.1142/s0217751x14501553 ◽

2014 ◽

Vol 29 (27) ◽

pp. 1450155 ◽

Cited By ~ 2

Author(s):

Goran S. Djordjevic ◽

Ljubisa Nesic ◽

Darko Radovancevic

Keyword(s):

Loop Quantum Gravity ◽

Initial Conditions ◽

Planck Scale ◽

The Other ◽

Frw Cosmology ◽

Signature Change ◽

Discrete Nature ◽

Frw Metric ◽

The Universe ◽

Friedmann Robertson Walker

The significant matter for the construction of the so-called no-boundary proposal is the assumption of signature transition, which has been a way to deal with the problem of initial conditions of the universe. On the other hand, results of Loop Quantum Gravity indicate that the signature change is related to the discrete nature of space at the Planck scale. Motivated by possibility of non-Archimedean and/or noncommutative structure of space–time at the Planck scale, in this work we consider the classical, p-adic and (spatial) noncommutative form of a cosmological model with Friedmann–Robertson–Walker (FRW) metric coupled with a self-interacting scalar field.

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COSMOLOGICAL EFFECTS OF NONLINEAR ELECTRODYNAMICS

International Journal of Modern Physics A ◽

10.1142/s0217751x05024717 ◽

2005 ◽

Vol 20 (11) ◽

pp. 2421-2430 ◽

Cited By ~ 15

Author(s):

M. NOVELLO

Keyword(s):

Nonlinear Electrodynamics ◽

Global Properties ◽

The Universe

We present some consequences induced by nonlinear electrodynamics on the global properties of the universe.

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Emergent Universe as an interaction in the dark sector

Modern Physics Letters A ◽

10.1142/s0217732317501528 ◽

2017 ◽

Vol 32 (28) ◽

pp. 1750152

Author(s):

Emiliano Marachlian ◽

I. E. Sánchez G. ◽

Osvaldo P. Santillán

Keyword(s):

Dark Matter ◽

Dark Energy ◽

Equation Of State ◽

Linear Equation ◽

Vacuum Energy ◽

Cosmological Parameters ◽

Emergent Universe ◽

Dark Sector ◽

Cosmological Scenario ◽

Friedmann Robertson Walker

A cosmological scenario where dark matter interacts with a variable vacuum energy for a spatially flat Friedmann–Robertson–Walker (FRW) spacetime is proposed and analyzed to show that with a linear equation of state and a particular interaction in the dark sector it is possible to get a model of an Emergent Universe. In addition, the viability of two particular models is studied by taking into account the recent observations. The updated observational Hubble data and the JLA supernovae data are used in order to constraint the cosmological parameters of the models and estimate the amount of dark energy in the radiation era. It is shown that the two models fulfil the severe bounds of [Formula: see text] at the 2[Formula: see text] level of Planck.

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Can accelerated expansion of the universe be due to spacetime vorticity?

Modern Physics Letters A ◽

10.1142/s0217732318502401 ◽

2018 ◽

Vol 33 (40) ◽

pp. 1850240

Author(s):

Babur M. Mirza

Keyword(s):

Magnetic Field ◽

Accelerated Expansion ◽

Newtonian Gravity ◽

Hubble’S Parameter ◽

Cosmic Expansion ◽

Zero Curvature ◽

Expansion Of The Universe ◽

General Relativistic ◽

The Universe ◽

The Magnetic Field

We present here a general relativistic mechanism for accelerated cosmic expansion and the Hubble’s parameter. It is shown that spacetime vorticity coupled to the magnetic field density in galaxies causes the galaxies to recede from one another at a rate equal to the Hubble’s constant. We therefore predict an oscillatory universe, with zero curvature, without assuming violation of Newtonian gravity at large distances or invoking dark energy/dark matter hypotheses. The value of the Hubble’s constant, along with the scale of expansion, as well as the high isotropy of CMB radiation are deduced from the model.

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