scholarly journals A class of solitons in Maxwell-scalar and Einstein–Maxwell-scalar models

2020 ◽  
Vol 80 (1) ◽  
Author(s):  
Carlos A. R. Herdeiro ◽  
João M. S. Oliveira ◽  
Eugen Radu
Keyword(s):  
Electromagnetic Field ◽  
Scalar Field ◽  
Quantum Gravity ◽  
Exact Solutions ◽  
Point Charge ◽  
Coulomb Field ◽  
Specific Class ◽  
Minimal Coupling ◽  
Flat Spacetime ◽  
Physical Quantities

AbstractRecently, no-go theorems for the existence of solitonic solutions in Einstein–Maxwell-scalar (EMS) models have been established (Herdeiro and Oliveira in Class Quantum Gravity 36(10):105015, 2019). Here we discuss how these theorems can be circumvented by a specific class of non-minimal coupling functions between a real, canonical scalar field and the electromagnetic field. When the non-minimal coupling function diverges in a specific way near the location of a point charge, it regularises all physical quantities yielding an everywhere regular, localised lump of energy. Such solutions are possible even in flat spacetime Maxwell-scalar models, wherein the model is fully integrable in the spherical sector, and exact solutions can be obtained, yielding an explicit mechanism to de-singularise the Coulomb field. Considering their gravitational backreaction, the corresponding (numerical) EMS solitons provide a simple example of self-gravitating, localised energy lumps.

Electromagnetism and special relativity

2018 ◽  
Author(s):  
J. Pierrus
Keyword(s):  
Electromagnetic Field ◽  
Special Relativity ◽  
Point Charge ◽  
Reference Frames ◽  
Classical Electrodynamics ◽  
Covariant Form ◽  
Field Tensor ◽  
Electromagnetic Field Tensor ◽  
Preferred Reference Frame ◽  
Physical Quantities

In 1905, when Einstein published his theory of special relativity, Maxwell’s work was already about forty years old. It is therefore both remarkable and ironic (recalling the old arguments about the aether being the ‘preferred’ reference frame for describing wave propagation) that classical electrodynamics turned out to be a relativistically correct theory. In this chapter, a range of questions in electromagnetism are considered as they relate to special relativity. In Questions 12.1–12.4 the behaviour of various physical quantities under Lorentz transformation is considered. This leads to the important concept of an invariant. Several of these are encountered, and used frequently throughout this chapter. Other topics considered include the transformationof E- and B-fields between inertial reference frames, the validity of Gauss’s law for an arbitrarily moving point charge (demonstrated numerically), the electromagnetic field tensor, Maxwell’s equations in covariant form and Larmor’s formula for a relativistic charge.

scholarly journals A new approach to exact solutions construction in scalar cosmology with a Gauss–Bonnet term

2017 ◽  
Vol 32 (25) ◽  
pp. 1750129 ◽  
Author(s):  
I. V. Fomin ◽  
S. V. Chervon
Keyword(s):  
Scalar Field ◽  
Cosmological Model ◽  
Exact Solutions ◽  
Hubble Parameter ◽  
Inflationary Cosmology ◽  
Friedmann Universe ◽  
Minimal Coupling ◽  
New Approach ◽  
Bonnet Gravity ◽  
Bonnet Term

We study the cosmological model based on Einstein–Gauss–Bonnet gravity with non-minimal coupling of a scalar field to a Gauss–Bonnet term in four-dimensional (4D) Friedmann universe. We show how constructing the exact solutions by the method based on a confrontation of the Hubble parameter in the model under consideration is achieved with that in a standard scalar field inflationary cosmology.

scholarly journals Self similar collapse and the Raychaudhuri equation

2019 ◽  
Vol 79 (12) ◽  
Author(s):  
Shibendu Gupta Choudhury ◽  
Soumya Chakrabarti ◽  
Ananda Dasgupta ◽  
Narayan Banerjee
Keyword(s):  
Scalar Field ◽  
Exact Solutions ◽  
Gravitational Collapse ◽  
Similar Distribution ◽  
Raychaudhuri Equation ◽  
Conformally Flat ◽  
Flat Spacetime ◽  
Imperfect Fluid ◽  
Self Similar

AbstractThe role of the Raychaudhuri equation in studying gravitational collapse is discussed. A self-similar distribution of a scalar field along with an imperfect fluid in a conformally flat spacetime is considered for the purpose. The general focusing condition is found out and verified against the available exact solutions. The connection between the Raychaudhuri equation and the critical phenomena is also explored.

scholarly journals FERMIONIC AND SCALAR FIELDS AS SOURCES OF INTERACTING DARK MATTER–DARK ENERGY

2011 ◽  
Vol 20 (13) ◽  
pp. 2543-2558 ◽  
Author(s):  
SAMUEL LEPE ◽  
JAVIER LORCA ◽  
FRANCISCO PEÑA ◽  
YERKO VÁSQUEZ
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Scalar Field ◽  
Analytical Solution ◽  
Scalar Fields ◽  
Nonminimal Coupling ◽  
Field Equations ◽  
Fermionic Field ◽  
Minimal Coupling ◽  
Constant Type

From a variational action with nonminimal coupling with a scalar field and classical scalar and fermionic interaction, cosmological field equations can be obtained. Imposing a Friedmann–Lemaître–Robertson–Walker (FLRW) metric, the equations lead directly to a cosmological model consisting of two interacting fluids, where the scalar field fluid is interpreted as dark energy and the fermionic field fluid is interpreted as dark matter. Several cases were studied analytically and numerically. An important feature of the non-minimal coupling is that it allows crossing the barrier from a quintessence to phantom behavior. The insensitivity of the solutions to one of the parameters of the model permits it to find an almost analytical solution for the cosmological constant type of universe.

scholarly journals Gravity quantized: Loop quantum gravity with a scalar field

2010 ◽  
Vol 82 (10) ◽  
Author(s):  
Marcin Domagała ◽  
Kristina Giesel ◽  
Wojciech Kamiński ◽  
Jerzy Lewandowski
Keyword(s):  
Scalar Field ◽  
Quantum Gravity ◽  
Loop Quantum Gravity

scholarly journals The Einstein–Maxwell-aether-axion theory: Dynamo-optical anomaly in the electromagnetic response

2016 ◽  
Vol 25 (04) ◽  
pp. 1650048 ◽  
Author(s):  
Timur Yu. Alpin ◽  
Alexander B. Balakin
Keyword(s):  
Electromagnetic Field ◽  
Vector Field ◽  
Exact Solutions ◽  
Unit Vector ◽  
Anomalous Behavior ◽  
Electromagnetic Response ◽  
Symmetric Model ◽  
Electrodynamic System ◽  
Electric And Magnetic Fields ◽  
Pp Wave

We consider a pp-wave symmetric model in the framework of the Einstein–Maxwell-aether-axion theory. Exact solutions to the equations of axion electrodynamics are obtained for the model, in which pseudoscalar, electric and magnetic fields were constant before the arrival of a gravitational pp-wave. We show that dynamo-optical interactions, i.e. couplings of electromagnetic field to a dynamic unit vector field, attributed to the velocity of a cosmic substratum (aether, vacuum, dark fluid[Formula: see text]), provide the response of axionically active electrodynamic system to display anomalous behavior.

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