scholarly journals Quasi-geodesics in relativistic gravity

2021 ◽  
Vol 81 (1) ◽  
Author(s):  
Valerio Faraoni ◽  
Geneviève Vachon
Keyword(s):  
Pressure Gradient ◽  
Particle Production ◽  
Proper Time ◽  
Massive Particle ◽  
Particle Mass ◽  
Main Application ◽  
Affine Parameter

AbstractA four-force parallel to the trajectory of a massive particle can always be eliminated by going to an affine parametrization, but the affine parameter is different from the proper time. The main application is to cosmology, in which elements of the cosmic fluid are subject to a pressure gradient parallel to their four-velocities. Natural implementations of parallel four-forces occur when the particle mass changes, in scalar–tensor cosmology, and in cosmic antifriction due to particle production.

Geodesic structure of magnetically charged regular black hole

2017 ◽  
Vol 14 (09) ◽  
pp. 1750120 ◽  
Author(s):  
Muhammad Azam ◽  
Ghulam Abbas ◽  
Syeda Sumera ◽  
Abdul Rauf Nizami
Keyword(s):  
Black Hole ◽  
Effective Potential ◽  
Proper Time ◽  
Massive Particle ◽  
Circular Motion ◽  
Geodesic Path ◽  
Timelike Geodesic ◽  
Null Geodesics ◽  
Regular Black Hole ◽  
Geodesic Structure

The purpose of this paper is to study the geodesic structure of magnetically charged regular black hole (MCRBH). The behavior of timelike and null geodesics of MCRBH is investigated. The graphs have been plotted to show the relation between distance versus time and proper time for photon-like and massive particle. For radial and circular motion, the effective potential has been plotted with different parameters of BH. We conclude that massive particles move around the BH in timelike geodesic path.

scholarly journals The geodesics structure of Schwarzschild black hole immersed in an electromagnetic universe

2017 ◽  
Vol 26 (14) ◽  
pp. 1750169 ◽  
Author(s):  
A. Al-Badawi ◽  
M. Q. Owaidat ◽  
S. Tarawneh
Keyword(s):  
Black Hole ◽  
Analytical Solution ◽  
Exact Analytical Solution ◽  
Proper Time ◽  
Massive Particle ◽  
Schwarzschild Black Hole ◽  
Circular Orbits ◽  
Schwarzschild Metric ◽  
Effective Potentials ◽  
Em Field

The geodesic equations are considered in a spacetime that represents a Schwarzschild metric coupled to a uniform external electromagnetic (em) field. Due to the em field horizon shrinks and geodesics are modified. By analyzing the behavior of the effective potentials for the massless and massive particle we study the radial and circular trajectories. Radial geodesics for both photons and particles are solved exactly. It is shown that a particle that falls toward the horizon in a finite proper time slows down so that the particle reaches the singularity slower than Schwarzschild case. Timelike and null circular geodesics are investigated. We have shown that, there are no stable circular orbits for photons, however stable and unstable second-kind orbits exist for the massive particle. An exact analytical solution for the innermost stable circular orbits (ISCO) has been obtained. It has been shown that the radius of the ISCO shrinks due to the presence of the em field.

scholarly journals MASSIVE PARTICLE CREATION IN A STATIC (1 + 1)-DIMENSIONAL SPACE-TIME

1994 ◽  
Vol 09 (31) ◽  
pp. 2857-2869
Author(s):  
D. J. LAMB ◽  
A. Z. CAPRI ◽  
S. M. ROY
Keyword(s):  
Coordinate System ◽  
Particle Production ◽  
Dimensional Space ◽  
Massive Particle ◽  
Particle Creation ◽  
Vacuum State ◽  
Space Time ◽  
Physical Principle ◽  
Dimensional Space Time ◽  
Static Space

We show explicitly that there is particle creation in a static space-time. This is done by studying the field in a coordinate system based on a physical principle which has recently been proposed. There the field is quantized by decomposing it into positive and negative frequency modes on a particular space-like surface. This decomposition depends explicitly on the surface where the decomposition is performed, so that an observer who travels from one surface to another will observe particle production due to the different vacuum state.

Classical and quantum equations of motion of a 4-dimensional Schwarzschild–AdS and Reissner–Nordström–AdS black hole

2019 ◽  
Vol 28 (04) ◽  
pp. 1950061
Author(s):  
Eric Greenwood
Keyword(s):  
Black Hole ◽  
Wave Function ◽  
Domain Wall ◽  
Event Horizon ◽  
Particle Production ◽  
Proper Time ◽  
Oscillatory Solution ◽  
Finite Amount ◽  
Classical Singularity ◽  
Asymptotic Observer

We investigate the gravitational collapse of both a massive (Schwarzschild–AdS) and a massive-charged (Reissner–Nordström–AdS) 4-dimensional domain wall in AdS space. Here, we consider both the classical and quantum collapse, in the absence of quasi-particle production and backreaction. For the massive case, we show that, as far as the asymptotic observer is concerned, the collapse takes an infinite amount of time to occur in both the classical and quantum cases. Hence, quantizing the domain wall does not lead to the formation of the black hole in a finite amount of time. For the infalling observer, we find that the domain wall collapses to both the event horizon and the classical singularity in a finite amount of proper time. In the region of the classical singularity, however, the wave function exhibits both nonlocal and nonsingular effects. For the massive-charged case, we show that, as far as the asymptotic observer is concerned, the details of the collapse depend on the amount of charge present; that is, the extremal, nonextremal and overcharged cases. In the overcharged case, the collapse never fully occurs since the solution is an oscillatory solution which prevents the formation of a naked singularity. For the extremal and nonextremal cases, it takes an infinite amount of time for the outer horizon to form. For the infalling observer in the nonextremal case, we find that the domain wall collapses to both the event horizon and the classical singularity in a finite amount of proper time. In the region of the classical singularity, the wave function also exhibits both nonlocal and nonsingular effects. Furthermore, in the large energy density limit, the wave function vanishes as the domain wall approaches classical singularity implying that the quantization does not rid the black hole of its singular nature.

scholarly journals Quantum collapse of a charged n-dimensional BTZ-like domain wall

2017 ◽  
Vol 26 (04) ◽  
pp. 1750028 ◽  
Author(s):  
Eric Greenwood
Keyword(s):  
Black Hole ◽  
Wave Function ◽  
Domain Wall ◽  
Gravitational Collapse ◽  
Particle Production ◽  
Proper Time ◽  
Back Reaction ◽  
Finite Amount ◽  
Classical Singularity ◽  
Asymptotic Observer

We investigate both the classical and quantum gravitational collapse of a massive, charged, nonrotating [Formula: see text]-dimensional Bañados–Teitelboim–Zanelli (BTZ)-like domain wall in AdS space. In the classical picture, we show that, as far as the asymptotic observer is concerned, the details of the collapse depend on the amount of charge present in the domain wall; that is, if the domain wall is extremal, nonextremal or overcharged. In both the extremal and nonextremal cases, the collapse takes an infinite amount of observer time to complete. However, in the over-charged case, the collapse never actually occurs, instead one finds an oscillatory solution which prevents the formation of a naked singularity. As far as the infalling observer is concerned, in the nonextremal case, the collapse is completed within a finite amount of proper time. Thus, the gravitational collapse follows that of the typical formation of a black hole via gravitational collapse.Quantum mechanically, we take the absence of induced quasi-particle production and fluctuations of the metric geometry; that is, we ignore the effect of radiation and back-reaction. For the asymptotic observer, we find that, near the horizon, quantization of the domain wall does not allow the formation of the black hole in a finite amount of observer time. For the infalling observer, we are primarily interested in the quantum mechanical effect as the domain wall approaches the classical singularity. In this region, the main result is that the wave function exhibits nonlocal effects, demonstrated by the fact that the Hamiltonian depends on an infinite number of derivatives that cannot be truncated after a finite number of terms. Furthermore, in the large energy density limit, the wave function vanishes at the classical singularity implying that quantization does not rid the black hole of its singularity.

Activated Prominences; Mechanisms for Activation and Eruption

1979 ◽  
Vol 44 ◽  
pp. 307-313
Author(s):  
D.S. Spicer
Keyword(s):  
Pressure Gradient ◽  
Density Gradient ◽  
Current Density ◽  
Convective Instability ◽  
Tearing Mode ◽  
Magnetic Shear ◽  
Long Wavelength ◽  
Ideal Mhd ◽  
Gradient Change ◽  
Accelerated Particles

A possible relationship between the hot prominence transition sheath, increased internal turbulent and/or helical motion prior to prominence eruption and the prominence eruption (“disparition brusque”) is discussed. The associated darkening of the filament or brightening of the prominence is interpreted as a change in the prominence’s internal pressure gradient which, if of the correct sign, can lead to short wavelength turbulent convection within the prominence. Associated with such a pressure gradient change may be the alteration of the current density gradient within the prominence. Such a change in the current density gradient may also be due to the relative motion of the neighbouring plages thereby increasing the magnetic shear within the prominence, i.e., steepening the current density gradient. Depending on the magnitude of the current density gradient, i.e., magnetic shear, disruption of the prominence can occur by either a long wavelength ideal MHD helical (“kink”) convective instability and/or a long wavelength resistive helical (“kink”) convective instability (tearing mode). The long wavelength ideal MHD helical instability will lead to helical rotation and thus unwinding due to diamagnetic effects and plasma ejections due to convection. The long wavelength resistive helical instability will lead to both unwinding and plasma ejections, but also to accelerated plasma flow, long wavelength magnetic field filamentation, accelerated particles and long wavelength heating internal to the prominence.

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