Poynting vector, energy densities, and pressure of collective transverse electromagnetic fluctuations in unmagnetized plasmas

Schlickeiser, R.

doi:doi:10.1063/1.3671965

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A systematic calculation of the electromagnetic properties (Poynting vector, electromagnetic energy, and pressure) of the collective transverse fluctuations in unmagnetized plasmas with velocity-anisotropic plasma particle distributions functions is presented. Time-averaged electromagnetic properties for monochromatic weakly damped wave-like fluctuations and space-averaged electromagnetic properties for monochromatic weakly propagating and aperiodic fluctuations are calculated. For aperiodic fluctuations, the Poynting vector as well as the sum of the space-averaged electric and magnetic field energy densities vanish. However, aperiodic fluctuations possess a positive pressure given by its magnetic energy density. This finite pressure density p_a of aperiodic fluctuations has important consequences for the dynamics of cosmic unmagnetized plasmas such as the intergalactic medium after reionization. Adopting the standard cosmological evolution model, we show that this additional pressure changes the expansion law of the universe leading to further deceleration. Negative vacuum pressure counterbalances this deceleration to an accelerating universe provided that the negative vacuum pressure is greater than 1.5p_a, which we estimate to be of the order 2.1 · 10⁻¹⁶dyn cm⁻².

Article Outline

INTRODUCTION
BASIC EQUATIONS
1. Normal modes
2. Phase averaging
3. Aperiodic fluctuations ω _nR = 0
4. Wave-like fluctuations ω _nR ≠ 0
5. Simplification for unmagnetized plasmas
UNMAGNETIZED PLASMA
1. Weakly amplified/damped fluctuations
2. Weakly propagating fluctuations
3. An illustrative distribution function
  1. Nonrelativistic limit
  2. Ultrarelativistic limit
APERIODIC MONOCHROMATIC TRANSVERSE FLUCTUATIONS
1. Space-averaged Poynting vector
2. Space-averaged magnetic energy density
3. Space-averaged electric energy density
4. Space-averaged force stress tensor
WAVE-LIKE MONOCHROMATIC TRANSVERSE FLUCTUATIONS
1. Time-averaged Poynting vector
2. Time-averaged magnetic energy density
3. Time-averaged electric energy density
4. Time-averaged force stress tensor
DECELERATION OF INTERGALACTIC MEDIUM AFTER REIONIZATION
SUMMARY AND CONCLUSIONS

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KEYWORDS and PACS

Keywords

plasma dielectric properties, plasma fluctuations, plasma instability, plasma oscillations, plasma pressure

PACS

52.25.Gj

Fluctuation and chaos phenomena
52.25.Mq

Dielectric properties
52.35.Fp

Electrostatic waves and oscillations (e.g., ion-acoustic waves)
52.35.Py

Macroinstabilities (hydromagnetic, e.g., kink, fire-hose, mirror, ballooning, tearing, trapped-particle, flute, Rayleigh-Taylor, etc.)