nLab phantom dark energy

Idea

What is called phantom dark energy (Caldwell 02) is dark energy with an equation of state with $w \lt 1$, hence with stress-energy tensor of the form

$$T_{\mu \nu} \;=\; (\epsilon - P) u_\mu u_\nu - g_{\mu \nu} P$$

(for $u$ its density/flow vector field and $P \in \mathbb{R}$ the pressure) with

(1)$$w \;\coloneqq\; \frac{P}{\epsilon} \;\lt\; 1 \,.$$

It has been argued that data of observational cosmology actually prefers phantom dark energy over a plain cosmological constant (which correspondes to $w = 1$), see e.g. Caldwell 02, Di Valentino-Melchiorri-Silk 20.

As an effective phenomenon

Taken at face value a fundamental field (physics) with such an equation of state with $w \lt 1$ (1) appears to be inconsistent, as it violates the null energy condition. (Though this is subtle in itself, even fields with $w \gt -1$ may violate the null energy condition Sawicku-Vikman 12).

But apparent phantom dark energy may appear as an effective description of more fundamental effects, for instance of an inhomogeneous cosmology (Ludwick 15, Ludwick 18, review in Ludwick 17, Section 6)

Related concepts

• dark energy

• quintessence

• Witten's Dark Fantasy

References

Review:

• Kevin J. Ludwick, The Viability of Phantom Dark Energy: A Brief Review, Modern Physics Letters A 32, 28 (2017) (arXiv:1708.06981)

Original articles:

• R.R. Caldwell, A Phantom Menace? Cosmological consequences of a dark energy component with super-negative equation of state, Phys. Lett. B545:23-29, 2002 (arXiv:astro-ph/9908168)

• Ignacy Sawicki, Alexander Vikman, Hidden Negative Energies in Strongly Accelerated Universes, Phys. Rev. D 87, 067301 (2013) (arXiv:1209.2961)

• Kevin J. Ludwick, Examining the Viability of Phantom Dark Energy, Phys. Rev. D 92, 063019 (2015) (arXiv:1507.06492)

• Kevin J. Ludwick, The Viability of Phantom Dark Energy as a Quantum Field in 1st-Order FLRW Space, Phys. Rev. D 98, 043519 (2018) (arXiv:1804.02987)

Observation:

• Eleonora Di Valentino, Alessandro Melchiorri, Joseph Silk, Cosmic Discordance: Planck and luminosity distance data exclude LCDM (arXiv:2003.04935)