A model of holographic dark energy is no longer unstable

Scientists at BFU named after Kant Immanuel, doctor of Physics and Mathematics Artyom V. Astashenok and Alexander S. Tepliakov have proved the viability of a holographic dark energy model. Such model was considered unstable and therefore wasn't widely used for describing the acceleration in the expansion of the Universe. The results of the research have been published in the Physics Letters B magazine.

In 1998, scientists discovered that our Universe expands with acceleration, and in order to explain this effect, such concept as dark matter was introduced. This is a special type of energy that fills up all of the existing space-time but is impossible to detect by direct methods. Its existence and features are portrayed in a standard cosmological model, but by now scientists have found a number of issues (for example, the cosmological constant problem, the fine-tuning problem) that cannot be adequately addressed by this model. So scientists develop new models that would allow to coherently describe the acceleration in the expansion of the Universe.

Scientists at BFU named after Kant Immanuel (Kaliningrad) considered an alternative model—a holographic dark energy model—and have proven its viability.

"It's a slightly different way of looking at the nature of accelerated expansion of the Universe. It stems from the holographic principle which follows from quantum gravity and string theory. According to it, all values inside a certain amount of volume can be described by parameters that are observed on its boundary. In other words, the Universe can be represented in the form of some hologram, and it can be described by the parameters on its boundaries" — says Alexander Tepliakov, junior researcher at the laboratory for mathematical modeling of complex and non-linear systems at BFU named after Kant Immanuel.

A new model of holographic dark energy was suggested within the holographical principle in 2004. However, the new model also had a drawback. The thing is, the dark energy is usually represented as some kind of liquid that homogenously and evenly fills the Universe. A special parameter called square of the sound velocity is used to analyze the fluctuations inside this liquid. If it turns out to be negative as a result of calculations, the model is considered unstable. Previous studies carried out as part of a holographic dark energy model had a negative sound speed square.

The researchers suggested that the holographic dark energy shouldn't be seen as a liquid. Instead, it must be considered as dark energy perturbations, taking into account its metric properties. They concluded that the model is in fact stable, meaning it's realistic.

"Now, we need to understand to what extent our model corresponds to observation data provided by space-based telescopes. In 2024 precise data became available for analysis: relationship between red shift for Type Ia supernovae, baryon acoustic oscillations. By comparing the proposed cosmological model with this data we are able to assess whether it describes the real Universe" — summarizes Alexander Tepliakov.

More information:
doi.org/10.1016/j.physletb.2024.138767

Provided by Immanuel Kant Baltic Federal University