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Carsten van de Bruck, Elsa M. Teixeira | Physical review. D/Physical review. D. | (2020)
Primary Link DOI Openalex Full text (OA)

Key Takeaways

Sample Definition And Size

The study investigates a cosmological model in which dark matter resides on a D3-brane moving in a higher-dimensional spacetime, with dark energy represented by the brane’s position scalar field. The analysis is theoretical and numerical, not based on observational sample data; thus, no sample size is applicable.

Study Type

This is a theoretical and numerical study of a cosmological model, involving analytical derivations of background and perturbation equations and numerical simulations using a modified Boltzmann code (CLASS). It is not an observational or experimental study.

Conflicts Of Interest

No conflicts of interest are declared in the provided text.

Results Summary

Key findings include: (1) Identification of two regimes of the disformal coupling between dark energy and dark matter—one with coupling always positive, another where coupling becomes negative at present. (2) The coupling is negligible at early times and grows during the late matter-dominated era. (3) Derivation of linear perturbation equations and an expression for the effective time-dependent gravitational coupling Geff between dark matter particles. In the subhorizon limit, Geff ≃ GN(1 + 2β²/γ), where β is the effective coupling. (4) Numerical results show deviations from ΛCDM in the cosmic microwave background anisotropy and matter power spectra, with enhanced or suppressed ISW effect depending on coupling sign, shifts in acoustic peaks, and scale-dependent modifications in structure growth. (5) Models with earlier coupling activation show larger deviations; some models predict σ₈ values above ΛCDM, others below.

Abstract

We study the cosmological predictions of the dark D-brane model, in which dark matter resides on a D-brane moving in a higher-dimensional space. By construction, dark matter interacts only gravitationally with the standard model sector in this framework. The dark energy scalar field is associated with the position of the D-brane, and its dynamics is encoded in a Dirac-Born-Infeld action. On the other hand, dark matter is identified with matter on the D-brane, that naturally couples to dark energy via a disformal coupling. We analyze the numerical evolution of the cosmological background, highlighting the fact that there are two regimes of interest: one in which the coupling is positive throughout and another in which the coupling is negative at the present. In the latter, there is the enticing possibility of having scenarios in which the coupling is positive for a significant part of the evolution, before decreasing toward negative values. In both cases, the coupling is very small at early times and starts to grow only during the late matter-dominated era. We also derive the equations for the linear cosmological perturbations and an expression for the effective time-dependent gravitational coupling between dark matter particles and present the numerical results for the cosmic microwave background anisotropy and matter power spectra. This allows for a direct comparison of the predictions for the growth of large-scale structure with other disformal quintessence models.

Referenced In

StarTalk

Season 17, Episode 19: Is Dark Matter Just Regular Matter in Another Universe?

Hey StarTalkians! Neil and Chuck got a treat this week, sitting down with Professor Brian Greene for a chat about hidden dimensions, string theory and Hilbert spaces. In the discussion, Professor Greene explained a little about “brane worlds” and how they interact with gravity:

Exploring Hidden Dimensions with Brian Greene - StarTalk Radio

(from 47:00)

There is a tantalizing question that comes out of all of this: what if dark matter was just regular matter in another brane?

The Basics of String Theory

The “basics” of string theory are actually easy enough to understand if you don’t delve into the math. It posits that, instead of multiple fundamental particles, the fundamental objects of the universe are actually one-dimensional “strings.”

In the same way guitar strings can produce multiple stable pitches, these cosmic strings can also vibrate in several different ways. These different vibrational “modes” lead to the particles in our universe. So like you can pluck out a whole scale along a guitar string, the cosmic strings create the symphony of matter we see around us.

Brane Worlds Explained

A “brane” is like a cosmic “membrane” that occupies some number of dimensions. A 0-dimensional brane is a particle, a 1-dimensional brane is a string, a flat 2D membrane is a 2-brane and so on.

These branes can have more dimensions, and crucially, get much bigger. It’s possible that a multi-dimensional brane got a huge boost of energy and inflated, ultimately forming our universe. There could equally be other brane worlds out there, alongside ours in a higher-dimensional space.  

Strings interact with these higher-dimensional branes. Strings are either closed (connected to itself) or open. The ends of open strings attach to branes, confining them to that brane world. Most of the forces (electromagnetism and the strong and weak nuclear forces) are confined in this way. Gravity, on the other hand, comes from closed strings, which can freely travel through the inter-brane space, leaking out of our universe.  

The “Dark Brane” and Dark Matter

That explains why gravity is so weak, as Brian pointed out. But it might also explain dark matter. Some physicists propose a hypothetical “dark brane”, which is filled with ordinary matter.

Electromagnetism is confined to the brane, so we can’t see this other world. But gravity is not, so maybe we can feel it, as what we call “dark matter.”

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