Dark Matter from Holography

Abstract: Previous studies have examined the holographic principle as a means of producing dark energy. Here we propose instead the possibility of holographic dark matter. In this case, dark matter does not arise in the framework of particle physics but is derived from the infrared cutoff set by the horizon scale. Using the Ricci cutoff, and a universe containing only baryons and radiation, we can account for the dark matter and naturally explain the coincidence between baryonic and nonbaryonic contributions to the density. In the presence of a pre-existing vacuum energy density our model reverses the sign of this density, thus accounting for the fact that certain string theories generically predict a negative vacuum energy, but observations require a positive value.

• The paper presents a holographic dark matter model using a Ricci cutoff that naturally matches the observed DM to baryon density ratio (approximately 5.3–5.4).
• It employs an information-theoretic approach linking horizon entropy with dark matter energy density, offering an emergent explanation that bypasses the need for exotic particles.
• The model integrates a negative effective vacuum energy in line with string theory predictions, while highlighting challenges in defining a microphysical Lagrangian for clustering.

Holographic Generation of Dark Matter: Implications and Theoretical Foundations

Introduction

"Dark Matter from Holography" (2511.10617) investigates the possibility that dark matter (DM), traditionally conceived as a particle physics phenomenon, can instead be explained via the holographic principle. This principle, crucial in quantum gravity, posits that the degrees of freedom in a region are bounded by its boundary’s area, rather than its volume. The paper builds upon the established use of holography for dark energy and proposes a Ricci cutoff-based holographic dark matter (HDM) model, exploring its compatibility with cosmological observations and its theoretical consistency within holographic frameworks.

The Holographic Energy Density Prescription

The holographic bound, as formulated by Cohen et al., constrains the total vacuum energy such that it never exceeds the threshold for gravitational collapse into black holes:

$L^3 \rho_\Lambda \le m_{Pl}^2 L$

Saturation yields the scaling:

$\rho_{HDE} = 3 c^2 m_{Pl}^2 L^{-2}$

Where $L$ is an infrared cutoff, typically related to cosmological horizon scales. While previous literature focused on this mechanism for dark energy, the paper recasts $\rho_{HDE}$ as the candidate dark matter density, defining the concept of holographic dark matter (HDM).

Ricci Cutoff and Model Construction

The Ricci cutoff, which avoids problematic extra radiation-like components seen in simpler horizon choices, is defined as:

$L^{-2} = \alpha H^2 + \beta \dot{H}$

Setting $\beta = \frac{\alpha}{2}$ leads to a model with favorable phenomenology; the resulting HDM density is:

$$\rho_{HDM} = \frac{\alpha}{4-\alpha} \rho_{B0} a^{-3} + 3K a^{4(1-\alpha)/\alpha}$$

Here, $\rho_{B0}$ is the present-day baryon density, $K$ is a constant of integration, and $a$ is the scale factor. Choosing $\alpha \approx 3.3$–$3.4$ matches the observed ratio $\rho_{DM}/\rho_b \approx 5.3$–$5.4$, predicting a natural coincidence between baryonic and dark matter densities—an empirical feature otherwise lacking robust theoretical grounding.

The second term, governed by $K$, can be set arbitrarily small to evade current observational limits, given the absence of empirical evidence for such an additional slowly-evolving energy component.

Effective Cosmological Constant and String Theory Compatibility

Upon the addition of a "bare" cosmological constant ($\rho_\Lambda$) into the Ricci cutoff-modified Friedmann framework, the model generates a negative effective contribution:

$$\rho_{\Lambda,eff} = \frac{1}{1-\alpha}\rho_\Lambda \approx -0.4\rho_\Lambda$$

Thus, observational consistency requires the bare vacuum energy to be negative—aligning the model with string theoretic predictions that favor a negative cosmological constant. The mechanism provides a route to reconciling theory with the empirical necessity of a positive vacuum energy, addressing a longstanding tension in quantum gravity and string cosmology scenarios.

Information-Theoretic Interpretation

The paper grounds HDM in an information-theoretic origin, echoing the microstate counting of quantum horizons:

$$\mathcal{N}(L) \sim \exp\left[\frac{A(L)}{4}\right]$$

where $A(L)$ is the area in Planck units. This entropy is mapped to energy density via:

$\rho_{\rm holo}(L) \propto L^{-2}$

Consequently, HDM is construed not as particulate matter but as emergent from information capacities of cosmic horizons, in line with QG frameworks like AdS/CFT and causal horizon thermodynamics. The covariant entropy bound further supports partitioning the holographic energy between matter and vacuum-like components:

$$S_{\rm matter}(L) + S_{\rm grav}(L) \leq \frac{A(L)}{4}$$

Clustering and Observational Viability

For cosmological viability, HDM must both scale correctly ($\propto a^{-3}$) and support structure formation. The adiabatic sound speed ($c_a$) is zero; however, the physically relevant perturbative sound speed ($c_s$) cannot be fully determined absent an underlying Lagrangian. $c_s = 0$ is required for clustering, and is typically imposed manually in the absence of a microphysical derivation. Thus, the ultimate test of this approach hinges on the future development of a consistent dynamical theory.

Implications and Future Directions

The holographic HDM model eliminates the need for undetected DM particles, remnants, or exotic fields, instead providing an emergent explanation predicated on horizon entropy limits. Notably, it predicts the baryon–DM density coincidence naturally and accommodates string theory's inclination toward negative vacuum energies. However, the lack of a microphysical Lagrangian and indeterminate clustering behavior remain significant open issues.

Future work will need to address the explicit construction of a sound speed-zero, clustering fluid from holographic principles, as well as develop phenomenological constraints sensitive to the potential existence of the slow-evolving $K$ component. More broadly, this approach suggests a paradigm shift wherein dark sector phenomenology may be reinterpreted within emergent gravity and horizon information frameworks.

Conclusion

The holographic dark matter model offers a theoretically motivated, information-theoretic route to explaining cosmological dark matter, its coincidence with baryonic matter, and compatibility with underlying quantum gravity principles. While observational constraints on extra radiation components restrict viable cutoff choices, the Ricci cutoff emerges as the preferred mechanism. The model also resolves the sign discrepancy between string-theoretic vacuum energy and astronomical requirements. Realizing HDM's full potential necessitates future progress in constructing a viable microphysical theory and probing its distinctive observational consequences.