⚛️ general relativity

Can UV meet IR in the Swiss cheese?

This paper investigates whether the ultraviolet modifications used to regularize black hole singularities can influence the expansion rate of the universe, ultimately finding that the observed accelerated expansion is best explained by models where these regular black holes are actually horizonless compact objects.

Original authors: Madina Abilmazhinova, Diana Kulubayeva, Hrishikesh Chakrabarty, Daniele Malafarina

Published 2026-02-10

📖 4 min read🧠 Deep dive

CC BY 4.0

Original authors: Madina Abilmazhinova, Diana Kulubayeva, Hrishikesh Chakrabarty, Daniele Malafarina

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The Big Idea: Can the Tiny Fix the Huge?

Imagine you are looking at two completely different problems in a house.

The Tiny Problem (UV): There is a microscopic crack in the foundation of a single brick. If left alone, it might cause the brick to crumble into nothingness (this is like the "singularity" at the center of a black hole, where physics breaks down).
The Huge Problem (IR): The entire house is slowly drifting away from the rest of the neighborhood, and nobody knows why (this is like "Dark Energy," the mysterious force pushing our universe apart).

Usually, scientists treat these as totally separate issues. But this paper asks a wild, beautiful question: What if fixing the crack in the brick is actually what’s causing the whole house to drift away?

In physics terms, they are asking if the "Ultraviolet" (UV) fixes we use to stop black holes from collapsing can explain the "Infrared" (IR) mystery of why the universe is expanding so fast.

The "Swiss Cheese" Universe

To study this, the researchers use a concept called the Swiss Cheese Model.

Imagine the universe is a giant, smooth block of Swiss cheese. The "holes" in the cheese are black holes. In the old way of thinking, these holes were just empty, dead spots. But in this paper, the researchers suggest that these holes aren't just empty; they are "regularized."

Instead of having a bottomless pit at the center (a singularity), these black holes have a "core" that is smooth and stable. This is like replacing a bottomless drain in your sink with a solid, bouncy ball.

The Connection: The "Bouncy Ball" Effect

Here is the magic trick of the paper: When you take these "smooth" black holes and embed them into the universe, they don't just sit there quietly. Because they are different from standard black holes, they actually "leak" a little bit of extra energy into the space around them.

Think of it like this: If you put a bunch of tiny, vibrating tuning forks inside a giant tub of jelly, the vibrations from those tiny forks will eventually make the entire tub of jelly wobble.

The researchers found that the "vibrations" (the mathematical corrections) from these regular black holes act exactly like Dark Energy. The tiny, microscopic changes needed to fix the black hole's center create a repulsive force that pushes the entire universe outward.

The Verdict: What did they find?

The scientists tested several different "blueprints" for these smooth black holes against real-world data from telescopes (like how fast galaxies are moving and how old the universe is).

Their findings were fascinating:

It works! Several of their models actually fit the observed data better than the current standard model of the universe ( $\Lambda$ CDM).
The "Horizonless" Twist: The best fit didn't come from standard black holes, but from something even weirder: "Horizonless Compact Objects."

Imagine a black hole is like a whirlpool in the ocean—once you go past a certain point, you can never get out. A "horizonless" object is more like a very intense, swirling whirlpool that is incredibly dense, but doesn't have that "point of no return." The data suggests that if the universe is being pushed apart by black holes, those black holes might not even be "true" black holes, but these exotic, ultra-dense "whirlpools" without a point of no return.

Summary in a Nutshell

The paper suggests that the mystery of the entire universe (why it's expanding) might be hidden inside the smallest parts of a black hole (how they avoid collapsing). By fixing the "tiny" math of black holes, we might accidentally solve the "huge" mystery of the cosmos.

Technical Summary: "Can UV meet IR in the Swiss cheese?"

Authors: Madina Abilmazhinova, Diana Kulubayeva, Hrishikesh Chakrabarty, and Daniele Malafarina (Nazarbayev University).
Date: February 10, 2026.

1. The Problem: The UV-IR Connection

The paper addresses a fundamental tension in modern physics: the disconnect between the Ultraviolet (UV) regime (small-scale, high-curvature physics where General Relativity fails due to singularities) and the Infrared (IR) regime (large-scale, cosmological distances where Dark Energy drives accelerated expansion).

Specifically, the authors investigate whether the theoretical modifications required to "regularize" black holes (removing the central singularity via UV corrections) could simultaneously provide a physical mechanism for the observed cosmic acceleration (an IR effect).

2. Methodology: The Swiss Cheese Framework

To bridge these scales, the authors employ the "Swiss Cheese" model, an exact solution in General Relativity that embeds local objects into a cosmological background.

The Setup: They match a spherically symmetric, regular black hole (the "cheese" hole) to an expanding Friedmann-Lemaître-Robertson-Walker (FLRW) universe (the "cheese").
Junction Conditions: Using the Israel junction conditions, they ensure the metric and the second fundamental form are continuous across the boundary. They focus on a co-moving boundary ( $r_b = \text{const.}$ ) to avoid the complexities of thin-shell layers.
Induced Dark Energy: By matching the regular black hole mass function $M(R)$ to the FLRW expansion, the authors derive modified Friedmann equations. The "UV corrections" to the black hole geometry manifest in the exterior universe as an additional effective fluid component ( $\rho_*$ ) with a specific equation of state $\omega_*(a)$ .
Models Tested: They analyze four specific regular black hole geometries:
1. Hayward: Based on non-linear electrodynamics.
2. Bardeen: Based on non-linear electrodynamics.
3. Dymnikova: A de Sitter core transitioning to a Schwarzschild vacuum.
4. Asymptotic Safety (AS): Derived from renormalization group approaches in quantum gravity.

3. Key Contributions

Theoretical Mapping: The paper provides a formal mathematical derivation showing how the UV cutoff parameter (the scale at which gravity is regularized) directly dictates the evolution of the cosmic expansion rate.
Cosmological Modeling: They transform local black hole parameters (like the non-linear charge $Q_{ned}$ or the AS scale $q_{AS}$ ) into cosmological parameters that can be tested against observational data.
Observational Testing: Unlike previous theoretical studies of regular black holes, this work subjects these models to rigorous statistical constraints using real-world cosmological datasets.

4. Results and Statistical Analysis

The authors performed a Markov Chain Monte Carlo (MCMC) analysis using three major datasets: Baryon Acoustic Oscillations (DESI), Cosmic Chronometers (CC), and Type Ia Supernovae (Pantheon+).

Model Performance: All four Cosmologically Coupled Regular Black Hole (CCRBH) models performed better than the standard $\Lambda$ CDM model in terms of the Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC).
Parameter Constraints:
- For the Hayward, Bardeen, and AS models, the data could only provide lower bounds on the charge parameters. This is because, at high charge values, these models become indistinguishable from the cosmological constant ( $\Lambda$ ).
- The Dymnikova model was the only one where the parameter could be constrained at both ends.
The "Horizonless" Finding: Interestingly, the best fits for the UV cutoff parameters correspond to values that would describe horizonless compact objects rather than traditional black holes. This suggests that if UV corrections drive dark energy, the "black holes" in our universe might actually be exotic, non-singular compact objects.

5. Significance

This paper proposes a provocative unified framework: Dark Energy may not be a new fundamental field, but a macroscopic manifestation of the quantum-gravitational corrections required to prevent black hole singularities.

While the authors conclude that current data is not yet sufficient to definitively prove or rule out this hypothesis, they establish a clear observational pathway. Future high-precision measurements of black hole shadows (like Sgr A*) and improved cosmological surveys will allow scientists to check if the "charge" required to explain the universe's expansion matches the "charge" observed in local black hole candidates.