Holographic dark energy from generalized entropies and extended infrared cut-offs

summary

The gist

The gist The study investigates holographic dark energy models constructed from generalized entropies and extended infrared cut-offs against joint DESI DR2 BAO, Pantheon+ and Planck compressed CMB

In short

The study tested nine holographic dark energy models by combining three generalized entropies (Barrow, S3, S5) with three different infrared cut-offs. Analysis against DESI DR2 BAO, Pantheon+, and Planck data showed that a higher-order cut-off (Cut-off 3) is preferred for Barrow and S5 models. The results suggest the data favor these extensions over simpler models, while confirming the Bekenstein-Hawking area law remains compatible with zero in the Barrow case.

Key concepts

Holographic Dark Energy (HDE): This model suggests vacuum energy density is limited by the size of a region, like a black hole. The energy density scales with $M^2/L^2$, where L is an infrared cut-off scale. Choosing the correct L is vital for describing dark energy's evolution in the universe.
Generalized Entropies (Barrow, S3, S5): These are different mathematical ways to define entropy that describe how information or disorder behaves in a system. The study uses three such entropies—Barrow, $S_3$, and $S_5$—to model the holographic dark energy density.
Infrared Cut-offs (GO, Cut-off 2, Cut-off 3): These represent different physical scales used to define the infrared limit L in HDE models. The Granda–Oliveros (GO) scale is local and present-epoch based. Cut-off 2 adds a $\gamma H^{-2}$ term, and Cut-off 3 adds a second-order $\gamma ilde{H}/H$ term, which allows for more complex cosmological dynamics.
Phantom Crossing: This refers to a behavior in the dark energy equation of state where the pressure becomes more negative than its energy density. The study found that models with $S_3$ and $S_5$ exhibit this phantom crossing behavior, indicating non-standard dark energy evolution.

Terminology used across episodes

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This episode discusses

The paper

Holographic dark energy from generalized entropies and extended infrared cut-offs · Read on arXiv

Ke Chen, Simone D’Onofrio, Sergei D. Odintsov, Tanmoy Paul

Institute of Space Sciences (ICE, CSIC) · Department of Physics, Visva-Bharati University · ICREA

Transcript

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Today's paper: "Holographic dark energy from generalized entropies and extended infrared cut-offs".

Jocelyn: The gist The study investigates holographic dark energy models constructed from generalized entropies and extended infrared cut-offs against joint DESI DR2 BAO,

Vera: First, who's behind it and why it matters.

Title and authors: Subrahmanyan: Moving onto what the paper actually finds, they determined that the overall best fit is actually Barrow entropy combined with cut-off three. Then you have S3 plus GO, and S5 plus cut-off three as the other strong contenders they found. They noted that all other models, including Barrow plus GO, are disfavored by an Akaike Information Criterion penalty greater than one hundred forty <ref:2610.11616#pg2>.

Jocelyn: That’s a pretty big penalty to be disfavored by; it suggests that the data strongly prefer those two specific combinations over the other seven models they tested in this study. It tells us which structure is most likely supported by what we're observing right now.

Vera: And there's a key finding about those extended cut-offs themselves—that gamma H-two term, which belongs to cut-off two—is unconstrained in every single case because they said it only becomes relevant in the far future and never improves on the GO cut-off <ref:2610.11616#pg1>.

Subrahmanyan: That’s important for understanding the physics there; it means that term is essentially a parameter for when we look really far into the late time low-H regime, not something that drives current fits.

The paper's summary: Vera: So, to summarize what this paper on "Holographic dark energy from generalized entropies and extended infrared cut-offs" actually tells us, it’s that the framework is built on Bekenstein–Hawking entropy, but they tested three different entropy shapes: Barrow, S3, and S5. They then paired each of those shapes with the Granda–Oliveros cut-off and two other extensions involving cut-off two or cut-off three <ref:2610.11616#pg1>.

Jocelyn: What they are trying to prove is which specific pairing works best when you look at all the cosmological data we have collected, like DESI BAO and Planck CMB data <ref:2610.11616#pg2>. They are also trying to see if those extended cut-offs offer real dynamical leverage beyond just the standard GO cut-off or if they just add unconstrained parameters as they mentioned on page two of this paper <ref:2610.11616#pg2>.

Subrahmanyan: The main structural thing they highlighted is that for each entropy shape, using cut-off three can cause a qualitative change in the structure, specifically appearing as a second-order or higher-order system <ref:2610.11616#pg2>. This is what makes the comparison between cut-off two and cut-off three so important.

The paper's improvements: Vera: They also found some interesting dynamical sensitivities within those models, particularly for S3 and S5 entropies, they found that the second-order dynamics are genuinely probed by the data when using cut-off three, which is a qualitative change of structure as they described on page two of this paper <ref:2610.11616#pg2>.

Jocelyn: That contrasts with that gamma H-two term in cut-off two, which they said fails to improve the fit across all three entropy cases because that term is entirely prior-dominated <ref:2610.11616#pg3>. It’s not helping much right now for fitting the data today.

Subrahmanyan: What they really point out is this dichotomy with cut-off three; for Barrow and S5, the second-order dynamics gets probed by the data, but for S3, the shooting parameter remains prior-dominated and gamma r is driven to zero <ref:2610.11616#pg3>.

Vera: So it seems like cut-off three is a much more powerful tool for probing higher-order dynamics in two of those entropy sectors compared to cut-off two or that specific gamma H-two term <ref:2610.11616#pg3>. It's telling us where the data is most sensitive.

Conclusion: Jocelyn: So wrapping up this paper "Holographic dark energy from generalized entropies and extended infrared cut-offs," the main implication is that meaningful extensions of the GO cut-off should act at intermediate redshifts where BAO and supernovae have constraining power, not just in asymptotic regimes.

Vera: That’s the practical lesson here. The data favors a higher-order infrared cut-off in two of those three entropy sectors, but it doesn't show a significant preference for changing the basic Barrow area law in those models.

Subrahmanyan: We see that the best fit is Barrow plus cut-off three, and the BIC confirms this choice, with a BIC of twenty-four point six one for S3 plus GO and sixty point six six for S5 plus cut-off three <ref:2610.11616#pg2>.

Jocelyn: It’s a systematic baseline now against which more refined tests of holographic dark energy can be measured moving forward, and we should keep watching how these constraints evolve.

Vera: Agreed. That's the end of our discussion on this paper today, and we'll move on to whatever new research is coming up next in the field.

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