DESI results and Dark Energy from QCD topological sectors

TL;DR

The paper presents a dark energy model based on QCD vacuum topology, where DE arises from the subtraction between the expanding FRW and Minkowski vacuum energies tied to QCD topological sectors. The resulting vacuum energy scales linearly with the Hubble parameter, ρ_DE ∝ H, near a de Sitter state, with the QCD scale Λ_QCD fixing the DE magnitude and the asymptotic Hubble constant. DESI-era observations allowing a time-varying w_DE, including possible crossings of w = -1, are accommodated by a phenomenological activation function β(t) that turns on DE gradually; the modified Friedmann equation yields H(a) and w_DE(z) that can deviate from ΛCDM while preserving a de Sitter future. The framework predicts a distinct correlation between H(z) and w_DE(z), testable with current and upcoming data, without invoking new fundamental fields, and carries further implications such as possible cosmic magnetic fields and a tabletop probe of topological Casimir effects. Overall, the work offers a novel SM-grounded, non-perturbative mechanism for dark energy that directly ties cosmic evolution to QCD topology and holographic-like holonomy effects.

Abstract

We present a physically motivated dark-energy (DE) model rooted in the topological structure of the Quantum ChromoDynamic (QCD) vacuum. In this framework, DE arises from the difference between the vacuum energy of an expanding FRW universe and Minkowski spacetime, induced by QCD topological sectors. The resulting DE term in the Friedmann equation scales with the Hubble rate, $ρ_{\rm DE}(t)\propto H(t)$, once DE dominates cosmic expansion, i.e. when the Universe is close to the de Sitter regime with $H\approx$ constant. The QCD scale, $Λ_{\rm QCD}\sim100~{\rm MeV}$, naturally fixes the DE density and explains why its influence becomes significant only recently. The construction relies solely on the Standard Model of particle physics, introducing no new fields or couplings. The most fundamental change is the possibility of modifying the evolution of the background cosmology in the Friedmann equation. Key predictions include: (a) A present-day equation of state parameter $w_{\rm DE,0}>-1$ that asymptotically approaches the de Sitter limit $w_{\rm DE}=-1$ in the future. (b) A present-day Hubble constant $H_0$ that asymptotically approaches a constant $\overline{H}$ set by $Λ_{\rm QCD}$. (b) For $z\ge 0$, $w_{\rm DE}(z)$ may lie above or below $-1$ and can cross this boundary multiple times at different $z$, behavior qualitatively consistent with the recent DESI findings. (c) In our framework, any deviation from $Λ$CDM leads to a corresponding deviation of $H(z)$, which can be tested with existing and future cosmological observations.

Figures (3)

• Figure 1: Plot of the two functions $\beta(t)$ given in Eq.(\ref{['eq:betas']}). $t_i=0.0465\;{\rm Gyr}$ corresponds to the anchor point with the Friedmann cosmology. it is very close to the Big-Bang so that $t-t_i=0$ can be considered to be the beginning of the expansion of the Universe. The grey area above $t-t_i=13.78\;{\rm Gyr}$ corresponds to the future.
• Figure 2: Plots comparing various quantities in our framework to the Planck2018 cosmology as function of redshift. Red and black curves correspond respectively to the activation functions $\beta_1(t)$ and $\beta_2(t)$. When present, the green curve correspond to the Planck 2018 cosmology. Panel (a): fractional difference of the Hubble parameter, panel (b): fractional difference for the DE mass density $\rho_{\rm DE}$, panel (c): DE dimensionless density parameter, panel (d): DE equation of state parameter $w_{\rm DE}$. The grey area for $z<0$ corresponds to the future.
• Figure 3: Commoving distance as a function redshift $z$ relative to the Planck cosmology. The red abd black curves correspond to the activation functions $\beta_1(t)$ and $\beta_2(t)$ in Eq.(\ref{['eq:betas']}).