Introduces Fractional Holographic Dark Energy (FHDE) via fractionally corrected entropy from a modified Wheeler-DeWitt equation and studies its late-time cosmology, field reconstructions, and extensions to modified gravity theories.
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Cosmological constant and vacuum energy: old and new ideas
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abstract
The cosmological constant (CC) term in Einstein's equations, Lambda, was first associated to the idea of vacuum energy density. Notwithstanding, it is well-known that there is a huge, in fact appalling, discrepancy between the theoretical prediction and the observed value picked from the modern cosmological data. This is the famous, and extremely difficult, "CC problem". Paradoxically, the recent observation at the CERN Large Hadron Collider of a Higgs-like particle, should actually be considered ambivalent: on the one hand it appears as a likely great triumph of particle physics, but on the other hand it wide opens Pandora's box of the cosmological uproar, for it may provide (alas!) the experimental certification of the existence of the electroweak (EW) vacuum energy, and thus of the intriguing reality of the CC problem. Even if only counting on this contribution to the inventory of vacuum energies in the universe, the discrepancy with the cosmologically observed value is already of 55 orders of magnitude. This is the (hitherto) "real" magnitude of the CC problem, rather than the (too often) brandished 123 ones from the upper (but fully unexplored!) ultrahigh energy scales. Such is the baffling situation after 96 years of introducing the Lambda-term by Einstein. In the following I will briefly (and hopefully pedagogically) fly over some of the old and new ideas on the CC problem. Since, however, the Higgs boson just knocked our door and recalled us that the vacuum energy may be a fully tangible concept in real phenomenology, I will exclusively address the CC problem from the original notion of vacuum energy, and its possible "running" with the expansion of the universe, rather than venturing into the numberless attempts to replace the CC by the multifarious concept of dark energy.
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Using Planck, DESI, supernovae, and redshift-space distortions, the authors infer that modified gravity, if present, must act only below ~30 Mpc and cannot modify the large scales previously considered.
A barotropic fluid with ω_s ≈ 0.29 and Ω_s ≈ 1.5×10^{-5} raises the inferred H0 to match SH0ES while remaining consistent with Planck CMB, DESI BAO, and Pantheon data.
QFT in FLRW spacetime yields a running vacuum energy density ρ_vac(H) that unifies mild dynamical dark energy today with H^4 inflation without an inflaton field.
A review summarizing the Hubble constant tension and proposed solutions from new physics that restore agreement between Planck CMB data and local H0 measurements within 1-2 sigma.
citing papers explorer
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An Interplay Between Fractional Calculus and Holographic Dark Energy
Introduces Fractional Holographic Dark Energy (FHDE) via fractionally corrected entropy from a modified Wheeler-DeWitt equation and studies its late-time cosmology, field reconstructions, and extensions to modified gravity theories.
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Signatures of Modified Gravity on Linear Scales in a Dynamical Dark Energy Background
Using Planck, DESI, supernovae, and redshift-space distortions, the authors infer that modified gravity, if present, must act only below ~30 Mpc and cannot modify the large scales previously considered.
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A barotropic alternative to Early Dark Energy for alleviating the $H_0$ tension
A barotropic fluid with ω_s ≈ 0.29 and Ω_s ≈ 1.5×10^{-5} raises the inferred H0 to match SH0ES while remaining consistent with Planck CMB, DESI BAO, and Pantheon data.
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Running Vacuum in the expanding Universe: a unified QFT paradigm for Inflation and Dark Energy
QFT in FLRW spacetime yields a running vacuum energy density ρ_vac(H) that unifies mild dynamical dark energy today with H^4 inflation without an inflaton field.
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In the Realm of the Hubble tension $-$ a Review of Solutions
A review summarizing the Hubble constant tension and proposed solutions from new physics that restore agreement between Planck CMB data and local H0 measurements within 1-2 sigma.