Cosmological constant problem on the horizon

Multiple Transitions in Vacuum Dark Energy and H 0 Tension

“…We consider a model that consists of some new energy density source X r arising from the quantum zero-point energy of the fields with the mass m. Depending on the type of the quantum field (boson or fermion) and the energy scale of interest, X r can be either positive (dS-like) or negative (AdS-like;Martin 2012;Firouzjahi 2022aFirouzjahi , 2022b. For the sake of simplicity, here first we consider the case of a single quantum field, while the procedure for the multiple field is straightforward thanks to our simplifying assumption that the vacuum energies of the free fields do not exchange with each other.…”

“…This is the time when the effects of dark energy become important. Right: long after the transition, many patches of the dS horizon associated with X r enter the FLRW horizon and the effects of Firouzjahi (2022b). The time of the transition in dark energy is determined by the mass of the quantum field, happening at the temperature T c ∼ m (Park 2021a(Park , 2021b.…”

“…In practice, motivated by EDE proposal, we take the position of the first step (the first transition) to be after the time of matter-radiation equality and before the CMB decoupling around the redshift z c ∼ 2000-3000, while the follow-up transitions can happen much later in the cosmic expansion history. Within the model of Firouzjahi (2022b) this corresponds to a field with the mass m ∼ eV. As a field with this mass is not within the spectrum of the SM, one needs a new physics beyond the SM.…”

“…Recently, a combined analysis of Planck (ℓ TT  1000) with ACT and SPT data for EDE models has also been performed, such as CMB+SPTpol (Chudaykin et al 2020(Chudaykin et al , 2021Jiang & Piao 2021) In this paper, we study a scenario with multiple transient phases of dark energy, both before and after the surface of last scattering, yielding a higher value of the current Hubble expansion rate compared to what is inferred from the ΛCDM model. This is a phenomenological model motivated by Firouzjahi (2022b), who studied the quantum vacuum zero-point energy in connection to the cosmological constant problem and the origin of dark energy. Alternatively, the current setup may be viewed as an independent phenomenological mechanism with some similarities to the EDE proposal.…”

Developed Method. Interactions and Their Quantum Picture

“…A lot of work has also been done to clear up some General Relativity challenges. An explanation for the problem of dark energy [10] and dark matter [11] is still being sought, and efforts are still b eing made to explain the origin of the cosmological constant [12], [13], [14].…”