Elahe Karimkhani | Searcharxiv

arXiv2016

Higgs potential from extended Brans-Dicke theory and the time-evolution of the fundamental constants

Despite the enormous significance of the Higgs potential in the context of the Standard Model of electroweak interactions and in Grand Unified Theories, its ultimate origin is fundamentally unknown and must be introduced by hand in accordance with the underlying gauge symmetry and the requirement of renormalizability. Here we propose a more physical motivation for the structure of the Higgs potential, which we link to gravity, and more specifically to an extended Brans-Dicke (BD) theory containing two interacting scalar fields. One of these fields is coupled to curvature as in the BD formulation, whereas the other is coupled to gravity both derivatively and non-derivatively through the curvature scalar and the Ricci tensor. By requiring that the cosmological solutions of the model are consistent with observations, we show that the effective scalar field potential adopts the Higgs potential form with a mildly time-evolving vacuum expectation value. Such residual vacuum dynamics could be responsible for the possible time variation of the fundamental constants. The approach is in part reminiscent of Bjorken's ideas on the cosmological constant problem.

gr-qc↗

arXiv2015

Background history and cosmic perturbations for a general system of self-conserved dynamical dark energy and matter

We determine the Hubble expansion and the general cosmic perturbations equations for a general system consisting of self-conserved matter and self-conserved dark energy (DE). While at the background level the two components are non-interacting, they do interact at the perturbations level. We show that the coupled system of matter and DE perturbations can be transformed into a single, third order, matter perturbation equation, which reduces to the (derivative of the) standard one in the case that the DE is just a cosmological constant. As a nontrivial application we analyze a class of dynamical models whose DE density $ρ_D$ consists of a constant term, $C_0$, and a series of powers of the Hubble rate. These models were previously analyzed from the point of view of dynamical vacuum models, but here we treat them as self-conserved DE models with a dynamical equation of state. We fit them to the wealth of expansion history and linear structure formation data and compare the obtained fit quality with that of the concordance $Λ$CDM model. Those with $C_0=0$ include the so-called "entropic-force" and "QCD-ghost" DE models, as well as the pure linear model $ρ_D\sim H$, all of which appear strongly disfavored. The models with $C_0\neq 0$, in contrast, emerge as promising dynamical DE candidates whose phenomenological performance is highly competitive with the rigid $Λ$-term inherent to the $Λ$CDM.

gr-qc↗