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Register a new userThe $Z$ boson in the Framed Standard Model
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Jose Bordes
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The framed standard model (FSM), constructed initially for explaining the existence of three fermion generations and the hierarchical mass and mixing patterns of quarks and leptons, suggests also a hidden sector of particles including some dark matter candidates. It predicts in addition a new vector boson $G$, with mass of order TeV, which mixes with the $gamma$ and $Z$ of the standard model yielding deviations from the standard mixing scheme, all calculable in terms of a single unknown parameter $m_G$. Given that standard mixing has been tested already to great accuracy by experiment, this could lead to contradictions, but it is shown here that for the three crucial and testable cases so far studied (i) $m_Z - m_W$, (ii) $Gamma(Z rightarrow ell^ + ell^-)$, (iii) $Gamma(Z rightarrow$ hadrons), the deviations are all within the present stringent experimental bounds provided $m_G > 1$ TeV, but should soon be detectable if experimental accuracy improves. This comes about because of some subtle cancellations, which might have a deeper reason that is not yet understood. By virtue of mixing, $G$ can be produced at the LHC and appear as a $ell^+ ell^-$ anomaly. If found, it will be of interest not only for its own sake but serve also as a window on to the hidden sector into which it will mostly decay, with dark matter candidates as most likely products.
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The high-energy scattering of massive electroweak bosons, known as vector boson scattering (VBS), is a sensitive probe of new physics. VBS signatures will be thoroughly and systematically investigated at the LHC with the large data samples available and those that will be collected in the near future. Searches for deviations from Standard Model (SM) expectations in VBS facilitate tests of the Electroweak Symmetry Breaking (EWSB) mechanism. Current state-of-the-art tools and theory developments, together with the latest experimental results, and the studies foreseen for the near future are summarized. A review of the existing Beyond the SM (BSM) models that could be tested with such studies as well as data analysis strategies to understand the interplay between models and the effective field theory paradigm for interpreting experimental results are discussed. This document is a summary of the EU COST network VBScan workshop on the sensitivity of VBS processes for BSM frameworks that took place December 4-5, 2019 at the LIP facilities in Lisbon, Portugal. In this manuscript we outline the scope of the workshop, summarize the different contributions from theory and experiment, and discuss the relevant findings.
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The framed standard model (FSM) predicts a $0^+$ boson with mass around 20 MeV in the hidden sector, which mixes at tree level with the standard Higgs $h_W$ and hence acquires small couplings to quarks and leptons which can be calculated in the FSM apart from the mixing parameter $rho_{Uh}$. The exchange of this mixed state $U$ will contribute to $g - 2$ and to the Lamb shift. By adjusting $rho_{Uh}$ alone, it is found that the FSM can satisfy all present experimental bounds on the $g - 2$ and Lamb shift anomalies for $mu$ and $e$, and for the latter for both hydrogen and deuterium. The FSM predicts also a $1^-$ boson in the hidden sector with a mass of 17 MeV, that is, right on top of the Atomki anomaly $X$. This mixes with the photon at 1-loop level and couples thereby like a dark photon to quarks and leptons. It is however a compound state and is thought likely to possess additional compound couplings to hadrons. By adjusting the mixing parameter and the $X$s compound coupling to nucleons, the FSM can reproduce the production rate of the $X$ in beryllium decay as well as satisfy all the bounds on $X$ listed so far in the literature. The above two results are consistent in that the $U$, being $0^+$, does not contribute to the Atomki anomaly if parity and angular momentum are conserved, while $X$, though contributing to $g - 2$ and Lamb shift, has smaller couplings than $U$ and can, at first instance, be neglected there. Despite the tentative nature of the 3 anomalies in experiment and of the FSM as theory, the accommodation of the former in the latter has strengthened the credibility of both. If this FSM interpretation were correct, it would change the whole aspect of the anomalies from just curiosities to windows into a vast hitherto hidden sector comprising at least in part the dark matter which makes up the bulk of our universe.
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