Abstract
We present a minimal extension of the Standard Model that can simultaneously account for the anomalies in semi-leptonic B meson decays and the muon g − 2, give large CP violation in charm decays (up to the value recently measured by LHCb), and provide thermal-relic dark matter, while evading all constraints set by other flavour observables, LHC searches, and dark matter experiments. This is achieved by introducing only four new fields: a vectorlike quark, a vectorlike lepton, and two scalar fields (a singlet and a doublet) that mix due to the electroweak symmetry breaking and provide the dark matter candidate. The singlet-doublet mixing induces chirally-enhanced dipole transitions, which are crucial for the explanation of the muon g − 2 discrepancy and the large charm CP violation, and allows to achieve the observed dark matter density in wide regions of the parameter space.
Highlights
Muon g-2 experiment at Fermilab [1], this discrepancy would unambiguously require new particles interacting with muons at the TeV scale or below: cf. [2] for a review
We present a minimal extension of the Standard Model that can simultaneously account for the anomalies in semi-leptonic B meson decays and the muon g − 2, give large CP violation in charm decays, and provide thermal-relic dark matter, while evading all constraints set by other flavour observables, LHC searches, and dark matter experiments
This follows from the ‘Weakly Interacting Massive Particle (WIMP) miracle’, the remarkable observation that, assuming a standard thermal history of the universe, the dark matter (DM) relic density measured from observations of the Cosmic Microwave Background (CMB) can be accounted for by particles in the mass range of the electroweak-breaking scale, annihilating with a cross section of the typical electroweak size, cf. the reviews [6, 7]
Summary
We introduce the following set of new fields that are all odd under an unbroken Z2 symmetry under which the SM fields are even: a singlet complex scalar, a complex scalar doublet, and two vectorlike pairs of Weyl fermions (that combine into two Dirac fermions) with the quantum numbers of the SM quark and lepton doublets. The charged scalar mass is at the tree level given by the mass parameter of the scalar doublet: MS± = MD.. The charged scalar mass is at the tree level given by the mass parameter of the scalar doublet: MS± = MD.2 Another effect of the electroweak breaking is that the term λQ in eq (2.3) induces couplings of the components of the vectorlike quark Q to LH up and down quarks that we denote respectively as λQu and λQd. Another effect of the electroweak breaking is that the term λQ in eq (2.3) induces couplings of the components of the vectorlike quark Q to LH up and down quarks that we denote respectively as λQu and λQd These couplings have a relative misalignment in the flavour space given by a CKM rotation.
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