First-generation new physics in simplified models: from low-energy parity violation to the LHC

Abstract

New-physics (NP) constraints on first-generation quark-lepton interactions are particularly interesting given the large number of complementary processes and observables that have been measured. Recently, first hints for such NP effects have been observed as an apparent deficit in first-row CKM unitarity, known as the Cabibbo angle anomaly, and the CMS excess in $$ q\overline{q} $$ q q ¯ → e+e−. Since the same NP would inevitably enter in searches for low-energy parity violation, such as atomic parity violation, parity-violating electron scattering, and coherent neutrino-nucleus scattering, as well as electroweak precision observables, a combined analysis is required to assess the viability of potential NP interpretations. In this article we investigate the interplay between LHC searches, the Cabibbo angle anomaly, electroweak precision observables, and low-energy parity violation by studying all simplified models that give rise to tree-level effects related to interactions between first-generation quarks and leptons. Matching these models onto Standard Model effective field theory, we derive master formulae in terms of the respective Wilson coefficients, perform a complete phenomenological analysis of all available constraints, point out how parity violation can in the future be used to disentangle different NP scenarios, and project the constraints achievable with forthcoming experiments.

Explaining the hints for lepton flavour universality violation with three $S_2$ leptoquark generations

“…In this context, models including a SU (2) L leptoquark doublet S 2 that transforms under the SM gauge group SU (3) c × SU (2) L × U (1) Y as 3, 2, 7 6 , from now on called Φ 2 (in the literature also called R 2 ), are particularly interesting. This LQ can restore the agreement between theory and data for b → s + − observables via a W -box contribution [104], for b → cτ ν observables and the excess [161] in CMS di-lepton data [162] via tree-level contributions [159,160], and for (g − 2) µ via an m t /m µ chirally enhanced effect. Furthermore, the tension in the difference of the B → D * ν forward-backward asymmetries (∆A FB ) [163,164] can be softened [165], and the global EW fit can be improved through the generation of a shift in the Wboson mass predictions [166], where a constructive effect is currently preferred [167], via LQ interactions with the Higgs field [168].…”

“…LQs were originally proposed in the Pati-Salam model [63] and in Grand Unified Theories (GUTs) [64][65][66][67][68], and it has been shown that the anomalies in b → s + − , R(D ( * ) ) [69, 70, 72-76, 78-80, 82, 83, 87-90, 92-96, 98-133], b → cτ ν [69, 70, 72-76, 78-80, 82, 83, 87-90, 92-96, 98-128, 130-136], and (g − 2) µ [92,93,95,102,110,113,116,127,133, can all be explained by them. Moreover, LQs can provide an explanation for the CMS excess in non-resonant di-electron production [159,160].…”

Explaining the Cabibbo Angle Anomaly

“…Leptoquark solutions have been discussed in Refs. [37,38], where it is shown that the scalar triplet can address the anomaly once an additional mechanism to compensate the effect in D 0 − D0 is introduced. Eventually, there is the Singly Charged Scalar Singlet, which is a SU(2) L × SU(3) C singlet with hypercharge +1.…”

Searching for new physics from SMEFT and leptoquarks at the P2 experiment

“…(CEνNS), since they lead to analogous interactions of neutrinos with nuclei. However, currently CEνNS is not competitive with other constraints in this respect [75]. The current order of magnitude can be estimated by noting that the best constraints on neutrino Non-Standard Interactions (NSI) from CEνNS are at the order of V 0.5 for vector interactions, while bounds on axial interactions are weaker [76,77].…”