In recent years, hints for multi-lepton anomalies have been accumulated by the analysis of Large Hadron Collider (LHC) data, pointing towards the existence of beyond the Standard Model (SM) Higgs bosons: a new scalar particle $S$ with a mass $m_S$ in
the range between $130,$GeV and $160,$GeV, produced from the decay of a heavier new scalar particle, $H$. Motivated by this observation, we perform a search for the signatures of $S$ within this mass region, which has been studied by CMS and ATLAS as a by-product of the SM Higgs searches in the side-bands of the kinematic regions. Combining the $gammagamma$ and $Zgamma$ channels, with associated leptons, di-jets, bottom quarks and missing energy, we obtain a local (global) significance of 5.1$sigma$ (4.8$sigma$) for a mass of $m_S= 151.5$,GeV and provide the preferred ranges for the corresponding (fiducial) cross sections. This is a strong indication for a scalar resonance $S$ decaying into photons, and, to a lesser extent to $Zgamma$, in association with missing energy, jets or leptons. Hints for the decays into, or production in association with, bottom quarks are statistically less significant. In order to test this hypothesis, we propose a search for $Hrightarrow gammagamma boverline{b},tau^+tau^- boverline{b}$ in asymmetric configurations that has not yet been performed by ATLAS and CMS.
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 obs
erved as an apparent deficit in first-row CKM unitarity, known as the Cabibbo angle anomaly, and the CMS excess in $qbar qto e^+e^-$. 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.
In recent years, intriguing hints for the violation of lepton flavour universality have accumulated. In particular, deviations from the Standard-Model (SM) predictions in $Bto D^{(*)}tau u/Bto D^{(*)}ell u$, in the anomalous magnetic moment of the mu
on and {in} $bto sell^+ell^-$ data were observed with a significance of $!>3,sigma$, $>!4,sigma$ and $>!5,sigma$, respectively. Furthermore, in a recent re-analysis of 2018 Belle data, it was found that the forward-backward asymmetry of $bar B to D^{*}mubar u$ vs $bar Bto D^{*}ebar u$ disagrees with the SM prediction by $approx!!4,sigma$ which would be an additional sign of lepton flavour universality violation. Since one naturally expects muon-related new effects to also emerge at some point in $b to cmu u$ decays, the above putative deviation might share a common origin with the other flavour anomalies. We show that a tensor operator is necessary to significantly improve the global fit w.r.t. the SM, which can only be induced (at tree-level in a renormalizable model) by a scalar leptoquark. Interestingly, among the two possible representations, the $SU(2)_L$-singlet $S_1$ and the doublet $S_2$, which can both also account for the anomalous magnetic moment of the muon, only $S_1$ can provide a good fit as it naturally gives rise to the scenario $C_{VL}, C_{SL}=-4 C_T$. While the constraints from (differences of) other angular observables prefer a smaller value $Delta A_{rm FB}$, this scenario is significantly preferred ($approx 3 sigma$) over the SM hypothesis and compatible with constraints such as $Bto K^* u u$ and electroweak precision bounds.
Leptoquarks (LQs) have attracted increasing attention within recent years, mainly since they can explain the flavor anomalies found in $R(D^{(*)})$, $b rightarrow s ell^+ ell^-$ transitions and the anomalous magnetic moment of the muon. In this artic
le, we lay the groundwork for further automated analyses by presenting the complete Lagrangian and the corresponding set of Feynman rules for scalar leptoquarks. This means we consider the five representations $Phi_1, Phi_{tilde1}, Phi_2, Phi_{tilde2}$ and $Phi_3$ and include the triple and quartic self-interactions, as well as couplings to the Standard Model (SM) fermions, gauge bosons and the Higgs. The calculations are performed using FeynRules and all model files are publicly available online at https://gitlab.com/lucschnell/SLQrules.
New neutral heavy gauge bosons ($Z^prime$) are predicted within many extensions of the Standard Model. While in case they couple to quarks the LHC bounds are very stringent, leptophilic $Z^prime$ bosons (even with sizable couplings) can be much light
er and therefore lead to interesting quantum effects in precision observables (like $(g-2)_mu$) and generate flavour violating decays of charged leptons. In particular, $elltoell^prime ubar u$ decays, anomalous magnetic moments of charged leptons, $elltoell^primegamma$ and $ellto3ell^prime$ decays place stringent limits on leptophilic $Z^prime$ bosons. Furthermore, in case of mixing $Z^prime$ with the SM $Z$, $Z$ pole observables are affected. In light of these many observables we perform a global fit to leptophilic $Z^prime$ models with the main goal of finding the bounds for the $Z^prime$ couplings to leptons. To this end we consider a number of scenarios for these couplings. While in generic scenarios correlations are weak, this changes once additional constraints on the couplings are imposed. In particular, if one considers an $L_mu-L_tau$ symmetry broken only by left-handed rotations, or considers the case of $tau-mu$ couplings only. In the latter setup, on can explain the $(g-2)_mu$ anomaly and the hint for lepton flavour universality violation in $tautomu ubar u/tauto e ubar u$ without violating bounds from electroweak precision observables.
In this addendum to arXiv:2101.07811 we discuss the implications of the recent CMS analysis of lepton flavour universality violation in non-resonant di-lepton pairs for first generation leptoquarks. As CMS finds more electron events than expected fro
m background, this analysis prefers the LQ representations $tilde{S}_1, S_2, S_3, tilde{V}_1, V_2,(kappa_2^{RL} e 0)$ and $V_3$ which lead to constructive interference with the SM. In principle the excess could also be (partially) explained by the representations $tilde{S}_2, V_1,(kappa_1^R e 0), V_2,(kappa_2^{LR} e 0), tilde{V}_2$ which are interfering destructively, as this would still lead to the right effect in bins with high invariant mass where the new physics contribution dominates. However, in these cases large couplings would be required which are excluded by other observables. The representations $S_1, V_1, (kappa_1^{L} e 0)$ cannot improve the fit to the CMS data compared to the SM.
With the long-standing tension between experiment and Standard-Model (SM) prediction in the anomalous magnetic moment of the muon $a_mu$ recently reaffirmed by the Fermilab experiment, the crucial question becomes which other observables could be sen
sitive to the underlying physics beyond the SM to which $a_mu$ may be pointing. While from the effective field theory (EFT) point of view no direct correlations exist, this changes in specific new physics models. In particular, in the case of explanations involving heavy new particles above the electroweak (EW) scale with chiral enhancement, which are preferred to evade exclusion limits from direct searches, correlations with other observables sensitive to EW symmetry breaking are expected. Such scenarios can be classified according to the $SU(2)_L$ representations and the hypercharges of the new particles. We match the resulting class of models with heavy new scalars and fermions onto SMEFT and study the resulting correlations with $htomumu$ and $Ztomumu$ decays, where, via $SU(2)_L$ symmetry, the latter process is related to $Zto u u$ and modified $W$-$mu$-$ u$ couplings.
In addition to the existing strong indications for lepton flavour university violation (LFUV) in low energy precision experiments, CMS recently released an analysis of non-resonant di-lepton pairs which could constitute the first sign of LFUV in high
-energy LHC searches. In this article we show that the Cabibbo angle anomaly, an (apparent) violation of first row and column CKM unitarity with $approx3,sigma$ significance, and the CMS result can be correlated and commonly explained in a model independent way by the operator $[Q_{ell q}^{(3)}]_{1111} = (bar{ell}_1gamma^{mu}sigma^Iell_1)(bar{q}_1gamma_{mu}sigma^Iq_1)$. This is possible without violating the bounds from the non-resonant di-lepton search of ATLAS (which interestingly also observed slightly more events than expected in the electron channel) nor from $R(pi)=pi tomu u/pi to e u$. We find a combined preference for the new physics hypothesis of $4.5,sigma$ and predict $1.0004<R(pi)<1.0009$ (95%~CL) which can be tested in the near future with the forthcoming results of the PEN experiment.
The Fermi constant ($G_F$) is extremely well measured through the muon lifetime, defining one of the key fundamental parameters in the Standard Model (SM). Therefore, to search for physics beyond the SM (BSM) via $G_F$, the constraining power is dete
rmined by the precision of the second-best independent determination of $G_F$. The best alternative extractions of $G_F$ proceed either via the global electroweak (EW) fit or from superallowed $beta$ decays in combination with the Cabibbo angle measured in kaon, $tau$, or $D$ decays. Both variants display some tension with $G_F$ from muon decay, albeit in opposite directions, reflecting the known tensions within the EW fit and hints for the apparent violation of CKM unitarity, respectively. We investigate how BSM physics could bring the three determinations of $G_F$ into agreement using SM effective field theory and comment on future perspectives.
In this article we perform a combined analysis of low energy precision constraints and LHC searches for leptoquarks which couple to first generation fermions. Considering all ten leptoquark representations, five scalar and five vector ones, we study
at the precision frontier the constraints from $Ktopi u u$, $Ktopi e^+e^-$, $K^0-bar K^0$ and $D^0-bar D^0$ mixing, as well as from experiments searching for parity violation (APV and QWEAK). We include LHC searches for $s$-channel single resonant production, pair production and Drell-Yan-like signatures of leptoquarks. Interestingly, we find that the recent non-resonant di-lepton analysis of ATLAS provides stronger bounds than the resonant searches recasted so far to constrain $t$-channel production of leptoquarks. Taking into account all these bounds, we observe that none of the leptoquark representations can address the so-called Cabibbo angle anomaly via a direct contribution to super-allowed beta decays.
