Physics of leptoquarks in precision experiments and at particle colliders

We present a comprehensive review of physics effects generated by leptoquarks (LQs), i.e., hypothetical particles that can turn quarks into leptons and vice versa, of either scalar or vector nature. These considerations include discussion of possible completions of the Standard Model that contain LQ fields. The main focus of the review is on those LQ scenarios that are not problematic with regard to proton stability. We accordingly concentrate on the phenomenology of light leptoquarks that is relevant for precision experiments and particle colliders. Important constraints on LQ interactions with matter are derived from precision low-energy observables such as electric dipole moments, (g-2) of charged leptons, atomic parity violation, neutral meson mixing, Kaon, B, and D meson decays, etc. We provide a general analysis of indirect constraints on the strength of LQ interactions with the quarks and leptons to make statements that are as model independent as possible. We address complementary constraints that originate from electroweak precision measurements, top, and Higgs physics. The Higgs physics analysis we present covers not only the most recent but also expected results from the Large Hadron Collider (LHC). We finally discuss direct LQ searches. Current experimental situation is summarized and self-consistency of assumptions that go into existing accelerator-based searches is discussed. A progress in making next-to-leading order predictions for both pair and single LQ productions at colliders is also outlined.Comment: 136 pages, 22 figures, typographical errors fixed, the Physics Reports versio

Is diet partly responsible for differences in COVID-19 death rates between and within countries?

Correction: Volume: 10 Issue: 1 Article Number: 44 DOI: 10.1186/s13601-020-00351-w Published: OCT 26 2020Reported COVID-19 deaths in Germany are relatively low as compared to many European countries. Among the several explanations proposed, an early and large testing of the population was put forward. Most current debates on COVID-19 focus on the differences among countries, but little attention has been given to regional differences and diet. The low-death rate European countries (e.g. Austria, Baltic States, Czech Republic, Finland, Norway, Poland, Slovakia) have used different quarantine and/or confinement times and methods and none have performed as many early tests as Germany. Among other factors that may be significant are the dietary habits. It seems that some foods largely used in these countries may reduce angiotensin-converting enzyme activity or are anti-oxidants. Among the many possible areas of research, it might be important to understand diet and angiotensin-converting enzyme-2 (ACE2) levels in populations with different COVID-19 death rates since dietary interventions may be of great benefit.Peer reviewe

Prospects of discovering new physics in rare charm decays

The LHCb bounds on the branching ratio of rare decay $D^0 \to \mu^+ \mu^-$ and the constraints on the branching ratio of $D^+ \to \pi^+ \mu^+ \mu^-$ in the nonresonant regions enable us to improve constraints on new physics contributions. Using the effective Lagrangian approach we determine sizes of the Wilson coefficients allowed by the existing LHCb bounds on rare charm decays. Then we discuss contributions to rare charm meson decay observables in several models of new physics: a model with an additional spin-1 weak triplet, leptoquark models, Two Higgs doublets model of type III, and a $Z'$ model. Here we complement the discussion by $D^0 - \bar D^0$ oscillations data. Among considered models, only leptoquarks can significantly modify Wilson coefficients. Assuming that the differential decay width for $D^+ \to \pi^+ \mu^+ \mu^-$ receives NP contribution, while the differential decay width for $D^+ \to \pi^+ e^+ e^-$ is Standard Model-like, we find that lepton flavor universality can be violated and might be observed at high dilepton invariant mass.Comment: 13 pages, 3 figure

Physics of the HL-LHC, and perspectives at the HE-LH: report from working group 4: opportunities in flavour physics at the HL-LHC and HE-LHC

Motivated by the success of the flavour physics programme carried out over the last decade at the Large Hadron Collider (LHC), we characterize in detail the physics potential of its High-Luminosity and High-Energy upgrades in this domain of physics. We document the extraordinary breadth of the HL/HE-LHC programme enabled by a putative Upgrade II of the dedicated flavour physics experiment LHCb and the evolution of the established flavour physics role of the ATLAS and CMS general purpose experiments. We connect the dedicated flavour physics programme to studies of the top quark, Higgs boson, and direct high-pT searches for new particles and force carriers. We discuss the complementarity of their discovery potential for physics beyond the Standard Model, affirming the necessity to fully exploit the LHC’s flavour physics potential throughout its upgrade eras

Vector leptoquark resolution of RK and RD(⁎) puzzles

We propose that three recent anomalies in B meson decays, RD(⁎), RK, and P5′, might be explained by only one vector leptoquark weak triplet state. The constraints on the parameter space are obtained by considering t→bτ+ν data, lepton flavor universality tests in the kaon sector, bounds on the lepton flavor violating decay B→Kμτ, and b→cμ−ν¯ decays. The presence of such vector leptoquark could be exposed in precise measurements of top semitauonic decays to b quark. The model predicts enhanced decay rate of B→Kν¯ν, approximate equality of lepton flavor universality ratios RK⁎, RK, and suppressed branching fraction of Bs→μ+μ−

Footprints of leptoquarks: from RK(∗) R_{K^{(*)}} RK(∗) to K→πννˉ K \rightarrow \pi \nu \bar{\nu } K→πνν¯

Abstract Rare $$K \rightarrow \pi \nu \bar{\nu }$$ K→πνν¯ decays, being dominated by short distance contributions within the standard model (SM), open a window for new physics (NP) searches at low energies. The $$K \rightarrow \pi \nu \bar{\nu }$$ K→πνν¯ branching ratios are expected to be measured with $$\sim 10\%$$ ∼10% accuracies by NA62/CERN and KOTO/JPARC. The theoretical uncertainties of branching ratios within the SM are well under control. In the B sector, it is tentative to explain the B-meson anomalies $$R_{D^{(*)}}$$ RD(∗) and/or $$R_{K^{(*)}}$$ RK(∗) by effects of physics beyond the SM. Although NP seems to be present in the third fermion generation it might also manifest in the flavor changing neutral current transition $$s \rightarrow d$$ s→d . Together with the anticipated good experimental sensitivities and accurate theoretical predictions for $$K\rightarrow \pi \nu \bar{\nu }$$ K→πνν¯ , this motivates studies of correlated effects of NP in rare $$K\rightarrow \pi \nu \bar{\nu }$$ K→πνν¯ and $$B \rightarrow K^{(*)} \mu ^+ \mu ^-$$ B→K(∗)μ+μ- decays. Here we consider the loop induced effects in $$K \rightarrow \pi \nu \bar{\nu }$$ K→πνν¯ in two leptoquark models designed to address lepton-flavor universality violation in the $$R_{K^{(*)}}$$ RK(∗) anomalies