Flavor-Changing Higgs Decays in Grand Unification with Minimal Flavor Violation

We consider the flavor-changing decays of the Higgs boson in a grand unified theory framework which is based on the SU(5) gauge group and implements the principle of minimal flavor violation. This allows us to explore the possibility of connecting the tentative hint of the Higgs decay $h\to\mu\tau$ recently reported in the CMS experiment to potential new physics in the quark sector. We look at different simple scenarios with minimal flavor violation in this context and how they are subject to various empirical restrictions. In one specific case, the relative strengths of the flavor-changing leptonic Higgs couplings are determined mainly by the known quark mixing parameters and masses, and a branching fraction ${\cal B}(h\to\mu\tau)\sim1\%$ is achievable without the couplings being incompatible with the relevant constraints. Upcoming data on the Higgs leptonic decays and searches for the $\mu\to e\gamma$ decay with improved precision can offer further tests on this scenario.Comment: 18 pages, 2 figures, somewhat expanded, references added, main conclusions unchanged, matches published versio

Connecting b→sℓℓˉb\to s\ell\bar\ell anomalies to enhanced rare nonleptonic Bˉs0\bar{B}_s^0 decays in Z′Z' model

The present data on a number of observables in $b\to s\mu^+\mu^-$ processes manifest some tensions with the standard model (SM). Assuming that these anomalies have a new physics origin, we consider the possibility that a $Z'$ boson is responsible for them. We further assume that its interactions with quarks also affect rare nonleptonic decays of the $\bar B_s^0$ meson which are purely isospin-violating and tend to be dominated by electroweak-penguin contributions, namely $\bar B_s^0\to(\eta,\eta',\phi)(\pi^0,\rho^0)$. Most of these decays are not yet observed, and their rates are expected to be relatively small in the SM. Taking into account constraints from various measurements, including the evidence for $\bar B_s^0\to\phi\rho^0$ recently seen by LHCb, we find that the $Z'$ effects on $\bar B_s^0\to(\eta,\phi)\pi^0$ can make their rates bigger than the SM predictions by up to an order of magnitude. For $\bar B_s^0\to\eta'\pi^0,(\eta,\eta')\rho^0$, the enhancement factors are at most a few. Since the $Z'$ contributions to the different channels depend on different combinations of its couplings, observations of more of these decays in future experiments, along with improved $b\to s\mu^+\mu^-$ data, will probe this $Z'$ scenario more thoroughly.Comment: 17 pages, 4 figures, somewhat revised, comments & references added, matches publicatio

Minimal Lepton Flavor Violation Implications of the b→sb\to s Anomalies

The latest measurements of rare $b\to s$ decays in the LHCb experiment have led to results in tension with the predictions of the standard model (SM), including a tentative indication of the violation of lepton flavor universality. Assuming that this situation will persist because of new physics, we explore some of the potential consequences in the context of the SM extended with the seesaw mechanism involving right-handed neutrinos plus effective dimension-six lepton-quark operators under the framework of minimal flavor violation. We focus on a couple of such operators which can accommodate the LHCb anomalies and conform to the minimal flavor violation hypothesis in both their lepton and quark parts. We examine specifically the lepton-flavor-violating decays $B\to K^{(*)}\ell\ell'$, $B_s\to\phi\ell\ell'$, $B\to(\pi,\rho)\ell\ell'$, and $B_{d,s}\to\ell\ell'$, as well as $K_L\to e\mu$ and $K\to\pi e\mu$, induced by such operators. The estimated branching fractions of some of these decay modes with $\mu\tau$ in the final states are allowed by the pertinent experimental constraints to reach a few times $10^{-7}$ if other operators do not yield competitive effects. We also look at the implications for $B\to K^{(*)}\nu\nu$ and $K\to\pi\nu\nu$, finding that their rates can be a few times larger than their SM values. These results are testable in future experiments.Comment: 16 pages, no figures, clarifying comments added, references updated, matches journal versio

Rare hyperon decays with missing energy

We explore the strangeness-changing decays of the lightest hyperons into another baryon plus missing energy within and beyond the standard model (SM). In the SM these processes arise from the loop-induced quark transition $s\to d\nu\bar\nu$ and their branching fractions are estimated to be less than $10^{-11}$. In the presence of new physics (NP) the rates of these hyperon decays with missing energy could increase significantly with respect to the SM expectations because of modifications to the SM process or contributions from additional modes with new invisible particles. Adopting a model-independent approach and taking into account constraints from the kaon sector, we find that the current data on $K\to\pi\nu\bar\nu$ do not permit sizable NP impact on the hyperon decays via underlying operators having mainly parity-even quark parts. In contrast, NP operators with primarily parity-odd quark parts are much less restricted by the existing bounds on $K\to\rm invisible$ and $K\to\pi\pi\nu\bar\nu$ and consequently could produce substantially amplifying effects on the hyperon modes. Their NP-enhanced branching fractions could reach levels potentially observable in the ongoing BESIII experiment.Comment: 16 pages, no figure, slightly enlarged, references added, typos corrected, matches publicatio