We offer a new solution to an old puzzle in the penguin-dominated $Btopi K$ decays. The puzzle is the inconsistency among the measurements of the branching ratios and CP asymmetries of the four $Btopi K$ decays: $B^+ to pi^+ K^0$, $B^+to pi^0 K^+$, $
B_d^0topi^- K^+$, $B_d^0topi^0 K^0$. We solve the $Btopi K$ puzzle by considering the effect of an axion-like particle (ALP) that mixes with the $pi^0$ and has mass close to the $pi^0$ mass. We show that the ALP can also explain the anomalies in the electron and muon anomalous magnetic moments.
The Standard Model Neutrino Effective Field Theory (SMNEFT) is the Standard Model Effective Field Theory (SMEFT) augmented with right-handed neutrinos. Building on our previous work, arXiv:2010.12109, we calculate the Yukawa coupling contributions to
the one-loop anomalous dimension matrix for the 11 dimension-six four-fermion SMNEFT operators. We also present the new contributions to the anomalous dimension matrix for the 14 four-fermion SMEFT operators that mix with the SMNEFT operators through the Yukawa couplings of the right-handed neutrinos.
Standard Model Neutrino Effective Field Theory (SMNEFT) is an effective theory with Standard Model (SM) gauge-invariant operators constructed only from SM and right-handed neutrino fields. For the full set of dimension-six SMNEFT operators, we presen
t the gauge coupling terms of the one-loop anomalous dimension matrix for renormalization group evolution (RGE) of the Wilson coefficients between a new physics scale and the electroweak scale. We find that the SMNEFT operators can be divided into five subsets which are closed under RGE. Our results apply for both Dirac and Majorana neutrinos. We also discuss the operator mixing pattern numerically and comment on some interesting phenomenological implications.
At present, the measurements of $R_{D^{(*)}}$ and $R_{J/psi}$ hint at new physics (NP) in $b to c tau^- {bar u}$ decays. The angular distribution of ${bar B} to D^* (to D pi) , tau^{-} {bar u}_tau$ would be useful for getting information about the NP
, but it cannot be measured. The reason is that the three-momentum ${vec p}_tau$ cannot be determined precisely since the decay products of the $tau^-$ include an undetected $ u_tau$. In this paper, we construct a measurable angular distribution by considering the additional decay $tau^- to pi^- u_tau$. The full process is ${bar B} to D^* (to D pi) , tau^{-} (to pi^- u_tau) {bar u}_tau$, which includes three final-state particles whose three-momenta can be measured: $D$, $pi$, $pi^-$. The magnitudes and relative phases of all the NP parameters can be extracted from a fit to this angular distribution. One can measure CP-violating angular asymmmetries. If one integrates over some of the five kinematic parameters parametrizing the angular distribution, one obtains (i) familiar observables such as the $q^2$ distribution and the $D^*$ polarization, and (ii) new observables associated with the $pi^-$ emitted in the $tau$ decay: the forward-backward asymmetry of the $pi^-$ and the CP-violating triple-product asymmetry.
We investigate the implications of the latest LHCb measurement of $R_K$ for NP explanations of the $B$ anomalies. The previous data could be explained if the $b to s mu^+ mu^-$ NP is in (I) $C_{9,{rm NP}}^{mumu}$ or (II) $C_{9,{rm NP}}^{mumu} = -C_{1
0,{rm NP}}^{mumu}$, with scenario (I) providing a better explanation than scenario (II). This continues to hold with the new measurement of $R_K$. However, for both scenarios, this measurement leads to a slight tension of $O(1sigma)$ between separate fits to the $b to s mu^+ mu^-$ and $R_{K^{(*)}}$ data. In this paper, we investigate whether this tension can be alleviated with the addition of NP in $b to s e^+ e^-$. In particular, we examine the effect of adding such NP to scenarios (I) and (II). We find several scenarios in which this leads to improvements in the fits. $Z$ and LQ models with contributions to both $b to s mu^+ mu^-$ and $b to s e^+ e^-$ can reproduce the data, but only within scenarios based on (II). If the tension persists in future measurements, it may be necessary to consider NP models with more than one particle contributing to $b to s ell^+ ell^-$.
In order to explain the observed anomalies in the measurements of $R_{D^{(*)}}$ and $R_{J/psi}$, a variety of new-physics (NP) models that contribute to $bto ctau^-{bar u}$ have been proposed. In this paper, we show how CP-violating observables can b
e used to distinguish these NP models. Because ${vec p}_tau$ cannot be measured (the decay products of the $tau$ include the undetected $ u_tau$), obtaining the angular distribution of ${bar B}^0to D^{*+}tau^{-}{bar u}_tau$ is problematic. Instead, we focus here on ${bar B}^0to D^{*+}(to D^0 pi^+)mu^- {bar u}_mu$. This process may also receive contributions from the same NP, and LHCb intends to measure the CP-violating angular asymmetries in this decay. There are two classes of NP models that contribute to $bto cmu^-{bar u}_mu$. These involve (i) a $W$ (two types) or (ii) a leptoquark (LQ) (six types). The most popular NP models predict no CP-violating effects, so the measurement of nonzero CP-violating symmetries would rule them out. Furthermore these measurements allow one to distinguish the $W$ and LQ models, and to differentiate among several LQ models.
The recent measurement of $R_{K^*}$ is yet another hint of new physics (NP), and supports the idea that it is present in $bto smu^+mu^-$ decays. We perform a combined model-independent and model-dependent analysis in order to deduce properties of thi
s NP. Like others, we find that the NP must obey one of two scenarios: (I) $C_9^{mumu}({rm NP}) < 0$ or (II) $C_9^{mumu}({rm NP}) = - C_{10}^{mumu}({rm NP}) < 0$. A third scenario, (III) $C_9^{mumu}({rm NP}) = - C_{9}^{prime mumu}({rm NP})$, is rejected largely because it predicts $R_K = 1$, in disagreement with experiment. The simplest NP models involve the tree-level exchange of a leptoquark (LQ) or a $Z$ boson. We show that scenario (II) can arise in LQ or $Z$ models, but scenario (I) is only possible with a $Z$. Fits to $Z$ models must take into account the additional constraints from $B^0_s$-${bar B}^0_s$ mixing and neutrino trident production. Although the LQs must be heavy, O(TeV), we find that the $Z$ can be light, e.g., $M_{Z} = 10$ GeV or 200 MeV.
$R_K$ and $R_{D^{(*)}}$ are two $B$-decay measurements that presently exhibit discrepancies with the SM. Recently, using an effective field theory approach, it was demonstrated that a new-physics model can simultaneously explain both the $R_K$ and $R
_{D^{(*)}}$ puzzles. There are two UV completions that can give rise to the effective Lagrangian: (i) $VB$: a vector boson that transforms as an $SU(2)_L$ triplet, as in the SM, (ii) $U_1$: an $SU(2)_L$-singlet vector leptoquark. In this paper, we examine these models individually. A key point is that $VB$ contributes to $B^0_s$-${bar B}^0_s$ mixing and $tau to 3mu$, while $U_1$ does not. We show that, when constraints from these processes are taken into account, the $VB$ model is just barely viable. It predicts ${cal B} (tau^-tomu^-mu^+mu^-) simeq 2.1 times 10^{-8}$. This is measurable at Belle II and LHCb, and therefore constitutes a smoking-gun signal of $VB$. For $U_1$, there are several observables that may point to this model. Perhaps the most interesting is the lepton-flavor-violating decay $Upsilon(3S) to mu tau$, which has previously been overlooked in the literature. $U_1$ predicts ${cal B}(Upsilon(3S) to mu tau)|_{rm max} = 8.0 times 10^{-7}$. Thus, if a large value of ${cal B}(Upsilon(3S) to mu tau)$ is observed -- and this should be measurable at Belle II -- the $U_1$ model would be indicated.
According to the Particle Data Group, the measurements of ${cal B}(W^+ to tau^+ u_tau)$ and ${cal B}(W^+ to ell^+ u_ell)$ ($ell = e,mu$) disagree with one another at the $2.3sigma$ level. In this paper, we search for a new-physics (NP) explanation
of this $W to tau u$ puzzle. We consider two NP scenarios: (i) the $W$ mixes with a $W$ boson that couples preferentially to the third generation, (ii) $tau_{L,R}$ and $ u_{tau L}$ mix with isospin-triplet leptons. Unfortunately, once other experimental constraints are taken into account, neither scenario can explain the above experimental result. Our conclusion is that the $W to tau u$ puzzle is almost certainly just a statistical fluctuation.
It is an intriguing possibility that dark matter (DM) could have flavor quantum numbers like the quarks. We propose and investigate a class of UV-complete models of this kind, in which the dark matter is in a scalar triplet of an SU(3) flavor symmetr
y, and interacts with quarks via a colored flavor-singlet fermionic mediator. Such mediators could be discovered at the LHC if their masses are $sim 1$ TeV. We constrain the DM-mediator couplings using relic abundance, direct detection, and flavor-changing neutral-current considerations. We find that, for reasonable values of its couplings, scalar flavored DM can contribute significantly to the real and imaginary parts of the $B_s$-$bar B_s$ mixing amplitude. We further assess the potential for such models to explain the galactic center GeV gamma-ray excess.
