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Register a new userSearching for New Physics with Flavor Violating Observables
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Authors
Wolfgang Altmannshofer
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In this talk, I review the status and prospects of several low energy flavor observables that are highly sensitive to New Physics effects. In particular I discuss the implications for possible New Physics in b --> s transitions coming from the recent experimental results on the B_s mixing phase, the branching ratio of the rare decay B_s --> mu+mu-, and angular observables in the B --> K* mu+mu- decay. Also the recent evidence for direct CP violation in singly Cabibbo suppressed charm decays and its interpretation in the context of New Physics models is briefly discussed.
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We study new top flavor violating resonances that are singly produced in association with a top at the LHC. Such top flavor violating states could be responsible for the Tevatron top forward-backward asymmetry. Since top flavor violating states can directly decay to a top (or anti-top) and jet, and are produced in conjunction with another (oppositely charged) top, the direct signature of such states is a t j (or tbar j) resonance in t tbar j events. In general, these states can be very light and have O(1) couplings to the top sector so that they are copiously produced. We present a search strategy and estimate the discovery potential at the early LHC by implementing the strategy on simulated data. For example, with 1 fb^-1 at 7 TeV, we estimate that a W coupling to d_R tbar_R can be constrained at the 3 sigma level for g_R = 1 and m_W = 200 GeV, weakening to g_R = 1.75 for m_W = 600 GeV. With the search we advocate here, a bound at a similar level could be obtained for top flavor violating Zs, as well as triplet and sextet diquarks.
In recent years, intriguing hints for the violation of Lepton Flavour Universality (LFU) have been accumulated in semileptonic $B$ decays, both in the neutral-current transitions $bto sell^+ell^-$ (i.e., $R_K$ and $R_{K^*}$) and the charged-current transitions $bto cell^-bar u_ell$ (i.e., $R_D$, $R_{D^*}$ and $R_{J/psi}$). LHCb has reported deviations from the Standard Model (SM) expectations in $bto smu^+mu^-$ processes as well as in the ratios $R_K$ and $R_{K^*}$, which together point at New Physics (NP) affecting muons with a high significance. Furthermore, hints for LFU violation in $R_{D^{(*)}}$ and $R_{J/psi}$ point at large deviations from the SM in processes involving tau leptons. Together, these hints for NP motivate the possibility of huge LFU-violating effects in $bto stau^+tau^-$ transitions. In this article we predict the branching ratios of $Bto Ktau^+tau^-$, $Bto K^{*}tau^+tau^-$ and $B_sto phi tau^+tau^-$ taking into account NP effects in the Wilson coefficients $C_{9()}^{tautau}$ and $C_{10()}^{tautau}$. Assuming a common NP explanation of $R_{D^{}}$ , $R_{D^{(*)}}$ and $R_{J/psi}$, we show that a very large enhancement of $bto stau^+tau^-$ processes, of around three orders of magnitude compared to the SM, can be expected under fairly general assumptions. We find that the branching ratios of $B_sto tau^+tau^-$, $B_sto phi tau^+tau^-$ and $Bto K^{(*)}tau^+tau^-$ under these assumptions are in the observable range for LHCb and Belle II.
The PADME experiment is searching for the Dark Photon $A$ in the $e^{+}e^{-} to gamma A$ process, assuming a $A$ decay into invisible particles. In extended Dark Sector models, a Dark Higgs $h$ can be produced alongside $A$ in the process $e^{+}e^{-} to h A$. If the $h$ mass is greater than twice the $A$ mass the final state will be composed by three $e^{+}e^{-}$ pairs. Such extremely rare process is explorable by the PADME experiment, which could get a first measure and impose limits on models of physics beyond the Standard Model.
LHCb found hints for physics beyond the Standard Model (SM) in $Bto K^*mu^+mu^-$, $R(K)$ and $B_stophimu^+mu^-$. These intriguing hints for NP have recently been confirmed by the LHCb measurement of $R(K^*)$ giving a combined significance for NP above the $5,sigma$ level. In addition, the BABAR, BELLE and LHCb results for $Bto D^{(*)}tau u$ also point towards lepton flavour universality (LFU) violating new physics (NP). Furthermore, there is the long-standing discrepancy between the measurement and the theory prediction of the anomalous magnetic moment of the muon ($a_mu$) at the $3,sigma$ level. Concerning NP effects, $bto smu^+mu^-$ data can be naturally explained with a new neutral gauge bosons, i.e. a $Z^prime$ but also with heavy new scalars and fermions contributing via box diagrams. Another promising solution to $bto smu^+mu^-$, which can also explain $Bto D^{(*)}tau u$, are leptoquarks. Interestingly, leptoquarks provide also a viable explanation of $a_mu$ which can be tested via correlated effects in $Ztomu^+mu^-$ at future colliders. Considering leptoquark models, we show that an explanation of $Bto D^{(*)}tau u$ predicts an enhancement of $bto stau^+tau^-$ processes by around three orders of magnitude compared to the SM. In case of a simultaneous explanation of $Bto D^{(*)}tau u$ and $bto smu^+mu^-$ data, sizable effects in $bto staumu$ processes are predicted.
We propose a method to quantify the Standard Model uncertainty in B to K pi decays using the experimental data, assuming that power counting provides a reasonable estimate of the subleading terms in the 1/mb expansion. Using this method, we show that present B to K pi data are compatible with the Standard Model. We analyze the pattern of subleading terms required to reproduce the B to K pi data and argue that anomalously large subleading terms are not needed. Finally, we find that S(KS pi0) is fairly insensitive to hadronic uncertainties and obtain the Standard Model estimate S(KS pi0)=0.74 +- 0.04.
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