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Register a new userSuSeFLAV: A program for calculating supersymmetric spectra and lepton flavor violation
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We introduce the program SuSeFLAV for computing supersymmetric mass spectra with flavor violation in various supersymmetric breaking scenarios with/without seesaw mechanism. A short user guide summarizing the compilation, executables and the input files is provided.
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We present a comprehensive analysis of the potential sensitivity of the Electron-Ion Collider (EIC) to charged lepton flavor violation (CLFV) in the channel $epto tau X$, within the model-independent framework of the Standard Model Effective Field Theory (SMEFT). We compute the relevant cross sections to leading order in QCD and electroweak corrections and perform simulations of signal and SM background events in various $tau$ decay channels, suggesting simple cuts to enhance the associated estimated efficiencies. To assess the discovery potential of the EIC in $tau$-$e$ transitions, we study the sensitivity of other probes of this physics across a broad range of energy scales, from $pp to e tau X$ at the Large Hadron Collider to decays of $B$ mesons and $tau$ leptons, such as $tau to e gamma$, $tau to e ell^+ ell^-$, and crucially the hadronic modes $tau to e Y$ with $Y in { pi, K, pi pi, K pi, ...}$. We find that electroweak dipole and four-fermion semi-leptonic operators involving light quarks are already strongly constrained by $tau$ decays, while operators involving the $c$ and $b$ quarks present more promising discovery potential for the EIC. An analysis of three models of leptoquarks confirms the expectations based on the SMEFT results. We also identify future directions needed to maximize the reach of the EIC in CLFV searches: these include an optimization of the $tau$ tagger in hadronic channels, an exploration of background suppression through tagging $b$ and $c$ jets in the final state, and a global fit by turning on all SMEFT couplings, which will likely reveal new discovery windows for the EIC.
We inspect consequences of the latest B_s mixing phase measurements on lepton flavor violation in a supersymmetric SU(5) theory. The O(1) phase, preferring a non-vanishing squark mixing, generically implies tau -> (e + mu) gamma and mu -> e gamma. Depending on the gaugino and the scalar mass parameters as well as tan beta, the rates turn out to be detectable or even already excessive, if the RR mass insertion of down-type squarks is nonzero. We find that it becomes easy to reconcile B_s mixing phase with lepton flavor violation given: gaugino to scalar squared mass ratio around 1/12, both LL and RR insertions with decent sizes, and low tan beta.
The see-saw mechanism to generate small neutrino masses is reviewed. After summarizing our current knowledge about the low energy neutrino mass matrix we consider reconstructing the see-saw mechanism. Low energy neutrino physics is not sufficient to reconstruct see-saw, a feature which we refer to as ``see-saw degeneracy. Indirect tests of see-saw are leptogenesis and lepton flavor violation in supersymmetric scenarios, which together with neutrino mass and mixing define the framework of see-saw phenomenology. Several examples are given, both phenomenological and GUT-related. Variants of the see-saw mechanism like the type II or triplet see-saw are also discussed. In particular, we compare many general aspects regarding the dependence of LFV on low energy neutrino parameters in the extreme cases of a dominating conventional see-saw term or a dominating triplet term. For instance, the absence of mu -> e gamma or tau -> e gamma in the pure triplet case means that CP is conserved in neutrino oscillations. Scanning models, we also find that among the decays mu -> e gamma, tau -> e gamma and tau -> mu gamma the latter one has the largest branching ratio in (i) SO(10) type I see-saw models and in (ii) scenarios in which the triplet term dominates in the neutrino mass matrix.
In the minimal Standard Model (SM) with four generations (the so called SM4) and in standard two Higgs doublets model (2HDM) setups, e.g., the type II 2HDM with four fermion generations, the contribution of the 4th family heavy leptons to the muon magnetic moment is suppressed and cannot accommodate the measured $ sim 3 sigma$ access with respect to the SM prediction. We show that in a 2HDM for the 4th generation (the 4G2HDM), which we view as a low energy effective theory for dynamical electroweak symmetry breaking, with one of the Higgs doublets coupling only to the 4th family leptons and quarks (thus effectively addressing their large masses), the loop exchanges of the heavy 4th generation neutrino can account for the measured value of the muon anomalous magnetic moment. We also discuss the sensitivity of the lepton flavor violating decays $mu to e gamma$ and $tau to mu gamma$ and of the decay $B_s to mu mu$ to the new couplings which control the muon g-2 in our model.
Flavor symmetric model is one of the attractive Beyond Standard Models (BSMs) to reveal the flavor structure of the Standard Model (SM). A lot of efforts have been put into the model building and we find many kinds of flavor symmetries and setups are able to explain the observed fermion mass matrices. In this paper, we look for common predictions of physical observables among the ones in flavor symmetric models, and try to understand how to test flavor symmetry in experiments. Especially, we focus on the BSMs for leptons with extra Higgs $SU(2)_L$ doublets charged under flavor symmetry. In many flavor models for leptons, remnant symmetry is partially respected after the flavor symmetry breaking, and it controls well the Flavor Changing Neutral Currents (FCNCs) and suggests some crucial predictions against the flavor changing process, although the remnant symmetry is not respected in the full lagrangian. In fact, we see that $tau^- to e^+ mu^- mu^-$ $( mu^+ e^- e^-)$ and $e^+ e^- to tau^+tau^-$ $(mu^-mu^+)$ processes are the most important in the flavor models that the extra Higgs doublets belong to triplet representation of flavor symmetry. For instance, the stringent constraint from the $mu to e gamma$ process could be evaded according to the partial remnant symmetry. We also investigate the breaking effect of the remnant symmetry mediated by the Higgs scalars, and investigate the constraints from the flavor physics: the flavor violating $tau$ and $mu$ decays, the electric dipole moments, and the muon anomalous magnetic moment. We also discuss the correlation between FCNCs and nonzero $theta_{13}$, and point out the physical observables in the charged lepton sector to test the BSMs for the neutrino mixing.
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