Vectorlike leptons and inert scalar triplet: Lepton flavor violation, $g-2$, and collider searches

We investigate simplified models involving an inert scalar triplet and vectorlike leptons that can account for the muon $g-2$ anomaly. These simplified scenarios are embedded in a model that features W’ and Z’ bosons, which are subject to stringent collider bounds. The constraints coming from the muon $g-2$ anomaly are put into perspective with collider bounds, as well as bounds coming from lepton flavor violation searches. The region of parameter space that explains the $g-2$ anomaly is shown to be within reach of lepton flavor violation probes and future colliders such as HL-LHC and HE-LHC.

Figure 1

Overall correction to $g-2$ as a function of the energy scale of 3-3-1 symmetry breaking for $M_{\varphi }=0.1v_{\chi }$ (black curve) and $M_{\varphi }=0.05v_{\chi }$ (brown curve) due to the presence of an inert scalar triplet. In this plot, we considered ${\lambda }_{22}=1$. The green lines delimit the region of parameter space that explains $g-2$. The LHC, HL-LHC and HE-LHC limits are displayed according to Eqs. (19)–(21). The horizontal red lines represent the current and projected $1\sigma$ bounds by requiring the new physics contribution to be within the $1\sigma$ error bar. One can clearly see that if we take $v_{\chi }\sim 10–12\mathrm{TeV}$ we can explain the $g-2$ anomaly while being consistent with current LHC bounds. See the text for further details.

Figure 2

Overall correction to $g-2$ as a function of the energy scale of 3-3-1 symmetry breaking for $M_{\varphi }=0.01v_{\chi }$ (black curve) and $M_{\varphi }=0.005v_{\chi }$ (brown curve) due to the presence of an exotic lepton with $m_E=200\mathrm{GeV}$, for the case where ${\lambda }_{22}=2$. The green lines delimit the region of parameter space that explains $g-2$. The LHC, HL-LHC and HE-LHC bounds are displayed according to Eqs. (19)–(21). The horizontal red lines represent the current and projected $1\sigma$ bounds by requiring the new physics contribution to be within the $1\sigma$ error bar. One can clearly see that if we take $v_{\chi }\sim 20\mathrm{TeV}$ we explain the $g-2$ anomaly while being consistent with current and future collider bounds. See the text for further details.

Figure 3

Same as Fig. 2 but for $m_E=400\mathrm{GeV}$ and ${\lambda }_{22}=3$. Now the scale of symmetry breaking is in agreement to higher values, until approximately 25 TeV for $M_{\varphi }\sim 0.01v_{\chi }$, and 40 TeV for $M_{\varphi }\sim 0.005v_{\chi }$. Both scenarios can be probed by HE-LHC. For $M_{\varphi }\sim 0.01v_{\chi }$, the parameter space is completely probed by HE-LHC. It is interesting to see that the current and projected $g-2$ bounds are stronger than those arising from collider searches.

Figure 4

Contour plot of the regions that explain $g-2$ as a function of the scale of symmetry breaking, $v_{\chi }$. We assumed ${\lambda }_{21}=2*{\lambda }_{22}\times 10^{-5}$. The two distinct regions are for $M_{\varphi }=0.05v_{\chi }$ and $M_{\varphi }=0.1v_{\chi }$. The vertical blue lines delimit the HL-LHC and HE-LHC projected exclusion regions.

Figure 5

Contour plot of the regions that explain $g-2$ as a function of the scale of symmetry breaking in the presence of an exotic charged lepton with $m_E=200\mathrm{GeV}$. We assumed ${\lambda }_{21}=3.0*{\lambda }_{22}\times 10^{-}5$. The two distinct regions are for $M_{\varphi }=0.005v_{\chi }$ and $M_{\varphi }=0.01v_{\chi }$. The shaded black region is excluded by LHC searches and the vertical black lines delimit the HL-LHC (continuous) and HE-LHC (dashed) projected exclusion regions.

Figure 6

Same as Fig. 5 but for $m_E=400\mathrm{GeV}$ and $M_{\varphi }=0.005v_{\chi }$.