Charged lepton flavor violation in light of muon $$g-2$$ g - 2

Wei-Shu Hou (Department of Physics, National Taiwan University, Taipei, 10617, Taiwan) ; Girish Kumar (Department of Physics, National Taiwan University, Taipei, 10617, Taiwan)

The recent confirmation of the muon $$g-2$$ g - 2 anomaly by the Fermilab $$g-2$$ g - 2 experiment may harbinger a new era in $$\mu $$ μ and $$\tau $$ τ physics. In the context of general two Higgs doublet model, the discrepancy can be explained via one-loop exchange of sub-TeV exotic scalar and pseudoscalars, namely H and A, that have flavor changing neutral couplings $$\rho _{\tau \mu }$$ ρ τ μ and $$\rho _{\mu \tau }$$ ρ μ τ at $$\sim 20$$ 20 times the usual tau Yukawa coupling, $$\lambda _\tau $$ λ τ . Taking $$\rho _{\ell \ell ^\prime }\sim \lambda _{ \mathrm min(\ell , \ell ^\prime )}$$ ρ λ m i n ( , ) , we show that the above solution to muon $$g-2$$ g - 2 then predicts enhanced rates of various charged lepton flavor violating processes, which should be accessible at upcoming experiments. We cover muon related processes such as $$\mu \rightarrow e \gamma $$ μ e γ , $$\mu \rightarrow eee$$ μ e e e and $$\mu N \rightarrow e N$$ μ N e N , and $$\tau $$ τ decays $$\tau \rightarrow \mu \gamma $$ τ μ γ and $$\tau \rightarrow \mu \mu \mu $$ τ μ μ μ . A similar one-loop diagram with $$\rho _{e\tau }= \rho _{\tau e} = \mathcal{O}(\lambda _e)$$ ρ e τ = ρ τ e = O ( λ e ) induces $$\mu \rightarrow e\gamma $$ μ e γ , bringing the rate right into the sensitivity of the MEG II experiment. The $$\mu e\gamma $$ μ e γ dipole can be probed further by $$\mu \rightarrow 3e$$ μ 3 e and $$\mu N \rightarrow eN$$ μ N e N . With its promised sensitivity range and ability to use different nuclei, the $$\mu N \rightarrow eN$$ μ N e N conversion experiments can not only make discovery, but access the extra diagonal quark Yukawa couplings $$\rho _{qq}$$ ρ qq . For the $$\tau $$ τ lepton, we find that $$\tau \rightarrow \mu \gamma $$ τ μ γ would probe $$\rho _{\tau \tau }$$ ρ τ τ down to $$\lambda _\tau $$ λ τ or lower, while $$\tau \rightarrow 3\mu $$ τ 3 μ would probe $$\rho _{\mu \mu }$$ ρ μ μ to $$\mathcal{O}(\lambda _{\mu })$$ O ( λ μ ) .

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      "title": "Charged lepton flavor violation in light of muon  $$g-2$$  <math> <mrow> <mi>g</mi> <mo>-</mo> <mn>2</mn> </mrow> </math>"
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  "abstracts": [
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      "source": "Springer", 
      "value": "The recent confirmation of the muon  $$g-2$$  <math> <mrow> <mi>g</mi> <mo>-</mo> <mn>2</mn> </mrow> </math>   anomaly by the Fermilab  $$g-2$$  <math> <mrow> <mi>g</mi> <mo>-</mo> <mn>2</mn> </mrow> </math>   experiment may harbinger a new era in  $$\\mu $$  <math> <mi>\u03bc</mi> </math>   and  $$\\tau $$  <math> <mi>\u03c4</mi> </math>   physics. In the context of general two Higgs doublet model, the discrepancy can be explained via one-loop exchange of sub-TeV exotic scalar and pseudoscalars, namely H and A, that have flavor changing neutral couplings  $$\\rho _{\\tau \\mu }$$  <math> <msub> <mi>\u03c1</mi> <mrow> <mi>\u03c4</mi> <mi>\u03bc</mi> </mrow> </msub> </math>   and  $$\\rho _{\\mu \\tau }$$  <math> <msub> <mi>\u03c1</mi> <mrow> <mi>\u03bc</mi> <mi>\u03c4</mi> </mrow> </msub> </math>   at  $$\\sim 20$$  <math> <mrow> <mo>\u223c</mo> <mn>20</mn> </mrow> </math>   times the usual tau Yukawa coupling,  $$\\lambda _\\tau $$  <math> <msub> <mi>\u03bb</mi> <mi>\u03c4</mi> </msub> </math>  . Taking  $$\\rho _{\\ell \\ell ^\\prime }\\sim \\lambda _{ \\mathrm min(\\ell , \\ell ^\\prime )}$$  <math> <mrow> <msub> <mi>\u03c1</mi> <mrow> <mi>\u2113</mi> <msup> <mi>\u2113</mi> <mo>\u2032</mo> </msup> </mrow> </msub> <mo>\u223c</mo> <msub> <mi>\u03bb</mi> <mrow> <mi>m</mi> <mi>i</mi> <mi>n</mi> <mo>(</mo> <mi>\u2113</mi> <mo>,</mo> <msup> <mi>\u2113</mi> <mo>\u2032</mo> </msup> <mo>)</mo> </mrow> </msub> </mrow> </math>  , we show that the above solution to muon  $$g-2$$  <math> <mrow> <mi>g</mi> <mo>-</mo> <mn>2</mn> </mrow> </math>   then predicts enhanced rates of various charged lepton flavor violating processes, which should be accessible at upcoming experiments. We cover muon related processes such as  $$\\mu \\rightarrow e \\gamma $$  <math> <mrow> <mi>\u03bc</mi> <mo>\u2192</mo> <mi>e</mi> <mi>\u03b3</mi> </mrow> </math>  ,  $$\\mu \\rightarrow eee$$  <math> <mrow> <mi>\u03bc</mi> <mo>\u2192</mo> <mi>e</mi> <mi>e</mi> <mi>e</mi> </mrow> </math>   and  $$\\mu N \\rightarrow e N$$  <math> <mrow> <mi>\u03bc</mi> <mi>N</mi> <mo>\u2192</mo> <mi>e</mi> <mi>N</mi> </mrow> </math>  , and  $$\\tau $$  <math> <mi>\u03c4</mi> </math>   decays  $$\\tau \\rightarrow \\mu \\gamma $$  <math> <mrow> <mi>\u03c4</mi> <mo>\u2192</mo> <mi>\u03bc</mi> <mi>\u03b3</mi> </mrow> </math>   and  $$\\tau \\rightarrow \\mu \\mu \\mu $$  <math> <mrow> <mi>\u03c4</mi> <mo>\u2192</mo> <mi>\u03bc</mi> <mi>\u03bc</mi> <mi>\u03bc</mi> </mrow> </math>  . A similar one-loop diagram with  $$\\rho _{e\\tau }= \\rho _{\\tau e} = \\mathcal{O}(\\lambda _e)$$  <math> <mrow> <msub> <mi>\u03c1</mi> <mrow> <mi>e</mi> <mi>\u03c4</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>\u03c1</mi> <mrow> <mi>\u03c4</mi> <mi>e</mi> </mrow> </msub> <mo>=</mo> <mi>O</mi> <mrow> <mo>(</mo> <msub> <mi>\u03bb</mi> <mi>e</mi> </msub> <mo>)</mo> </mrow> </mrow> </math>   induces  $$\\mu \\rightarrow e\\gamma $$  <math> <mrow> <mi>\u03bc</mi> <mo>\u2192</mo> <mi>e</mi> <mi>\u03b3</mi> </mrow> </math>  , bringing the rate right into the sensitivity of the MEG II experiment. The  $$\\mu e\\gamma $$  <math> <mrow> <mi>\u03bc</mi> <mi>e</mi> <mi>\u03b3</mi> </mrow> </math>   dipole can be probed further by  $$\\mu \\rightarrow 3e$$  <math> <mrow> <mi>\u03bc</mi> <mo>\u2192</mo> <mn>3</mn> <mi>e</mi> </mrow> </math>   and  $$\\mu N \\rightarrow eN$$  <math> <mrow> <mi>\u03bc</mi> <mi>N</mi> <mo>\u2192</mo> <mi>e</mi> <mi>N</mi> </mrow> </math>  . With its promised sensitivity range and ability to use different nuclei, the  $$\\mu N \\rightarrow eN$$  <math> <mrow> <mi>\u03bc</mi> <mi>N</mi> <mo>\u2192</mo> <mi>e</mi> <mi>N</mi> </mrow> </math>   conversion experiments can not only make discovery, but access the extra diagonal quark Yukawa couplings  $$\\rho _{qq}$$  <math> <msub> <mi>\u03c1</mi> <mrow> <mi>qq</mi> </mrow> </msub> </math>  . For the  $$\\tau $$  <math> <mi>\u03c4</mi> </math>   lepton, we find that  $$\\tau \\rightarrow \\mu \\gamma $$  <math> <mrow> <mi>\u03c4</mi> <mo>\u2192</mo> <mi>\u03bc</mi> <mi>\u03b3</mi> </mrow> </math>   would probe  $$\\rho _{\\tau \\tau }$$  <math> <msub> <mi>\u03c1</mi> <mrow> <mi>\u03c4</mi> <mi>\u03c4</mi> </mrow> </msub> </math>   down to  $$\\lambda _\\tau $$  <math> <msub> <mi>\u03bb</mi> <mi>\u03c4</mi> </msub> </math>   or lower, while  $$\\tau \\rightarrow 3\\mu $$  <math> <mrow> <mi>\u03c4</mi> <mo>\u2192</mo> <mn>3</mn> <mi>\u03bc</mi> </mrow> </math>   would probe  $$\\rho _{\\mu \\mu }$$  <math> <msub> <mi>\u03c1</mi> <mrow> <mi>\u03bc</mi> <mi>\u03bc</mi> </mrow> </msub> </math>   to  $$\\mathcal{O}(\\lambda _{\\mu })$$  <math> <mrow> <mi>O</mi> <mo>(</mo> <msub> <mi>\u03bb</mi> <mi>\u03bc</mi> </msub> <mo>)</mo> </mrow> </math>  ."
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Published on:
24 December 2021
Publisher:
Springer
Published in:
European Physical Journal C , Volume 81 (2021)
Issue 12
Pages 1-8
DOI:
https://doi.org/10.1140/epjc/s10052-021-09939-3
arXiv:
2107.14114
Copyrights:
The Author(s)
Licence:
CC-BY-4.0

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