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SUMMARY:How large can lepton mixing be?
DTSTART;VALUE=DATE-TIME:20251120T091500Z
DTEND;VALUE=DATE-TIME:20251120T093000Z
DTSTAMP;VALUE=DATE-TIME:20260420T161234Z
UID:indico-contribution-28642@indico.ific.uv.es
DESCRIPTION:Speakers: Rafael Sánchez López (Universidad de Granada)\nWe 
 show that\, contrary to common expectations\, the observed charged leptons
  can have a substantial mixing with new\, heavier fermions. This can happe
 n\, in the language of effective theories\, when the effect of mixing with
  heavier fermions vanishes at tree level in operators of mass-dimension 6 
 (or it is suppressed by the small charged lepton masses)\, a cancellation 
 that can be naturally ensured by symmetries. Other observable effects from
  fermion mixing appear then\, either at tree-level via operators of mass d
 imension 8\, or at one-loop order in operators of mass-dimension 6. \nUsin
 g a model that realizes this scenario we consider all current direct and i
 ndirect constraints and show that experimental constraints on the mixing a
 re so mild that\, given the current direct limit on the mass of the heavy 
 fermions\, theoretical considerations\, mainly instability of the Higgs po
 tential\, presence of Landau poles and strong coupling\, become the leadin
 g current constraints on the mixing. \nCurrently the right handed electron
  could have a $21\\%$ component of EW non-singlet and still be compatible 
 with all current experimental and theoretical constraints. The equivalent 
 limits for muons and taus are\, respectively\, $18\\%$ and $16\\%$. Future
  experiments\, including the high-luminosity of the LHC and\, most notably
 \, the FCC-ee\, will be precise enough to make the experimental limits on 
 the mixing surpase the theoretical ones.\n\nhttps://indico.ific.uv.es/even
 t/8035/contributions/28642/
LOCATION:
URL:https://indico.ific.uv.es/event/8035/contributions/28642/
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