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In grand unified theories of the SU(5) or SO(10) type, there is a mass relation predicted between the electron and the down quark, the muon and the strange quark and the tau lepton and the bottom quark called the Georgi-Jarlskog mass relations. The relations were formulated by Howard Georgi and Cecilia Jarlskog.

At GUT scale, these are sometimes quoted as:

$m_{e}\approx {\frac {1}{3}}m_{d}$

$m_{\mu }\approx 3m_{s}$

$m_{\tau }\approx m_{b}$

and sometimes as:

${\frac {m_{d}}{m_{s}}}\approx 9{\frac {m_{e}}{m_{\mu }}}$

${\frac {m_{s}}{m_{b}}}\approx {\frac {1}{3}}{\frac {m_{\mu }}{m_{\tau }}}$

Current values for Lepton and Quark masses

Symbol	Description	Renormalization scheme (point)	Value
me	Electron mass		511 keV
md	Down quark mass	μTemplate:Overline = 2 GeV	4.4 MeV
mu	Up quark mass	μ[[MSbar scheme|Template:Overline]] = 2 GeV	1.9 MeV
mμ	Muon mass		105.7 MeV
ms	Strange quark mass	μTemplate:Overline = 2 GeV	87 MeV
mc	Charm quark mass	μTemplate:Overline = mc	1.32 GeV
mτ	Tau mass		1.78 GeV
mb	Bottom quark mass	μTemplate:Overline = mb	4.24 GeV
mt	Top quark mass	On-shell scheme	172.7 GeV

References

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