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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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