How many as yet undiscovered particles do we need to make the standard model work?
Physicists have developed a theory called The standard model to explain how particles holds the universe together.
The standard model basically includes 6 leptons,6 quarks,Force carrier particles.
The quarks are classified as up,down,top,bottom,charm,strange.
The leptons are classified as electron,muon,tau,electron neutrino,muon neutrino,tau neutrino.
The force carriers include photons,gluons,W boson,Z boson.
The graviton is needed for our theories of gravity
Some as yet unknown particle is needed to make dark matter work.
WIMPs and MACHOs http://www.astro.caltech.edu/~george/ay21/eaa/eaa-wimps-machos.pdf
But the standard model does not deal with gravity, nor does it deal with a solution to the dark matter problem. Since the are open problems, we have no idea what is required.
Also, current gravitational theories do not require a graviton. Quantisations of them do.
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