Physics Goals of a ${\mu }^{+}{\mu }^{-}$ Collider

This working group report focuses on the physics potential of ${\mu }^{+}{\mu }^{-}$ colliders beyond what can be accomplished at linear $e^{+}{e}^{-}$ colliders and the LHC. Particularly interesting possibilities include (i)~$s$-channel resonance production to discover and study heavy Higgs bosons with $ZZ$ and $WW$ couplings that are suppressed or absent at tree-level (such as the $H$ and $A$ Higgs bosons of supersymmetric models), (ii)~study of the strongly interacting electroweak sector, where higher energies give larger signals, and (iii)~measurements of the masses and properties of heavy supersymmetric particles.