What forces can constrain a left-right mirror of the Standard Model?

A left-right symmetric extension of the Standard Model, motivated by grand unification, has a richer Higgs sector than the familiar theory. The authors derived all constraints that keep the theory mathematically consistent: unitarity (particles can't scatter with probability > 1), vacuum stability (the universe doesn't spontaneously decay), and perturbativity (coupling strengths don't blow up). Running these constraints from electroweak energies up to 10^16 GeV tightens the allowed masses of exotic charged and neutral Higgs bosons to 1–6 TeV, making them potentially discoverable at the Large Hadron Collider.