Hierarchy problem and naturalness of the Higgs mass

5 problems

• Is the weak scale set by cosmological dynamics or selection?

  Open

  Instead of new particles at the TeV scale, the Higgs mass might have been adjusted during the early universe by a slowly evolving field, or selected among many possible universes. Such ideas predict light, weakly coupled particles instead of heavy ones.

• Is the Higgs boson elementary or a composite bound state?

  Open

  The Higgs could be a point-like particle or a bound state of new strongly interacting constituents, much as a pion is made of quarks. A composite Higgs would show small deviations in how it couples to other particles.

• Do color-neutral top partners, as in Twin Higgs models, exist?

  Open

  Some proposals keep the Higgs light with partner particles that do not feel the strong force, so the LHC barely produces them. They would show up as small shifts in Higgs couplings, or as Higgs decays to hidden-sector particles that fly a measurable distance before decaying.

• Why is the electroweak scale so far below the Planck scale?

  Open

  The Higgs field sets the masses of most particles at about $246\,\mathrm{GeV}$, roughly 1e17 times below the scale where gravity becomes strong. No known principle explains this huge gap without extreme fine cancellations.

• Do colored top partners exist below a few TeV?

  Open

  Most proposed fixes for the light Higgs predict a heavy cousin of the top quark (a top partner) that cancels the top quark's large push on the Higgs mass. If such particles exist, they should appear at colliders with masses not far above 1 TeV.