In the Standard Model, the masses of bosons are modified via interrelations with other bosons and fermions. This creates what are called ghost fields. Continually perturbing the ground state, matter radiates over these ghost fields, stirring up what has been termed quantum foam.
Boson-fermion interactions are called ghost fields because they are presumed to not exist. Ghost fields are instead treated as a computational tool: a mathematical necessity to maintain consistency in the Standard Model.
But then, ghost fields originate the virtual particles that appear 4d out of the ground state that comprises only vacuum energy. Virtual particles are now taken for granted as existing.
There is a paradox in granting virtual particles existence but considering their creator – ghost fields – to be a fictional construct. It portrays the Standard Model as purely mathematical mumbo-jumbo, despite SM’s many points of convergence with actuality.
Ghost fields play a critical role in producing a loopy hierarchy of particles in SM, thus creating considerable complexity in the Standard Model construct. This hierarchy problem prompted theoretical physicists to derive a more elegant mathematical solution, called supersymmetry (SUSY).
Alas, several SUSY predictions are contradicted by evidence. For example, supersymmetry predicts that electrons have a slightly oval deformation, owing to their having an electric dipole moment, which has yet to be found. Instead, electrons are perfectly spherical.
Supersymmetry is not the only alternative to the Standard Model. Another – string theory – predates SM. While not mainstream, string theory and its offshoot, brane theory, have many adherents.