Where We Stand

At present, the standard model of particle physics stands triumphant. It has survived testing far beyond the range of energies for which it was crafted, and to fargreater precision.
Even the “ugly” parts look good. Unlike the gauge part of the standard model, whose parameters are few in number (namely, three) and have a beautiful geometric interpretation, the part dealing with fermion masses and mixings contains many parameters (about two dozen in the minimal model) that appear merely as abstract numbers describing the magnitudes of Yukawa type couplings of one or more hypothetical Higgs fields. In the present state of theory all these numbers must be taken from experiment. Nevertheless, the framework is very significantly constrained and predictive.
From the underlying hypotheses of renormalizable local quantum field theory, and three generation structure, we derive that a 3 × 3 unitary matrix, the CKM (Cabibbo, Kobayashi, Maskawa) matrix, must describe a multitude of a priori independent decay rates and mixing phenomena, including several manifestations of CP violation.
Phenomena associated with neutrino masses, and with gravity, are commonly regarded as beyond, or at least outside, the standard model. Of course, where one draws the boundary of the standard model is largely a matter of taste. But it’s appropriate to emphasize that our working descriptions both of neutrino masses and of gravity fit smoothly and naturally into the conceptual framework associated with the “core” standard model of strong and electroweak interactions. Specifically, neutrino masses can be accommodated using dimension 5 operators, and gravity through the Einstein-Hilbert curvature term and minimal coupling to matter (we can also include a cosmological term). The deep guiding principles that underlie the standard model, to wit local quantum field heory based on operators of the lowest available mass dimension, also work to give theories of neutrino masses and of gravity that describe all existing observations in terms of a small number of parameters.
Altogether, the standard model supplies an economical, precise and (we now know) xtraordinarily accurate description of an enormous range of phenomena. It supplies, in particular, firm and adequate foundations for chemistry (including biochemistry), materials science, and most of astrophysics. We should be very proud of what we, as a community stretching across continents and generations, have accomplished.