The Kaxion

Abstract

Nearly a century ago, astronomers found that galaxies move as though they hold far more matter than we can see. Stars at the edges of spinning galaxies orbit too fast; the afterglow of the Big Bang bears the imprint of a substance outweighing ordinary atoms five to one. We call it dark matter, and no experiment has yet identified what it is. This paper offers an answer not invented for the purpose. In earlier papers of this series we built a theory from a few founding rules and showed that, with no adjustable numbers, it reproduces the known particles and forces. That same construction is forced to contain one more field: an exceedingly light, electrically neutral relic of the geometry we call the Kaxion. It is automatically dark, stable, and cold, and the early universe makes it in just the observed amount — about 27 percent of the cosmos. As a bonus, it explains why the strong nuclear force respects mirror symmetry so exactly. Because nothing about the Kaxion can be tuned, the theory makes hard promises: the precise microwave frequency at which to listen, near 1.95 gigahertz; the faintness of its glow into light; and two fingerprints — every signal is a pair of tones split by one part in thirty-five, in two channels locked five to two. Two experiments now being built to hunt dark matter are aimed almost exactly at this frequency and faintness, and should find the Kaxion — or rule it out — within a few years. If they do, the substance that first gathered the galaxies will have been sounding one faint note since the universe's opening microsecond — a pitch fixed by a handful of whole numbers.