Wave dark matter on The Broken-Born program

Occupation number: particles or waves

Mon, 01 Jan 0001 00:00:00 +0000

The occupation number is the average number of particles that share one quantum state, or mode, of a gas. When it is much smaller than one, the particles behave as separate particles; when it is much larger than one, so many quanta share each mode that the gas behaves as a classical wave, in the way that the enormous number of photons per mode in a radio broadcast behaves as an electromagnetic wave. For dark matter it is set by the particle mass, the halo’s density and the spread of its velocities, and it equals the number of particles inside a cube whose side is the de Broglie wavelength. In the Broken-Born program it is the quantity that divides the dark-matter question into a particle island and a wave island.

Wave kinetics and Bose-star formation

Mon, 01 Jan 0001 00:00:00 +0000

Wave kinetics is the theory of how a field made of many waves with random phases relaxes when the waves scatter off one another. In a dark-matter halo made of a very light boson, the waves interact through gravity, and each scattering moves power toward the lowest-energy modes at a rate that grows with how many quanta those modes already hold. The result is a dense, coherent ground-state core, a Bose star, which forms at the halo’s center and then grows. Levkov, Panin and Tkachev (LPT) worked out this kinetic condensation and followed it in simulations. The Broken-Born program’s Debt-3 calculation used it as the anchor for a gated version driven by conjugate matter’s self-attraction.

Attractive condensates: critical mass and the bosenova

Mon, 01 Jan 0001 00:00:00 +0000

An attractive condensate is a Bose star — a self-gravitating clump of a light boson field, all in one coherent state — whose particles also attract one another through a self-interaction. Gravity and the self-attraction both pull inward against the outward pressure that comes from the field’s wave nature, and the self-attraction grows faster with density, so such a condensate has a maximum stable mass. Above it the condensate collapses, throws off part of its mass as fast waves in a burst called a bosenova, and the remnant grows again. In the Broken-Born program this cycle is the endpoint that, in Scenario A of the wave island, would have drained the dark matter out of the ultra-faint dwarf galaxies; Scenario A is dead.

The misalignment mechanism

Mon, 01 Jan 0001 00:00:00 +0000

The misalignment mechanism is a way of producing dark matter as a coherent field rather than as a thermal gas of particles. In the early universe a very light scalar field starts at some value away from the minimum of its potential and stays frozen there while the universe expands faster than the field can oscillate; once the expansion rate falls below the field’s mass, the field oscillates about its minimum, and the energy of the oscillation then thins out with the expansion as cold matter does. It is the standard production route for axions. The Broken-Born program borrows it as the production channel for the wave branch of conjugate matter, a channel the particle branch still lacks; the ratio of dark to ordinary matter stays unexplained on both.

Bounds on fuzzy dark matter

Mon, 01 Jan 0001 00:00:00 +0000

The bounds on fuzzy dark matter are observational lower limits on the mass of wave dark matter at its light extreme, where the particles are so light that their de Broglie wavelength is comparable to the core of a small galaxy. Two kinds of observation set them. In a fuzzy halo the interfering dark-matter waves form density fluctuations that heat stars over time, so the compact, cold stellar populations of ultra-faint dwarf galaxies exclude the lightest masses; and fuzzy dark matter suppresses small-scale structure, which the Lyman-α forest — the absorption lines of intergalactic hydrogen in quasar spectra — would reveal. In the Broken-Born program these bounds set the lower edge of the wave island and close the light-mass escape from the falsification of Scenario A.