Dark Matter Superfluidity

TL;DR

This paper discusses a theory where dark matter forms a superfluid in galaxy centers, with phonons mediating forces that explain galactic dynamics, unifying dark matter and modified gravity phenomena.

Contribution

It introduces a superfluid dark matter model with axion-like particles that reproduces galactic scaling relations through phonon-mediated forces.

Findings

Superfluid phase forms in galaxy centers.

Phonon excitations reproduce Milgrom's law.

Unified framework for dark matter and modified gravity.

Abstract

In these lectures I describe a theory of dark matter superfluidity developed in the last few years. The dark matter particles are axion-like, with masses of order eV. They Bose-Einstein condense into a superfluid phase in the central regions of galaxy halos. The superfluid phonon excitations in turn couple to baryons and mediate a long-range force (beyond Newtonian gravity). For a suitable choice of the superfluid equation of state, this force reproduces the various galactic scaling relations embodied in Milgrom's law. Thus the dark matter and modified gravity phenomena represent different phases of a single underlying substance, unified through the rich and well-studied physics of superfluidity.