Universes without the Weak Force: Astrophysical Processes with Stable
  Neutrons
  We investigate a class of universes in which the weak interaction is not in
operation. We consider how astrophysical processes are altered in the absence
of weak forces, including Big Bang Nucleosynthesis (BBN), galaxy formation,
molecular cloud assembly, star formation, and stellar evolution. Without weak
interactions, neutrons no longer decay, and the universe emerges from its early
epochs with a mixture of protons, neutrons, deuterium, and helium. The
baryon-to-photon ratio must be smaller than the canonical value in our universe
to allow free nucleons to survive the BBN epoch without being incorporated into
heavier nuclei. At later times, the free neutrons readily combine with protons
to make deuterium in sufficiently dense parts of the interstellar medium, and
provide a power source before they are incorporated into stars. Almost all of
the neutrons are incorporated into deuterium nuclei before stars are formed. As
a result, stellar evolution proceeds primarily through strong interactions,
with deuterium first burning into helium, and then helium fusing into carbon.
Low-mass deuterium-burning stars can be long-lived, and higher mass stars can
synthesize the heavier elements necessary for life. Although somewhat different
from our own, such universes remain potentially habitable.
