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I've been wondering about how exactly the Pauli exclusion principle works--how it acts like a sort of repulsive "force" which doesn't allow one fermion to "be in the same place" as another. I understand that it is not a force, and from this answer it is more like something that magnifies the already-existing forces between particles. From what I understand, it seems to me that the Pauli exclusion principle just describes a consequence of how particles interact, rather than describing a force, kind of like how we think of centrifugal force as not really a force, just a consequence of reference frames and such.

My question is among neutrinos, is it the weak interaction that serves as the "repulsive" force? I have found descriptions of neutrino-neutrino scattering mediated by the Z boson.

Related to this, I have also wondered about "neutrino stars." Given that neutrinos are chargeless it seems to be that the existence of a neutrino star à la neutron star should be reasonable albeit improbable. However, what about the weak force? Are neutrinos repulsed by each other via this force? Would this force dominate at neutrino star scales?

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Weak interaction is not repulsive in the sense that particles charged with weak isospin (the "charge" of weak interaction) don't attract or repulse each other.

Neutrino stars would be huge, having a radius of several thousands of light-years due to their tiny mass and interaction cross section. It is possible that they would clump to galactic haloes, forming a part of the dark matter. This StackExchange post should answer your questions about neutrino stars.

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  • $\begingroup$ The exponential scale height of an isothermal atmosphere is $kT/mg$, but the neutrino mass is tiny. Since neutrinos interact weakly (even with nuclear matter) many energetic neutrinos could simply have escaped at the time they were formed by inverse beta decay, instead of equilibrating. $\endgroup$
    – Bert Barrois
    Commented Feb 2, 2018 at 12:59

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