= Dineutron
A <dineutron> is a two-<neutron> system. There is no vacuum <bound state> at physical parameters. In the low-<energy> $s$-wave channel, the spatial state is symmetric, and two <neutrons> have symmetric isospin; the <Pauli exclusion principle> therefore requires antisymmetric total <spin>, the spin-singlet channel. Other <orbital angular momentum> channels have different exchange constraints. An unbound vacuum pair does not rule out correlated <neutron> pairs inside a larger <atomic nucleus> or <neutron> pairing in dense matter.<Modern Theory of Nuclear Forces by Evgeny Epelbaum and others>[§I.B: low-energy two-nucleon channels, the unbound singlet channel and the deuteron]{ref}
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