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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.^[ref]

A theoretical nuclear physicist who develops descriptions of nuclear forces through effective field theory. His joint review relates the allowed low-energy interactions of nucleons to symmetries of quantum chromodynamics. Organizing interactions systematically makes it possible to improve a nuclear calculation in stages and compare few-body predictions with measured nuclear properties.^[ref]

A theoretical nuclear physicist working on effective field theory descriptions of nuclear forces. His review with Evgeny Epelbaum and Ulf-G. Meißner compares descriptions at different resolution scales. Selecting the relevant low-energy degrees of freedom permits controlled calculations of few-nucleon systems while retaining constraints from quantum chromodynamics.^[ref]

The residual strong interaction between nucleons. Its long-distance part involves pion exchange and depends on spin and isospin. It is distinct from directly exchanging gluons between color-singlet nucleons.

Why do protons and neutrons bind into an atomic nucleus, even though protons repel electrically? An attractive nuclear force can lower the total energy below that of separated nucleons, producing nuclear binding energy. The deuteron, containing one proton and one neutron, is the simplest such bound state.

In quantum chromodynamics, nucleons are composite colour singlets built from quarks and gluons. Their residual nuclear force has a longest-range strong contribution from one-pion exchange, with additional interactions at shorter distances.^[ref]

Although the pion has spin zero, one-pion exchange depends on nucleon spin and isospin and includes a nuclear tensor force. Shorter-range and multiple-nucleon interactions also matter. The scalar Yukawa potential isolates a range mechanism rather than specifying the complete nuclear force.^[ref]

In a pure $L=0,S=1$ stretched state both spins point along the total angular momentum, with no orbital contribution. The nuclear magnetic moment would beThe measured $0.857{\mu }_N$ differs. More decisively, a pure S wave spatial state is isotropic and has zero electric quadrupole moment. Its nonzero value requires a nonspherical component of the quantum charge distribution.

Positive parity allows even $L$; coupling $S=1$ to $J=1$ permits $L=0$ and $L=2$. The state contains a deuteron D-state admixture:with radial wavefunctions implicit. A nuclear tensor force couples the orbital components. The quadrupole moment involves their interference as well as a D-state contribution, making it sensitive to a small admixture. This is a quantum angular correlation, not two particles permanently fixed in space.

In the nonrelativistic one-body magnetic-moment approximation,The D-state coupling has $⟨S_z⟩=-1/2$ and $⟨L_z⟩=3/2$ at $J_z=1$; the proton supplies approximately half the relative orbital magnetic moment. ThusThe robust conclusion is a predominantly S wave state with a small tensor-induced D wave component. The 4% estimate is model dependent: exchange currents and other corrections also affect the magnetic moment, and a wavefunction component probability is not itself a uniquely measured observable.^[ref]

A theoretical nuclear physicist who studies nuclear forces using effective field theory. His joint review with Evgeny Epelbaum and Hans-Werner Hammer explains how the symmetries of quantum chromodynamics constrain low-energy interactions between nucleons. The approach organizes increasingly accurate calculations without treating a nucleus directly as a collection of interacting quarks.^[ref]