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The joint energy-momentum spectrum lies in the closed forward light cone. In axiomatic quantum field theory, this condition permits analytic continuation of Wightman functions in suitable complex spacetime domains. Together with Lorentz invariance, microcausality and the positivity of the physical state space, it is one of the hypotheses behind the CPT theorem.

A quantum field is an operator-valued distribution on spacetime: smearing $\Phi (x)$ against a smooth test function gives an operator, whereas pointwise products can require renormalization. For example, a free complex scalar field contains particle annihilation operators and antiparticle creation operators. Its microcausality condition makes field commutators vanish at spacelike separation. For fermions, the corresponding locality condition uses anticommutators. This combines quantum operators with the spacetime locality of a quantum field theory.

A description of quantum states and dynamics compatible with special relativity. Relativistic one-particle equations have a useful domain, while interactions that create or destroy particles generally require quantum field theory.

A renormalizable quantum field theory permits ultraviolet divergences to be absorbed into a fixed finite set of parameters and field normalizations. In ordinary four-dimensional perturbative power counting in quantum field theory, its interaction coefficients have nonnegative mass dimension.

The S-matrix maps incoming asymptotic states to outgoing asymptotic states. Its connected transition matrix elements contain an overall energy-momentum Dirac delta function and an invariant scattering amplitude. In quantum field theory, the LSZ reduction formula obtains these elements from amputated field correlators.

The Standard Model is the quantum field theory of quarks, leptons and their strong, weak and electromagnetic interactions, organized by the gauge group $SU(3{)}_c\times SU(2{)}_L\times U(1{)}_Y$. Quantum chromodynamics describes the color sector; the electroweak interaction combines the remaining gauge fields with the Higgs field.

Electroweak symmetry breaking leaves the electromagnetic $U(1{)}_Q$ unbroken. The W bosons and Z boson become massive, while the photon stays massless; Yukawa interactions generate charged-fermion masses. This structure relates scattering, decay and particle-production processes using a common set of couplings. Predictions require specifying parameters and the approximation used, not only listing the group.

The minimal renormalizable field content has massless neutrinos. Observed neutrino oscillations require masses and mixing, motivating extensions such as the Weinberg operator or additional neutrino fields. The Standard Model also does not supply a quantum description of gravity.

A quantum field theory assigning vector spaces to closed spatial manifolds and linear maps to interpolating spacetime cobordisms, compatibly with composition and disjoint union. Its TQFT partition function on $\Sigma \times S^1$ is the trace of the identity of the state space on $\Sigma$, hence its dimension.

A two-dimensional conformal field theory is a quantum field theory with local conformal transformations. In Euclidean complex coordinates, infinitesimal transformations separate into holomorphic and antiholomorphic sectors, organized by two copies of the Virasoro algebra.

This symmetry strongly constrains correlation functions. A primary field's conformal weights fix its two-point dependence, while three-point functions are fixed up to constants; higher-point functions retain dependence on conformal cross-ratios. The operator product expansion combines local fields and records the remaining dynamical data. A free boson conformal field theory provides an explicit example. In string theory, this framework describes gauge-fixed worldsheet dynamics and connects the central charge to quantum consistency.

For a stable relativistic quantum field theory in Minkowski space, a vacuum is a lowest-energy state for the chosen time evolution; a physical vacuum is normally also invariant under spacetime translations. It need not have zero fluctuations or vanish under every field operator. A free field's Fock vacuum is annihilated by its annihilation operators, while an interacting vacuum need not equal the free-theory Fock state. Multiple degenerate vacua permit spontaneous symmetry breaking. In curved spacetime the choice of time evolution and positive-frequency modes introduces additional vacuum ambiguity in a nonstationary spacetime.