In
physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which ...
, a Dirac fermion is a
spin-½ particle (a
fermion) which is different from its
antiparticle. The vast majority of fermions – perhaps all – fall under this category.
Description
In
particle physics
Particle physics or high energy physics is the study of fundamental particles and forces that constitute matter and radiation. The fundamental particles in the universe are classified in the Standard Model as fermions (matter particles) an ...
, all fermions in the
standard model
The Standard Model of particle physics is the theory describing three of the four known fundamental forces ( electromagnetic, weak and strong interactions - excluding gravity) in the universe and classifying all known elementary particles. It ...
have distinct antiparticles (''perhaps'' excepting
neutrinos) and hence are Dirac fermions. They are named after
Paul Dirac
Paul Adrien Maurice Dirac (; 8 August 1902 – 20 October 1984) was an English theoretical physicist who is regarded as one of the most significant physicists of the 20th century. He was the Lucasian Professor of Mathematics at the Univer ...
, and can be modeled with the
Dirac equation.
A Dirac fermion is equivalent to two
Weyl fermions.
The counterpart to a Dirac fermion is a
Majorana fermion
A Majorana fermion (, uploaded 19 April 2013, retrieved 5 October 2014; and also based on the pronunciation of physicist's name.), also referred to as a Majorana particle, is a fermion that is its own antiparticle. They were hypothesised by ...
, a particle that must be its own
antiparticle.
Dirac quasi-particles
In
condensed matter physics, low-energy excitations in
graphene
Graphene () is an allotrope of carbon consisting of a Single-layer materials, single layer of atoms arranged in a hexagonal lattice nanostructure. and
topological insulators, among others, are fermionic
quasiparticles described by a pseudo-relativistic Dirac equation.
See also
*
Dirac spinor
In quantum field theory, the Dirac spinor is the spinor that describes all known fundamental particles that are fermions, with the possible exception of neutrinos. It appears in the plane-wave solution to the Dirac equation, and is a certain co ...
, a wavefunction-like description of a Dirac fermion
*
Dirac–Kähler fermion, a geometric formulation of Dirac fermions
*
Majorana fermion
A Majorana fermion (, uploaded 19 April 2013, retrieved 5 October 2014; and also based on the pronunciation of physicist's name.), also referred to as a Majorana particle, is a fermion that is its own antiparticle. They were hypothesised by ...
, an alternate category of
fermion, possibly describing
neutrinos
*
Spinor, mathematical details
References
Fermions
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