- Asymptotic freedom: It is the property of some gauge theories in which the interaction between the particles, such as quarks, becomes arbitrarily weak at ever shorter distances, i.e. length scales that asymptotically converge to zero (or, equivalently, energy scales that become arbitrarily large).
- Baryon number: It is an approximate conserved quantum number of a system.
It is defined as:
Where is the number of quarks, and is the number of antiquarks.
- Colour confinement, often called just confinement: It is the physics phenomenon that colour charged particles (such as quarks) cannot be isolated. The quarks are confined with other quarks by the strong interaction to form pairs or triplets so that the net colour is neutral, to obey the Pauli Exclusion Principle. Quarks in mesons must be of a colour and the corresponding anti-colour to achieve colour neutralism; in baryons a red-green-blue mixture (or its anti-colour equivalent in an antiparticle) must be achieved.
- Coupling constant (g): It is a number that determines the strength of an interaction. Usually the Lagrangian or the Hamiltonian of a system can be separated into a kinetic part and an interaction part. The coupling constant determines the strength of the interaction part with respect to the kinetic part, or between two sectors of the interaction part. For example, the electric charge of a particle is a coupling constant.
- C, P, and T symmetries: The Standard model of particle physics has three
related natural near-symmetries. These state that the universe is indistinguishable
from one where:
C-symmetry (charge symmetry) - every particle is replaced with its antiparticle.
P-symmetry (parity symmetry) - the universe is reflected as in a mirror.
T-symmetry (time symmetry) - the direction of time is reversed.
Each of these symmetries is broken, but the Standard Model predicts that the combination of the three (that is, the three transformations at the same time) must be a symmetry, known as CPT symmetry. CP violation, the violation of the combination of C and P symmetry, is a currently fruitful area of particle physics research, as well as being necessary for the presence of significant amounts of matter in the universe and thus the existence of life.
- Eightfold Way: It is the name given by Murray Gell-Mann for a theory
organizing subatomic baryons and mesons into octets. The theory was independently
proposed by Israeli physicist Yuval Ne'eman and led to the subsequent development
of the quark model.
The meson octet. Particles along the same horizontal line share the same
strangeness, s, while those on the same diagonals share the same charge,
q. In addition to organizing the mesons and spin-1/2 baryons into octets,
the principles of the Eightfold Way also applied to the spin-3/2 baryons,
forming a decuplet. However, one of its particles had never been previously
observed. Gell-Mann called this particle the ?? and predicted that it would
have a strangeness ?3, electric charge ?1 and a mass near 1680 MeV/c².
In 1964 a particle closely matching these predictions was discovered, making
the Eightfold Way a triumphant success.
- Electromagnetic interaction: The electromagnetic interaction acts on charged particles, leaving the particles unchanged. It caused like particles to repel.
- Fermi constant: The strength of Fermi's interaction is given by the Fermi
constant GF. In modern terms:
Here g is the coupling constant of the weak interaction, and mW is the mass
of the W boson.
- Fermi's interaction: It is an old explanation of the weak force. Four fermions directly interact with one another. For example, this interaction is directly able to split a neutron (or a two down-quarks and an up-quark) to an electron, antineutrino and a proton (or two up-quarks and a down-quark).
- Goldstone's theorem or Nambu-Goldstone Theorem: It states that whenever a continuous symmetry is spontaneously broken, new massless (or light, if the symmetry was not exact) scalar particles appear in the spectrum of possible excitation. There is one scalar particle -called a Goldstone or Goldstone Nanbu boson - for each generator of the symmetry that is broken, i.e., that does not preserve the ground state. In theories with gauge symmetry, the Goldstone bosons are "eaten" by the gauge bosons. The latter become massive and their new, longitudinal polarization is provided by the Goldstone boson.
- Hierarchy problem: It is the question why the weak force is 1032 times stronger than gravity. Both of these forces involve constants of nature, Fermi's constant for the weak force and Newton's constant for gravity. Furthermore if the Standard Model is used to calculate the quantum corrections to Fermi's constant, it appears that Fermi's constant is unnaturally large and should be closer to Newton's constant unless there is a delicate cancellation between the bare value of Fermi's constant and the quantum corrections to it.
- Higgs interaction: The Higgs field is thought to fill space like a fluid, impeding the W and Z bosons and then limiting the range of weak interactions. The Higgs also interacts with quarks and leptons, endowing them with mass.
- Internal energy: In a thermodynamic system, or a body with well-defined boundaries, denoted by U, or sometimes E, it is the total of the kinetic energy due to the motion of molecules (translational, rotational, vibrational) and the potential energy associated with the vibrational and electric energy of atoms within molecules or crystals. It includes the energy in all the chemical bonds, and the energy of the free, conduction electrons in metals. The internal energy is a thermodynamic potential and for a closed thermodynamic system held at constant entropy, it will be minimized.
- Ionization; It is the physical process of converting an atom or molecule into an ion by changing the difference between the number of protons and electrons. This process works slightly differently depending on whether an ion with a positive or a negative electric charge is being produced. A positive electric charge is produced when an electron bond to an atom or molecule absorbs enough energy from an external source to escape from the electric potential barrier that originally confined it, where the amount of energy required is called the Ionization potential. A negative electric charge is produced when a free electron collides with an atom and is subsequently caught inside the electric potential barrier, releasing any excess energy.
- Instanton or pseudoparticle: It is a notion appearing in theoretical and mathematical physics. Mathematically, a Yang-Mills instanton is a self-dual or anti-self-dual connection in a principal bundle over a four-dimensional Riemannian manifold that plays the role of physical space-time in nonabelian gauge theory. Instantons are topologically nontrivial solutions of Yang-Mills equations that absolutely minimize the energy functional within their topological type.
- Large Hadron Collider (LHC): It is the world's largest and highest-energy particle accelerator, intended to collide opposing particle beams, of either protons at an energy of 7 TeV/particle, or lead nuclei at an energy of 574 TeV/nucleus. The Large Hadron Collider was built by the European Organization for Nuclear Research (CERN) with the intention of testing various predictions of high-energy physics, including the existence of the hypothesised Higgs boson and of the large family of new particles predicted by supersymmetry. It lies in a tunnel 27 kilometres (17 mi) in circumference, as much as 175 metres (570 ft) beneath the Franco-Swiss border near Geneva, Switzerland.
- Mass number (A), also called atomic mass number: It is the number of nucleons (protons and neutrons) in an atomic nucleus. The mass number is unique for each isotope of an element. For example, carbon-12 (12C) has 6 protons and 6 neutrons. The full isotope symbol would also have the atomic number (Z) as a subscript to the left of the element symbol directly below the mass number: C. The difference between the mass number and the atomic number gives the number of neutrons (N) in a given nucleus: N=A?Z.
- Neutrino oscillation: This is a quantum mechanical phenomenon whereby a neutrino created with a specific lepton flavour (electron, muon or tau) can later be measured to have a different flavour. The probability of measuring a particular flavour for a neutrino varies periodically as it propagates.
- Rest Mass, invariant mass or intrinsic mass or proper mass or just mass is a measurement or calculation of the mass of an object that is the same for all frames of reference. For any frame of reference, the invariant mass may be determined from a calculation involving an object's total energy and momentum.
- Riemannian manifold (Riemannian metric): It is a real differentiable manifold M in which each tangent space is equipped with an inner product g in a manner which varies smoothly from point to point. This allows one to define various notions such as angles, lengths of curves, areas (or volumes), curvature, gradients of functions and divergence of vector fields. In other words, a Riemannian manifold is a differentiable manifold in which the tangent space at each point is a finite-dimensional Hilbert space.
- Standard Model of particle physics: It is a theory that describes three of the four known fundamental interactions between the elementary particles that make up all matter. It unifies the electroweak theory and quantum chromodynamics into a structure denoted by the gauge groups SU(3)×SU(2)×U(1). It is a quantum field theory which is consistent with both quantum mechanics and special relativity. To date, almost all experimental tests of the three forces described by the Standard Model have agreed with its predictions. However, the Standard Model falls short of being a complete theory of fundamental interactions, primarily because of its lack of inclusion of gravity, the fourth known fundamental interaction, but also because of the eighteen numerical parameters (such as masses and coupling constants) that must be put "by hand" into the theory.
- Statistical mechanics: It is the application of probability theory, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force. It provides a framework for relating the microscopic properties of individual atoms and molecules to the macroscopic or bulk properties of materials that can be observed in everyday life, therefore explaining thermodynamics as a natural result of statistics and mechanics (classical and quantum) at the microscopic level.
- Strangeness (S): It is a property of particles, expressed as a quantum
number for describing decay of particles in strong and electro-magnetic
reactions, which occur in a short period of time. The strangeness of a particle
is defined as:
where represents the number of strange anti-quarks
( ) and represents the number of strange quarks.
The derivation of the phrase "strange" or "strangeness" precedes the discovery of the quark, and was adopted after its discovery in order to preserve the continuity of the phrase; strangeness of anti-particles being referred to as +1, and particles as -1 as per the original definition. For all the quark flavour quantum numbers (strangeness, charm, topness and bottomness) the convention is that the flavour charge and the electric charge of a quark have the same sign. With this, any flavour carried by a charged meson has the same sign as its charge.
- Sum-over-paths, also known as Feynman sum-over-paths and sum-over-histories: It is an approach to visualizing the movement of particles that is mathematically described by the equations of quantum mechanics. This model competes with the concept of probability waves, though it is numerically identical. Richard Feynman first articulated this idea and contended that fast moving subatomic particles travel from point A to point B not by a single path but by all possible paths. By taking the sum of all possible paths, he reached the same conclusions he would have reached by associating probability waves with each travelling particle. That is, he found the exact probabilities for the outcomes predicted by other theories and by experimental results.
- Superpartner: It is a particle related to a more standard particle by supersymmetry. In this physical theory, it is proposed that every fermion should have a "partner" boson (the fermion's superpartner), and vice versa. Exact unbroken supersymmetry would predict that a particle and its superpartners would have the same mass. No superpartners of the Standard Model particles have yet been found. If a superpartner is found, its mass would determine the scale at which supersymmetry is broken. For real scalar particles (such as an axion), there is a fermion superpartner as well as a second, real scalar field. For axions, these particles are often referred to as axinos and saxions. In extended supersymmetry there may be more than one superparticle for a given particle. In zero dimensions (often known as matrix mechanics), it is possible to have supersymmetry, but no superpartners. This is the only case where supersymmetry does not imply the existence of superpartners.
- Supersymmetry (SUSY): It is a symmetry that relates elementary particles of one spin to other particles that differ by half a unit of spin and are known as superpartners. In other words, in a supersymmetric theory, for every type of boson there exists a corresponding type of fermion, and vice-versa. As of 2008 there is no direct evidence that supersymmetry is a symmetry of nature. Since superpartners of the particles of the Standard Model have not been observed, supersymmetry, if it exists, must be a broken symmetry allowing the 'sparticles' to be heavy.
- van der Waals force: It refers to the attractive or repulsive forces
between molecules (or between parts of the same molecule) other than those
due to covalent bonds or to the electrostatic interaction of ions with one
another or with neutral molecules. The term includes:
. dipole-dipole forces
. dipole-induced dipole forces
It is also sometimes used loosely as a synonym for the totality of intermolecular
forces. Van der Waals forces are relatively weak compared to normal chemical
bonds.
- Weinberg angle or weak mixing angle: It is a parameter in the Weinberg-Salam
theory of the electroweak force. It gives a relationship between the W-
and Z-masses, as well as the ratio of Z-Boson mediated interaction which
behaves like a photon, i.e. its mixing.