Hypothetical Non-Abelian particles with fractional 1/3 electrical charge. These are not quarks.
Un-observed hypothetical dark-matter set of particles. They are very light (between 10-5 and 10 10-1eV), possess no electrical charge, are un-stable and will interact with other matter only feebly. Axions are predicted to appear and constantly interchange into photons in the presence of an very strong magnetic fields. Axions were first proposed to so that the equations of Quantum Chromo Dynamics (QCD) did not predict Charge-Parity conservation (CP) violations in the strong force. [CP conservation violation has never been observed with the strong force; it is exhibited only by some intactions involving the weak force]. Without axions, some interactions involving the strong force would vioate charge-parity conservation. Another text says that axions were proposed to explain the absence of an electrical dipole moment in a neutron. Axions should decay into X-rays. One theorist wildly speculates that the reason our Sun has an otherwise apparently un-explainable X-ray glow around it is because our sun generates axions in the nuclear reactions within its core, they travel outwards from the sun, and, being heavy (in his senario, in others, axions are very light!), orbit the sun in a halo, where they decay into X-rays. Others say that proposition is akin to coming home, finding the front door ajar, and suspecting Martians! There could be many other simpler explanations for the suns' mysterious X-ray halo. Moreover, the type of (heavy) axions proposed for the Suns X-rays can only exist in a Universe with more than 4 spacial dimensions; and so far there is no evidence of more than three. [Forwards in all directions!]
If they exist at all, axions are thought to have been produced in abundance during the Big Bang with high velocities. But because the axions would couple with the instanton field of the primordial universe as if travelling through treacle, they would be robbed of their kinetic energy during the aquisition of mass following cosmic inflation, the resulting axions should now all be very cold, with hardly any kinetic energy. So cold, in fact, that they should now be in a Bose-Einstein Condensate, and be contributing to the cold dark matter of the Universe.
Higgs particles are hypothetical bosonic particles which supposedly give mass to all the other particles, including itself. All, that is, that have non-zero mass afterwards. Particles which are unaffected by the Higgs particle, such as the photon, have zero mass.
Quarks are asymptotically bound to each other by a gluon field, mediated by gluons which glue the quarks together. The gluon field can even glue itself up, twisting itself up with others to form a kink in four-dimensional space. This kink could be likened to a twist in a rubber band, but the twist occurs in four spatial dimensions. These kinks or vortexes in space are instantons, being solitons. The instantons also pervade and permeate the vacuum, and exist throughout all of space. They have an intricate structure that determines how matter itself is built. They distort the space through which quarks have to weave. The instantons are virtual, appearing and disappearing in an instant, which is whereby they got their name. When a quark interacts with an instanton, it flips the helicity, or handed-ness of any quark or fermion interacting with them, from being left-handed to right-handed, or vice versa. Or, in other words, they destroy a left-handed particle whilst creating a right handed particle, or vice versa. They also change the winding number of a particle by one unit. This process is one of breaking chiral symmetry. This continual twisting of the handed-ness of quarks results in the quark gaining energy, or mass, making quarks up to 60 times more massive than they would otherwise be. The mass of quarks contributes some 95% to the mass of protons and neutrons, and hence of atoms also. This handed-ness exchanging and increasing of mass has many parallels with what Higgs particles do.
In the particle accelerator at Brookhaven, they accelerated particles to such high energies that the resulting fireball was some 16 ×1012Celsius or 300 million times hotter than the surface of the sun. This was enough to melt the vacuum, with the gluons losing their stickiness which resulted in the instantons un-twisting themselves from their gordian knot and disappearing. The quarks were then unconstrained, free to roam, and presumably lost a great deal of their mass since there were no instantons with which to interact. See Quark/Gluon Plasma.
A hypothetical particle coming in two varieties, a lone north magnetic pole, and a lone south magnetic pole. If they exist, they are extremely massive, about 1016 times the mass of a proton. There is no reason why a magnetic monopole should not exist, after all electric monopoles exist, like for instance an electron or a positron.
A hypothetical particle, which, if it exists, breaks the hitherto un-broken law of Lepton Conservation. Neutrinos exist as either neutrinos and anti-neutrinos OR neutrinos and anti-neutrinos are identical and a neutrino is its own anti-particle. In the latter case it is called a Majorana neutrino, named after the Italian Ettore Majorana who first proposed such a scheme for the neutrino in 1937. As yet, no one has ever observed neutrinos behaving this way, but they may do so in a process called neutrino-less double beta decay.
These are a set of hypothetical particles, whereby every particle has a mirror counterpart; this includes both particles and anti-particles. Thus both an electron and a positron would have mirror particles, if they exist at all. Mirror matter was invoked to redress the imbalance in nature with respect to chirality, or left-right symmetry. The neutrino, for example, is known only with left handed spin. The mirror neutrino would, if it existed, possess right-handed spin. Mirror matter particles would not interact with ordinary particles, they would be invisible to us. Mirror matter is thus a prime candidate for dark matter. But mirror photons, should they exist, would interact, albeit very weakly, with normal photons. So far no one has detected them.
The neutralino, if it exists, is the lightest of the super-symmetric particles and is the most popular candidate for the dark-matter WIMPs (weakly interacting massive particles). If neutralinos really do exist, they should congregate at the centre of stars like the sun where they would decay into other particles like quarks and very high-energy neutrinos which should be detectable.
Heavy Sterile Neutrinos
If they exist at all, these are 10's of millions of times heavier than normal neutrinos. They may have been part of the dark matter of the Universe at much earlier epochs in its history, but decayed into radiation long ago.
Rishons or Preons
The Rishons (or Preons) are a set of two hypothetical particles (the T and the V) of which both quarks and leptons may contain triplets.
Supersymmetric particles were proposed so that the number of dimensions that the Universe needed in order to describe particles in the quantum version of String Theory, which is 26 dimensions, could be reduced to just 10 dimensions: one of time, the rest spacial dimensions. In Super-symmetric theory, each fermion is partnered with a super-symmetric boson; and each boson with a super-symmetric fermion. Thus the fermion 'electron' would be partnered with a super-symmetric boson called a 'selectron'. All other particles of nature would have a super-symmetric partner; their names derived by adding an initial 's' to their observed partners. The pairing of bosons with fermions has the effect of cancelling out the infinities that occur with both fermions and bosons when, for instance, calculating the interaction of two electrons, etc. But despite intense efforts at findind these super-symmetric particles, not one has been found to date.
Hypothetical particles that travel faster than the speed of light and which are forbidden to go slower than the speed of light. Contrast this with ordinary non-zero rest mass particles, sometimes called Tardyons, which are forbidden to go faster than the speed of light. Both become inertially heavier the closer they approach the speed of light, and at the speed of light they possess infinite mass; it is this property which prevents them from attaining the speed of light. [Ordinary particles which have zero rest mass (being the mass they have at zero velocity) such as the photon, are allowed to travel at the speed of light]. Not so with tachyons, zero rest mass tachyons would travel at infinite speed. To slow a tachyon down to the speed of light would require an infinite amount of energy; it cannot be done. With respect to ordinary particles, Tachyons travel backwards in time. Once thought to be an odd quirk of relativity theory and un-real, Tachyons are now turning up in other theories, amongst them string theory. They may even account for the mysterious dark matter.
WIMPs and Wimpzillas
Wimpzillas are hypothetical WIMPs (weakly interacting massive particles) that are supermassive. WIMPs themselves are hypothetical massive particles, between 50 to 100 times the mass of a proton, and they interact weakly with other matter which have not been detected possibly because they intaract with ordinary matter so weakly, passing straight through undetected. Dark matter, if it exists, is perhaps composed of WIMPs. Wimpzillas, on the other hand, are super-massive WIMPs, highly energetic, about 1010 times the mass of WIMPs, that may have been created at the very start of the Big Bang. Wimpzillas may explain the ultra-high energy cosmic rays; the annihilation of wimpzillas producing observed high energy particles. If ultra-high energy cosmic rays are produced by the annihilation of wimpzillas, then they should be composed mostly of high-energy gamma rays rather than protons or atomic nuclei.
W+, W- and Z0 particles
Unlike most particles on this page, these three particles are known and have been observed. The weak force is carried by 3 bosons, two charged (W+ and W-), and one neutral Z0. These bosons are responsible for mediating beta (and inverse beta) decay. They are all massive, hence beta decay is an improbable event. All have spin-1. These bosons, being very heavy, must travel less than the speed of light. The mass of the W particles is 80.413GeV, that of the Z0 particle 91.177GeV; heavier than 5 water molecules.
X gauge boson
X gauge bosons or X-particle, a hypothetical particle, but with the unusual electrical charge of 4/3. It is thought to be extremely massive, and if it exists, would enable the decay of a proton. It is also postulated to account for the extremely high energy primary cosmic rays >5×1019eV that appear to be coming our way, when because of their high energy and assumed great originating distance, should have long since dissipated by travelling through the microwave background photons. If the decay of X-particles were the source of the extremely high energy cosmic rays, then they could be relatively nearby. The X-particle, if it exists, would have a mass of some 1012GeV and a lifetime of 1010years, the long lifetime being attributed to either them being trapped in topological defects in the Universe (like the great wall), or through them having only a very weak interaction with lighter particles. Either way, X-particles are thought to have been generated at the birth of the Big Bang, and essentially store energy from a much earlier and very much more violent epoch in the Universe's life.
It is interesting to note that X-particles, with their electrical charge of 4/3, would, in Rogers' Twisted Tri-Prism Theory, be represented by a circular loop of triangular prism having been twisted by 4/3rds of a turn before being joined.
X and Y-particles
X-particles are leptoquarks, which, if they exist, may allow the stable proton to decay, see Proton Decay. Lepto-Quarks are very massive, meaning heavy, they have a mass of 1.4×1014eV, which is 1012 times heavier than a lead atom.