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(tăk`ēŏn'), hypothetical elementary particleelementary particles,
the most basic physical constituents of the universe. Basic Constituents of Matter

Molecules are built up from the atom, which is the basic unit of any chemical element. The atom in turn is made from the proton, neutron, and electron.
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 that travels only at speeds exceeding that of light. According to the theory of relativityrelativity,
physical theory, introduced by Albert Einstein, that discards the concept of absolute motion and instead treats only relative motion between two systems or frames of reference.
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, the speed of light is the limiting velocity for all ordinary material particles. Particles having nonzero rest mass can approach, but not reach, the speed of light, since their mass would become infinite at that speed. On the other hand, particles with zero rest mass, such as the photonphoton
, the particle composing light and other forms of electromagnetic radiation, sometimes called light quantum. The photon has no charge and no mass. About the beginning of the 20th cent.
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, must always travel at the speed of light; they cannot be brought to rest or even slowed down. Theorists have argued that since nothing in principle prohibits the existence of a third class of particles that travel only at speeds exceeding that of light, such particles, called tachyons [Gr. tachys,=swift] may exist although no evidence for them has been found. In the terminology of the theory, the particles that travel only at the speed of light are called luxons, and those that travel at lesser speeds are called tardyons. Like the original theory of relativity, the theory of tachyons has several aspects that appear to contradict common sense but that are fully self-consistent. For example, a tachyon must have an imaginary (in the mathematical sense) rest mass, or proper mass, and it must travel faster rather than slow down when it loses energy.
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A hypothetical faster-than-light particle consistent with the special theory of relativity. According to this theory, a free particle has an energy E and a momentum p which form a Lorentz four-vector. The length of this vector is a scalar, having the same value in all inertial reference frames. One writes

Eq. (1), where c is the speed of light and the parameter m2 is a property of the particle, independent of its momentum and energy. Three cases may be considered: m2 may be positive, zero, or negative. The case m2 > 0 applies for atoms, nuclei, and the macroscopic objects of everyday experience. The positive root m is called the rest-mass. If m2 = 0, the particle is called massless. A few of these are known: the electron neutrino, the muon neutrino, the photon, and the graviton. The name tachyons (after a Greek word for swift) has been given to particles with m2 < 0.

In general, the particle speed is given by Eq. (2). If m2 < 0,

Eq. (1) implies E > c p and Eq. (2) gives v < c. If m2 = 0, then E = c p and v = c. In case m2 < 0, one finds E < c p and v > c. Tachyons exist only at faster-than-light speeds. See Elementary particle, Relativity

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.


(particle physics)
A hypothetical particle that travels faster than light, consistent with the theory of relativity.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In order to keep the Higgs doublet soft mass under control, so as to obtain a higgsino-like LSP after EWSB, and avoid tachyonic physical states, numerical scans are in this situation driven to large negative [A.sub.0] and/or larger soft scalar mass.
Debnath, "Thermodynamics of Modified Chaplygin Gas and Tachyonic Field," International Journal of Theoretical Physics, vol.
In a larger and even more speculative sense I see this information constituting a voxelated distribution (PATH-QF) throughout spacetime accessible through tachyonic interaction with the matter constituting the brain and nervous systems of sentient beings.
We analytically studied its GF, ACS, and DR for massive scalar fields; however, we considered tachyonic scalar particles instead of ordinary ones.
Evidence for a steady-state, holographic, tachyonic and super-symmetric cosmology, Galilean Electrodynamics, 2009, v.
Benaoum, "Accelerated Universe from Modified Chaplygin Gas and Tachyonic Fluid," https://arxiv.org/abs/hep-th/ 0205140.
Because the latter direction is transverse to the original tachyonic? [x.sup.1]-motion?
Nakamura, "Stability of Randall-Sundrum brane-world and tachyonic scalar," Physical Review D, vol.
Narison, "Strange quark, tachyonic gluon masses and [absolute value of ([V.sub.us])] from hadronic tau decays," Physics Letters B, vol.
Recall that the original mimetic theories formulated in 2010 were found to suffer from a tachyonic instability [390]; therefore, the question of whether mimetic gravity is stable is totally pertinent.
From these equations, we can see that the tachyonic modes in spectrum are excluded.
Banijamali, "Dynamics of interacting tachyonic teleparallel dark energy," Advances in High Energy Physics, vol.