particle physics Particle physics or high-energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the s ...

, the top quark condensate theory (or top condensation) is an alternative to the

Standard Model The Standard Model of particle physics is the Scientific theory, theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions – excluding gravity) in the unive ...

fundamental

Higgs field The Higgs boson, sometimes called the Higgs particle, is an elementary particle in the Standard Model of particle physics produced by the excited state, quantum excitation of the Higgs field, one of the field (physics), fields in particl ...

, where the Higgs boson is a composite field, composed of the

top quark The top quark, sometimes also referred to as the truth quark, (symbol: t) is the most massive of all observed elementary particles. It derives its mass from its coupling to the Higgs field. This coupling is very close to unity; in the Standard ...

and its

antiquark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly ...

. The

pairs are bound together by a new force called topcolor, analogous to the binding of

Cooper pairs In condensed matter physics, a Cooper pair or BCS pair (Bardeen–Cooper–Schrieffer pair) is a pair of electrons (or other fermions) bound together at low temperatures in a certain manner first described in 1956 by American physicist Leon Coope ...

in a BCS superconductor, or mesons in the strong interactions. The top quark is very heavy, with a measured mass of approximately 174

GeV In physics, an electronvolt (symbol eV), also written electron-volt and electron volt, is the measure of an amount of kinetic energy gained by a single electron accelerating through an electric potential difference of one volt in vacuum. When us ...

(comparable to the electroweak scale), and so its Yukawa coupling is of order unity, suggesting the possibility of strong coupling dynamics at high energy scales. This model attempts to explain how the electroweak scale may match the top quark mass.

History

The idea was described by

Yoichiro Nambu was a Japanese-American physicist and professor at the University of Chicago. Known for his groundbreaking contributions to theoretical physics, Nambu was the originator of the theory of spontaneous symmetry breaking, a concept that revoluti ...

and subsequently developed by Miransky, Tanabashi, and Yamawaki (1989) and William A. Bardeen, Christopher T. Hill, and Manfred Lindner (1990), who connected the theory to the

renormalization group In theoretical physics, the renormalization group (RG) is a formal apparatus that allows systematic investigation of the changes of a physical system as viewed at different scales. In particle physics, it reflects the changes in the underlying p ...

, and improved its predictions. The renormalization group reveals that top quark condensation is fundamentally based upon the ''

infrared fixed point In physics, an infrared fixed point is a set of coupling constants, or other parameters, that evolve from arbitrary initial values at very high energies (short distance) to fixed, stable values, usually predictable, at low energies (large distance ...

'' for the top quark Higgs-Yukawa coupling, proposed by Pendleton and Ross (1981) and Hill. The "infrared" fixed point originally predicted that the top quark would be heavy, contrary to the prevailing view of the early 1980s. Indeed, the

was discovered in 1995 at the large mass of 174 GeV. The infrared-fixed point implies that it is strongly coupled to the Higgs boson at very high energies, corresponding to the

Landau pole In physics, the Landau pole (or the Moscow zero, or the Landau ghost) is the momentum (or energy) scale at which the coupling constant (interaction strength) of a quantum field theory becomes infinite. Such a possibility was pointed out by the ph ...

of the Higgs-Yukawa coupling. At this high scale a bound-state Higgs forms, and in the "infrared", the coupling relaxes to its measured value of order unity by the

. The Standard Model

fixed point prediction is about 220 GeV, and the observed top mass is roughly 20% lower than this prediction. The simplest top condensation models are now ruled out by the

LHC The Large Hadron Collider (LHC) is the world's largest and highest-energy particle accelerator. It was built by the European Organization for Nuclear Research (CERN) between 1998 and 2008, in collaboration with over 10,000 scientists, and ...

discovery of the Higgs boson at a mass scale of 125 GeV. However, extended versions of the theory, introducing more particles, can be consistent with the observed top quark and Higgs boson masses.

Future

The composite Higgs boson arises "naturally" in Topcolor models, that are extensions of the standard model using a hypothetical force analogous to

quantum chromodynamics In theoretical physics, quantum chromodynamics (QCD) is the study of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type of ...

. To be "natural", that is, without excessive fine-tuning (i.e. to stabilize the Higgs mass from large radiative corrections), the hypothesis requires new physics at a relatively low energy scale. Placing new physics at 10 TeV, for instance, the model predicts the top quark to be significantly heavier than observed (at about 600 GeV vs. 171 GeV). ''Top Seesaw'' models, also based upon Topcolor, circumvent this difficulty. The predicted top quark mass would come into improved agreement with the fixed point if there are many additional Higgs scalars beyond the standard model. This may be indicating a rich spectroscopy of new composite Higgs fields at energy scales that can be probed with the LHC and its upgrades.

References

{{Quantum field theories Physics beyond the Standard Model

History

Future

See also

References