Recent from talks
Composite Higgs models
Knowledge base stats:
Talk channels stats:
Members stats:
Composite Higgs models
In particle physics, composite Higgs models (CHM) are speculative extensions of the Standard Model (SM) where the Higgs boson is a bound state of new strong interactions. These scenarios are models for physics beyond the SM presently tested at the Large Hadron Collider (LHC) in Geneva.
In all composite Higgs models the Higgs boson is not an elementary particle (or point-like) but has finite size, perhaps around 10−18 meters. This dimension may be related to the Fermi scale (100 GeV) that determines the strength of the weak interactions such as in β-decay, but it could be significantly smaller. Microscopically the composite Higgs will be made of smaller constituents in the same way as nuclei are made of protons and neutrons.
Often referred to as "natural" composite Higgs models, CHMs are constructions that attempt to alleviate fine-tuning or "naturalness" problem of the Standard Model. These typically engineer the Higgs boson as a naturally light pseudo-Goldstone boson or Nambu-Goldstone field, in analogy to the pion (or more precisely, like the K-mesons) in QCD. These ideas were introduced by Georgi and Kaplan as a clever[according to whom?] variation on technicolor theories to allow for the presence of a physical low mass Higgs boson. These are forerunners of Little Higgs theories.
In parallel, early composite Higgs models arose from the heavy top quark and its renormalization group infrared fixed point, which implies a strong coupling of the Higgs to top quarks at high energies. This formed the basis of top quark condensation theories of electroweak symmetry breaking in which the Higgs boson is composite at extremely short distance scales, composed of a pair of top and anti-top quarks. This was described by Yoichiro Nambu and subsequently developed by Miransky, Tanabashi, and Yamawaki and Bardeen, Hill, and Lindner, who connected the theory to the renormalization group and improved its predictions. While these ideas are still compelling, they suffer from a "naturalness problem", a large degree of fine-tuning.
To remedy the fine tuning problem, Chivukula, Dobrescu, Georgi and Hill introduced the "Top See-Saw" model in which the composite scale is reduced to the several TeV (trillion electron volts, the energy scale of the LHC). A more recent version of the Top Seesaw model of Dobrescu and Cheng has an acceptable light composite Higgs boson. Top Seesaw models have a nice geometric interpretation in theories of extra dimensions, which is most easily seen via dimensional deconstruction (the latter approach does away with the technical details of the geometry of the extra spatial dimension and gives a renormalizable D-4 field theory). These schemes also anticipate "partial compositeness". These models are discussed in the extensive review of strong dynamical theories of Hill and Simmons.
CHMs typically predict new particles with mass around a TeV (or tens of TeV as in the Little Higgs schemes) that are excitations or ingredients of the composite Higgs, analogous to the resonances in nuclear physics. The new particles could be produced and detected in collider experiments if the energy of the collision exceeds their mass or could produce deviations from the SM predictions in "low energy observables" – results of experiments at lower energies. Within the most compelling scenarios each Standard Model particle has a partner with equal quantum numbers but heavier mass. For example, the photon, W and Z bosons have heavy replicas with mass determined by the compositeness scale, expected around 1 TeV. Though naturalness requires that new particles exist with mass around a TeV which could be discovered at LHC or future experiments, nonetheless as of 2018, no direct or indirect signs that the Higgs or other SM particles are composite has been detected.
From the LHC discovery of 2012, it is known that there exists a physical Higgs boson (a weak iso-doublet) that condenses to break the electro-weak symmetry. This differs from the prediction ordinary technicolor theories where new strong dynamics directly breaks the electro-weak symmetry without the need of a physical Higgs boson.
The CHM proposed by Georgi and Kaplan was based on known gauge theory dynamics that produces the Higgs doublet as a Goldstone boson. It was later realized, as with the case of Top Seesaw models described above, that this can naturally arise in five-dimensional theories, such as the Randall–Sundrum scenario or by dimensional deconstruction. These scenarios can also be realized in hypothetical strongly coupled conformal field theories (CFT) and the AdS-CFT correspondence. This spurred activity in the field. At first the Higgs was a generic scalar bound state. In the influential[according to whom?] work the Higgs as a Goldstone boson was realized in CFTs. Detailed phenomenological studies showed that within this framework agreement with experimental data can be obtained with a mild tuning of parameters.
Hub AI
Composite Higgs models AI simulator
(@Composite Higgs models_simulator)
Composite Higgs models
In particle physics, composite Higgs models (CHM) are speculative extensions of the Standard Model (SM) where the Higgs boson is a bound state of new strong interactions. These scenarios are models for physics beyond the SM presently tested at the Large Hadron Collider (LHC) in Geneva.
In all composite Higgs models the Higgs boson is not an elementary particle (or point-like) but has finite size, perhaps around 10−18 meters. This dimension may be related to the Fermi scale (100 GeV) that determines the strength of the weak interactions such as in β-decay, but it could be significantly smaller. Microscopically the composite Higgs will be made of smaller constituents in the same way as nuclei are made of protons and neutrons.
Often referred to as "natural" composite Higgs models, CHMs are constructions that attempt to alleviate fine-tuning or "naturalness" problem of the Standard Model. These typically engineer the Higgs boson as a naturally light pseudo-Goldstone boson or Nambu-Goldstone field, in analogy to the pion (or more precisely, like the K-mesons) in QCD. These ideas were introduced by Georgi and Kaplan as a clever[according to whom?] variation on technicolor theories to allow for the presence of a physical low mass Higgs boson. These are forerunners of Little Higgs theories.
In parallel, early composite Higgs models arose from the heavy top quark and its renormalization group infrared fixed point, which implies a strong coupling of the Higgs to top quarks at high energies. This formed the basis of top quark condensation theories of electroweak symmetry breaking in which the Higgs boson is composite at extremely short distance scales, composed of a pair of top and anti-top quarks. This was described by Yoichiro Nambu and subsequently developed by Miransky, Tanabashi, and Yamawaki and Bardeen, Hill, and Lindner, who connected the theory to the renormalization group and improved its predictions. While these ideas are still compelling, they suffer from a "naturalness problem", a large degree of fine-tuning.
To remedy the fine tuning problem, Chivukula, Dobrescu, Georgi and Hill introduced the "Top See-Saw" model in which the composite scale is reduced to the several TeV (trillion electron volts, the energy scale of the LHC). A more recent version of the Top Seesaw model of Dobrescu and Cheng has an acceptable light composite Higgs boson. Top Seesaw models have a nice geometric interpretation in theories of extra dimensions, which is most easily seen via dimensional deconstruction (the latter approach does away with the technical details of the geometry of the extra spatial dimension and gives a renormalizable D-4 field theory). These schemes also anticipate "partial compositeness". These models are discussed in the extensive review of strong dynamical theories of Hill and Simmons.
CHMs typically predict new particles with mass around a TeV (or tens of TeV as in the Little Higgs schemes) that are excitations or ingredients of the composite Higgs, analogous to the resonances in nuclear physics. The new particles could be produced and detected in collider experiments if the energy of the collision exceeds their mass or could produce deviations from the SM predictions in "low energy observables" – results of experiments at lower energies. Within the most compelling scenarios each Standard Model particle has a partner with equal quantum numbers but heavier mass. For example, the photon, W and Z bosons have heavy replicas with mass determined by the compositeness scale, expected around 1 TeV. Though naturalness requires that new particles exist with mass around a TeV which could be discovered at LHC or future experiments, nonetheless as of 2018, no direct or indirect signs that the Higgs or other SM particles are composite has been detected.
From the LHC discovery of 2012, it is known that there exists a physical Higgs boson (a weak iso-doublet) that condenses to break the electro-weak symmetry. This differs from the prediction ordinary technicolor theories where new strong dynamics directly breaks the electro-weak symmetry without the need of a physical Higgs boson.
The CHM proposed by Georgi and Kaplan was based on known gauge theory dynamics that produces the Higgs doublet as a Goldstone boson. It was later realized, as with the case of Top Seesaw models described above, that this can naturally arise in five-dimensional theories, such as the Randall–Sundrum scenario or by dimensional deconstruction. These scenarios can also be realized in hypothetical strongly coupled conformal field theories (CFT) and the AdS-CFT correspondence. This spurred activity in the field. At first the Higgs was a generic scalar bound state. In the influential[according to whom?] work the Higgs as a Goldstone boson was realized in CFTs. Detailed phenomenological studies showed that within this framework agreement with experimental data can be obtained with a mild tuning of parameters.