Dynamical electroweak symmetry breaking

In theories of dynamical electroweak symmetry breaking, the electroweak interactions are broken to electromagnetism by the vacuum expectation value of a fermion bilinear. These theories may thereby avoid the introduction of fundamental scalar particles, of which we have no examples in nature. In this note, we review the status of experimental searches for the particles predicted in technicolor, topcolor, and related models.     

Flavor symmetry breaking and strangeness in the nucleon

We suggest that breaking of SU(3) flavor symmetry mainly resides in the baryon wave functions while the charge operators have no (or only small) explicit symmetry-breaking components. We utilize the collective coordinate approach to chiral soliton models to support this picture. In particular we compute the g _A /g _V ratios for hyperon beta-decay and the strangeness contribution to the nucleon axial current matrix elements and analyze their variation with increasing flavor symmetry breaking.Received: 30 September 2002, Published online: 22 October 2003PACS: 12.39.Dc Skyrmions - 12.39.Fe Chiral Lagrangians - 13.30.Ce Leptonic, semileptonic, and radiative decays - 14.20.Jn HyperonsH. Weigel: Heisenberg-Fellow;     

Dynamical symmetry breaking in transport through molecules

We analyze the interplay between vibrational and electronic degrees of freedom in charge transport across a molecular single-electron transistor. We focus on the wide class of molecules which possess quasidegenerate vibrational eigenstates, while no degeneracy occurs for their anionic configuration. We show that the combined effect of a thermal environment and coupling to leads, involving tunneling events charging and discharging the molecule, leads to a dynamical symmetry breaking where quasidegenerate eigenstates acquire different occupations. This imbalance gives rise to a characteristic asymmetry of the current versus an applied gate voltage.     

Dynamical symmetry breaking of extended gauge symmetries

We construct asymptotically free gauge theories exhibiting dynamical breaking of the left-right gauge group G(LR)=SU(3)(c) x SU(2)(L) x SU(2)(R) x U(1)(B-L), and its extension to the Pati-Salam gauge group G(422)=SU(4)(PS) x SU(2)(L) x SU(2)(R). The models incorporate technicolor for electroweak breaking, and extended technicolor for the breaking of G(LR) and G422 and the generation of fermion masses. They include a seesaw mechanism for neutrino masses, without a grand unified theory (GUT) scale. These models explain why G(LR) and G422 break to SU(3)(c) x SU(2)(L) x U(1)(Y), and why this takes place at a scale (approximately 10(3) TeV) large compared to the electroweak scale, but much smaller than a GUT scale.     

Dynamical symmetry breaking and the effective potential method

The energetic favourability of a dynamical symmetry breakdown in a renormalizable, O(2) invariant, theory is examined. A representation of the effective potential for composite operators is given and discussed.In the appendix the ambiguity inherent in the definition of the generating functional W[J], used in the study of dynamical symmetry breaking, is analysed for a completely solvable case and the spontaneiously broken modes related to the Riemann sheet structure of W[J]. Conclusions regarding symmetry breakdown are no longer found to be unique, differing results holding in each of three disjoint regions.     

Dynamical symmetry breaking in models with the Yukawa interaction

The models with a massless fermion and a self-interacting massive scalar field with the Yukawa interaction are discussed. The chiral condensate and the fermion mass are calculated analytically through a one-loop approximation in (1 + 1)-dimensions. It is shown that the models have a phase transition as a function of the squared mass of the scalar field.     

Dynamical symmetry breaking due to vacuum misalignment

We show that under a certain assumption systems with second-class constraints can be regarded as gauge-fixed systems with first-class constraints. The massive Yang-Mills theory, a point particle on a sphere and theO(N) symmetric non-linear σ-model are considered as concrete examples.     

Dynamical symmetry breaking as the origin of the pomeranchuk singularity

We consider the viewpoint that Reggeons are built out of Reggeized quarks and that an O(2) symmetry between two kinds of quarks (“heavy” and “light”) is dynamically broken by their interaction. The Goldstone boson thus generated is associated with the Pomeron, and it is argued that it naturally has a smaller slope than the other Reggeons which are ordinary bound states of the quarks.     

Dynamical symmetry breaking in the SU (2) gauge theory

Properties of vacua of the SU(2) gauge theory containing massless and massive fermions are investigated within the one-loop approximation. As a result of a condensation of composite scalar made of gauge fields, some gauge fields acquire a mass and the original SU(2) gauge symmetry is suggested to breake down to U (1). We evaluate the effective potential for the constant magnetic field and then extract the so-called dielectric permeability κ from it. The phase is called paramagnetism for positive κ, perfect paramagnetism for vanishing κ and ferromagnetism for negative κ. The choice of a favorable phase is determined by the value of the coupling constant and the number and the mass of fermions. The perfect paramagnetic phase is most precisely studied. It is shown that solitons with non-zero charges carry divergent energies. Then, the electric flux around the charge is shown to be squeezed into a string in that phase.     

Dynamical electroweak symmetry breaking with a heavy fourth generation

A heavy fourth generation with a mass of the order of 400 GeV or more could trigger dynamical electroweak symmetry breaking by forming condensates through the exchange of a fundamental Higgs scalar doublet. The dynamics leading to these condensates is studied within the framework of the Schwinger–Dyson equation. This scenario leads to the presence of three (two composite and one fundamental) Higgs doublets, with interesting phenomenological implications. In addition, this dynamical phenomenon occurs in the vicinity of the energy scale where the restoration of scale symmetry might happen.     

Dynamical symmetry breaking in SYM theories as a non-semiclassical effect

We study supersymmetry breaking effects in N=1 SYM from the point of view of quantum effective actions. Restrictions on the geometry of the effective potential from superspace are known to be problematic in quantum effective actions, where explicit supersymmetry breaking can and must be studied. On the other hand the true ground state can be determined from this effective action, only. We study the problem whether some parts of superspace geometry are still relevant for the effective potential and discuss whether the ground states found this way justify a low energy approximation based on this geometry. The answer to both questions is negative. Essentially non-semiclassical effects change the behavior of the auxiliary fields completely and lead to the demand of a new interpretation of superspace geometry. These non-semiclassical effects can break supersymmetry. Received: 10 January 2002 / Revised version: 13 April 2002 / Published online: 18 October 2002 RID="*" ID="*" Work supported in part by the Schweizerischer Nationalfonds RID="a" ID="a" e-mail: bergamin@tph.tuwien.ac.at