Custodial SU(2) Violation and the Origin of Fermion Masses

Custodial $SU(2)$ breaking due to dynamical fermion masses is studied in a rather general context and it is shown how some well known limiting cases are correctly described. The type of ``gap equation'' which can systematically lead to extra negative contributions to the so--called $\rho$--parameter is emphasized. Furthermore general model independent features are discussed and it is shown how electro--weak precision measurements can be sensitive to the fermion content and/or dynamical features of a given theory.Comment: HD-THEP-92-55, 18 pages and 2 pages of figures appended as Postscript fil

Higher Dimensional Operators in Top Condensation from a Renormalization Group Point of View

The predictive power of top-condensation models strongly depends on the behaviour of higher dimensional operators. These are analyzed in this paper by an extension of the standard renormalization group (RG) arguments which turns out to be a surprisingly powerful tool. Top-condensation models intermediated by underlying scalar exchange can be shown to be mere reparametrizations of the standard model. Further on, RG-arguments show that dynamical vector states cannot be lowered in top-condensation models. Finally we give a general argument concerning the size of higher dimensional operators of heavy vector exchange.Comment: 21 pages, latex2e, axodraw.sty, epsfig.sty, 4 postscript figures. Some of the discussions extended and clarifie

Vacuum replicas in QCD

The properties of the vacuum are addressed in the two- and four-dimensional quark models for QCD. It is demonstrated that the two-dimensional QCD ('t Hooft model) possesses only one possible vacuum state - the solution to the mass-gap equation, which provides spontaneous breaking of the chiral symmetry (SBCS). On the contrary, the four-dimensional theory with confinement modeled by the linear potential supplied by the Coulomb OGE interaction, not only has the chirally-noninvariant ground vacuum state, but it possesses an excited vacuum replica, which also exhibits SBCS and can realize as a metastable intermediate state of hadronic systems. We discuss the influence of the latter on physical observables as well as on the possibility to probe the vacuum background fields in QCD.Comment: RevTeX4, 26 pages, 8 EPS figures, extended references, corrected some typos, to appear in Phys.Rev.

Quark Schwinger-Dyson equation in temporal Euclidean space

We present an elementary nonperturbative method to obtain Green's functions (GFs) for timelike momenta. We assume there are no singularities in the first and third quadrants of the complex plane of space momentum components and perform a 3d analogue of Wick rotation. This procedure defines Greens functions in a timelike Euclidean space. As an example we consider the quark propagator in QCD. While for weak coupling, this method is obviously equivalent to perturbation theory, for a realistic QCD coupling a complex part of the quark mass and renormalization wave function has been spontaneously generated even below the standard perturbative threshold. Therefore, our method favors a confinement mechanism based on the lack of real poles.Comment: 11 pages, grammar and typos correcte

Condensation effects beyond one loop in the Top-mode Standard Model without gauge bosons

We study dynamical symmetry breaking in the Standard Model including the next-to-leading order terms. We introduce at a high, but finite, energy scale Lambda a top quark condensate H={t {bar t}} and derive, using path integral methods, the effective potential including quadratic fluctuations in the scalar field H. We neglect the contributions of all components of the massive electroweak gauge bosons. The existence of a non-trivial minimum in the effective potential leads to the condition that the cut-off Lambda is limited from above: Lambda < Lambda_{crit} approx 4.7 m_t^{phys.} (for N_c = 3), and to a new lower bound for the 4-fermion coupling a = (G N_c Lambda^2)/(8 pi^2) > 1.60. Similar results are obtained if we demand, instead, that the next-to-leading order contributions not shift the location z=(m_t^{bare}/Lambda)^2 of the minimum drastically, e.g.~by not more than a factor of 2. The results are reproduced diagrammatically, where the leading plus all the next-to-leading order diagrams in the (1/N_c)-expansion are included. Dominant QCD effects are also included, but their impact on the numerical results is shown to be small.Comment: 30 pages, LaTeX, 9 figures included in a separate tar-compressed and uuencoded PostScript file; QCD effects included, formulations improved, new figures 1a-1

Dynamical Left-Right Symmetry Breaking

We study a left--right symmetric model which contains only elementary gauge boson and fermion fields and no scalars. The phenomenologically required symmetry breaking emerges dynamically leading to a composite Higgs sector with a renormalizable effective Lagrangian. We discuss the pattern of symmetry breaking and phenomenological consequences of this scenario. It is shown that a viable top quark mass can be achieved for the ratio of the VEVs of the bi--doublet $\tan\beta\equiv\kappa/\kappa'$ =~ 1.3--4. For a theoretically plausible choice of the parameters the right--handed scale can be as low as $\sim 20 TeV$; in this case one expects several intermediate and low--scale scalars in addition to the \SM Higgs boson. These may lead to observable lepton flavour violation effects including $\mu\to e\gamma$ decay with the rate close to its present experimental upper bound.Comment: 51 pages, LaTeX and uuencoded, packed Postscript figures. The complete paper, including figures, is also available via WWW at http://www.cip.physik.tu-muenchen.de/tumphy/d/T30d/PAPERS/ TUM-HEP-222-95.ps.g

Physics of leptoquarks in precision experiments and at particle colliders

We present a comprehensive review of physics effects generated by leptoquarks (LQs), i.e., hypothetical particles that can turn quarks into leptons and vice versa, of either scalar or vector nature. These considerations include discussion of possible completions of the Standard Model that contain LQ fields. The main focus of the review is on those LQ scenarios that are not problematic with regard to proton stability. We accordingly concentrate on the phenomenology of light leptoquarks that is relevant for precision experiments and particle colliders. Important constraints on LQ interactions with matter are derived from precision low-energy observables such as electric dipole moments, (g-2) of charged leptons, atomic parity violation, neutral meson mixing, Kaon, B, and D meson decays, etc. We provide a general analysis of indirect constraints on the strength of LQ interactions with the quarks and leptons to make statements that are as model independent as possible. We address complementary constraints that originate from electroweak precision measurements, top, and Higgs physics. The Higgs physics analysis we present covers not only the most recent but also expected results from the Large Hadron Collider (LHC). We finally discuss direct LQ searches. Current experimental situation is summarized and self-consistency of assumptions that go into existing accelerator-based searches is discussed. A progress in making next-to-leading order predictions for both pair and single LQ productions at colliders is also outlined.Comment: 136 pages, 22 figures, typographical errors fixed, the Physics Reports versio