7 research outputs found
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
Chiral Hierarchies, Compositeness and the Renormalization Group
A wide class of models involve the fine--tuning of significant hierarchies
between a strong--coupling ``compositeness'' scale, and a low energy dynamical
symmetry breaking scale. We examine the issue of whether such hierarchies are
generally endangered by Coleman--Weinberg instabilities. A careful study using
perturbative two--loop renormalization group methods finds that consistent
large hierarchies are not generally disallowed.Comment: 22 pp + 5 figs (uuencoded and submitted separately),
SSCL-Preprint-490; FERMI-PUB-93/035-
Spectroscopy and Renormalisation Group Flow of a Lattice Nambu-Jona-Lasinio Model
We investigate a lattice Nambu--Jona-Lasinio model both by the Monte Carlo
method and Schwinger-Dyson equations. A comparison allows the discussion of
finite size effects and the extrapolation to infinite volume. We pay special
attention to the identification of particles and resonances. This enables us to
discuss renormalisation group flows in the neighbourhood of the critical
coupling where the chiral symmetry breaking phase transition takes place. In no
region of the bare parameter space do we find renormalisability for the model.Comment: 66 pages, latex and postscript figures. The postscript file for this
paper (called njl.ps) is also available from ftp://dirac.physik.fu-berlin.de/
in the directory nj
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