871 research outputs found
On the S-matrix renormalization in effective theories
This is the 5-th paper in the series devoted to explicit formulating of the
rules needed to manage an effective field theory of strong interactions in
S-matrix sector. We discuss the principles of constructing the meaningful
perturbation series and formulate two basic ones: uniformity and summability.
Relying on these principles one obtains the bootstrap conditions which restrict
the allowed values of the physical (observable) parameters appearing in the
extended perturbation scheme built for a given localizable effective theory.
The renormalization prescriptions needed to fix the finite parts of
counterterms in such a scheme can be divided into two subsets: minimal --
needed to fix the S-matrix, and non-minimal -- for eventual calculation of
Green functions; in this paper we consider only the minimal one. In particular,
it is shown that in theories with the amplitudes which asymptotic behavior is
governed by known Regge intercepts, the system of independent renormalization
conditions only contains those fixing the counterterm vertices with
lines, while other prescriptions are determined by self-consistency
requirements. Moreover, the prescriptions for cannot be taken
arbitrary: an infinite number of bootstrap conditions should be respected. The
concept of localizability, introduced and explained in this article, is closely
connected with the notion of resonance in the framework of perturbative QFT. We
discuss this point and, finally, compare the corner stones of our approach with
the philosophy known as ``analytic S-matrix''.Comment: 28 pages, 10 Postscript figures, REVTeX4, submitted to Phys. Rev.
Reconsidered estimates of the 10th order QED contributions to the muon anomaly
The problem of estimating the 10th order QED corrections to the muon
anomalous magnetic moment is reconsidered. The incorporation of the recently
improved contributions to the and - corrections to
within the renormalization-group inspired scheme-invariant approach
leads to the estimate . It is in good
agreement with the estimate , obtained
by Kinoshita and Nio from the numerical calculations of 2958 10-th order
diagrams, which are considered to be more important than the still uncalculated
6122 10th-order -dependent vertex graphs, and 12672 5-loop
diagrams, responsible for the mass-independent constant contribution both to
and . This confirms Kinoshita and Nio guess about dominance of
the 10-th order diagrams calculated by them. Comparisons with other estimates
of the - contributions to , which exist in the literature,
are presented.Comment: 19 pages, LaTeX, some misprints in the text and literature corrected.
Results unchaged, to appear in Phys.Rev.
Fine Tuning in One-Higgs and Two-Higgs Standard Models
The fine-tuning principles are examined to predict the top-quark and
Higgs-boson masses. The modification of the Veltman condition based on the
compensation of vacuum energies is developed. It is implemented in the Standard
Model and in its minimal extension with two Higgs doublets. The top-quark and
Higgs-boson couplings are fitted in the SM for the lowest ultraviolet scale
where the fine-tuning can be stable under rescaling. It yields the low-energy
values .Comment: 13 pages, LaTeX, Preprint PITHA-94-23 (July 1993
Role of a "Local" Cosmological Constant in Euclidean Quantum Gravity
In 4D non-perturbative Regge calculus a positive value of the effective
cosmological constant characterizes the collapsed phase of the system. If a
local term of the form is
added to the gravitational action, where is a subset of the
hinges and are positive constants, one expects that the volumes
, , ... tend to collapse and that the excitations of the
lattice propagating through the hinges are damped. We study
the continuum analogue of this effect. The additional term may represent
the coupling of the gravitational field to an external Bose condensate.Comment: LaTex, 18 page
Physical Unitarity for Massive Non-abelian Gauge Theories in the Landau Gauge: Stueckelberg and Higgs
We discuss the problem of unitarity for Yang-Mills theory in the Landau gauge
with a mass term a la Stueckelberg. We assume that the theory
(non-renormalizable) makes sense in some subtraction scheme (in particular the
Slavnov-Taylor identities should be respected!) and we devote the paper to the
study of the space of the unphysical modes. We find that the theory is unitary
only under the hypothesis that the 1-PI two-point function of the vector mesons
has no poles (at p^2=0). This normalization condition might be rather crucial
in the very definition of the theory. With all these provisos the theory is
unitary. The proof of unitarity is given both in a form that allows a direct
transcription in terms of Feynman amplitudes (cutting rules) and in the
operatorial form. The same arguments and conclusions apply verbatim to the case
of non-abelian gauge theories where the mass of the vector meson is generated
via Higgs mechanism. To the best of our knowledge, there is no mention in the
literature on the necessary condition implied by physical unitarity.Comment: References added. 22 pages. Final version to appear in the journa
Torsion Gravity: a Reappraisal
The role played by torsion in gravitation is critically reviewed. After a
description of the problems and controversies involving the physics of torsion,
a comprehensive presentation of the teleparallel equivalent of general
relativity is made. According to this theory, curvature and torsion are
alternative ways of describing the gravitational field, and consequently
related to the same degrees of freedom of gravity. However, more general
gravity theories, like for example Einstein-Cartan and gauge theories for the
Poincare and the affine groups, consider curvature and torsion as representing
independent degrees of freedom. By using an active version of the strong
equivalence principle, a possible solution to this conceptual question is
reviewed. This solution favors ultimately the teleparallel point of view, and
consequently the completeness of general relativity. A discussion of the
consequences for gravitation is presented.Comment: RevTeX, 34 pages. Review article to be published by Int. J. Mod.
Phys.
Heat Bath Particle Number Spectrum
We calculate the number spectrum of particles radiated during a scattering
into a heat bath using the thermal largest-time equation and the
Dyson-Schwinger equation. We show how one can systematically calculate
{d}/{d\omega} to any order using modified real time
finite-temperature diagrams. Our approach is demonstrated on a simple model
where two scalar particles scatter, within a photon-electron heat bath, into a
pair of charged particles and it is shown how to calculate the resulting
changes in the number spectra of the photons and electrons.Comment: 29 pages, LaTeX; 14 figure
Generalized Weinberg Sum Rules in Deconstructed QCD
Recently, Son and Stephanov have considered an "open moose" as a possible
dual model of a QCD-like theory of chiral symmetry breaking. In this note we
demonstrate that although the Weinberg sum rules are satisfied in any such
model, the relevant sums converge very slowly and in a manner unlike QCD.
Further, we show that such a model satisfies a set of generalized sum rules.
These sum rules can be understood by looking at the operator product expansion
for the correlation function of chiral currents, and correspond to the absence
of low-dimension gauge-invariant chiral symmetry breaking condensates. These
results imply that, regardless of the couplings and F-constants chosen, the
open moose is not the dual of any QCD-like theory of chiral symmetry breaking.
We also show that the generalized sum rules can be "solved", leading to a
compact expression for the difference of vector- and axial-current correlation
functions. This expression allows for a simple formula for the S parameter
(L_10), which implies that S is always positive and of order one in any
(unitary) open linear moose model. Therefore the S parameter is positive and
order one in any "Higgsless model" based on the continuum limit of a linear
moose regardless of the warping or position-dependent gauge-coupling chosen.Comment: 12 pages, 5 eps figures; reference to overlapping work adde
High-Energy Vector-Boson Scattering with Non-Standard Interactions and the Role of a Scalar Sector
The high-energy behavior of vector-boson scattering amplitudes is examined
within an effective theory for non-standard self-interactions of electroweak
vector-bosons. Irrespectively of whether this theory is brought into a gauge
invariant form by including non-standard interactions of a Higgs particle I
find that terms that grow particularly strongly with increasing scattering
energy are absent. Different theories are compared concerning their high-energy
behavior and the appearance of divergences at the one-loop level.Comment: 21 pages LaTeX, condensed version of BI-TP 93/5
Inelastic Channels in WW Scattering
If the electroweak symmetry-breaking sector becomes strongly interacting at
high energies, it can be probed through longitudinal scattering. We present
a model with many inelastic channels in the scattering process,
corresponding to the production of heavy fermion pairs. These heavy fermions
affect the elastic scattering of 's by propagating in loops, greatly
reducing the amplitudes in some charge channels. We conclude that the
symmetry-breaking sector cannot be fully explored by using, for example, the
mode alone, even when no resonance is present; all scattering modes must be measured.Comment: phyzzx, 13 pp. plus 4 figures, JHU-TIPAC-930005, MSUHEP-93/0
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