1,378 research outputs found
Implications of Dynamical Generation of Standard-Model Fermion Masses
We point out that if quark and lepton masses arise dynamically, then in a
wide class of theories the corresponding running masses exhibit
the power-law decay for Euclidean momenta
, where is a fermion of generation , and
is the maximal scale relevant for the origin of . We estimate
resultant changes in precision electroweak quantities and compare with current
data. It is found that this data allows the presence of such corrections. We
also note that this power-law decay renders primitively divergent fermion mass
corrections finite.Comment: 4 pages, late
Extended Technicolor Models with Two ETC Groups
We construct extended technicolor (ETC) models that can produce the large
splitting between the masses of the and quarks without necessarily
excessive contributions to the parameter or to neutral flavor-changing
processes. These models make use of two different ETC gauge groups, such that
left- and right-handed components of charge quarks transform under the
same ETC group, while left- and right-handed components of charge -1/3 quarks
and charged leptons transform under different ETC groups. The models thereby
suppress the masses and relative to , and and
relative to because the masses of the quarks and charged leptons
require mixing between the two ETC groups, while the masses of the
quarks do not. A related source of the differences between these mass
splittings is the effect of the two hierarchies of breaking scales of the two
ETC groups. We analyze a particular model of this type in some detail. Although
we find that this model tends to suppress the masses of the first two
generations of down-type quarks and charged leptons too much, it gives useful
insights into the properties of theories with more than one ETC group.Comment: 14 pages, 4 figure
An alternative heavy Higgs mass limit
After commenting on the present value of the Higgs particle mass from
radiative corrections, we explore the phenomenological implications of an
alternative, non-perturbative renormalization of the scalar sector where the
mass of the Higgs particle does not represent a measure of observable
interactions at the Higgs mass scale. In this approach the Higgs particle could
be very heavy, even heavier than 1 TeV, and remain nevertheless a relatively
narrow resonance.Comment: 17 pages. Version accepted for publication in Journal of Physics
Low-Energy Effective Theory, Unitarity, and Non-Decoupling Behavior in a Model with Heavy Higgs-Triplet Fields
We discuss the properties of a model incorporating both a scalar electroweak
Higgs doublet and an electroweak Higgs triplet. We construct the low-energy
effective theory for the light Higgs-doublet in the limit of small (but
nonzero) deviations in the rho parameter from one, a limit in which the triplet
states become heavy. For small deviations in the rho parameter from one,
perturbative unitarity of WW scattering breaks down at a scale inversely
proportional to the renormalized vacuum expectation value of the triplet field
(or, equivalently, inversely proportional to the square-root of the deviation
of the rho parameter from one). This result imposes an upper limit on the
mass-scale of the heavy triplet bosons in a perturbative theory; we show that
this upper bound is consistent with dimensional analysis in the low-energy
effective theory. Recent articles have shown that the triplet bosons do not
decouple, in the sense that deviations in the rho parameter from one do not
necessarily vanish at one-loop in the limit of large triplet mass. We clarify
that, despite the non-decoupling behavior of the Higgs-triplet, this model does
not violate the decoupling theorem since it incorporates a large dimensionful
coupling. Nonetheless, we show that if the triplet-Higgs boson masses are of
order the GUT scale, perturbative consistency of the theory requires the
(properly renormalized) Higgs-triplet vacuum expectation value to be so small
as to be irrelevant for electroweak phenomenology.Comment: Revtex, 11 pages, 7 eps figures included; references updated and
three footnotes adde
Post-Wick theorems for symbolic manipulation of second-quantized expressions in atomic many-body perturbation theory
Manipulating expressions in many-body perturbation theory becomes unwieldily
with increasing order of the perturbation theory. Here I derive a set of
theorems for efficient simplification of such expressions. The derived rules
are specifically designed for implementing with symbolic algebra tools. As an
illustration, we count the numbers of Brueckner-Goldstone diagrams in the first
several orders of many-body perturbation theory for matrix elements between two
states of a mono-valent system.Comment: J. Phys. B. (in press); Mathematica packages available from
http://wolfweb.unr.edu/homepage/andrei/WWW-tap/mathematica.htm
Dropping rho and A_1 Meson Masses at Chiral Phase Transition in the Generalized Hidden Local Symmetry
We study the chiral symmetry restoration using the generalized hidden local
symmetry (GHLS) which incorporates the rho and A_1 mesons as the gauge bosons
of the GHLS and the pion as the Nambu-Goldstone boson consistently with the
chiral symmetry of QCD. We show that a set of parameter relations, which
ensures the first and second Weinberg's sum rules, is invariant under the
renormalization group evolution. Then, we found that the Weinberg's sum rules
together with the matching of the vector and axial-vector current correlators
inevitably leads to {\it the dropping masses of both rho and A_1 mesons} at the
symmetry restoration point, and that the mass ratio as well as the mixing angle
between the pion and A_1 meson flows into one of three fixed points.Comment: 17 pages, 7 figures; references added and discussions expande
Approximate gauge symmetry of composite vector bosons
It can be shown in a solvable field theory model that the couplings of the
composite vector bosons made of a fermion pair approach the gauge couplings in
the limit of strong binding. Although this phenomenon may appear accidental and
special to the vector boson made of a fermion pair, we extend it to the case of
bosons being constituents and find that the same phenomenon occurs in more an
intriguing way. The functional formalism not only facilitates computation but
also provides us with a better insight into the generating mechanism of
approximate gauge symmetry, in particular, how the strong binding and global
current conservation conspire to generate such an approximate symmetry. Remarks
are made on its possible relevance or irrelevance to electroweak and higher
symmetries.Comment: Correction of typos. The published versio
Non locality and causal evolution in QFT
Non locality appearing in QFT during the free evolution of localized field
states and in the Feynman propagator function is analyzed. It is shown to be
connected to the initial non local properties present at the level of quantum
states and then it does not imply a violation of Einstein's causality. Then it
is investigated a simple QFT system with interaction, consisting of a classical
source coupled linearly to a quantum scalar field, that is exactly solved. The
expression for the time evolution of the state describing the system is given.
The expectation value of any arbitrary ``good'' local observable, expressed as
a function of the field operator and its space and time derivatives, is
obtained explicitly at all order in the field-matter coupling constant. These
expectation values have a source dependent part that is shown to be always
causally retarded, while the non local contributions are source independent and
related to the non local properties of zero point vacuum fluctuations.Comment: Submitted to Journal of Physics B: 16 pages: 1 figur
Leading quantum gravitational corrections to QED
We consider the leading post-Newtonian and quantum corrections to the
non-relativistic scattering amplitude of charged spin-1/2 fermions in the
combined theory of general relativity and QED. The coupled Dirac-Einstein
system is treated as an effective field theory. This allows for a consistent
quantization of the gravitational field. The appropriate vertex rules are
extracted from the action, and the non-analytic contributions to the 1-loop
scattering matrix are calculated in the non-relativistic limit. The
non-analytical parts of the scattering amplitude are known to give the long
range, low energy, leading quantum corrections, are used to construct the
leading post-Newtonian and quantum corrections to the two-particle
non-relativistic scattering matrix potential for two massive fermions with
electric charge.Comment: 14 pages, 29 figures, format RevTex
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