840 research outputs found
Phase Structure of Non-Compact QED3 and the Abelian Higgs Model
We review the phase structure of a three-dimensional, non-compact Abelian
gauge theory (QED3) as a function of the number of 4-component massless
fermions. There is a critical up to which there is dynamical fermion
mass generation and an associated global symmetry breaking. We discuss various
approaches to the determination of , which lead to estimates ranging from
to . This theory with N=2 has been employed as an effective
continuum theory for the 2D quantum antiferromagnet where the observed Neel
ordering corresponds to dynamical fermion mass generation. Thus the value of
is of some physical interest. We also consider the phase structure of the
model with a finite gauge boson mass (the Abelian Higgs model).Comment: 14 pages, corrected the normalization of the fermion condensate in
section V, corrected a typo in the reference
The Zero Temperature Chiral Phase Transition in SU(N) Gauge Theories
We investigate the zero temperature chiral phase transition in an SU(N) gauge
theory as the number of fermions is varied. We argue that there exists a
critical number of fermions , above which there is no chiral symmetry
breaking or confinement, and below which both chiral symmetry breaking and
confinement set in. We estimate and discuss the nature of the phase
transition.Comment: 13 pages, LaTeX, version published in PR
Breaking Discrete Symmetries in Broken Gauge Theories
We study the spontaneous breaking of discrete symmetries in theories with
broken gauge symmetry. The intended application is to CP breaking in theories
with gauged flavor symmetries, but the analysis described here is preliminary.
We dispense with matter fields and take the gauge theory to be weakly coupled
and broken spontaneously by unspecified, short-distance forces. We develop an
effective-field-theory description of the resultant low energy theory, and ask
whether this theory by itself can describe the subsequent breaking of discrete
symmetries. We conclude that this can happen depending on the parameters of the
effective theory, and that the intrinsic violation is naturally of order unity.Comment: 9 pages, 1 figure, corrected typos, added a referenc
Postmodern Technicolor
Using new insights into strongly coupled gauge theories arising from analytic
calculations and lattice simulations, we explore a framework for technicolor
model building that relies on a non-trivial infrared fixed point, and an
essential role for QCD. Interestingly, the models lead to a simple relation
between the electroweak scale and the QCD confinement scale, and to the
possible existence of exotic leptoquarks with masses of several hundred GeV.Comment: LaTeX, 13 pages, version published in PR
2+1 Dimensional QED and a Novel Phase Transition
We investigate the chiral phase transition in 2+1 dimensional QED. Previous
gap equation and lattice Monte-Carlo studies of symmetry breaking have found
that symmetry breaking ceases to occur when the number of fermion flavors
exceeds a critical value. Here we focus on the order of the transition. We find
that there are no light scalar degrees of freedom present as the critical
number of flavors is approached from above (in the symmetric phase). Thus the
phase transition is not second order, rendering irrelevant the renormalization
group arguments for a fluctuation induced transition. However, the order
parameter vanishes continuously in the broken phase, so this transition is also
unlike a conventional first order phase transition.Comment: 11 pages, Late
The Phase Structure of an SU(N) Gauge Theory with N_f Flavors
We investigate the chiral phase transition in SU(N) gauge theories as the
number of quark flavors, , is varied. We argue that the transition takes
place at a large enough value of so that it is governed by the infrared
fixed point of the function. We study the nature of the phase
transition analytically and numerically, and discuss the spectrum of the theory
as the critical value of is approached in both the symmetric and broken
phases. Since the transition is governed by a conformal fixed point, there are
no light excitations on the symmetric side. We extend previous work to include
higher order effects by developing a renormalization group estimate of the
critical coupling.Comment: 34 pages, 1 figure. More references adde
Low-energy sector of 8-dimensional General Relativity: Electro-Weak model and neutrino mass
In a Kaluza-Klein space-time , we demonstrate that the
dimensional reduction of spinors provides a 4-field, whose associated SU(2)
gauge connections are geometrized. However, additional and gauge-violating
terms arise, but they are highly suppressed by a factor , which fixes
the amount of the spinor dependence on extra-coordinates. The application of
this framework to the Electro-Weak model is performed, thus giving a lower
bound for from the request of the electric charge conservation.
Moreover, we emphasize that also the Higgs sector can be reproduced, but
neutrino masses are predicted and the fine-tuning on the Higgs parameters can
be explained, too.Comment: 14 pages, 1 figure, to appear on Int. J. Mod. Phys.
Fermion Masses and Mixing in Extended Technicolor Models
We study fermion masses and mixing angles, including the generation of a
seesaw mechanism for the neutrinos, in extended technicolor (ETC) theories. We
formulate an approach to these problems that relies on assigning right-handed
quarks and charged leptons to ETC representations that are conjugates
of those of the corresponding left-handed fermions. This leads to a natural
suppression of these masses relative to the quarks, as well as the
generation of quark mixing angles, both long-standing challenges for ETC
theories. Standard-model-singlet neutrinos are assigned to ETC representations
that provide a similar suppression of neutrino Dirac masses, as well as the
possibility of a realistic seesaw mechanism with no mass scale above the
highest ETC scale of roughly TeV. A simple model based on the ETC group
SU(5) is constructed and analyzed. This model leads to non-trivial, but not
realistic mixing angles in the quark and lepton sectors. It can also produce
sufficiently light neutrinos, although not simultaneously with a realistic
quark spectrum. We discuss several aspects of the phenomenology of this class
of models.Comment: 74 pages, revtex with embedded figure
The Effective Lagrangian of the Two Higgs Doublet Model
We consider the two Higgs doublet model extension of the Standard Model in
the limit where all physical scalar particles are very heavy; too heavy, in
fact, to be experimentally produced in forthcoming experiments. The symmetry
breaking sector can thus be described by an effective chiral Lagrangian. We
obtain the values of the coefficients of the O(p^4) operators relevant to the
oblique corrections and investigate to what extent some non-decoupling effects
may remain at low energies.Comment: 16 pages, LaTeX, 2 figure
The Electroweak Chiral Lagrangian and CP-Violating Effects in Technicolor Theories
We estimate the CP-violating and anomalous form factors,
arising from CP-violating interactions in extended technicolor theories, and
discuss their future experimental detectability. The electric dipole moment of
the boson is found to be as large as {\cal O}(10^{-21}) \; \mbox{e cm}.
We connect the CP-odd and couplings to the corresponding
CP-violating electroweak chiral lagrangian operators. The electric dipole
moments of the neutron and the electron in technicolor theories are estimated
to be as large as {\cal O}(10^{-26}) \; \mbox{e cm} and {\cal O}(10^{-29})
\; \mbox{e cm} respectively. We also suggest the potential to observe large
CP-violating technicolor effects in the decay .Comment: 34 pages, YCTP-P9-94, LaTex. (minor changes in wording and notation,
the figures are appended at the end as one postscript file
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