182 research outputs found
The Three Site Model at One-Loop
In this paper we compute the one-loop chiral logarithmic corrections to all
O(p^4) counterterms in the three site Higgsless model. The calculation is
performed using the background field method for both the chiral- and
gauge-fields, and using Landau gauge for the quantum fluctuations of the gauge
fields. The results agree with our previous calculations of the
chiral-logarithmic corrections to the S and T parameters in 't Hooft-Feynman
gauge. The work reported here includes a complete evaluation of all one-loop
divergences in an SU(2) x U(1) nonlinear sigma model, corresponding to an
electroweak effective Lagrangian in the absence of custodial symmetry.Comment: 40 pages, nine included eps figures. Minor corrections mad
Radiative Corrections to \zbb from Colored Scalars in a Model with Dynamical Symmetry Breaking
Isodoublet color-octet scalar bosons appear in the low-energy limit of a
natural extension of the Standard Model in which the electroweak symmetry is
broken by a condensate. We briefly discuss the model and show that
radiative corrections (involving these scalars) to the branching ratio
are
negative and thus place a stringent lower bound on the masses of the colored
scalars. This turns out to be GeV with GeV and increases
quadratically with . It is emphasized that is a parameter that is
well-determined experimentally and that theoretical estimates are relatively
free from uncertainties emanating from hadronic corrections and are
comparatively insensitive to the value of the top mass.Comment: 9 pages + 3 figures (available upon request), TeX file. Saha
Institute Preprint no. SINP-TNP/93-22 (December 1993
Conformal Phase Transition and Fate of the Hidden Local Symmetry in Large N_f QCD
It is observed that the Hidden Local Symmetry (HLS) for the vector mesons in
the ordinary QCD with smaller N_f plays the role of the "Higgsed magnetic gauge
symmetry" for the Seiberg duality in the SUSY QCD. For large N_f where the
conformal phase transition with chiral restoration and deconfinement is
expected to take place, we find that the HLS model also exhibits the chiral
restoration by the loop corrections (including the quadratic divergence) in a
manner similar to that in the CP^{N-1} model, provided that the bare HLS
Lagrangian respects the Georgi's vector limit at a certain N_f (\approx 7).Comment: 4 Pages (RevTeX), 3 PS figures are included Minor corrections are
made for the introductory part. This is the version to appear in Physical
Review Letter
Gauged Nambu-Jona-Lasinio model with extra dimensions
We investigate phase structure of the D (> 4)-dimensional gauged
Nambu-Jona-Lasinio (NJL) model with extra dimensions
compactified on TeV scale, based on the improved ladder Schwinger-Dyson (SD)
equation in the bulk. We assume that the bulk running gauge coupling in the SD
equation for the SU(N_c) gauge theory with N_f massless flavors is given by the
truncated Kaluza-Klein effective theory and hence has a nontrivial ultraviolet
fixed point (UVFP). We find the critical line in the parameter space of two
couplings, the gauge coupling and the four-fermion coupling, which is similar
to that of the gauged NJL model with fixed (walking) gauge coupling in four
dimensions. It is shown that in the presence of such walking gauge interactions
the four-fermion interactions become ``nontrivial'' even in higher dimensions,
similarly to the four-dimensional gauged NJL model. Such a nontriviality holds
only in the restricted region of the critical line (``nontrivial window'') with
the gauge coupling larger than a non-vanishing value (``marginal triviality
(MT)'' point), in contrast to the four-dimensional case where such a
nontriviality holds for all regions of the critical line except for the pure
NJL point. In the nontrivial window the renormalized effective potential yields
a nontrivial interaction which is conformal invariant. The exisitence of the
nontrivial window implies ``cutoff insensitivity'' of the physics prediction in
spite of the ultraviolet dominance of the dynamics. In the formal limit D -> 4,
the nontrivial window coincides with the known condition of the nontriviality
of the four-dimensional gauged NJL model, .Comment: 34 pages, 6 figures, references added, to appear in Phys.Rev.D. The
title is changed in PR
Infrared enhanced analytic coupling and chiral symmetry breaking in QCD
We study the impact on chiral symmetry breaking of a recently developed model
for the QCD analytic invariant charge. This charge contains no adjustable
parameters, other than the QCD mass scale , and embodies asymptotic
freedom and infrared enhancement into a single expression. Its incorporation
into the standard form of the quark gap equation gives rise to solutions for
the dynamically generated mass that display a singular confining behaviour at
the origin. Using the Pagels-Stokar method we relate the obtained solutions to
the pion decay constant , and estimate the scale parameter ,
in the presence of four active quarks, to be about 880 MeV.Comment: 14 pages, 3 figures; to appear in J. Phys.
Vector Manifestation and Fate of Vector Mesons in Dense Matter
We describe in-medium properties of hadrons in dense matter near chiral
restoration using a Wilsonian matching to QCD of an effective field theory with
hidden local symmetry at the chiral cutoff . We find that chiral
symmetry is restored in vector manifestation \`a la Harada and Yamawaki at a
critical matter density . We express the critical density in terms of QCD
correlators in dense matter at the matching scale. In a manner completely
analogous to what happens at the critical and at the critical
temperature , the vector meson mass is found to vanish (in the chiral
limit) at chiral restoration. This result provides a support for Brown-Rho
scaling predicted a decade ago.Comment: 14 pages, 2 figure
Non-compact Lattice QED with Two Charges: Phase Diagram and Renormalization Group Flow
The phase diagram of non-compact lattice QED in four dimensions with
staggered fermions of charges 1 and is investigated. The renormalized
charges are determined and found to be in agreement with perturbation theory.
This is an indication that there is no continuum limit with non-vanishing
renormalized gauge coupling, and that the theory has a validity bound for every
finite value of the renormalized coupling. The renormalization group flow of
the charges is investigated and an estimate for the validity bound as a
function of the cut-off is obtained. Generalizing this estimate to all fermions
in the Standard Model,it is found that a cut-off at the Planck scale implies
that has to be less than . Due to spontaneous chiral symmetry
breaking, strongly bound fermion-antifermion composite states are generated.
Their spectrum is discussed.Comment: 35 pages, LATEX, 26 PostScript figures (uuencoded
Asymptotic behavior in a model with Yukawa interaction from Schwinger-Dyson equations
A system of Schwinger-Dyson equations for pseudoscalar four-dimensional
Yukawa model in the two-particle approximation is investigated. The simplest
iterative solution of the system corresponds to the mean-field approximation
(or, equivalently, to the leading order of 1/N-expansion) and includes a
non-physical Landau pole in deep-Euclidean region for the pseudoscalar
propagator . It is argued, however, that a full solution may be free
from non-physical singularities and has the self-consistent asymptotic behavior
. An approximate solution
confirms the positivity of and the absence of Landau pole.Comment: 15 pages; journal versio
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