2,500 research outputs found
Model-independent study of the QCD sum rule for the pi NN coupling constant
We reinvestigate the QCD sum rule for the pi NN coupling constant, g,
starting from the vacuum-to-pion matrix element of the correlation function of
the interpolating fields of two nucleons. We study in detail the physical
content of the correlation function without referring to the effective theory.
We consider the invariant correlation functions by splitting the correlation
function into different Dirac structures. We show that the coefficients of the
double-pole terms are proportional to g but that the coefficients of the
single-pole terms are not determined by g. In the chiral limit the single-pole
terms as well as the continuum terms are ill defined in the dispersion
integral. Therefore, the use of naive QCD sum rules obtained from the invariant
correlation functions is not justified. A possible procedure to avoid this
difficulty is discussed.Comment: 20 pages, 2 figure
Flipping SU(5) Towards Five Dimensional Unification
It is shown that embedding of flipped SU(5) in a five-dimensional SO(10)
enables exact unification of the gauge coupling constants. The demand for the
unification uniquely determines both the compactification scale and the cutoff
scale. These are found to be 5.5 \times 10^{14} GeV and 1.0 \times 10^{17} GeV
respectively. The theory explains the absence of d=5 proton-decay operators
through the implementation of the missing partner mechanism. On the other hand,
the presence of d=6 proton-decay operators points towards the bulk localization
of the first and the second family of matter fields.Comment: 21 pages, references added, 3 Postscript figures, ReVTeX
Fermion masses and proton decay in a minimal five-dimensional SO(10) model
We propose a minimal SO(10) model in 5 space-time dimensions. The single
extra spatial dimension is compactified on the orbifold S^1/(Z_2 x Z_2')
reducing the gauge group to that of Pati-Salam. The breaking down to the
standard model group is obtained through an ordinary Higgs mechanism taking
place at the Pati-Salam brane, giving rise to a proper gauge coupling
unification. We achieve a correct description of fermion masses and mixing
angles by describing first and second generations as bulk fields, and by
embedding the third generation into four multiplets located at the Pati-Salam
brane. The Yukawa sector is simple and compact and predicts a neutrino spectrum
of normal hierarchy type. Concerning proton decay, dimension five operators are
absent and the essentially unique localization of matter multiplets implies
that the minimal couplings between the super-heavy gauge bosons and matter
fields are vanishing. Non-minimal interactions are allowed but the resulting
dimension six operators describing proton decay are too suppressed to produce
observable effects, even in future, super-massive detectors.Comment: 21 pages, 3 figure
Pertinent Dirac structure for QCD sum rules of meson-baryon coupling constants
Using general baryon interpolating fields for
without derivative, we study QCD sum rules for meson-baryon couplings and their
dependence on Dirac structures for the two-point correlation function with a
meson i\int d^4x e^{iqx} \bra 0|{\rm T}[J_B(x)\bar{J}_B(0)] |{\cal M}(p)\ket.
Three distinct Dirac structures are compared: ,
i\gamma_5\fslash{p}, and structures.
From the dependence of the OPE on general baryon interpolating fields, we
propose criteria for choosing an appropriate Dirac structure for the coupling
sum rules. The sum rules satisfy the
criteria while the sum rules beyond the chiral limit do not. For
the i\gamma_5\fslash{p} sum rules, the large continuum contributions prohibit
reliable prediction for the couplings. Thus, the structure seems pertinent for realistic predictions. In the SU(3) limit,
we identify the OPE terms responsible for the ratio. We then study the
dependence of the ratio on the baryon interpolating fields. We conclude the
ratio for appropriate choice of the interpolating fields.Comment: To be published in Phys.Rev.C ; 21 pages,8 figures, revtex ;
references are adde
Anomalies on orbifolds with gauge symmetry breaking
We embed two 4D chiral multiplets of opposite representations in the 5D N=2
gauge theory compactified on an orbifold .
There are two types of orbifold boundary conditions in the extra dimension to
obtain the 4D N=1 gauge theory from the bulk: in
Type I, one has the bulk gauge group at and the unbroken gauge group at
while in Type II, one has the unbroken gauge group at both fixed
points. In both types of orbifold boundary conditions, we consider the zero
mode(s) as coming from a bulk -plet and brane fields at the fixed
point(s) with the unbroken gauge group. We check the consistency of this
embedding of fields by the localized anomalies and the localized FI terms. We
show that the localized anomalies in Type I are cancelled exactly by the
introduction of a bulk Chern-Simons term. On the other hand, in some class of
Type II, the Chern-Simons term is not enough to cancel all localized anomalies
even if they are globally vanishing. We also find that for the consistent
embedding of brane fields, there appear only the localized log FI terms at the
fixed point(s) with a U(1) factor.Comment: LaTeX file of 19 pages with no figure, published versio
Possible Supersymmetric Effects on Angular Distributions in Decays
We investigate the angular distributions of the rare B decay, , in general supersymmetric extensions of the standard
model. We consider the new physics contributions from the operators
in small invariant mass region of lepton pair. We show that the
azimuthal angle distribution of the decay can tell us the new physics effects
clearly from the behavior of the distribution, even if new physics does not
change the decay rate substantially from the standard model prediction
Model Building with Gauge-Yukawa Unification
In supersymmetric theories with extra dimensions, the Higgs and matter fields
can be part of the gauge multiplet, so that the Yukawa interactions can arise
from the gauge interactions. This leads to the possibility of gauge-Yukawa
coupling unification, g_i=y_f, in the effective four dimensional theory after
the initial gauge symmetry and the supersymmetry are broken upon orbifold
compactification. We consider gauge-Yukawa unified models based on a variety of
four dimensional symmetries, including SO(10), SU(5), Pati-Salam symmetry,
trinification, and the Standard Model. Only in the case of Pati-Salam and the
Standard Model symmetry, we do obtain gauge-Yukawa unification. Partial
gauge-Yukawa unification is also briefly discussed.Comment: 23 page
Family Unification on an Orbifold
We construct a family-unified model on a Z_2xZ_2 orbifold in five dimensions.
The model is based on a supersymmetric SU(7) gauge theory. The gauge group is
broken by orbifold boundary conditions to a product of grand unified SU(5) and
SU(2)xU(1) flavor symmetry. The structure of Yukawa matrices is generated by an
interplay between spontaneous breaking of flavor symmetry and geometric factors
arising due to field localization in the extra dimension.Comment: 13 page
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