15,700 research outputs found
Magnetic Moments of Heavy Baryons in Light Cone QCD Sum Rules
The magnetic moments of heavy baryons containing a single charm or
bottom quark are calculated in the framework of light cone QCD sum rules
method. A comparison of our results with the predictions of the quark models is
presented.Comment: 26 Pages, 8 Figures and 1 Tabl
Positive and negative-parity flavor-octet baryons in coupled QCD sum rules
We apply the method of the QCD sum rule, in which positive- and
negative-parity baryons couple with each other, to the flavor-octet hyperons
and investigate the parity splittings. We also reexamine the nucleon in the
method, which was studied in our previous paper, by carefully choosing the
Borel weight. Both in the nucleon and hyperon channels the obtained sum rules
turn out to have a very good Borel stability and also have a Borel window, an
energy region in which the OPE converges and the pole contribution dominates
over the continuum contribution. The predicted masses of the positive- and
negative-parity baryons reproduce the experimental ones fairly well in the
and channels, if we assign the and the
to the parity partners of the and the ,
respectively. This implies that the is not the party partner of
the and may be a flavor-singlet or exotic state. In the
channel, the sum rule predicts the mass of the negative-parity state to be
about 1.8 GeV, which leads to two possibilities; one is that the observed state
with the closest mass, , is the parity partner and the other is that
the parity partner is not yet found but exists around 1.8 GeV.Comment: 15 pages, 4 figure
D_s (2317) as a four-quark state in QCD sum rules
We perform a QCD sum rule study of the open-charmed as a
four-quark state. Using the diquark-antidiquark picture for the four-quark
state, we consider four possible interpolating fields for , namely,
scalar-scalar, pseudoscalar-pseudoscalar, vector-vector, and
axial-vector--axial-vector types. We test all four currents by constructing
four separate sum rules. The sum rule with the scalar-scalar current gives a
stable value for the mass which qualitatively agrees with the
experimental value, and the result is not sensitive to the continuum threshold.
The vector-vector sum rule also gives a stable result with small sensitivity to
the continuum threshold and the extracted mass is somewhat lower than the
scalar-scalar current value. On the other hand, the two sum rules in the
pseudoscalar and axial-vector channels are found to yield the mass highly
sensitive to the continuum threshold, which implies that a four-quark state
with the combination of pseudoscalar-pseudoscalar or axial-vector--axial-vector
type would be disfavored. These results would indicate that is a
bound state of scalar-diquark and scalar-antidiquark and/or vector-diquark and
vector-antidiquark.Comment: 10 pages, 4 figures, REVTeX, 1 fig. added. to appear in Phys. Rev.
Higgs Phenomenology of Minimal Universal Extra Dimensions
The minimal model of Universal Extra Dimensions (MUED) is briefly reviewed.
We explain how the cross-sections for Higgs production via gluon fusion and
decay into two photons are modified, relative the the Standard Model (SM)
values, by KK particles running in loops, leading to an enhancement of the gg
to h to two photons and gg to h to W+W- cross-sections. ATLAS and CMS searches
for the SM Higgs in these channels are reinterpreted in the context of MUED and
used to place new limits on the MUED parameter space. Only a small region of
between 1 and 3 GeV around mh = 125 GeV for 500 GeV < 1/R < 1600 GeV remains
open at the 95 % confidence level.Comment: Presented at the 2011 Hadron Collider Physics symposium (HCP-2011),
Paris, France, November 14-18 2011, 3 pages, 4 figure
Light-cone sum rules for the transitions for real photons
We examine the radiative transition at the real photon
point using the framework of light-cone QCD sum rules. In particular,
the sum rules for the transition form factors and are
determined up to twist 4. The result for agrees with experiment within
10% accuracy. The agreement for is also reasonable. In addition, we
derive new light-cone sum rules for the magnetic moments of nucleons, with a
complete account of twist-4 corrections based on a recent reanalysis of photon
distribution amplitudes.Comment: 34 pages, 9 figures, revised version, published in Phys. Rev. D, one
misplaced reference correcte
g_phi-pion-gamma coupling constant in light cone QCD sum rules
The coupling constant of g_phi-pion-gamma decay is calculated using light
cone QCD sum rules. A comparison of our result with the ones existing in the
literature is presented.Comment: 9 pages, 2 figure
Generalized Density Matrix Revisited: Microscopic Approach to Collective Dynamics in Soft Spherical Nuclei
The generalized density matrix (GDM) method is used to calculate
microscopically the parameters of the collective Hamiltonian. Higher order
anharmonicities are obtained consistently with the lowest order results, the
mean field [Hartree-Fock-Bogoliubov (HFB) equation] and the harmonic potential
[quasiparticle random phase approximation (QRPA)]. The method is applied to
soft spherical nuclei, where the anharmonicities are essential for restoring
the stability of the system, as the harmonic potential becomes small or
negative. The approach is tested in three models of increasing complexity: the
Lipkin model, model with factorizable forces, and the quadrupole plus pairing
model.Comment: submitted to Physical Review C on 08 May, 201
Tree Level Unitarity Bounds for the Minimal B-L Model
We have derived the unitarity bounds in the high energy limit for the minimal
B-L extension of the Standard Model by analysing the full class of Higgs and
would-be Goldstone boson two-to-two scatterings at tree level. Moreover, we
have investigated how these limits could vary at some lower critical value of
the energy.Comment: 20 pages, 4 figures, 2 tables; 1d figure modified, typos corrected,
bibliography augmented; published in PRD after minor adjustmen
The Z' boson of the minimal B-L model at future Linear Colliders in e+e- --> mu+mu-
We study the capabilities of future electron-positron Linear Colliders, with
centre-of-mass energy at the TeV scale, in accessing the parameter space of a
boson within the minimal model. We carry out a detailed comparison
between the discovery regions mapped over a two-dimensional configuration space
( mass and coupling) at the Large Hadron Collider and possible future
Linear Colliders for the case of di-muon production. As known in the literature
for other models, we confirm that leptonic machines, as compared to the
CERN hadronic accelerator, display an additional potential in discovering a
boson as well as in allowing one to study its properties at a level of
precision well beyond that of any of the existing colliders.Comment: 5 pages, proceeding of LC09 (Perugia), published by the Italian
Physical Society in the Nuovo Cimento C (Colloquia
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