9,117 research outputs found
Glueballs in Peripheral Heavy-Ion Collisions
We estimate the cross-section for glueball production in peripheral heavy-ion
collisions through two-photon and double-Pomeron exchange, at energies that
will be available at RHIC and LHC. Glueballs will be produced at large rates,
opening the possibility to study decays with very small branching ratios. In
particular, we discuss the possibility of observing the subprocess .Comment: 11 page
Short Distance QCD Contribution to the Electroweak Mass Difference of Pions
It is known that the short distance QCD contribution to the mass difference
of pions is quadratic on the quark masses, and irrelevant with respect to the
long distance part. It is also considered in the literature that its
calculation contain infinities, which should be absorbed by the quark mass
renormalization. Following a prescription by Craigie, Narison and Riazuddin, of
a renormalization group improved perturbation theory to deal with the
electromagnetic mass shift problem in QCD, we show that the short distance QCD
contribution to the electroweak pion mass difference (with ) is
finite and, of course, its value is negligible compared to other contributions.Comment: 8 pages, Revtex, submitted to Phys.Rev.
Hadronic physics in peripheral heavy ion collisions
We discuss the production of hadronic resonances in very peripheral heavy ion
collisions, where the ions collide with impact parameter larger than twice the
nuclear radius and remain intact after the collision. We compare the resonance
production through two-photon and double Pomeron exchange, showing that when we
impose the condition for a peripheral interaction the process
dominates over the Pomeron interaction, due to the short range propagation of
this last one. We also discuss the observation of light resonances through the
subprocess , which is a clean signal
for glueball candidates as well as one way to check the existence of a possible
scalar meson.Comment: 11 pages, 5 figures, revtex, contribution to the proceedings of the
XXII Brazilian National Meeting on Particles and Fields, Sao Lourenco, 200
QCD phenomenology with infrared finite SDE solutions
Recent progress in the solution of Schwinger-Dyson equations (SDE), as well
as lattice simulation of pure glue QCD, indicate that the gluon propagator and
coupling constant are infrared (IR) finite. We discuss how this
non-perturbative information can be introduced into the QCD perturbative
expansion in a consistent scheme, showing some examples of tree level hadronic
reactions that successfully fit the experimental data with the gluon propagator
and coupling constant depending on a dynamically generated gluon mass. This
infrared mass scale acts as a natural cutoff and eliminates some of the ad hoc
parameters usually found in perturbative QCD calculations. The application of
these IR finite Green's functions in the case of higher order terms of the
perturbative expansion is commented.Comment: Talk at International Workshop on QCD Green's Functions, Confinement
and Phenomenology, September 7-11, 2009, ECT, Trento, Italy, 12 pages, 7
figure
Energy criterion to select the behavior of dynamical masses in technicolor models
We propose a quite general ansatz for the dynamical mass in technicolor
models. We impose on this ansatz the condition for formation of the tightest
composite boson state, or the criterion that it should lead to the deepest
minimum of energy. This criterion indicates a particular form of the
technifermion self energy.Comment: 4 pages, 3 figures; to appear in Phys. Lett.
Schwinger-Dyson equation boundary conditions induced by ETC radiative corrections
The technicolor (TC) Schwinger-Dyson equations (SDE) should include radiative
corrections induced by extended technicolor (ETC) interactions when TC is
embedded into a larger theory including also QCD. These radiative corrections
couple the different strongly interacting Dyson equations. We discuss how the
boundary conditions of the coupled SDE system are modified by these
corrections, and verify that the ultraviolet behavior of the self-energies are
described by a function that decreases logarithmically with momentum.Comment: 15 pages, 2 figure
Scalar bosons in Minimal and Ultraminimal Technicolor: Masses, trilinear couplings and widths
We compute masses, trilinear self-couplings and decay widths into weak bosons
of the scalar composite bosons in the case of the Minimal and Ultraminimal
technicolor models. The masses, computed via the Bethe-Salpeter equation, turn
out to be light and the trilinear couplings smaller than the one that would be
expected when compared to a fundamental Standard Model scalar boson with the
same mass. The decay widths into electroweak bosons of the Ultraminimal model
scalars bosons are much smaller than the one of the Minimal model.Comment: 15 pages, 1 figure, improved discussion, new references and typos
corrected, matchs version to be publishe
Deciphering the minimum of energy of some walking technicolor models
There are quasi-conformal theories, like the Minimal and Ultraminimal
Technicolor models, which may break dynamically the gauge symmetry of the
Standard Model and at the same time are compatible with electroweak precision
data. The main characteristic of this type of models is their fermionic content
in one or more higher dimensional representations, therefore it is not
immediate to know which model leads to the most attractive channel or the
minimum vacuum energy state. We discuss the effective potential for composite
operators for these models, verifying that their vacuum energy values are
different, with the Ultraminimal model having a deeper minimum of energy.Comment: 4 pages, 2 figures, published version
The origin of the first and third generation fermion masses in a technicolor scenario
We argue that the masses of the first and third fermionic generations, which
are respectively of the order of a few MeV up to a hundred GeV, are originated
in a dynamical symmetry breaking mechanism leading to masses of the order
, where is a small coupling constant and , in the
case of the first fermionic generation, is the scale of the dynamical quark
mass ( MeV). For the third fermion generation is the value
of the dynamical techniquark mass ( GeV). We discuss how this
possibility can be implemented in a technicolor scenario, and how the mass of
the intermediate generation is generated.Comment: 10 pages, 9 figures as eps files, Latex; Abridged version of the
previous preprint. Title changed. Results remain the sam
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