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 $\gamma \gamma (PP) \rightarrow G \rightarrow \gamma \gamma$.Comment: 11 page

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 $\gamma \gamma$ 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 $\gamma \gamma \to R \to \gamma \gamma$, which is a clean signal for glueball candidates as well as one way to check the existence of a possible scalar $\sigma$ meson.Comment: 11 pages, 5 figures, revtex, contribution to the proceedings of the XXII Brazilian National Meeting on Particles and Fields, Sao Lourenco, 200

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 $m_u=m_d\neq0$) is finite and, of course, its value is negligible compared to other contributions.Comment: 8 pages, Revtex, submitted to Phys.Rev.

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

Schwinger-Dyson approach and its application to generate a light composite scalar

We discuss the possibility of generating a light composite scalar boson, in a scenario that we may generically call Technicolor, or in any variation of a strongly interacting theory, where by light we mean a scalar composite mass about one order of magnitude below the characteristic scale of the strong theory. Instead of most of the studies about a composite Higgs boson, which are based on effective Lagrangians, we consider this problem in the framework of non-perturbative solutions of the fermionic Schwinger-Dyson and Bethe-Salpeter equations. We study a range of mechanisms proposed during the recent years to form such light composite boson, and verify that such possibility seems to be necessarily associated to a fermionic self-energy that decreases slowly with the momentum.Comment: 35 pages, 6 figures, few typos corrected. Version to appear in IJMP

A 125 GeV Scalar Boson and SU(N_{TC})\otimes SU(3)_{{}_{L}}\otimes U(1)_{{}_{X}} models

We verify that SU(N)_{{}_{TC}}\otimes SU(3)_{{}_{L}}\otimes U(1)_{{}_{X}} models, where the gauge symmetry breaking is totally dynamical and promoted by the non-Abelian technicolor (TC) group and the strong Abelian interactions, are quite constrained by the LHC data. The theory contains a T quark self-energy involving the mixing between the neutral gauge bosons, which introduces the coupling between the light and heavy composite scalar bosons of the model. We determine the lightest scalar boson mass for these models from an effective action for composite operators, assuming details about the dynamics of the strong interaction theories. Comparing the value of this mass with the ATLAS and CMS observation of a new boson with a mass M_{\phi} \sim 125GeV and considering the lower bound determined by the LHC Collaborations on the heavy neutral gauge boson (Z^\prime) present in these models, we can establish constraints on the possible models. For example, if SU(N)_{{}_{TC}}\equiv SU(2)_{{}_{TC}}, with technifermions in the fundamental representation, the model barely survives the confrontation with the LHC data.Comment: 19 pages, 3 figure