arXiv subjects
Publications and source records attributed to S. De Curtis.
An effective lagrangian describing a strong interacting electroweak sector is considered. It contains new vector and axial-vector resonances all degenerate in mass and mixed with $W$ and $Z$. The model, for large mass of these degenerate gauge bosons, becomes identical to the standard model in the classical limit of infinite Higgs mass. The limits on the parameter space of this model from future $e^+e^-$ colliders are presented.
Review of prospects for discovery of new physics signals at LEP2. The areas covered include SUSY, exotic fermions, BESS models, leptoquarks, virtual effects and CP violating observables.
We discuss possible symmetries of effective theories describing spinless and spin 1 bosons, mainly to concentrate on an intriguing phenomenological possibility: that of a hardly noticeable strong electroweak sector at relatively low energies. Specifically, a model with both vector and axial vector strong interacting bosons may possess a discrete symmetry imposing degeneracy of the two sets of bosons (degenerate BESS model). In such a case its effects at low energies become almost invisible and the model easily passes all low energy precision tests. The reason lies essentially in the fact that the model automatically satisfies decoupling, contrary to models with only vectors. For large mass of the degenerate spin one bosons the model becomes identical at the classical level to the standard model taken in the limit of infinite Higgs mass. For these reasons we have thought it worthwhile to fully develop the model, together with its possible generalizations, and to study the expected phenomenology. For instance, just because of its invisibility at low energy, it is conceivable that degenerate BESS has low mass spin one states and gives quite visible signals at existing or forthcoming accelerators.
We present some results on the usefulness of upgraded Tevatron, LHC proton proton collider and linear e+e- colliders in the TeV range to test the idea of a strongly interacting sector as responsible for the electroweak symmetry breaking. The calculations are performed within an effective lagrangian description, called the BESS model, which provides for a rather general frame based on the standing point of custodial symmetry and gauge invariance, without specifying any dynamical scheme.
We discuss the possible symmetries of the effective lagrangian describing interacting pseudoscalar-, vector-, and axial-vector mesons. Specific choices of the parameters give rise to an $[SU(2)\otimes SU(2)]^3$ symmetry. This symmetry can be obtained either {\it á la} Georgi, with all states in the spectrum remaining massless, or in a new realization, implying decoupling of the pseudoscalar bosons from degenerate vector and axial-vector mesons. This second possibility, when minimally coupled with $SU(2)\otimes U(1)$ electroweak gauge vector bosons, seems particularly appealing. All deviations in the low-energy electroweak parameters are strongly suppressed, and the vector and axial-vector states turn out to be quite narrow. A nearby strong electroweak sector would then be conceivable and in principle it could be explored with relatively low energy accelerators.
In this paper the low energy limit of the BESS model is studied in a systematic way. The method consists in eliminating the heavy vector field, by use of its classical equations of motion, in the infinite mass limit. After the elimination of the heavy degrees of freedom we get additional terms to the Standard Model lagrangian. After a finite renormalization of the ordinary gauge bosons wave functions, and redefinition of the lagrangian couplings in terms of $M_Z$, the fine structure constant and the Fermi constant, we can read directly the deviations from the Standard Model. By this procedure we can extend a result previously derived to the case in which the heavy vector bosons have a direct coupling to fermions. Consequences for the anomalous trilinear couplings are discussed.
We consider the production of the lightest pseudo-Goldstone bosons at future colliders through the vector resonances predicted by the extended BESS model, which consists of an effective lagrangian parametrization with dynamical symmetry breaking, describing scalar, vector and axial-vector bound states in a rather general framework. We find that the detection of pseudo-Goldstone pairs at LHC requires a careful evaluation of backgrounds. For e+e- collisions in the TeV range the backgrounds can be easily reduced and the detection of pseudo-Goldstone pairs is generally easier.
We consider the possibility of detecting vector resonances from a strong electroweak sector, in the framework of the BESS model, at future $e^+ e^-$ colliders up to the TeV range. If the mass $M_V$ of the new vector boson multiplet is not far above or if it is below the maximum machine energy, such a contribution would be manifest. The process of $W$-pair production by $e^+e^-$ annihilation allows for sensitive tests of the strong sector, especially if the $W$ polarizations are reconstructed. Contribution to the proceedings of the Workshop on Physics and Experiment at Linear $e^+ e^-$ Colliders - Munich, Annecy, Hamburg 1993.
The existence of a strongly interacting sector responsible for the electroweak symmetry breaking is assumed. As a consequence vector and axial-vector bound states may be formed. These resonances mix with the Standard Model gauge bosons and are of primary phenomenological importance for the LEP physics. The extended BESS model is an effective scheme based on the symmetry group $SU(8)_L\otimes SU(8)_R$, describing in a consistent way the interactions among the pseudo-Goldstone bosons, vector and axial-vector resonances and the standard gauge bosons. In a previous paper, the contribution from extended BESS to the electroweak oblique corrections was evaluated. However, only an estimate of the effects coming from mass and wave function renormalization of the new resonances, was given. Here we complete the evaluation by computing explicitly these effects. We confirm the previous result, that is, in spite of the great precision of the present LEP measurements, the extended BESS parameter space is not very much constrained.
Invited talk at the ``Workshop on Physics and Experiments at Linear e+e- Colliders'', Waikoloa, Hawaii, April 26-30, 1993 (presented by D. Dominici)
We explore the usefulness of very energetic linear $e^+e^-$ colliders in the $TeV$ range in studying an alternative scheme of electroweak symmetry breaking based on a strong interacting sector. The calculations are performed within the BESS model which contains new vector resonances. If the mass $M_V$ of the new boson multiplet lies not far from the maximum machine energy, or if it is lower, such a resonant contribution would be quite manifest. A result of our analysis is that also virtual effects are important. It appears that annihilation into a fermion pair in such machines, at the considered luminosities, would improve only marginally on existing limits if polarized beams are available and left-right asymmetries are measured. On the other hand, the process of $W$-pair production by $e^+e^-$ annihilation would allow for sensitive tests of the hypothesized strong sector, especially if the $W$ polarizations are reconstructed from their decay distributions, and the more so the higher the energy of the machine. An $e^+e^-$ collider with c.m. energy $\sqrt{s}=500~GeV$ could improve the limits on the model for the range $500<M_V(GeV)<1000$ when $W$ polarization is not reconstructed. If $W$ polarizations are reconstructed, then the bounds improve for the entire expected range of $M_V$. These bounds become more stringent for larger energy of the collider. We have also studied the detectability of the new resonances through the fusion subprocesses, but this channel does not seem to be interesting even for a collider with a c.m. energy $\sqrt{s}=2~TeV$.