arXiv subjects
Publications and source records attributed to R. Casalbuoni.
We discuss the prospects for detecting at a muon collider the massive new vector resonances V and light pseudo-Nambu-Goldstone bosons P of a typical strongly interacting electroweak sector (as represented by the BESS model). Expected sensitivities to V's at a high energy collider are evaluated and the excellent prospects for discovering P's via scanning at a low energy collider are delineated.
In this work we have studied the phenomenological properties at future e+e- linear colliders of two models of strong electroweak symmetry breaking, characterized by the presence of new spin one strong interacting resonances.
A linear realization of a model of dynamical electroweak symmetry breaking describing additional heavy vector bosons is proposed. The model is a SU(2)_L x U(1) x SU(2)_L' x SU(2)_R' gauge theory, breaking at some high scale u to SU(2)_weak x U(1)_Y and breaking again in the standard way at the electroweak scale v to U(1)_(em). The model is renormalizable and reproduces the Standard Model in the limit u\to infinity. This decoupling property is shown to hold also at the level of radiative corrections by computing, in particular, the epsilon parameters.
The problem of quantizing theories defined over configuration spaces described by non-commuting parameters is considered. In this paper we describe the first step in this direction, that is the definition of an integral over a general algebra.
Within the composite operator formalism we derive a formula for the pion decay constant $f_π$, as defined directly from the residue at the pion pole of the meson propagator, rather than from the matrix element of the axial current. The calculation is performed under some simplifying assumptions, and we verify the complete consistency with soft-pion results, in particular with the Adler-Dashen relation. The formula one obtains for (the pole-defined) $f_π^2$ differs from the previous Pagels-Stokar expression by an additive term, and it still provides $f_π^2$ in terms of the quark self-energy. We make some numerical estimates leading to $(30 ÷40)%$ deviation for $f_π^2$ with respect to the Pagels-Stokar formula.
In this paper we consider the problem of quantizing theories defined over configuration spaces described by non-commuting parameters. If one tries to do that by generalizing the path-integral formalism, the first problem one has to deal with is the definition of integral over these generalized configuration spaces. This is the problem we state and solve in the present work, by constructing an explicit algorithm for the integration over a general algebra. Many examples are discussed in order to illustrate our construction.
In this paper we consider a general $SU(2)_L\otimes SU(2)_R$ invariant Lagrangian describing scalar, vector and axial-vector resonances. By expanding the WW and the ZZ scattering amplitude up to the fourth order in the external momenta we can compare the parameters of our Lagrangian with the ones used in the effective chiral Lagrangian formalism. In the last approach there has been a recent study of the fusion processes at future e^+e^- colliders at energies above 1 TeV. We use these results to put bounds on the parameter space of our model and to show that for the case of vector resonances the bounds obtained from the annihilation channel in fermion pairs are by far more restrictive, already at energies of the order of 500 GeV.
We study the expected phenomenology at present (Tevatron) and future (Tevatron Upgrade, LHC) hadronic colliders of a model describing a strong electroweak symmetry breaking sector with both vector and axial vector strong interacting bosons degenerate in mass. Due to decoupling, this model at low energies is almost indistinguishable from the Standard Model, passing therefore all low energy precision tests at LEPI. We will show that it gives quite visible signals at forthcoming hadronic accelerators. The new charged vector bosons can be detected more easily than the neutral ones.
In this paper we do an analysis of the reaction $e^+e^-\to W^+W^-$ for various options of the Next Linear Colliders (NLC), by considering the possibility of deviations from the Standard Model induced by anomalous trilinear vector boson couplings and non-standard fermionic couplings. We show that there are strong correlations among these parameters. By studying the high-energy behaviour of the helicity amplitudes we show that the error made in linearizing the cross-section in the anomalous and non-standard couplings increases with the square of the center of mass energy. We consider also the option of longitudinally polarized electron beams by showing that, in this case, the restrictions on the anomalous and non-standard parameters are greatly enhanced.
We perform a 1/N-expansion of the partition function of the massive Gross-Neveu model in 1+1 dimensions. The procedure allows for the inclusion of the contribution of scalar and pseudoscalar composites (of order 1/N) to the equation of state. The naive expectation that the bosonic fluctuations correct significantly the mean field approximation at low temperatures is confirmed by our calculations. Actually the relevant degrees of freedom of hadronic matter at low temperatures are found to be pion-like excitations, rather than the fundamental constituents.
We present a renormalizable model of electroweak interactions containing an extra $SU(2)'_L\otimes SU(2)'_R$ symmetry. The masses of the corresponding gauge bosons and of the associated Higgs particles can be made heavy by tuning a convenient vacuum expectation value. According to the way in which the heavy mass limit is taken we obtain a previously considered non-linear model (degenerate BESS) which, in this limit, decouples giving rise to the Higgsless Standard Model (SM). Otherwise we can get a model which decouples giving the full SM. In this paper we argue that in the second limit the decoupling holds true also at the level of radiative corrections. Therefore the model discussed here is not distinguishable from the SM at low energy. Of course the two models differ deeply at higher energies.
The approximate symmetries of Quantum ChromoDynamics in the infinite heavy quark ($Q=c,b$) mass limit ($m_Q \to \infty$) and in the chiral limit for the light quarks ($m_q \to 0,\;q=\,u,\,d,\,s$) can be used together to build up an effective chiral lagrangian for heavy and light mesons describing strong interactions among effective meson fields as well as their couplings to electromagnetic and weak currents, including the relevant symmetry breaking terms. The effective theory includes heavy ($Q \bar q$) mesons of both negative and positive parity, light pseudoscalars, as well as light vector mesons. We summarize the estimates for the parameters entering the effective lagrangian and discuss in particular some phenomenologically important couplings, such as $g_{B^* B π}$. The hyperfine splitting of heavy mesons is discussed in detail. The effective lagrangian allows for the possibility to describe consistently weak couplings of heavy ($B,\, D$) to light ($π,\, ρ, \, K^*,\,$ etc.) mesons. The method has however its own limitations, due to the requirement that the light meson momenta should be small, and we discuss how such limitations can be circumvented through reasonable ansatz on the form factors. Flavour conserving (e. g. $B^* \to B\, γ$) and flavour changing (e. g. $B \to K^* \, γ$) radiative decays provide another field of applications of effective lagrangians; they are discussed together with their phenomenological implications. Finally we analyze effective lagrangians describing heavy charmonium- like ($\bar Q Q$) mesons and their strong and electromagnetic interactions. The role of approximate heavy quark symmetries for this case and the phenomenological tests of these models are also discussed.
We present a derivation of the bosonic contribution to the thermodynamical potential of four fermion models by means of a $1/N_c$-expansion of the functional integral defining the partition function. This expansion turns out to be particularly useful to correct the mean field approximation expecially at low temperatures, where the relevant degrees of freedom are low-mass bosonic excitations (pseudogoldstones).
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 simulate the formation and growth of disoriented chiral condensate (DCC) regions which follow the expansion of a high energy density region into the ``cold'' vacuum. The numerical study is based on the one-loop effective potential for the massive 2+1-dimensional Gross-Neveu model. We pay attention to the setting of the initial conditions and to determining which parameters are relevant for a strong amplification of the pion field. We find that the size of the ``hot'' source plays a significant role. For large enough source radii, we observe strong correlation phenomena, corresponding to the growth of large regions where the pion field oscillates along a given direction. We give our results in terms of the $θ$ angle which defines the DCC disorientation, of the other $O(4)$ angles distributions, of the local ratios $R_{a}=π_{a}^{2}/{\vecπ}^2$ $(a=1,2,3)$, and of the energies associated with the fields at representative times.
We study top production at Tevatron collider in the extended BESS model, which is an effective lagrangian parametrization of a dynamical symmetry breaking of the electroweak symmetry. The existence of a colored octet of gauge vector bosons can increase top production at a rate still consistent with recent experimental data and lead to distorsions in the transverse momentum spectrum of the top.