Search

Non resonant production of WW pairs is the most important background in the Higgs search in the range 155 \ltap M_H \ltap 170 GeV at the LHC. We consider QCD corrections to WW pair production in hadron collisions and present a calculation which consistently combines NLO corrections with soft-gluon resummation at small transverse momenta of the WW pair. Spin correlations are fully taken into account in our calculation. We study the impact of the resummation on the leptonic observables and perform a comparison with results obtained at NLO and with the MC@NLO event generator., Comment: 4 pages, 5 figures, presented at the XLIst Rencontres de Moriond, QCD and Hadronic interactions, La Thuile, Italy

This Report summarises the activities of the "SM and Higgs" working group for the Workshop "Physics at TeV Colliders", Les Houches, France, 2-20 May, 2005. On the one hand, we performed a variety of experimental and theoretical studies on standard candles (such as W, Z, and ttbar production), treating them either as proper signals of known physics, or as backgrounds to unknown physics; we also addressed issues relevant to those non-perturbative or semi-perturbative ingredients, such as Parton Density Functions and Underlying Events, whose understanding will be crucial for a proper simulation of the actual events taking place in the detectors. On the other hand, several channels for the production of the Higgs, or involving the Higgs, have been considered in some detail. The report is structured into four main parts. The first one deals with Standard Model physics, except the Higgs. A variety of arguments are treated here, from full simulation of processes constituting a background to Higgs production, to studies of uncertainties due to PDFs and to extrapolations of models for underlying events, from small-$x$ issues to electroweak corrections which may play a role in vector boson physics. The second part of the report treats Higgs physics from the point of view of the signal. In the third part, reviews are presented on the current status of multi-leg, next-to-leading order and of next-to-next-to-leading order QCD computations. Finally, the fourth part deals with the use of Monte Carlos for simulation of LHC physics., Comment: 234 pages, 173 figures. Web page of the workshop (with links to the talks): http://lappweb.in2p3.fr/conferences/LesHouches/Houches2005/

We present QCD predictions for the transverse momentum (q_T) distribution of the Higgs boson at the LHC. At small q_T the logarithmically-enhanced terms are resummed to all orders up to next-to-next-to-leading logarithmic accuracy. The resummed component is consistently matched to the next-to-leading order calculation valid at large q_T. The results, which implement the most advanced perturbative predictions available at present for this observable, show a good stability with respect to theoretical uncertainties. The numerical program HqT, used to perform the calculation, is briefly discussed., Comment: 4 pages, 2 figures, to appear in the Proceedings of the International Europhysics Conference on High Energy Physics, July 21st - 27th 2005, Lisboa, Portugal

We consider QCD radiative corrections to WW pair production in hadron collisions. We perform a calculation that consistently combines next-to-leading order predictions with soft-gluon resummation valid at small transverse momenta ptWW of the WW pair. We present results for the ptWW distribution at the LHC up to (almost) next-to-next-to-leading logarithmic accuracy, and study the effect of resummation on the charged-lepton distributions. Soft-gluon effects are typically mild, but they can be strongly enhanced when hard cuts are applied. The relevant distributions are generally well described by the MC@NLO event generator., Comment: 15 pages, 12 postscript figures. Error corrected in NLO plot for WW transverse-mass distribution. Results unchanged

We consider the transverse-momentum (q_T) distribution of generic high-mass systems (lepton pairs, vector bosons, Higgs particles, ....) produced in hadron collisions. At small q_T, we concentrate on the all-order resummation of the logarithmically-enhanced contributions in QCD perturbation theory. We elaborate on the $b$-space resummation formalism and introduce some novel features: the large logarithmic contributions are systematically exponentiated in a process-independent form and, after integration over q_T, they are constrained by perturbative unitarity to give a vanishing contribution to the total cross section. At intermediate and large q_T, resummation is consistently combined with fixed-order perturbative results, to obtain predictions with uniform theoretical accuracy over the entire range of transverse momenta. The formalism is applied to Standard Model Higgs boson production at LHC energies. We combine the most advanced perturbative information available at present for this process: resummation up to next-to-next-to-leading logarithmic accuracy and fixed-order perturbation theory up to next-to-leading order. The results show a high stability with respect to perturbative QCD uncertainties., Comment: 48 pages, 13 postscript figures

We propose a framework for the implementation of a subtraction formalism at NNLO in QCD, based on an observable- and process-independent cancellation of infrared singularities. As a first simple application, we present the calculation of the contribution to the e+e- dijet cross section proportional to C_F T_R, Comment: 42 pages Latex; 7 figures included. Modifications to the text, and references added; the results are unchanged

We consider the back-to-back region in the energy--energy correlation in e^+e^- collisions. We present the explicit expression of the O(as^2) logarithmically enhanced contributions up to next-to-next-to-leading logarithmic accuracy. We study the impact of the results in a detailed comparison with precise LEP and SLC data. We find that, when hadronization effects are taken into account as is customarily done in QCD analysis in e^+e^- annihilations, the extracted value of as(M_Z) is in good agreement with the current world average., Comment: 15 pages, 8 figures

We present perturbative predictions for the transverse momentum (q_T) distribution of the Higgs boson at the LHC. At small q_T the logarithmically-enhanced terms are resummed to all orders up to next-to-next-to-leading logarithmic accuracy. The resummed component is consistently matched to the next-to-leading order calculation valid at large q_T. The results, which implement the most advanced perturbative information that is available at present for this observable, show a good stability with respect to perturbative QCD uncertainties., Comment: 6 pages, 3 figures, presented at the XXXIXth Rencontres de Moriond, QCD and Hadronic interactions, La Thuile, Italy

Theoretical progress in Higgs boson production and background processes is discussed with particular emphasis on QCD corrections at and beyond next-to-leading order as well as next-to-leading order electroweak corrections. The residual theoretical uncertainties of the investigated processes are estimated in detail. Moreover, recent investigations of the MSSM Higgs sector and other extensions of the SM Higgs sector are presented. The potential of the LHC and a high-energy linear e+e- collider for the measurement of Higgs couplings is analyzed., Comment: 169 pages, Proceedings 3rd Les Houches Workshop: Physics at TeV Colliders, Les Houches, France, 26 May - 6 Jun 2003

This report documents the results obtained by the Working Group on Quantum Chromodynamics and the Standard Model for the Workshop `Physics at TeV Colliders'', Les Houches, France, 26 May - 6 June 2003. After a Monte Guide description, the first contributions report on progress in describing multiple interactions, important for the LHC, and underlying events. An announcement of a Monte Carlo database, under construction, is then followed by a number of contributions improving parton shower descriptions. Subsequently, a large number of contributions address resummations in various forms, after which follow studies of QCD effects in pion pair, top quark pair and photon pair plus jet production. After a study of electroweak corrections to hadronic precision observables, the report ends by presenting recent progress in methods to compute finite order corrections at one-loop with many legs, and at two-loop., Comment: 119pp

This paper describes a comparison of most of the available predictions for the cross section and transverse momentum distribution for a 125 GeV mass Higgs at the LHC, including those from the PYTHIA and HERWIG parton shower Monte Carlos and from four resummation calculations., Comment: 7 pages, submitted to proceedings of the Workshop on Physics at TeV Colliders, Les Houches 2003

A simulation of the search for the Standard Model Higgs boson at the LHC, in the channel gg -> H -> WW -> lnu lnu, is described. Higher-order QCD corrections are taken into account by using a reweighting procedure, which allows us to combine event rates obtained with the PYTHIA Monte Carlo program with the most up-to-date theoretical predictions for the transverse-momentum spectra of the Higgs signal and its corresponding WW background. With this method the discovery potential for Higgs masses between 140 and 180 GeV is recalculated and the potential statistical significance of this channel is found to increase considerably. For a Higgs mass of 165 GeV a signal-to-background ratio of almost 2:1 can be obtained. A statistical significance of five standard deviations might already be achieved with an integrated luminosity close to 0.4 fb^{-1}. Using this approach, an experimental effective K-factor of about 2.04 is obtained for the considered Higgs signature, which is only about 15 % smaller than the theoretical inclusive K-factor., Comment: 16 pages, 8 eps figures, comparison of jet veto efficiencies between PYTHIA and HERWIG added, to appear on JHEP

We consider QCD corrections to Higgs boson production through gluon--gluon fusion in hadron collisions. We compute the cross section, performing the all-order resummation of multiple soft-gluon emission at next-to-next-to-leading logarithmic level. Known fixed-order results (up to next-to-next-to-leading order) are consistently included in our calculation. We give phenomenological predictions for Higgs boson production at the Tevatron and at the LHC. We estimate the residual theoretical uncertainty from perturbative QCD contributions. We also quantify the differences obtained by using the presently available sets of parton distributions., Comment: 44 pages, 17 postscript figures

We consider the transverse-momentum (q_T) distribution of Higgs bosons produced at hadron colliders. We use a formalism that uniformly treats both the small-q_T and large-q_T regions in QCD perturbation theory. At small q_T (q_T << M_H, M_H being the mass of the Higgs boson), we implement an all-order resummation of logarithmically-enhanced contributions up to next-to-next-to-leading logarithmic accuracy. At large q_T (q_T \gtap M_H), we use fixed-order perturbation theory up to next-to-leading order. The resummed and fixed-order approaches are consistently matched by avoiding double-counting in the intermediate-q_T region. In this region, the introduction of unjustified higher-order terms is avoided by imposing unitarity constraints, so that the integral of the q_T spectrum exactly reproduces the perturbative result for the total cross section up to next-to-next-to-leading order. Numerical results at the LHC are presented. These show that the main features of the q_T distribution are quite stable with respect to perturbative QCD uncertainties., Comment: 9 pages, 2 postscript figures

Studies of hadronic final states are entering a new phase where very precise experimental measurements require better theoretical predictions for a meaningful comparison. Recent results and future developments are briefly reviewed both for the experiments and the theory., Comment: 9 pages, 5 ps figures, summary talk of the Hadronic Physics session at ``IFAE'', the XIV italian meeting of High Energy Physics, Parma April 2002

We consider QCD corrections to Higgs boson production through gluon-gluon fusion in hadron collisions. We compute the effects of soft-gluon emission to all orders. We present numerical results at the Tevatron and the LHC., Comment: Presented at the 31st International conference of High energy physics, ICHEP, Amsterdam, July 2002. Typos corrected

We consider Higgs boson production through gluon--gluon fusion in hadron collisions, when a veto is applied on the transverse momenta of the accompanying hard jets. We compute the QCD corrections to this process at NLO and NNLO, and present numerical results at the Tevatron and the LHC., Comment: 5 pages, 4 ps figures, presented at the XXXVIIth Rencontres de Moriond, QCD and Hadronic interactions, Les Arc1800, France

This Report documents the results obtained by the Working Group on Quantum ChromoDynamics and the Standard Model for the Workshop ``Physics at TeV Colliders'', Les Houches, France, 21 May - 1 June 2001. The account of uncertainties in Parton Distribution Functions is reviewed. Progresses in the description of multiparton final states at Next-to-Leading Order and the extension of calculations for precision QCD observables beyond this order are summarized. Various issues concerning the relevance of resummation for observables at TeV colliders is examined. Improvements to algorithms of jet reconstruction are discussed and predictions for diphoton and photon pi-zero production at the LHC are made for kinematic variables of interest regarding searches for a Higgs boson decaying into two photons. Finally, several improvements implemented in Monte-Carlo event generators are documented.

Report of the Higgs working group for the Workshop `Physics at TeV Colliders', Les Houches, France, 21 May - 1 June 2001. It contains 7 separate sections: A. Theoretical Developments B. Higgs Searches at the Tevatron C. Experimental Observation of an invisible Higgs Boson at LHC D. Search for the Standard Model Higgs Boson using Vector Boson Fusion at the LHC E. Study of the MSSM channel $A/H \to \tau \tau$ at the LHC F. Searching for Higgs Bosons in $t\bar t H$ Production G. Studies of Charged Higgs Boson Signals for the Tevatron and the LHC, Comment: 120 pages, latex, many figures, proceedings of the Workshop `Physics at TeV Colliders', Les Houches, France, 21 May - 1 June 2001, full Author list included in paper. Typos corrected, author list and acknowledgements completed. Convernors: D. Cavalli, A. Djouadi, K. Jakobs, A. Nikitenko, M. Spira, C.E.M. Wagner, W.-M. Yao

We consider Higgs boson production through gluon--gluon fusion in hadron collisions, when a veto is applied on the transverse momenta of the accompanying hard jets. We compute the QCD radiative corrections to this process at NLO and NNLO. The NLO calculation is complete. The NNLO calculation uses the recently evaluated NNLO soft and virtual QCD contributions to the inclusive cross section. We find that the jet veto reduces the impact of the NLO and NNLO contributions, the reduction being more sizeable at the LHC than at the Tevatron., Comment: 22 pages, 12 postscript figures

We consider the region of small transverse momenta in the production of high-mass systems in hadronic collisions. By using the current knowledge on the infrared behaviour of tree-level and one-loop QCD amplitudes at O(alpha_s^2), we analytically compute the general form of the logarithmically-enhanced contributions up to next-to-next-to-leading logarithmic accuracy. By comparing the results with q_T-resummation formulae we extract the coefficients that control the resummation of the large logarithmic contributions for both quark and gluon channels. Our results show that within the conventional resummation formalism the Sudakov form factor is actually process-dependent., Comment: 38 pages, 2 figures included

The TESLA Technical Design Report Part III: Physics at an e+e- Linear Collider, Comment: 192 pages, 131 figures. Some figures have reduced quality. Full quality figures can be obtained from http://tesla.desy.de/tdr. Editors - R.-D. Heuer, D.J. Miller, F. Richard, P.M. Zerwas

We compute the soft and virtual NNLO QCD corrections to Higgs production through gluon-gluon fusion at hadron colliders. We present numerical results obtained at the LHC and at the Tevatron Run II., Comment: latex, 5 pages, presented at the XXXVIth Rencontres de Moriond, QCD and Hadronic interactions, Les Arc1800, France and at the 9th International Workshop on Deep Inelastic Scattering DIS2001, Bologna, Italy

The main production channels of the Higgs boson at hadron colliders are briefly reviewed and recent developments in the calculation of QCD effects are discussed., Comment: Latex, 4 pages. Invited talk given at the XIII italian meeting on high energy physics ``LEPTRE'', Rome April 18-20 2001, to appear in the proceedings

I briefly review the progress in perturbative QCD calculations in LEP era and discuss the prospects for the extension of their accuracy to higher orders., Comment: Latex, 5 pages. Invited talk given at the XIII italian meeting on high energy physics ``LEPTRE'', Rome April 18-20 2001, to appear in the proceedings

We consider QCD corrections to Higgs boson production through gluon-gluon fusion in hadron collisions. Using the recently evaluated two-loop amplitude for this process and the corresponding factorization formulae for soft-gluon bremsstrahlung at O(alpha_s^2), we compute the soft and virtual contributions to the NNLO cross section. We also discuss soft-gluon resummation at next-to-next-to-leading logarithmic accuracy. Numerical results for Higgs boson production at the LHC are presented., Comment: 17 pages, 4 figures included. One note and one reference added

We consider the resummation of the logarithmic contributions to the region of small transverse momenta in the distributions of high-mass systems (lepton pairs, vector bosons, Higgs particles, ....) produced in hadron collisions. We point out that the resummation formulae that are usually used to compute the distributions in perturbative QCD involve process-dependent form factors and coefficient functions. We present a new universal form of the resummed distribution, in which the dependence on the process is embodied in a single perturbative factor. The new form simplifies the calculation of non-leading logarithms at higher perturbative orders. It can also be useful to systematically implement process-independent non-perturbative effects in transverse-momentum distributions. We also comment on the dependence of these distributions on the factorization and renormalization scales., Comment: misprints corrected in Eqs. (6), (7) and (12), results unchanged

We study the region of small transverse momenta in qqbar- and gg-initiated processes with no colored particle detected in the final state. We present the universal expression of the O(alpha_s^2) logarithmically enhanced contributions up to next-to-next-to-leading logarithmic accuracy. From there we extract the coefficients that allow the resummation of the large logarithmic contributions. We find that the coefficient known in the literature as B^{(2)} is process dependent, since it receives a hard contamination from the one loop correction to the leading order subprocess. We present the general result of B^{(2)} for both quark and gluon channels. In particular, in the case of Higgs production, this result will be relevant to improve the matching between resummed predictions and fixed order calculations., Comment: LaTeX, 8 pages. Few typos corrected, particularly Eq.(25). Two references added, to be published in PRL

We study the soft limit of one-loop QCD amplitudes and we derive the process-independent factorization formula that controls the singular behaviour in this limit. This is obtained from the customary eikonal factorization formula valid at tree (classical) level by introducing a generalized soft-gluon current that embodies the quantum corrections. We compute the explicit expression of the soft-gluon current at one-loop order. It contains purely non-abelian correlations between the colour charges of each pair of hard-momentum partons in the matrix element. This leads to colour correlations between (two and) three hard partons in the matrix element squared. Exploiting colour conservation, we recover QED-like factorization for the square of the matrix elements with two and three hard partons., Comment: latex, 20 pages, 4 eps figures

We discuss issues of QCD at the LHC including parton distributions, Monte Carlo event generators, the available next-to-leading order calculations, resummation, photon production, small x physics, double parton scattering, and backgrounds to Higgs production., Comment: 115 pages, Latex, 47 figures, to appear in the Report of the ``1999 CERN Workshop on SM Physics (and more) at the LHC'', S. Catani, M. Dittmar, D. Soper, W.J. Stirling, S. Tapprogge (convenors)

We review the prospects for studies in electroweak physics at the LHC., Comment: 114 pages, ~50 figures (some bitmapped), Latex. S. Haywood, P.R. Hobson, W. Hollik, Z. Kunszt (conveners), the Electroweak Physics Working Group of the `1999 CERN Workshop on SM physics (and more) at the LHC', to appear in the workshop report

We study the infrared behaviour of tree-level QCD amplitudes and we derive infrared-factorization formulae that are valid at any perturbative order. We explicitly compute all the universal infrared factors that control the singularities in the various soft and/or collinear limits at O(as^2)., Comment: latex, 38 pages, 11 eps figures

I consider the singular behaviour of tree-level QCD amplitudes when the momenta of three partons become simultaneously parallel and I discuss the universal factorization formula that controls the singularities of the multiparton matrix elements in this collinear limit., Comment: 3 pages, 1 eps figure, talk given at the DIS99 Workshop, Zeuthen, Germany, April 19-23, 1999

We discuss semi-inclusive Deep Inelastic Scattering (DIS) in the z -> 1 limit, in particular the relationship between fracture functions, generalised cut vertices and Green functions of the composite operators arising in the OPE. The implications, in the spin-polarised case, for testing whether the "proton spin" effect is target-independent are explored. Explicit calculations in (phi^3)_6 theory are presented which are consistent with our observations., Comment: 22 pages, 25 figures, LaTeX 2e; uses graphics package

Inclusive associated production of a light Higgs boson (m_H < m_t) with one jet in pp collisions is studied in next-to-leading order QCD. Transverse momentum (p_T < 30 GeV) and rapidity distributions of the Higgs boson are calculated for the LHC in the large top-quark mass limit. It is pointed out that, as much as in the case of inclusive Higgs production, the K-factor of this process is large (~1.6) and depends weakly on the kinematics in a wide range of transverse momentum and rapidity intervals. Our result confirms previous suggestions that the production channel p+p -> H+jet -> gamma+gamma+jet gives a measurable signal for Higgs production at the LHC in the mass range 100-140 GeV, crucial also for the ultimate test of the Minimal Supersymmetric Standard Model., Comment: 7 pages, 3 eps figures included

We consider the singular behaviour of tree-level QCD amplitudes when the momenta of three partons become simultaneously parallel. We discuss the universal factorization formula that controls the singularities of the multiparton matrix elements in this collinear limit and present the explicit expressions of the corresponding splitting functions. The results fully include spin (azimuthal) correlations up to ${\cal O}(\as^2)$. In the case of spin-averaged splitting functions we confirm similar results obtained by Campbell and Glover., Comment: latex, 10 pages, minor corrections in the references

Present data, both from direct Higgs search and from analysis of electroweak data, are starting to become rather restrictive on the possible values for the mass of the standard model Higgs. We discuss a new physics scenario based on a model with decoupling (both in a linear and in a non linear version) showing how it allows for an excellent fit to the present values of the $\epsilon$ parameters and how it widens the allowed ranges for the Higgs mass (thought as elementary in the linear version, or as composite in the non linear one)., Comment: 10 pages, 3 Figures Latex

Fracture functions and their evolution equations are reviewed. Some phenomenological applications are briefly discussed., Comment: latex, 4 pages including 2 postscript figures; Talk given at the DIS98 Workshop, Brussels, 4-8, 1998

By using Jet Calculus as a consistent framework to describe multiparton dynamics we explain the peculiar evolution equation of fracture functions by means of the recently introduced extended fracture functions., Comment: 12 pages, 1 postscript figure, version to appear on Phys. Lett. B

Cut vertices, a generalization of matrix elements of local operators, are revisited, and an expansion in terms of minimally subtracted cut vertices is formulated. An extension of the formalism to deal with semi-inclusive deep inelastic processes in the target fragmentation region is explicitly constructed. The problem of factorization is discussed in detail., Comment: LaTex2e, 24 pages including 17 postscript figures

I present a calculation of the one particle deep inelastic cross section in the target fragmentation region in (\phi^3)_6. The renormalized cross section gets a large logarithmic correction whose coefficient is precisely the scalar DGLAP kernel. The result is found to be consistent with an extended factorization hypothesis and with infrared power counting., Comment: latex, 11 pages, 5 figures, to appear in the Proceedings of QCD Euroconference 97, Montpellier, July 1997

Using a generalized cut vertex expansion we introduce the concept of an extended fracture function for the description of semi-inclusive deep inelastic processes in the target fragmentation region. Extended fracture functions are shown to obey a standard homogeneous DGLAP-type equation which, upon integration over t, becomes the usual inhomogeneous evolution equation for ordinary fracture functions., Comment: latex, 15 pages including 7 postscript figures

One particle inclusive cross sections in the target fragmentation region are considered and an explicit calculation is performed in (\phi^3)_6 model field theory. The collinear divergences can be correctly absorbed into a parton density and a fragmentation function but the renormalized cross section gets a large logarithmic correction as expected in a two scale regime. We find that the coefficient of such a correction is precisely the scalar DGLAP kernel. Furthermore the consistency of this result with an extended factorization hypothesis is investigated., Comment: latex, 16 pages including 8 postscript figures

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., Comment: 39 pages, 16 Figures, Latex

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., Comment: 13+2 pages, LaTex

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., Comment: 8 pages, 4 Postscript figures, LaTeX (uses epsf), Proceedings of the workshop: Physics with e+e- linear colliders, Annecy, Gran Sasso, Hamburg 1995

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., Comment: 37 pages, LaTeX, 14 figures (uuencoded)

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 \'a 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., Comment: paper unchanged, figure replaced (using new version of uufiles)