S. De Curtis

Effective Weak Interaction Theory with Possible New Vector Resonance from a Strong Higgs Sector

Abstract We consider the effective lagrangian for electroweak interactions in the limit of a strong interacting Higgs sector ( m H → ∞). We assume that the appearing SU(2) v hidden local symmetry is realized through a new dynamical vector boson resonance V. We derive the physical admixtures and masses of W, Z and V bosons and calculate the couplings of the physical bosons to fermions. No physical Higgs remains in the spectrum. We find that the standard low energy phenomenology of weak interactions, as well as the W-, Z-masses and properties, may be rather closely reproduced in our effective theory, even for low values of the mass of the new vector resonance, within presently accessible energies.

Non-Linear realization of supersymmetry algebra from supersymmetric constraint

Abstract We discuss spontaneous symmetry breaking of global supersymmetry for a single scalar superfield in an arbitrary Kahler manifold. We show that when the curvature of the manifold goes to infinity (or, equivalently, the masses of the scalar partners of the goldstino go to infinity) a non-linear realization of supersymmetry is obtained. The model can be described, in perfect analogy to the ordinary σ-models, by means of a supersymmetric constraint on the superfield Φ, of the form Φ2=0. The non-linear realization we obtain is different from that of Volkov and Akulov. The differences among the two realizations are discussed.

Physical implications of possible J = 1 bound states from strong Higgs

Abstract A strongly interacting Higgs sector could give rise to new bound states. Among them, spin-1 bosonic states would, through their mixing with γ, W and Z, significantly modify some phenomenological predictions. For a first attempt at describing such a situation we have employed the local hidden symmetry formulation of the non-linear σ-model, used as a simulation of the strong Higgs sector, and have conjectured the appearance of the boson kinetic term. The relatively simple description that we obtain allows for a calculation of the mixing and couplings, for a fit of all the low-energy phenomenology, and for a discussion of the experimental predictions. In particular, we find that accurate measurements of the W and Z masses could permit a test of these ideas.

Chiral-symmetry breaking in QCD at finite temperature and density

Abstract We make a theoretical study of chiral symmetry breaking for a QCD-like gauge theory at finite temperature and density. We use a composite-operator functional formalism based on an effective action extending previous calculations for zero temperature and density. Study of the phase diagram shows the existence on the critical line of a point separating second order from first order phase transitions.

Low energy strong electroweak sector with decoupling.

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.

A gravitino-goldstino high-energy equivalence theorem

Abstract We show that in spontaneously broken supergravity S-matrix elements with longitudinally polarized gravitinos are asymptotically equal, to order m 3 2 s , to corresponding matrix elements where each longitudinally polarized gravitino is replaced by the corresponding goldstino.

Moose models with vanishing S parameter

In the linear moose framework, which naturally emerges in deconstruction models, we show that there is a unique solution for the vanishing of the S parameter at the lowest order in the weak interactions. We consider an effective gauge theory based on K SU(2) gauge groups, K+1 chiral fields, and electroweak groups SU(2){sub L} and U(1){sub Y} at the ends of the chain of the moose. S vanishes when a link in the moose chain is cut. As a consequence one has to introduce a dynamical nonlocal field connecting the two ends of the moose. Then the model acquires an additional custodial symmetry which protects this result. We examine also the possibility of a strong suppression of S through an exponential behavior of the link couplings as suggested by the Randall Sundrum metric.

Playing with fermion couplings in Higgsless models

We discuss the fermion couplings in a four dimensional SU(2) linear moose model by allowing for direct couplings between the left-handed fermions on the boundary and the gauge fields in the internal sites. This is realized by means of a product of nonlinear {sigma}-model scalar fields which, in the continuum limit, is equivalent to a Wilson line. The effect of these new nonlocal couplings is a contribution to the {epsilon}{sub 3} parameter which can be of opposite sign with respect to the one coming from the gauge fields along the string. Therefore, with some fine-tuning, it is possible to satisfy the constraints from the electroweak data.

Bounds on new physics from the new data on parity violation in atomic cesium

Abstract We assume the latest experimental determination of the weak charge of atomic cesium and analyze its implications for possible new physics. We notice that the data would imply positive upper and lower bounds on the new physics contribution to the weak charge, δNQW. The required new physics should be of a type not severely constrained by the high energy precision data. A simplest possibility would be new neutral vector bosons almost un-mixed to the Z and with sizeable couplings to fermions. The lower positive bound would however forbid zero or negative δNQW and exclude at 99% CL not only the standard model but also models with sequential Z′, in particular simple-minded towers of Z-like excitations from extra-dimensions. The bound would also imply an upper limit on the Z′ mass within the models allowed. Conclusions are also derived for models of four-fermion contact interactions.

SM Kaluza-Klein excitations and electroweak precision tests

Abstract We consider a minimal extension to higher dimensions of the Standard Model, having one compactified dimension, and we study its experimental tests in terms of electroweak data. We discuss tests from high-energy data at the Z -pole, and low-energy tests, notably from atomic parity violation data. This measurement combined with neutrino scattering data strongly restricts the allowed region of the model parameters. Furthermore this region is incompatible at 95% CL with the restrictions from high-energy experiments. Of course a global fit to all data is possible but the χ 2 min for degree of freedom is unpleasantly large.