Physics

We investigate the dynamics of a double tearing mode in presence of a shear flow. In fusion devices, the double tearing mode can exist whenever the plasma has two rational surfaces. In such reversed magnetic shear plasma situations, internal transport barrier can be observed [1].

We consider the production of W and Z in p~ collisions with longitudinally polarized protons. We calculate the spin asymmetries of the observed electrons coming from the chain decays: Z ~ fi+6-or W ~ ~, where 6 and b denote the supersymmetric partners of the electron and neutrino followed by 6 ~ e+ "~ (photino). It is found that the resulting asymmetries of such events could greatly help to identify these scalar particles.

A new handed interaction between subconstituents of quarks could be at the origin of some small parity violating effects in one-jet inclusive production. Within a few years, the Relativistic Heavy Ion Collider (RHIC) will be used as a polarized proton-proton collider. In this context, we analyse the possibilities of disentangling some new parity violating effects from the standard spin asymmetries which are expected due to the Standard Model QCD-Weak interference. We also explore the possibilities of placing some more stringent limits on the quark compositeness scale Λ thanks to measurements of such spin asymmetries.

Supernovae searches have shown that a simple matter-dominated and decelerating universe should be ruled out. However a determination of the present deceleration parameter q 0 through a simple kinematical description is not exempt of possible drawbacks. We show that, with a time dependent equation of state for the dark energy, a bias is present for q 0 : models which are very far from the so-called Concordance Model can be accommodated by the data and a simple kinematical analysis can lead to wrong conclusions. We present a quantitative treatment of this bias and we present our conclusions when a possible dynamical dark energy is taken into account.

We calculate explicitly the electromagnetic mass splittings induced within the ground state baryons by the mass difference between the u and d quarks. This is performed in the framework of the non-relativistic potential model with an accurate treatment of the three-body problem. We also discuss the charge radius of the neutron.

Beam polarization would allow the measurement of spin-dependent observable quantities at LHC and SSC. Within this context we complete some previous analysis on the identification of new neutral gauge bosons by extending to some ingenious but more exotic models recently discussed in the literature. Comparison with some alternative models of composite origin is also performed.

In the context of general SU(2) L ⊗ SU(2) R ⊗ U(1) models a relatively light W is still allowed in some scenarios with a heavy right-handed neutrino and a quark mixing matrix U R close to unity. We explore the consequences of the presence of this new charged current on the parity violating spin asymmetries which could be induced in one-jet inclusive production in polarized proton-proton or proton-neutron collisions. Such measurements could be performed within a few years at the Brookhaven Relativistic Heavy Ion Collider (RHIC) running part of the time as a polarized hadronic collider.

We study the production of right-handed W's decaying into Standard WZ bosons at LHC, when one of the proton beams is polarized. We show that the single helicity asymmetry is a sensitive tool to get a handle on the symmetry breaking pattern of the model and also on the value of the ratio ga/gL of the gauge coupling constants. 304

Theoretical and phenomenological arguments are in favor of an elusive new neutral vector boson Z ′ with a relatively low mass, chiral couplings to ordinary quarks and whose couplings to ordinary leptons are suppressed (leptophobia). We point out that this new particle could induce some parity violating spin asymmetries which could be measured soon at the Brookhaven Relativistic Heavy Ion Collider (RHIC), running part of the time as a polarized hadronic collider.

We propose to use massive lepton pair production by polarized protons to study the spin properties of the constituents. We have established restrictive bounds on the up-down asymmetry and we have calculated the proton spin-muon spin asymmetry. Both should be tested experimentally. Many large-p± experiments at high energy are usually interpreted in a parton picture in which hadrons are assumed to be made of constituents. These constituents (valence quarks, antiquarks and gluons) which share the momentum of a fast proton can produce particles at large p± after a single large-angle 2 ~ 2 scattering [1 ]. The hadronic constituents are not spinless objects and one needs to know in the case of a fully polarized proton, how its spin is distributed among them, how well the constituents remember the spin state of the proton. This important question has been partially answered for the valence quarks from recent experiments with polarized electron beams at SLAC which allow one to study spin dependence in deep inelastic scattering [2]. These results show that the asymmetry A "rp is positive, in agreement with the naive parton model [3], but for large x values it grows above 5•9, the SU(6) limit. Although this has to be confirmed by more accurate measurements, there is a tendency for the longitudinally polarized quarks to remember the parent proton's helicity at large x [4] which leads to an asymmetry A~P of 100% for x = 1. Of course, since gluons do not interact directly with leptons and photons, we learn nothing from deep inelastic scattering about their spin distributions within the polarized proton. On the contrary, production of massive lepton pairs in ha&on

In view of a possible upgrade of the RHIC-Spin program at BNL, concerning both the machine and the detectors, we give some predictions concerning the potentialities of New Physics detection with polarized proton beams. We focus on parity-violating asymmetries in one-jet production due to contact terms or to a new leptophobic neutral gauge boson. We comment on the main uncertainties and we compare with unpolarized searches at Tevatron.