On the importance of Lorentz structure in the parton model: target mass corrections, transverse momentum dependence, positivity bounds

We show that respecting the underlying Lorentz structure in the parton model has very strong consequences. Failure to insist on the correct Lorentz covariance is responsible for the existence of contradictory results in the literature for the polarized structure function g_2(x), whereas with the correct imposition we are able to derive the Wandzura-Wilczek relation for g_2(x) and the target-mass corrections for polarized deep inelastic scattering without recourse to the operator product expansion. We comment briefly on the problem of threshold behaviour in the presence of target-mass corrections. Careful attention to the Lorentz structure has also profound implications for the structure of the transverse momentum dependent parton densities often used in parton model treatments of hadron production, allowing the k_T dependence to be derived explicitly. It also leads to stronger positivity and Soffer-type bounds than usually utilized for the collinear densities.Comment: RevTeX4, 17 pages, 7 eps figure

Single Spin Asymmetry in Inclusive Pion Production

It is shown how the single spin asymmetry observed in inclusive pion production is related, in the helicity basis, to the imaginary part of the product of two different distribution amplitudes, rather than to the usual quark and gluon distribution functions; there is then no reason why it should be zero even in massless perturbative QCD, provided the quark intrinsic motion is taken into account. A simple model is constructed which reproduces the main features of the data.Comment: (To appear in the proceedings of the XI International Symposium on High Energy Spin Physics, September 15-22, Bloomington, Indiana). 5 pages + 1 figure, LaTeX 2.09, report DFTT47/94, INFNCA-TH-94-21. (figure appended as uuencoded, tar-compressed postscript file; uncompressed ps file available under request from [email protected]

Parton intrinsic motion: suppression of the Collins mechanism for transverse single spin asymmetries in p(transv. polarised) p --> pion + X

We consider a general formalism to compute inclusive polarised and unpolarised cross sections within pQCD and the factorisation scheme, taking into account parton intrinsic motion in distribution and fragmentation functions, as well as in the elementary dynamics. Surprisingly, the intrinsic partonic motion, with all the correct azimuthal angular dependences, produces a strong suppression of the transverse single spin asymmetry arising from the Collins mechanism. As a consequence, and in contradiction with earlier claims, the Collins mechanism is unable to explain the large asymmetries found in p(transv. polarised) p --> pion + X at moderate to large Feynman x_F. The Sivers effect is not suppressed.Comment: LaTeX, 21+1 pages, 1 ps figur

Can the Collins mechanism explain the large transverse single spin asymmetries observed in p(transv. polarized) p --> pion X?

We present a calculation of inclusive polarised and unpolarised cross sections within pQCD and the factorisation scheme, taking into account the parton intrinsic motion, k_T, in distribution and fragmentation functions, as well as in the elementary dynamics. We show, in contradiction with earlier claims, that the Collins mechanism is suppressed and unable to explain the large asymmetries found in p(transv. polarized) p --> pion X at moderate to large Feynman x_F. The Sivers effect is not suppressed.Comment: LaTeX 2e, 5 pages, 1 ps figure, uses ws-procs9x6. Talk delivered by U. D'Alesio at the ``16th International Spin Physics Symposium'', SPIN2004, October 10-16, 2004, Trieste, Ital

The Gluon Sivers Distribution in D production at RHIC

The single transverse spin asymmetry in D meson production at RHIC can provide a clean measure of the gluon Sivers distribution function. At intermediate rapidity, D production is largely dominated by the elementary gg -> c c-bar channel, where there cannot be any transverse spin transfer. Therefore, any transverse single spin asymmetry observed for D's produced in polarized proton-proton interactions can only originate from the Sivers effect in the gluon distribution functions. A sizeable transverse single spin asymmetry measured by PHENIX or STAR experiments would then give direct information on the size of the gluon Sivers distribution function.Comment: 4 pages, 2 postscript figures, talk given by M. Boglione at SPIN04, 16th International Spin Physics Symposium, Trieste, Oct. 11-16 200

General partonic structure for hadronic spin asymmetries

The high energy and large p_T inclusive polarized process, (A, S_A) + (B, S_B) --> C + X, is considered under the assumption of a generalized QCD factorization scheme. For the first time all transverse motions, of partons in hadrons and of hadrons in fragmenting partons, are explicitly taken into account; the elementary interactions are computed at leading order with noncollinear exact kinematics, which introduces many phases in the expressions of their helicity amplitudes. Several new spin and k_T dependent soft functions appear and contribute to the cross sections and to spin asymmetries; we put emphasis on their partonic interpretation, in terms of quark and gluon polarizations inside polarized hadrons. Connections with other notations and further information are given in some Appendices. The formal expressions for single and double spin asymmetries are derived. The transverse single spin asymmetry A_N, for p(transv. polarized) p --> pion + X processes is considered in more detail, and all contributions are evaluated numerically by saturating unknown functions with their upper positivity bounds. It is shown that the integration of the phases arising from the noncollinear kinematics strongly suppresses most contributions to the single spin asymmetry, leaving at work predominantly the Sivers effect and, to a lesser extent, the Collins mechanism.Comment: RevTeX, 46 pages, 5 ps figures. v2: some clarifying comments and appendix on kinematics added, references updated, published versio

The precariousnesses of young knowledge workers. A subject-oriented approach

Over the past decades, a number of EU member states have recorded large rises in the use of temporary employment. Young people are far more likely than other groups to be employed in precarious jobs, independently of their education and skills. In the midst of the global economic-financial crisis, in fact, the assault on the conditions of knowledge workers goes on, according to the different lines of the neoliberalistic logics, which juxtapose with the current precarisation processes like underpayment and misalignment between subjects’ educations and their working activities. How do young precarious knowledge workers recount their experiences? What relation holds between a high education level and the possibility of effectively deploying the competences and skills acquired? How do knowledge workers represent and deal with their precarious conditions? To answer these questions, this article proposes a definition of the concepts of ‘precarity’, ‘precariousness’ and ‘precariat’ and then focuses specifically on the precariousness experienced by young knowledge workers in Italy and the importance of investigating precarisation processes in light of their experiences. Hence, the present article discusses the invisible face of the conditions of young knowledge workers, which collides with the official face. The latter superficially presents them as ‘independent professionals’, although they increasingly experience conditions similar to those of dependent workers and at the same time suffer the effects of the further precarisation brought about by the crisis, but missing trade-unions support or political representation

General helicity formalism for Single and Double Spin Asymmetries in p p --> pion + X

We consider within a generalized QCD factorization approach, the high energy inclusive polarized process p p --> pion + X, including all intrinsic partonic motions. Several new spin and k_T-dependent soft functions appear and contribute to cross sections and spin asymmetries. We present here formal expressions for transverse single spin asymmetries and double longitudinal ones. The transverse single spin asymmetry, A_N, is considered in detail, and all contributions are evaluated numerically. It is shown that the azimuthal phase integrations strongly suppress most contributions, leaving at work mainly the Sivers effect.Comment: LaTeX, 5 pages, 1 eps figure, uses epsfig, wrapfig. Talk delivered by S. Melis at the ``XI Workshop on High Energy Spin Physics'', SPIN 05, September 27 - October 1, 2005, Dubna, Russi

Helicity Formalism and Spin Asymmetries in Hadronic Processes

We present a generalized QCD factorization scheme for the high energy inclusive polarized process, (A, S_A) + (B, S_B) -> C + X, including all intrinsic partonic motions. This introduces many non-trivial azimuthal phases and several new spin and k_T dependent soft functions. The formal expressions for single and double spin asymmetries are discussed. Numerical results for A_N[p(transv. polarized) p -> pi + X] are presented.Comment: 8 pages, 4 ps figures, uses ws-procs9x6.cls and rotating_pr.sty (included). Talk delivered by F. Murgia at the "International Workshop on Transverse Polarisation Phenomena in Hard Processes" (TRANSVERSITY 2005), September 7-10 2005, Como, Ital