A new framework is sketched for the treatment of the hadronisation of a highly-virtual quark and anti-quark jet pair created in electron-positron annihilations. As in such a case, factorization theorem does not work, a new scale-evolution equation is proposed for the fragmentation functions. In this approach, the virtuality of the leading parton (taken to be equal to the mass of the jet it induces) is used as fragmentation scale.
Quark spin effects in hadronization have been recently included in the PYTHIA 8 event generator for the simulation of the deep inelastic scattering (DIS) process off a polarized nucleon target via the external StringSpinner package. The spin effects can be simulated for the production of pseudoscalar mesons using the string+${}^3P_0$ model of polarized quark fragmentation and parametrizations of the transversity PDFs. We present here a major development of StringSpinner which includes the production of vector mesons in the polarized PYTHIA 8 string fragmentation as well as their polarized deca…
One-loop on-shell and off-shell decays $H\rightarrow VV$ with $VV=γγ, Zγ, ZZ$ are presented in this paper. The effects of one-loop on-shell and off-shell Higgs decays in Higgs productions at $e^-e^-$ collisions are also then examined. We find that the impacts of one-loop Higgs decays are significant and they are must be taken into account at $e^-e^-$ collision.
The consistent construction of scattering amplitudes for processes with off-shell initial partons and involving electro-weak interactions is addressed.
We calculate one loop scattering amplitudes for arbitrary number of positive helicity on-shell gluons and one off-shell gluon treated within the quasi-multi Regge kinematics. The result is fully gauge invariant and possesses the correct on-shell limit. Our method is based on embedding the off-shell process, together with contributions needed to retain gauge invariance, in a bigger fully on-shell process with auxiliary quark or gluon line.
A method to define and calculate one-loop amplitudes with an off-shell space-like, or $k_T$-dependent, gluon is presented. It introduces a practical regularization to deal with the divergencies that appear due to linear denominators, and can be applied to arbitarary partonic scattering processes.
Off-shell effects in generalized parton distributions (GPDs) of the pion, appearing, e.g., in the Sullivan process, are considered. Due to the lack of crossing symmetry, the moments of GPDs involve also odd powers of the skewness (longitudinal momentum transfer) parameter, which results in emergence of new off-shell form factors. With current-algebra techniques, we derive exact relations between the four off-shell gravitational form factors of the pion, in analogy to the electromagnetic case. Our results place stringent constraints on the off-shell GPDs of the pion. We provide an explicit real…
We evaluate drag and diffusion transport coefficients comparing a quasi-particle approximation with on-shell constituents of the QGP medium and a dynamical quasi-particles model with off-shell bulk medium at finite temperature T. We study the effects of the width $γ$ of the particles of the bulk medium on the charm quark transport properties exploring the range where $γ< M_{q,g}$. We find that off-shell effects are in general quite moderate and can induce a reduction of the drag coefficient at low momenta that disappear already at moderate momenta, $p \gtrsim 2-3\, \rm GeV$. We also observe a …
