Lattice QCD Constraints on the Nuclear Equation of State

Based on the quasi-particle description of the QCD medium at finite temperature and density we formulate the phenomenological model for the equation of state that exhibits crossover or the first order deconfinement phase transition. The models are constructed in such a way to be thermodynamically consistent and to satisfy the properties of the ground state nuclear matter comply with constraints from intermediate heavy--ion collision data. Our equations of states show quite reasonable agreement with the recent lattice findings on temperature and baryon chemical potential dependence of relevant thermodynamical quantities in the parameter range covering both the hadronic and quark--gluon sectors. The model predictions on the isentropic trajectories in the phase diagram are shown to be consistent with the recent lattice results. Our nuclear equations of states are to be considered as an input to the dynamical models describing the production and the time evolution of a thermalized medium created in heavy ion collisions in a broad energy range from SIS up to LHC.Comment: 13 pages, 11 figure

The contribution of the four-parton final states to gamma* gamma* -> hadrons

In the analysis of the total cross section for the gamma* gamma* -> hadrons process, we include the four parton final states, which are part of the O(alpha_s^2) corrections. The four-parton final states contain the diagrams with gluon exchange in the crossed channel, which constitute the leading order of the BFKL resummation. We show that the diagrams with gluon exchange in the crossed channel play an important role in the large Y region, however their contribution to the cross section must be evaluated exactly. In fact, the high-energy limit, which constitutes the kinematic framework of the BFKL resummation, is not sufficiently accurate at LEP2 energies. The inclusion of the diagrams with gluon exchange in the crossed channel reduces the discrepancy between the theory and the LEP2 data collected by the L3 Collaboration, but the data still lie above the theory, even allowing for a large scale uncertainty in the theory. Thus, in order to describe accurately the data for gamma* gamma* -> hadrons in the large Y region, corrections of an order higher than O(alpha_s^2) seem to be necessary.Comment: 32 pages, 10 figures, published versio

Model-independent analysis of Higgs spin and CP properties in the process e+e−→ttˉΦe^+ e^- \to t \bar t \Phi

In this paper we investigate methods to study the $t\bar{t}$ Higgs coupling. The spin and CP properties of a Higgs boson are analysed in a model-independent way in its associated production with a $t\bar{t}$ pair in high-energy $e^+e^-$ collisions. We study the prospects of establishing the CP quantum numbers of the Higgs boson in the CP-conserving case as well as those of determining the CP-mixing if CP is violated. We explore in this analysis the combined use of the total cross section and its energy dependence, the polarisation asymmetry of the top quark and the up-down asymmetry of the antitop with respect to the top-electron plane. We find that combining all three observables remarkably reduces the error on the determination of the CP properties of the Higgs Yukawa coupling. Furthermore, the top polarisation asymmetry and the ratio of cross sections at different collider energies are shown to be sensitive to the spin of the particle produced in association with the top quark pair