[en] The effective restoration of the chiral U_A( 1) symmetry in strong interactions is studied using the linear chiral SU(3)xSU(3) model at finite temperatures. We find that the disappearance of the chiral anomaly causes a considerable change in the meson mass spectrum. We propose several signals for detecting this chiral phase in ultrarelativistic heavy-ion collisions: The η/π⁰ ratio is enhanced by an order of magnitude, the a₀ is suppressed in the KK(bar sign) mass spectrum, and the scalar κ meson appears as a peak just below the K^*(892) in the invariant πK mass spectrum. (c) 2000 The American Physical Society

[en] Gribov's scenario of supercritical charges in QCD is investigated. We perform a numerical study of the corresponding equation for the Green function of light quarks. This is done in an approximation which neglects all pion contributions. Different types of solutions in the Euclidean region are discussed and the mass function of the quark is calculated. The solutions of the equation are shown to have a qualitatively different behaviour if the strong coupling constant α_s exceeds a critical value α_c=0.43 in the infrared region. Chiral symmetry breaking is found to occur at supercritical coupling. The analytic structure of the solutions is investigated. Earlier results obtained by Gribov are confirmed and extended. (orig.)

[en] The production of high-transverse energy jets in hadron-hadron collisions is sensitive to the presence of new contact interactions between quarks. If proton polarization were available, the measurement of some parity-violating spin asymmetries in one-jet production at large transverse energy would complement the usual search for deviations from the expected QCD cross section. At the same time, unique information on the chirality structure of the new interaction could be obtained. In this context, we compare the potentialities of various pp and p bar p colliders that are planned or have been proposed, with the additional requirement of beam polarization. copyright 1997 The American Physical Society

[en] Using a manifestly gauge-invariant approach we show that the set of low-energy constants in the electroweak chiral Lagrangian currently used in the literature is redundant. In particular, by employing the equations of motion for the gauge fields, one can choose to remove two low-energy constants which contribute to the self-energies of the gauge-bosons. The relation of this result to the experimentally determined values for the oblique parameters S, T and U is discussed. We then evaluate the matching relation between gauge-invariant Green's functions in the full and the effective theory for the case of the standard model with a heavy Higgs boson and compare the results for the independent low-energy constants with those for a simple technicolor model. Since the pattern of the low-energy constants is very different in these two models it may be misleading to mimic any strongly interacting symmetry breaking sector by a heavy Higgs boson. From our investigation we conclude that current electroweak precision data do not really rule out such strongly interacting models. (orig.)

[en] This analysis covers the measurement of differential di-jet event rates in deep inelastic ep scattering at high momentum transfer Q². The measurement is based on data taken with the H1 detector in 1995-97 at HERA. In contrast to Monte Carlo models perturbative QCD calculations in O(α_s²) describe well the measured distributions, obtained with two different jet algorithms. The value of α_s is extracted by comparison of the measurement with these calculations. Using the two jet algorithms the (correlated) results are α_s(M_Z²)=0.119±_0.011^0.009 and α_s(M_Z²)=0.119±_0.010^0.008, respectively. This is in agreement with the world average value of α_s. The measurement also investigates the scale dependence of the strong coupling. The observed dependence confirms the QCD expectation. (orig.)

[en] Deep-inelastic ep scattering data, taken with the H1 detector at HERA, are used to study the event shape variables thrust, jet broadening, jet mass, C parameter and two kinds of differential two-jet rate. The data cover a large range of the four-momentum transfer Q, which is considered to be the relevant energy scale, between 7 GeV and 100 GeV. The Q dependences of the mean values are compared with second order calculations of perturbative QCD applying power law corrections proportional to 1/Q^p to account for hadronization effects. The concept of power corrections is investigated by fitting simultaneously a non-perturbative parameter anti α_p-1 and the strong coupling constant α₃. (orig.)