Radiative corrections to the structure functions and sum rules in polarized DIS

The one-loop NLO radiative corrections to the observables in polarized DIS using assumption that a quark is an essential massive particle are considered. If compared with classical QCD formulae the obtained results are identical for the unpolarized and different for polarized sum rules, that can be explained as the influence of the finite quark mass effects on NLO QCD corrections. The explicit expression for one-loop NLO QCD contribution to the structure function g_2 is presented.Comment: 6 pages,1 figure. Talk given at the International Workshop "Symmetry And Spin" - PRAHA-SPIN'9

Reconciling the LEP and Slac Measurements of Sin^2(\Theta_W)

We consider whether a discrepancy between the SLAC and LEP measurements of \Sw can be explained by new physics. We find that only the contribution of a new neutral gauge boson, $Z^\prime$, nearly degenerate with the Z can affect the SLAC measurement while leaving the LEP observables almost unaffected. We briefly discuss possible signals for this new gauge boson, including changes in the $Z$ lineshape when measured with polarised electrons, small changes in $R_b$, $A^e_{FB}$, and larger changes in two jet and $t\bar{t}$ production at hadron colliders.Comment: 8 pages , CERN-TH.7474/94, OUTP9424

The Top Mass Upper Bound and Electroweak Radiative Corrections

We investigated the possibility of introducing sizeable negative corrections to the $\varepsilon_{N1}$ ($\delta \rho$) parameter without affecting $\varepsilon_{N3}$. We have found that a proper vector-like family of fermions can imply such corrections. Differently from supersymmetry \cite{bcf}, this can be realized without introducing light particles easily observable at LEP II. Our example can be of particular interest if no new particle is found at LEP II and the $\varepsilon_{N1}$ value is found to be small compared to the one expected in the case of a large top mass.Comment: 7 pages, Latex, IFUP-TH 3/9

Hard mtm_t Corrections as a Probe of the Symmetry Breaking Sector

Non-decoupling effects related to a large $m_t$ affecting non-oblique radiative corrections in vertices ($Z\bar{b}b$) and boxes ($B$-$\bar{B}$ mixing and $\epsilon_K$) are very sensitive to the particular mechanism of spontaneous symmetry breaking. We analyze these corrections in the framework of a chiral electroweak standard model and find that there is only one operator in the effective lagrangian which modifies the longitudinal part of the $W^+$ boson without touching the oblique corrections. The inclusion of this operator affects the $Z\bar{b}b$ vertex, the $B$-$\bar{B}$ mixing and the CP-violating parameter $\epsilon_K$, generating interesting correlations among the hard $m_t^4 \log m_t^2$ corrections to these observables, for example, the maximum vertex $Z b\bar{b}$ correction allowed by low energy physics is about one percent.Comment: LaTex, 8 pages, 1 postscript figure include

The Effective Use of Precision Electroweak Measurements

Several reasonably model-independent formulations of the implications of new physics for precision electroweak measurements have been developed over the past years, most notably by Peskin and Takeuchi, and by Altarelli \etal. These formulations work by identifying a small, but useful, set of parameters through which new physics often enters into well-measured physical observables. For the theories to which such an analysis applies, this approach greatly streamlines the confrontation with the data. Since the experimentally-allowed range for these parameters has been determined from global fits to the data, theorists need only compute their predictions for these parameters to constrain their models. These methods are summarized here, together with several recent generalizations which permit applications to wider classes of new physics, and which include the original approaches as special cases.Comment: 29 pages, latex, 3 figures available on reques