arXiv subjects
Publications and source records attributed to P. Gambino.
Recent calculations have significantly decreased the scheme and residual scale dependence of basic radiative corrections of the Standard Electroweak Model. This leads to a theoretically accurate prediction of the W-boson mass M(W), as well as a reduced upper bound for the Higgs boson mass M(H). The implications of a precise M(W) measurement on the M(H) estimate are emphasized.
In the supersymmetric extension of the Standard Model we derive the two-loop QCD corrections to the scalar quark contributions to the electroweak precision observables entering via the rho parameter. A very compact expression is derived for the gluon-exchange contribution. The complete analytic result for the gluino-exchange contribution is very lengthy; we give expressions for several limiting cases that were derived from the general result. The two-loop corrections, generally of the order of 10 to 30% of the one-loop contributions, canbe very significant. Contrary to the Standard Model case, where the QCD corrections are negative and screen the one-loop value, the corresponding corrections in the supersymmetric case are in general positive, therefore increasing the sensitivity in the search for scalar quarks through their virtual effects in high-precision electroweak observables.
We calculate the two-loop QCD correction to the scalar quark contributions to the electroweak gauge-boson self-energies at zero momentum-transfer in the supersymmetric extension of the Standard Model. We then derive the $O(α_s)$ correction to the contribution of the scalar top and bottom quark loops to the rho parameter, which is the most sizable supersymmetric contribution to the electroweak mixing angle and the W-boson mass. The two-loop corrections modify the one-loop contribution by up to 30%; the gluino decouples for large masses. Contrary to the SM case where the QCD corrections are negative and screen the one-loop value, the corresponding corrections in the supersymmetric case are in general positive, increasing the sensitivity in the search for scalar quarks through their virtual effects in high-precision electroweak observables.
The two-loop O(g^4 mt^2/mw^2) corrections are incorporated in the theoretical calculation of MW, sin^2 theta_MSbar(MZ), and sin^2 theta_eff, as functions of MH. The analysis is carried out in a previously proposed MSbar formulation and two novel on-shell resummation schemes. It is found that the inclusion of the new effects sharply decreases the scheme and residual scale dependence of the calculations. QCD corrections are incorporated in two different approaches. Comparison with the world average of sin^2 theta_eff leads to MH= 127 +143 -71 GeV and MW= 80.367 +/- 0.048 GeV, with small variations among the six calculations.
Estimates for longitudinal spin asymmetries which single out new polarized nucleon structure functions in deeply inelastic charged current interactions at HERA energies are given, exploiting their interpretation in terms of polarized quark distributions. These asymmetries turn out to be large and allow a measurement of the new polarized structure functions $g_1^{W}$ and $g_5^{W}$, which would add valuable tests and information on the spin content of quarks inside a polarized proton. We also show that single spin asymmetries in neutral current interactions are very small.
The O(alpha^2 mt^2/mw^2) correction to the relation between G_μand the vector boson masses is computed in the MSbar scheme, and the results are used to investigate the magnitude of the effect on the theoretical prediction of mw and sin^2θ_\msbar(mz) from alpha, G_μ, and mz.
Theoretical uncertainties affecting electroweak observables are reviewed and the relevance of two-loop electroweak radiative corrections for the precision tests of the Standard Model is discussed.
The assumption that two-loop top corrections are well approximated by the $O(G_mu^2 mt^4)$ contribution is investigated. It is shown that in the case of the ratio neutral-to-charged current amplitudes at zero momentum transfer the $O(G_mu^2 mt^2 M_Z^2)$ terms are numerically comparable to the $m_t^4$ contribution for realistic values of the top mass. An estimate of the theoretical error due to unknown two-loop top effect is presented for a few observables of LEP interest.
We present the QCD corrections to Higgs boson self-energies for arbitrary momentum transfer and for different internal quark masses, to treat the case of CP--even, CP--odd and charged Higgs bosons which appear in extensions of the Standard Model scalar sector. Using Ward Identities, we then relate these results obtained by directly evaluating the relevant two--loop Feynman diagrams to the known expressions for the electroweak vector boson vacuum polarization functions. Finally, we derive the exact analytical expressions for the QCD corrections to the decays of these Higgs particles into quark pairs in the general case, and reproduce in a completely independent way known results in some special cases.
At proton colliders, Higgs particles are dominantly produced in the gluon--gluon fusion mechanism. The Higgs--gluons coupling is mediated by heavy quark loops, and the process can serve to count the number of heavy strongly interacting particles whose masses are generated by the Higgs mechanism. We present the two--loop leading electroweak radiative correction to this coupling, which is quadratically proportional to the heavy quark masses. It turns out thatthis correction is well under control across the physically interesting quark mass ranges.
A comprehensive analysis of deep inelastic scattering of polarized charged leptons on polarized nucleons is presented; weak interaction contributions, both in neutral and charged current processes, are taken into account and the parity violating polarized nucleon structure functions are studied. Possible ways of their measurements and their interpretations in the parton model are discussed.
We present strong indirect evidence for the contribution of bosonic electroweak corrections in the Standard Model. Although important conceptually, these corrections give subleading contributions in current high energy experiments, and it was previously thought that they are difficult to detect. We also discuss the separate contribution of the Higgs boson.
The $O(G^2_μm_t^4)$ correction to the $ρ$ parameter is computed within the Standard Model using the current algebra formulation of radiative corrections. This approach is proved to be equivalent to the effective Lagrangian method proposed by Barbieri {\em et al.} Using the same framework, the $O(G^2_μm_t^2 m_z^2)$ correction to the ratio of neutral-to-charged current amplitudes is analysed in an $SU(2)$ model. The $O(G^2_μm_t^2 m_z^2)$ contribution is shown to be numerically comparable to the leading $O(G^2_μm_t^4)$ term for realistic values of the top mass. The resummation of higher-order effects is discussed.
The relation between $\sef$, frequently employed in LEP analyses, and the $\rm{\overline{MS}}$--parameter $\scr$ is discussed and their difference evaluated by means of an explicit calculation.
We present the (two--loop) QCD corrections to the longitudinal and transverse components of the electroweak gauge bosons self--energies for arbitrary momentum transfer and for different internal quark masses. Compact formulae for both the real and imaginary parts are given in the general case as well as in some physically interesting special cases. The dependence on the definition of the quark masses is discussed.
We derive the QCD corrections to the electroweak gauge bosons vacuum polarization functions at high and zero--momentum transfer in the case of arbitrary internal quark masses. We then discuss in this general case (i) the connection between the $O(αα_S)$ calculations of the vector bosons self--energies using dimensional regularization and the one performed via a dispersive approach and (ii) the QCD corrections to the $ρ$ parameter for a heavy quark isodoublet.