One loop electroweak corrections for single top production at LHC.

In this thesis we report and discuss the results for the first complete calcula- tion of the one-loop electroweak corrections for the two dominant processes of single Top production at the Large Hadron Collider: the tW-associated pro- duction and the t-channel process. We calculate the corrections working both in the Standard Model (SM) and in the minimal supersymmetric extension of the Standard Model (MSSM, as- suming a mSUGRA scenario), analysing the effect of the corrections on several observables and trying to understand whether deviations from the Standard Model prediction could be observable. The single Top production is the main source of information about the Top weak interaction, and a privileged laboratory to understand the symmetry breaking in the weak sector. Moreover at the hadronic colliders the single Top processes provide the only known way to measure directly the Vtb element of the CKM matrix, providing a fundamental test of the Standard Model struc- ture. For the tW production process we present the complete calculation of the one- loop electroweak effect, including the effect of the hard real photon emission; we combine our results with the available calculation for the QCD and SUSY QCD corrections, providing a complete one loop description of the process. Our interest has been concentrated on the particular quantities that we have defined as partial rates, with special emphasis on the low (400 GeV) final in- variant mass. In this region with the addition of SUSY QCD one-loop terms, the genuine SUSY contribution reaches an interesting 10% size. The analysis of t-channel process is limited to the pure electroweak componet (adding the soft photon emission only, to cancel the infrared divergences aris- ing from diagrams with virtual photon). The electroweak corrections for the t-channel are less sensitive to the presence of the SUSY particles: this conclusion holds for all the four examined bench- mark points in themSUGRA scheme. In addition, considering the small contri- bution of the known SUSY QCD corrections, we conclude that in themSUGRA scenario it will be probably impossible to detect at the LHC any deviation from the SM predictions. In the SMcontext the size of the electroweak correctionswithout the hard emis- sion seems to be very large, but we expect that the total effect should be con- siderably reduced adding the hard emission part.