Thesis

New theoretical approaches in the context of LHC: increasing precision with 4-dimensional regularization methods

• Call:

  PT-CERN Call 2022/2

• Academic Year:

  2022

• Domain:

  Astroparticle Physics

• Supervisor:

  Brigitte Hiller

• Co-Supervisor:

  Adriano Cherchiglia

• Institution:

  Universidade de Coimbra

• Host Institution:

  CFISUC - Centro de Fisica da Universidade de Coimbra

• Abstract:

  Computation of Feynman amplitudes involves the emergence of divergences in the loop integrals. As a consequence it is necessary the development of regularization and renormalization techniques that allow for a consistent treatment and removal of these divergences in a simple way. Implicit Regularization (IReg) is a regularization scheme that operates on the physical dimension of the theory and allows for an unambiguous separation of ultraviolet (UV) and infrared (IR) divergences to arbitrary loop order, making it an alternative to dimensional regularization methods. Nevertheless, compliance between IReg and KLN theorem is not yet proved and a systematic treatment of IR divergences to n-order is yet to be implemented. IReg has been applied to diverse physical computations to two-loop order processes spanning abelian and non-abelian theories with and without supersymmetry. It has been proved to fullfill unitarity, Lorenz invariance and locality. Being a non-dimensional scheme, IReg allows for a systematic treatment of objects that are only well defined in the dimension of the theory such as gamma5 matrices. In this work we will compute a set of processes which will serve as probes for the development of practical computations to deal with UV and IR divergences and test the compliance between IReg and the KLN theorem at NLO and beyond. We intend to consider processes involving scattering and decay of Standard Model particles, both with massive and massless particles in the final state first at NLO. These computations aim not only to shed light on the compliance of IReg to the KLN theorem but also to study the technique in a framework where different scales and physicals thresholds are present. Once the NLO computations are well established, we propose to address the N2LO contribution for the same set of processes described. In accomplishing these tasks, computational routines will be developed, which will help in the dissemination of the IReg method.