# Johan Rathsman

Senior lecturer

## Soft resummation and hard evolution : Renormalization group methods in effective theories and multi scalar models

Author

## Summary, in English

theoretical particle physics. While paper I is a precision calculation in an

effective theory of the Standard Model, paper II to V all deal with beyond the

Standard Model physics. Paper IV is a manual for the tools developed during our

work on paper II to V.

Paper I. We calculate the 2-loop soft function for the transverse momentum

spectrum of a color-neutral final state in proton collisions in the framework of

Soft-Collinear-Effective Theory. Also the 2-loop beam functions are derived in

the same framework by a comparison to other works. This framework relies on

rapidity renormalization group equations to resum logarithms, which gives an

improved handling of theoretical uncertainties in the resummation. With our

result, one can perform next-to-next-leading log resummation of the mentioned

observable.

Paper II. In this paper, we show that there is no need to introduce scalar

kinetic mixing for models containing several identical scalar fields. This is

shown by an explicit 1-loop calculation of the renormalization group equations

using a toy model. The calculation is performed in separate renormalization

schemes; with and without kinetic mixing. We also derive the renormalization

scale dependent transformations that relate each of these schemes to one

another.

Paper III. This paper analyzes how breaking an imposed Z2 symmetry spreads

during renormalization group evolution of the CP~conserved Two-Higgs-Doublet

Model. We derive the 2-loop renormalization group equations and perform

numerical parameter scans of several physical scenarios.

Paper IV. This is a manual for the software 2HDME that was developed to

perform the numerical calculations in paper III. The code can evolve any

Two-Higgs-Doublet Model at 2-loop order and perform many tree-level calculations

such as masses and oblique parameters, but also tests of stability and

unitarity.

Paper V. In this paper, we use 2HDME in a similar way to paper III, but

this time with the CP~violating Two-Higgs-Doublet Model. We also implement a

calculation of the electron's electric dipole moment that we use to constrain

the amount of CP~violation. We perform several numerical parameter scans of

scenarios with different levels of Z2 symmetry breaking.

Department/s

- Theoretical Particle Physics

Publishing year

2019

Language

English

Full text

Document type

Dissertation

Publisher

Department of Astronomy and Theoretical Physics, Lund University

Topic

- Subatomic Physics

Keywords

- Higgs
- Particle physics
- two-Higgs-doublet model
- Soft-Collinear-Effective Theory
- Renormalization

Status

Published

Supervisor

- Johan Rathsman
- Johan Bijnens

ISBN/ISSN/Other

- ISBN: 978-91-7895-255-7
- ISBN: 978-91-7895-256-4

Defence date

25 October 2019

Defence time

10:00

Defence place

Rydbergssalen, Fysicum, Sölvegatan 14A, Lund

Opponent

- Tilman Plehn (Professor)