### Conveners

#### Monday afternoon session 2: Theoretical particle physics

- Rikkert Frederix

Within the framework of the massive O($N$) nonlinear sigma model extended to the next-to-leading order in the chiral counting (for $N=3$ corresponding to the two(-quark)-flavor Chiral Perturbation Theory), we calculate the relativistic six-pion scattering amplitude at low energy up to and including terms $\mathcal{O}(p^4)$. Results for the pion mass, decay constant and the four-pion amplitude...

We present a framework to study the interactions among Nambu-Goldstone bosons (NGB), pseudo-NGB (pNGBs) and gauge bosons in Composite Higgs (CH) models at high energies, including operators of order $\mathcal{O}(p^4)$ and $\mathcal{O}(p^2g^2)$ in the chiral expansion and topological terms.

The set of (p)NGBs comprises the longitudinal modes of electroweak bosons, the Higgs boson, and...

In a few recent papers we introduced the chirality-flow formalism for tree-level scattering processes. This method, which builds on the separate SL(2,C) nature of left- and right-chiral states, makes it possible to directly write down the value of a Feynman diagram as a Lorentz scalar.

In this presentation I will review the method and make outlooks towards tree-level implementations,...

We compute the heavy quark momentum diffusion coefficient during the initial nonequilibrium evolution using QCD effective kinetic theory after an ultrarelativistic heavy-ion collision. We observe that the diffusion coefficient approaches its thermal value during the hydrodynamization process. We also give an introduction to thermalization/hydrodynamization in the weak coupling framework.

In the colour decomposition approach to treating the SU(3) colour gauge group in automated event generators, the size of the colour matrix grows factorially with the number of external particles in the process. As such, the treatment of the colour degrees of freedom becomes the bottleneck for high-multiplicity QCD processes. We propose to utilize the large-$N_C$ expansion to obtain a sparse...

Composite Higgs models together with partial compositeness predict the existence of vector-like top-partners above the TeV scale. A wide class of such models show significant barnching ratio of the top-partners decaying into the third generation quarks and exotic pseudo Goldstone bosons, thus opening up new search topologies at the LHC. We systematically study the exotic decays of the...

I am organising the meeting of the Swedish physical society in Lund next year and would like just 5-10 minutes to present it. I hope it can be mixed with partikeldagarna. The theme will be Swedish accelerator based research.