Symmetric teleparallel gravity (STG) offers an interesting avenue to formulate a theory of gravitation that relies neither on curvature nor torsion but only on non-metricity Q. Given the growing number of confirmed observations of gravitational waves (GWs) and their use to explore gravitational theories, in this work we investigate the GWs in various extensions of STG, focusing on their speed and polarization. We explore the plethora of theories that this new framework opens up, that is, as general relativity (GR) can be modified, so to can the symmetric teleparallel equivalent of general relativity (STEGR). In this work, we investigate the fate of GWs in the generalized irreducible decomposition of STEGR, generalizations of the STEGR Lagrangian, f (Q), a scalar field nonminimally coupled to the STEGR Lagrangian, and the general setup of f (Q, B) theory where B is the boundary term difference between the Ricci scalar and the STEGR Lagrangian. Coincidentally, f (Q, B) forms a more general theory than f (R) gravity since Q embodies the second order elements of the Ricci scalar while B takes on it's fourth order boundary terms. Our work deals mainly with the resulting scalar-vector-tensor polarization modes of the plethora of STG theories, and how they effect their respective speeds of propagation.

We supply recently obtained results from lattice EQCD with the correct UV limit to construct the collisional broadening kernel C(b⊥) in a QCD plasma. We discuss the limiting behavior of C(b⊥) at small and large impact parameters b⊥, and illustrate how the results can be used to compute medium-induced radiation rates.

We investigate the energy loss and equilibration of highly energetic particles/jets inside a QCD medium. Based on an effective kinetic description of QCD, including 2 ↔ 2 elastic processes, radiative 1 ↔ 2 processes, as well as the back-reaction of jet constituents onto the thermal medium, we describe the in-medium evolution of jets from the energy scale of the jet ∼ E all the way to the medium scale ∼ T. While elastic processes and back-reaction are important to describe the equilibration of soft fragments of the jet, we find that the energy loss is dominated by an inverse turbulent cascade due to successive radiative branchings, which has interesting implications for the energy spectra and chemistry of jet fragments.

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