Contributions to a conference proceedings

In the Standard Model, the $b \to s$ and $b \to d$ flavor-changing neutral currents (FCNC) are induced by loop effects. Rare semileptonic $B$-meson decays originated by these currents are standard channels for testing the Standard Model precisely and in searching for possible physics beyond it. [...]

With the Standard Model being unable to describe the observed baryon asymmetry or dark matter density in the universe, many models of New Physics introduce heavy neutrino species as a possible explanation for these effects. Dirac or Majorana neutrinos with masses above the electroweak scale could be produced at future linear e+e- colliders, such as the Compact LInear Collider (CLIC) or the International Linear Collider (ILC). [...]

Sterile neutrinos are a well motivated facet of the new physics landscape. From their role in the mechanism through which Standard Model (SM) neutrinos acquire mass, to their potential explanation of anomalies in oscillation experiments and even as Dark Matter candidates, these hypothetical particles are thought to play a central part in the near future of particle physics. [...]

Successful running of the LHC at collision energies of 5, 7, 8 and 13 TeV allowed for a wealth of precision tests of the quantum chromodynamics and for significant improvement of the exclusion limits on various exotic processes. Produced in proton-proton collisions at the LHC, the top quark, the most massive fundamental particle, plays important role in tests of self-consistency of the Standard Model and provides new insights into the structure of the proton. [...]

Microbial glycan degradation is essential to global carbon cycling. The marine bacterium Salegentibacter sp. [...]

Bimetallic iron-ruthenium and cobalt-ruthenium nanoparticles with systematic variations in the Fe:Ru and Co:Ru ratios are prepared following an organometallic approach and immobilized on an imidazolium-based supported ionic liquid phase (SILP). Resulting MxRu100-x@SILP materials are characterized by electron microscopy, X-ray diffraction and X-ray absorption spectroscopy, confirming the formation of small, well-dispersed and alloyed zero-valent bimetallic nanoparticles. [...]

We explore whether the axion which solves the strong CP problem can naturally be much lighter than the canonical QCD axion. The $Z_\mathcal{N}$ symmetry proposed by Hook, with $\mathcal{N}$ mirror and degenerate worlds coexisting in Nature and linked by the axion field, is considered and the associated phenomenology is studied in detail. [...]

Insight into the electroweak (EW) and Higgs sectors can be achieved through measurements of vector boson scattering (VBS) processes. The scattering of EW bosons are rare processes that are precisely predicted in the Standard Model (SM) and are closely related to the Higgs mechanism. [...]

Polarization of both beams at a future Linear Collider would be ideal for facing both expected and unforeseen challenges in searches for new physics: fixing the chirality of the couplings and enabling the higher precision for the polarization meas urement itself as well as for polarization-dependent observables, it provides a powerful tool for studying new physics at the future Linear Collider, such as discovering new particles, analyzing signals model-independently and resolving precisely the unde rlying model. Techniques and engineering designs for a polarized-positron source are well advanced. [...]

We review how theorists have been instrumental in launching and developing new experiments in the last decade, and comment on the challenges and opportunities for this program to continue to thrive going forward. This whitepaper is a solicited contribution to the Snowmass2021 Theory Frontier..