The neutral, scalar state uuddss (S) may be compact and relatively deeply bound, in which case it would be very long-lived or stable. Lattice QCD cannot yet reliably calculate the mass, so experiment must be our guide to its existence. I will show that such a particle would have have escaped detection in lab experiments to date and outline experimental strategies to discover it. If the S exists it can be a component of or possibly all of the dark matter, and I will outline some of the consequences and constraints. It can also provide a simultaneous resolution to the muon g-2 anomaly and explanation for why the lattice calculation of the Hadronic Vacuum Polarization disagrees with the experimental determination using the R-ratio method.
The possibility of doing precision measurements at hadron colliders has attracted lots of interest over the last few years. Among other processes, diboson production stands out as a way to probe EW and Higgs dynamics and indirectly constrain New Physics. This kind of process is already studied at LHC, despite being handicapped by the need for decay channels with high uncertainties. The higher luminosity and centre-of-mass energy of the future FCC-hh collider would allow us to probe these processes with rarer but cleaner final states that are inaccessible at the LHC. I will focus on the diphoton leptonic decay channels of the Wh and Zh production processes. I will discuss our study of these channels at the FCC-hh in the SMEFT framework and how doubly differential distributions can be used to gain even better sensitivity to certain higher-dimensional EFT operators. I will also compare our projections with those for future lepton colliders to emphasize their complementarity. Finally, I'll show some preliminary results using the bottom-pair decay channel of the Higgs boson at LHC, HL-LHC and FCC-hh.
I will analyse a class of extensions of the Standard Model through the lens of a novel exact parameterisation. This parameterisation is specially suitable to the analysis of extensions of the Standard Model with non-unitary mixing matrices, like models with vector-like fermions or right-handed neutrinos. The usefulness of this parameterisation is motivated with two example models: A) Standard Model with the addition of nu up and nd down singlet vector-like quarks and B) Standard Model with the addition of nR right-handed neutrinos. A discussion of the models developed under this framework in the following papers: 1711.06229 [hep-ph], 1912.05875 [hep-ph] and 2103.13409 [hep-ph], will follow.
The cosmological constant problem (CCP) and the formulation
of consistent quantum gravity belong to the shortlist of the
most important unsolved fundamental problems of physics. In
the case of CCP the problem is to explain the extremely precise
(55 orders in the Standard Model) fine-tuning between the
independent vacuum part and the induced one, that is a function
of symmetry breaking in the models of particle physics. The
situation with CCP is so difficult that it makes sense to give
up from attempting its solution and accept the need for a fine
tuning between the vacuum and induced counterparts of the
observed energy density of the vacuum. In this case, we meet
the challenging situation with the renormalization group running
of the vacuum or induced summands of the cosmological constant
at low energies.
Assuming the effective approach to quantum gravity and the
Vilkovisky-DeWitt scheme of unique effective action, one can
derive the exact, well-defined, renormalization group running
of the vacuum cosmological constant. It turns out that, owing
to the mentioned fine-tuning with the induced part, this
running imposes severe restrictions on the possible extensions
of the Minimal Standard Model of particle physics, concerning
the magnitude of the vacuum expectation value of the corresponding
Higgs fields.