Elijah Sheridan

We perform a feasibility study to search for axion-like particles (ALPs) using vector boson fusion (VBF) processes at the LHC. We work in an effective field theory framework with cutoff scale Λand ALP mass m_a , and assume that ALPs couple to photons with strength ∝1/Λ. Assuming proton-proton collisions at \sqrts = 13 TeV, we present the total VBF ALP production cross sections, ALP decay widths and lifetimes, and relevant kinematic distributions as a function of m_a and Λ. We consider the a\toγγdecay mode to show that the requirement of an energetic diphoton pair combined with two forward jets with large dijet mass and pseudorapidity separation can significantly reduce the Standard Model backgrounds, leading to a 5σdiscovery reach for 10 \text MeV ≲m_a ≲1 TeV with Λ≲2 TeV, assuming an integrated luminosity of 3000 fb^-1. In particular, this extends the LHC sensitivity to a previously unstudied region of the ALP parameter space.

Extensions of the Standard Model have been attempted from the bottom up and from the top down, yet there remains a largely unexplored middle ground. In this paper, using the Mathematica package LieART, we exhaustively enumerate embeddings of the Standard Model within the class of theories with bifundamental fermions in the product gauge group SU(a) \times SU(b) \times SU(c), with no more generators than E_6, while achieving SM family unification rather than replication. We incorporate simple phenomenological constrains and find 151 unique models, including 9 that have only vector-like particle content beyond the Standard Model (BSM), which we conjecture belong to 5 infinite families of such models. We describe the most viable models: namely, the 9 with strictly vector-like BSM content along with the 29 models we found with no more than 30 BSM chiral particles. These include models with fractional electric charge color singlets, and hence magnetic monopoles with multiple Dirac charge. This latter collection of models predicts chiral particles with masses near the electroweak scale accessible to current and future collider experiments.