Abstract
Axion-like particles (ALPs) are ubiquitous in models of new physics explaining some of the most pressing puzzles of the Standard Model. However, until relatively recently, little attention has been paid to its interplay with flavour. In this work, we study in detail the phenomenology of ALPs that exclusively interact with up-type quarks at the tree-level, which arise in some well-motivated ultra-violet completions such as QCD-like dark sectors or Froggatt-Nielsen type models of flavour. Our study is performed in the low-energy effective theory to highlight the key features of these scenarios in a model independent way. We derive all the existing constraints on these models and demonstrate how upcoming experiments at fixed-target facilities and the LHC can probe regions of the parameter space which are currently not excluded by cosmological and astrophysical bounds. We also emphasize how a future measurement of the currently unavailable meson decay D → π + invisible could complement these upcoming searches.
Highlights
Flavoured portal imprints the Standard Model (SM) flavour structure on the dark sector, leading to a variety of new phenomena [5, 6]
We study in detail the phenomenology of Axion-like particles (ALPs) that exclusively interact with up-type quarks at the tree-level, which arise in some well-motivated ultra-violet completions such as QCD-like dark sectors or Froggatt-Nielsen type models of flavour
The key feature in this case is the emergence of a light pseudo Nambu-Goldstone boson which dominantly couples to up-type quarks, which we dub a charming ALP, and which describes the phenomenology of the up-flavoured portal at low energies
Summary
We consider a general ALP, i.e. a pNGB which we will denote a, with flavour-violating couplings to RH up-quarks. The first two benchmarks are motivated by theories of ‘dark QCD’, where the SM is extended with a confining dark sector, composed of nd dark flavours transforming under SU(Nd) These models constitute a particular UV completion of the scenarios we have in mind, where light pNGB bosons do only interact at leading order with the SM RH up-quarks. This is a natural outcome when both sectors are mediated by a scalar, bifundamental of both confining groups, with hypercharge −2/3. To the previous cases, we assume that the anomalous gauge couplings and cH are negligible
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