Axion-like particles (ALPs) are pseudo Nambu-Goldstone bosons of spontaneously broken global symmetries in high-energy extensions of the Standard Model (SM). This makes them a prime target for future experiments aiming to discover new physics which addresses some of the open questions of the SM. While future high-precision experiments can discover ALPs with masses well below the GeV scale, heavier ALPs can be searched for at future high-energy lepton and hadron colliders. We discuss the reach of the different proposed colliders, focusing on resonant ALP production, ALP production in the decay of heavy SM resonances, and associate ALP production with photons, Z bosons or Higgs bosons. We consider the leading effective operators mediating interactions between the ALP and SM particles and discuss search strategies for ALPs decaying promptly as well as ALPs with delayed decays. Projections for the high-luminosity run of the LHC and its high-energy upgrade, CLIC, the future e + e − ring-colliders CEPC and FCC-ee, the future pp colliders SPPC and FCC-hh, and for the MATHUSLA surface array are presented. We further discuss the constraining power of future measurements of electroweak precision parameters on the relevant ALP couplings. arXiv:1808.10323v1 [hep-ph] 30 Aug 2018Axion-like particles (ALPs) are light, gauge-singlet pseudoscalar particles with derivative couplings to the Standard Model (SM). The name is inspired by the QCD axion, which is the pseudo-Nambu-Goldstone boson associated with the breaking of the Peccei-Quinn symmetry [1][2][3][4], proposed to address the strong CP problem. More generally, ALPs appear in any theory with a spontaneously broken global symmetry and possible ALP masses and couplings to SM particles range over many orders of magnitude. In certain regions of parameter space ALPs can be non-thermal candidates for Dark Matter [5] or, in other regions where they decay, mediators to a dark sector. For large symmetry breaking scales, the ALP can be a harbinger of a new physics sector at a scale Λ which would otherwise be experimentally inaccessible.Since the leading ALP couplings to SM particles scale as Λ −1 , ALPs become weakly coupled for large new-physics scales. Accessing the smallest possible couplings is thus crucial to reveal non-trivial information about a whole new physics sector.Depending on the region in parameter space spanned by the ALP mass and couplings, the search strategies vary greatly. For masses below twice the electron mass, the ALP can only decay into photons and the corresponding decay rate scales like the third power of the ALP mass. Thus, light ALPs are usually long-lived and travel long distances before decaying. Experiments probing long-lived ALPs include helioscopes such as CAST [6], SUMICO [7,8], as well as observations from the evolution of red giant stars [9-11] and the Supernova SN1987a [12,13]. In addition, a set of cosmological constraints from the modification to big-bang nucleosynthesis, distortions of the cosmic microwave background and extragalactic backgrou...
We construct an effective field theory describing the decays of a heavy vector resonance V into Standard Model particles. The effective theory is built using an extension of Soft-Collinear Effective Theory called SCETBSM, which provides a rigorous framework for parameterizing decay matrix elements with manifest power counting in the ratio of the electroweak scale and the mass of the resonance, λv/mV. Using the renormalization-group evolution of the couplings in the effective Lagrangian, large logarithms associated with this scale ratio can be resummed to all orders. We consider in detail the two-body decays of a heavy Z′ boson and of a Kaluza-Klein gluon at leading and subleading order in λ. We illustrate the matching onto SCETBSM with a concrete example of a UV-complete new-physics model.
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