Search

We study QCD axion or cosmological axion-like particles (ALPs) in a model inspired by the recent interest in 4-dimensional clockwork models, with the global symmetry being accidentally enforced by a gauge abelian quiver with scalar bifundamental fields. For the QCD axion, we analyze the connection between the degree of protection of the axion mass against gravitational corrections, the explanation of the hierarchy $f_a \ll M_P$ and the number of colored fermions needed to generate anomalous couplings to gluons, all linked together by the underlying gauge symmetries. Based on that model and on the comparison with earlier models in the literature, we derive certain general conclusions on QCD axion models that use accidental global symmetries. For the ALPs, assuming that their mass is solely given by gravitational corrections, we identify the parameter space where the decay constant and the mass are consistent with the DM abundance, and we show that this clockwork-inspired model is a particularly economical model for a very light ALP DM candidate., Version accepted in EPJC. Discussion extended in the introduction and in section 3.2. 13 pages + appendices, 7 Figures

The hierarchy problem in the Standard Model is usually understood as both a technical problem of stability of the calculation of the quantum corrections to the masses of the Higgs sector and of the unnatural difference between the Planck and gauge breaking scales. Leaving aside the gauge sector, we implement on a purely scalar model a mechanism for generating naturally light scalar particles where both of these issues are solved. In this model, on top of terms invariant under a continuous symmetry, a highly non-renormalizable term is added to the action that explicitly breaks this symmetry down to a discrete one. In the spontaneously broken phase, the mass of the pseudo-Goldstone is then driven by quantum fluctuations to values that are non-vanishing but that are generically, that is, without fine-tuning, orders of magnitude smaller than the UV scale., 5 pages, 1 figure

The calculation of the Higgs mass in general renormalisable field theories has been plagued by the so-called "Goldstone Boson Catastrophe", where light (would-be) Goldstone bosons give infra-red divergent loop integrals. In supersymmetric models, previous approaches included a workaround that ameliorated the problem for most, but not all, parameter space regions; while giving divergent results everywhere for non-supersymmetric models! We present an implementation of a general solution to the problem in the public code SARAH, along with new calculations of some necessary loop integrals and generic expressions. We discuss the validation of our code in the Standard Model, where we find remarkable agreement with the known results. We then show new applications in Split SUSY, the NMSSM, the Two-Higgs-Doublet Model, and the Georgi-Machacek model. In particular, we take some first steps to exploring where the habit of using tree-level mass relations in non-supersymmetric models breaks down, and show that the loop corrections usually become very large well before naive perturbativity bounds are reached., 45 pages, 12 figures

15 pp. (1999)., In a class of models of dynamical symmetry breaking not ruled out by the available data, the lightest neutral pseudo-Nambu-Goldstone boson $P^0$ contains only down-type techniquarks and charged technileptons. Its mass scale is naturally determined by the b-quark and therefore it is likely to be light. As the presence of pseudo-Nambu-Goldstone bosons in models of dynamical symmetry breaking is a quite general feature, the search of the $P^0$ at colliders is an interesting opportunity of putting limits on or discovering a dynamical electroweak symmetry breaking scenario. In this note we discuss the prospects for discovering and studying the $P^0$ at future $e^+e^-$ and gamma-gamma colliders.

230956 60 pp. (1987)., In these lectures I discuss mass issues both In QCD and in the standard electroweak theory. Among the topics treated are masses In the Goldstone sector of QCD, electromagnetic mass shifts and the values of quark masses. Issues connected with the Higgs mechanism and the generation of fermion masses and mixings are also examined, as well as the effect of radiative corrections for the W and Z masses. A general discussion of the U(1) problem, θ-vacua and the strong CP puzzle is given. The consequences of solving the strong CP puzzle by Imposing an additional chlral symmetry In the electroweak interactions are explored and some of the phenomenology of axions is reviewed. The possibility of constructing variant axion models, motivated by recent observations at GSI, is briefly touched upon in closing.