Abstract
Axionlike particles (ALPs) are interesting dark matter candidates from both the theoretical and the experimental perspective. Usually they are motivated as pseudo-Nambu-Goldstone bosons. In this case one of their most important features is that their coupling to other particles is suppressed by a large scale, the vacuum expectation value of the field breaking the symmetry that gives rise to them. This naturally endows them with very weak interactions but also restricts the maximal field value and therefore the regions where sufficient dark matter is produced. In this paper we investigate deviations from this simplest setup, where the potential and interactions are as expected for a pseudo-Nambu-Goldstone boson, but the kinetic term has singularities. This leads to a significantly increased area in parameter space where such particles can be dark matter and can be probed by current and near future experiments. We discuss cosmological limits and in the course of this give a simple derivation of a formula for isocurvature fluctuations in models with general anharmonic potentials. As an application of this formula we give an update of the isocurvature constraints for QCD axion dark matter models, using the most recent results for the QCD topological susceptibility and the newest Planck data.
Highlights
Axions and axionlike particles (ALPs) are a prediction of some of the best-motivated beyond the standard model physics scenarios
In this work we study the viability of ALPs with a noncanonical kinetic term as dark matter candidates from a purely phenomenological perspective
1 2 d lodgloFgTθðθÞ θ0 2 : ð59Þ. We apply this formula for both the canonical quantum chromodynamics (QCD) axion and for our noncanonical model, and obtain the results presented in Figs. 7 and 8, respectively
Summary
Axions and axionlike particles (ALPs) are a prediction of some of the best-motivated beyond the standard model physics scenarios (see, e.g., [1,2,3] for reviews). Some of the theoretically favored existing models require high decay constants for the ALPs to be able to account for all the dark matter energy density that we observe in our Universe. This means that some of the better-motivated combinations of ðm; faÞ are not in the best position to be tested, be it through gravitational interactions or through couplings to gluons and nucleons or photons. While the structure of interactions that we consider is inspired by that of pseudo-Nambu-Goldstone bosons, the essential qualitative features should apply in the case of more general scalars and only depends on the singularities of the noncanonical kinetic terms
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