ALPaca: The ALP Automatic Computing Algorithm

The ALP Automatic Computing Algorithm, ALPaca, is an open source Python library devoted to studying the phenomenology of Axion-Like Particles (ALPs) with masses in the ranges $m_a\in [0.01-10]$ GeV. ALPaca provides a flexible and comprehensive framework to define ALP couplings at arbitrary energy scales, perform Renormalisation Group evolution and matching down to the desired low energy scale, and compute a large variety of ALP observables, with particular care to the meson decay sector. The package includes support for UV completions, experimental constraints, and visualisation tools, enabling both detailed analyses and broad parameter space exploration.