The high-luminosity LHC will probe light new particles with masses below the electroweak scale with unprecedented sensitivity. In particular light new gauge bosons or axion-like particles could be discovered in a mass range which is well motivated by several extensions of the Standard Model. This includes direct production of such new particles, exotic Higgs or Z-decays and decays of heavy mesons, and is therefore an important focus of all LHC experiments. These searches are complementary to high precision experiments that can observe the effects of light particles in measurements of fundamental constants and direct searches for fifth forces. Atom interferometry and atomic clock experiments that can probe the same theories have made enormous progress over the last years.
The goal of this workshop is to bring together experts from the experimental and theoretical communities working on searches for light new physics at the LHC and at high-precision experiments and to construct a comprehensive map of the parameter space of different models for light new physics that can be observed or constrained by these experiments. This workshop will explore the complementarity of these different experiments and discuss novel techniques for the discovery of light particles. This workshop will serve as a starting point to guide a program of searches at the LHC and beyond, to maximise the discovery potential for those particles in the upcoming years.