New light physics beyond the Standard Model

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The project will involve studying the properties of possible new light particles beyond the Standard Model of particle physics and their astrophysical and cosmological signatures and constraints, with the aim to make predictions relevant to high energy theories, such as string theory, as well as upcoming experimental searches. The initial aim will be to reliably calculate the constraints on Kaluza Klein gravitons coming from the observation of a neutrino burst from supernoava 1987a, correcting previous calculations by taking into account plasma mixing effects (which might change the resulting limits on the coupling constants of such gravitons to visible sector matter by orders of magnitude). Such particles have been (controversially) predicted by string theory models as an inevitable consequence of the cosmological constant, and a strengthened constraint could rule out this scenario or open an avenue to a discovery. Plasma mixing effects have previously been considered for scalars (spin 0) and vectors (spin 1) but this would be the first ever computation for a spin 2 particle. The methodology will involve using techniques from finite temperature field theory to account for the in-medium effects on the production rate, and in particular the possibility of resonant production building on the previous work for the lower spin case. Depending on the results, it might also be interesting to investigate the impact of such finite temperature effects on the cosmological history of Kaluza Klein gravitons; since the Universe was extremely hot at early times such effects could again lead to dramatic changes compared to the previous prediction. This will enable a precise prediction of the Dark Matter relic abundance of such particles (which has previously been only estimated) and it might lead to predictions that can be feed into an experimental search programme. Subsequently, the scope will be widened to consider the constraints on other classes of new particles including axions, which are especially well motivated, as well as possible new light scalars that might play a role in sourcing Dark Energy. Again in this case, finite temperature and density effects have not been consistently accounted for. The overall impact of the project will be 1. On the immediate field of researchers in physics beyond the Standard Model and astroparticle physics. 2. On the field of string theory phenomenology, (part of which) has predicted such new light particles exist. 3. The experimental programme searching for new light particles in the UK and world-wide, by providing predictions and targets and complementary constraints.