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DARKHORIZONS Report Summary

Project ID: 648680
Funded under: H2020-EU.1.1.

Periodic Reporting for period 2 - DARKHORIZONS (Dark Matter and the Early Universe in the LHC Era)

Reporting period: 2017-03-01 to 2018-08-31

Summary of the context and overall objectives of the project

95% of the energy density in the Universe is missing. Some of it is in the form of dark matter which helps explain the structures of galaxies and clusters of galaxies. We would like to learn more about this dark matter.
This is not the first time that mankind has had indirect indications that there might be another form of matter in the Universe which has not been detected, in the 20th century there were indications that mysterious invisible particles existed called neutrinos but initially it was thought that we would never be able to detect them. Eventually these neutrinos were indeed detected and are now well studied, giving us information about the Sun, astrophysics, the Earth and the Universe.
We would like to do the same thing with dark matter, we would like to detect it and then use it to understand the Universe and how it operates. The trouble is that we don't know what the dark matter is or how we might be able to detect it.

There are a class of well motivated models for dark matter which suggest that we should be able to detect it in several ways, by creating the dark matter at particle colliders such as the LHC, by detecting the dark matter in sensitive instruments deep underground and by looking for the dark matter annihilating with itself up in space. There are however a few problems with this class of models. We don't know precisely what form the dark matter might take within the context of these models and we certainly haven't seen any of it yet. What's more as our underground detectors become more and more sensitive, we still haven't seen any indications of the presence of dark matter. As the detectors become more and more sensitive, we expect them to also start to see neutrinos from the Sun and from cosmic rays. These neutrinos create a dangerous background that we are unable to overcome, which will mean that it will be difficult to detect any dark matter, should it show its face in this way.

We also don't know precisely how the dark matter is likely to show up at particle colliders, we have some ideas, but we don't know how well motivated these are. At the same time, the scientists working at the LHC need precise predictions in order to be able to work out exactly what to look for.

The main goals of our project is therefore to think about what kind of agnostic approaches we can take to these models of dark matter. Which particle physics models are most mathematically consistent with the rest of particle physics? What predictions do they make? We are also motivated to learn whether it is possible to mitigate against the neutrino background in dark matter detectors, or, if not, to turn our enemy into our friend and use dark matter detectors to learn more about neutrinos.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

"So far in this project we have developed new ways to build dark matter detectors such that they could in principle screen out many of the neutrinos coming from the Sun. This involves applying techniques from nuclear magnetic resonance imaging normally used in hospitals to dark matter detectors, such that all the atoms in the detector might be aligned in one direction by a magnetic field. We have also studied what we will learn about particle physics when we do detect neutrinos with a dark matter detector, since this will probe a region of energy space that is very different from the normal energies involved in dark matter detection.

We have come up with a new class of models for dark matter at colliders that are still general extensions of the ""standard model"" i.e. the particles that we have already discovered. These new models contain dark matter particles which are anomaly free - they obey some rules of mathematical consistency that we think any particle physics model should obey. Because of these rules, we are able to focus on a smaller subset of the possible types on dark matter that one could imagine. We have worked to help the experimentalists make predictions for this class of models and shown how they might be detected.

We have also looked at quite different models of dark matter called axion models where the dark matter probably cannot be seen at the LHC. We have looked at new ways to detect axion dark matter, for example by looking for clumps of this dark matter as they pass in front of distant galaxies and act as a gravitational lens, momentarily making the stars in those galaxies brighter.

We have also looked at the physics of the early Universe and the dynamics of the particles around in those early times, studying how they might help us understand the initial stage of rapid expansion which we think occurred at the very start of the expansion of the Universe."

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Until the end of the project we hope to further develop our ideas on how to mitigate the neutrino background. The proposed polarised detector that we suggested used Helium-3 which is very expensive to buy in the quantities in which we would require it. We would like to therefore come up with a simpler less expensive idea which might be more easy to carry out in the short term.

We will continue to develop our models for dark matter particles at the LHC and investigate also whether they might shed light on some interesting anomalous results which have lately appeared at the LHCb experiment. We hope and wait for positive results in what is an ongoing search for dark matter on many fronts.
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