Periodic Reporting for period 1 - HIGGS-BSM-EFT (Higgs and Beyond the Standard ModelEffective Field Theory, systematic developments.)
Reporting period: 2015-04-01 to 2017-03-31
Being fundamental research, the implications for society are long-term. Through training and education of young researchers we prepare them for the future roles in society. In my own research, as EU Marie Curie Fellow, I have co-supervised two PhD students on the topic of this project, and I have also co-supervised two MSc students during this time. Two of these students have moved on to valuable positions in private industry and the third has continued to PhD-studies Oxford University. This is a great example of how the pursuit of fundamental research eventually can be of great benefit to society as a whole. I would also note that three of the four students were female which helps to address the gender imbalance in theoretical particle physics.
The overall objectives of this project are to establish a systematic and complete characterisation of extensions of the Standard Model of particle physics to use in studying data from the Large Hadron Collider, in particular with a view towards its Run II, which is ongoing. At the end of my two-year period I have made very substantial progress towards this overall objective.
The global fit papers are https://arxiv.org/abs/1502.02570 https://arxiv.org/abs/1508.05060 https://arxiv.org/abs/1606.06693. In these works, a global fit to experimental data was developed in the Standard Model effective field theory framework. We incorporated electroweak precision data, low energy data, and data from detectors that operated at the particle accelerators known by their acronyms: PEP, PETRA, TRISTAN, SpS, Tevatron, SLAC, LEPI and LEP II. We demonstrated how previously neglected corrections due to quantum mechanics and even higher order terms in the effective field theory expansion introduce a theoretical error into global fits of this form, and how reducing such errors requires further development of this theoretical formalism. These considerations relax bounds compared to a naive leading order analysis, and show that constraints that rise above the percent level are subject to substantial theoretical uncertainties.
In a parallel series of papers the one loop corrections to important Standard model processes were developed. In https://arxiv.org/abs/1505.02646 and https://arxiv.org/abs/1507.03568 we calculated the one loop corrections to the decay of the Higgs boson to two photons in the Standard Model Effective Field Theory. This is a critical experimental signal of the properties of the Higgs boson, that is expected to be measured with increase precision in the near future at the Large Hadron Collider. We showed how to overcome many technical challenges related to these calculations. In particular we showed how a modified gauge fixing procedure is required to perform these calculations. This calculation was developed to the first example of this form in the literature of a full one loop correction due to the local dimension six operators interfering with the Standard Model, which was reported in the prestigious journal Physical Review Letters. These results showed that for the most precise measurements of Standard Model processes it is clearly required to incorporate one loop corrections of this form in the effective field theory. This lead to a further paper, https://arxiv.org/abs/1611.09879 where we calculated one loop corrections to the decay of the Z boson in the large top Yukawa and Higgs self coupling limit.
These results have been highly cited in the literature, and lead to two prominent invited talks at the international conferences Moriond 2016 and 2017 in order to disseminate the results.
The expected impact of these results on society is long term. These works are aimed at a fundamental advance of our knowledge of the most fundamental theory in physics. Finding deviations in the properties of the Standard Model can lead to profound technological advancements in the long term based on a deeper understanding of a new fundamental theory of physics. This can occur in a manner that is similar to how our understanding of the theory of electromagnetism in the 1800's lead to profound technological change in the last century. Similarly, the development of quantum mechanics in the pursuit of fundamental physics understanding in the last century is currently leading to a revolution in quantum devices. If an advance in our understanding of the most fundamental interactions using these theoretical developments will lead to such long term socio-economic impacts on society is currently unknown. But history argues that such a profoundly beneficial long term return on investment for society as a whole is reasonable to expect.