Early Universe Vacuum Stability and Beyond the Standard Model Physics

Project Information

EUVSBSMP

Grant agreement ID: 786564

DOI

10.3030/786564

Project closed

EC signature date 28 March 2018

Start date 1 September 2019

End date 31 August 2021

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 136 582,80

EU contribution

€ 136 582,80

Coordinated by

KEEMILISE JA BIOLOOGILISE FUUSIKA INSTITUUT
Estonia

Periodic Reporting for period 1 - EUVSBSMP (Early Universe Vacuum Stability and Beyond the Standard Model Physics)

Reporting period: 2019-09-01 to 2021-08-31

Summary of the context and overall objectives of the project

The discovery of the Higgs boson was a ground breaking achievement, however many of its cosmological implications are yet to be explored. In particular, it recently has become apparent that the vacuum state of the Universe is in fact not a stable one but may cataclysmically decay. Currently, this process is suppressed and for all practical purposes cannot happen, however this might not be the case for the very early stages of cosmological evolution, specifically during or immediately after the cosmic epoch known as inflation when the Universe expands at an exponential rate. All of this is directly linked to the properties of the Higgs boson, whose existence is known, however the final theory of particle physics is currently shrouded in mystery. Neutrino masses and dark matter are just a few examples that do not yet have a proper particle physics explanation, with a large number of different theoretical suggestions proposed.

A vacuum collapse of the state of the Universe during its early stages is in direct conflict with current observations, simply put, we know that the Universe has not collapsed since we are here to observe it. This way of thinking may then be used as a means of constraining physics beyond the standard model of particle physics: many novel particle physics theories designed to address some of the issues dogging the standard model may suffer from a vacuum collapse or mechanisms very similar to it in the early Universe allowing one to effectively rule them out based on the cosmological implications alone, even when their predictions would be in complete agreement with experimental results from particle accelerators.

In a nutshell, the core of this project was to push our knowledge of fundamental particle physics forward by using our understanding of cosmology. The standard model is the most tested theory science knows and so far has been remarkably successful. However, it does have its limitations and probing the vast landscape of theories designed to address these issues is the only way humanity can ever hope to discover theories that explain current observations in a more complete manner. After all, the question “why are we here?” cannot be answered without first having a complete theory of particle physics.

The main objective of this action was thus to investigate all observable consequences from the mechanisms that may lead to vacuum collapse in the early Universe in the framework of beyond standard model particle physics. Furthermore, it was also investigated whether such mechanisms could in fact the be very reason matter (dark or ordinary) exists in the first place.

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

The work done in this project was entirely of theoretical nature. The early stages involved the derivation of novel theoretical tools needed to perform the main objective of the investigation, leading to intermediate yet important results along the way. The bulk of the work consisted of a proof-of-concept calculation that demonstrated the viability of the proposal. Achieving this result required heavy theoretical analysis as well as involving a strong numerical component. Finally, it was studied whether the instability mechanisms could in fact seed matter generation in a non-fatal manner, which also required extensive numerical work in addition to theoretical studies.

Overall, it may be summarized, that the quite non-trivial proposal is in fact viable: novel particle physics bounds can be derived by invoking the vacuum instability mechanisms present in the early Universe. As an intermediate result obtained when deriving the necessary mathematical technology needed for the project, state-of-the-art bounds for the Standard Model vacuum instability during cosmic inflation were discovered. It was also demonstrated that not only are novel bounds generated in this manner but it is also possible to construct viable particle physics models where such mechanisms seed the generation of observable or dark matter.
The results were disseminated to the scientific community via preprints, published articles, conferences and visits, often to quite an enthusiastic response. Beyond disseminating the research and the results to the research community, outreach to the public at large also played a major role in the project. Throughout the action members of the research group continuously interacted with individuals having fears over possible world ending scenarios implied by speculative proposals concerning the possible structure of unknown physical laws. Such fears seem to be rather common, often directed specifically towards the possibility of vacuum collapse and alleviating these worries is something experts of the field can in many cases accomplish.

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)

In a strictly scientific sense, highlighting the applicability and of the ever-increasing understanding and observable results of theoretical cosmology to particle physics may foster new and important ideas and applications as this field is still in its infancy with possibly many important results waiting to be discovered. The work performed here is one of the first to apply the described mechanisms for investigating beyond standard model physics, which likely will seed further studies as the idea was demonstrated to be viable. Quantifying specifically in which ways Early Universe physics can be used as an experimental tool resulting in non-trivial constraints provides a fresh line of attack in order to push elementary particle physics forward. Moreover, it can be said that the usefulness of cosmological observations to particle physics is likely only to increase in the foreseeable future and that the main topic of the project is at the moment one of the most actively studied fields involving the Higgs boson including many renowned researchers in theoretical physics. Therefore, it is quite plausible that this particular line of research will only increase in popularity making the project action a valuable investment of intellectual and scientific capital.

In wider sense a more thorough understanding of the interconnectedness of gravity and the other fundamental forces in the early Universe will lead to a more complete picture of the various epochs of cosmic evolution. Sharpening one's understanding of the cosmos is of significant value to the society at large: it provides a piece to complete the conundrum regarding the history and origin of humanity and life itself. This, undeniably, is of great philosophical value as it lies among the central questions with respect to the human condition.

Main results of the project summarized