Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - MadbaM (MadbaM: automated tools for precision calculations of the Baryon Asymmetry of the Universe in BSM models)

Teaser

The origin of the matter that composes our Universe is a relevant open question in modern fundamental physics. The widely established theory that accounts for the nature of fundamental particles and their interactions, known as Standard Model, predicts that after the Big Bang...

Summary

The origin of the matter that composes our Universe is a relevant open question in modern fundamental physics. The widely established theory that accounts for the nature of fundamental particles and their interactions, known as Standard Model, predicts that after the Big Bang the Universe is filled by a thermal plasma containing an equal amount of particles and anti-particles. If that configuration would have existed unchanged until today, as the Universe expands and cools down all particles would eventually annihilate with the corresponding antiparticles, leaving as a result a cold homogeneous Universe filled by low-energetic photons.
This is of course not what we observe today, meaning that at some point in the Universe evolution some asymmetry between the number of particles and anti-particles has been created (it is known as Baryon Asymmetry of the Universe or BAU), which after annihilation results in a net amount of matter that eventually composes what we observe today (galaxies, stars, planets, ourselves, etc.). Since the Standard Model does not provide any viable mechanism for the generation of the BAU, this implies that new (yet undiscovered) physics exists beyond it.
The study of possible solutions to the BAU problem and of their experimental verification represent thus a mean to advance our knowledge on fundamental particles, on their interactions and on the early Universe evolution, in the end deepening our understanding of Nature.
The overall objectives of the action were the theoretical study of the dynamics of leptogenesis (a viable mechanism to account for the BAU) with a focus on realisations that can be tested in current and near future experiments, and the study of the possibility to automate the baryogenesis computation in general scenarios beyond the Standard Model, with the final aim of providing a computer tool for the automated BAU computation.

Work performed

The study on the automation of the computation of general BAU processes consisted in the development of a module that receives as input the quantum theoretical observables of the underlying theory and computes the evolution of the particles in the early Universe as well as the final baryon asymmetry. The work on this module has been paired with the development of specific model files representing realistic and simplified scenarios beyond the Standard Model in the early Universe, that allow for the automated computation of the required quantum theoretical observables. The model files have been validated at the lowest order in the perturbative expansion of the theory, while the next-order accuracy (necessary to perform BAU computations) requires further debugging.
The theoretical study on the leptogenesis dynamics and its testability perspectives resulted in several publications: we deepened the understanding on possible connections between a global symmetry of the Standard Model (the lepton number) with leptogenesis and dark matter, provided new methods for the resolution of the evolution equations in leptogenesis that allowed for an efficient investigation of the considered models, and performed the first systematic analysis of the leptogenesis dynamics in the Standard Model extended with 3 right-handed neutrinos with masses at the GeV scale. In addition we focused on the testability perspectives of the considered models, exploring how the decay of meson and tau lepton particles can allow to look for the particles at the origin of leptogenesis, and we proposed and motivated the search for this kind of particles in the collision of heavy ions at the Large Hadron Collider.
Overall, the project resulted in 3 peer-review papers already accepted for publication, 2 pre-prints currently under peer-review process, the contribution to a community report paper, 5 conference proceedings, 12 talks at international conferences and workshops and 2 seminars before other research groups.

Final results

To the best of our knowledge the project represented the first systematic study on the automation of the BAU computation in general scenarios beyond the Standard Model of particles: it provided the model files describing the Standard Model and its simplest extensions in the early Universe, an algorithm to automatise the computation, and it identified three alternative strategies to achieve the required accuracy to perform automated BAU computations.
The advancements on the theoretical and phenomenological side included the first systematic analysis of the leptogenesis dynamics in the Standard Model extended with 3 right-handed neutrinos with masses at the GeV scale, finding qualitatively new behaviour (as for instance the possibility of a resonant enhancement of the produced asymmetry) and showing the testability of this scenario at the Large Hadron Collider.
We proposed as well a novel search strategy to look for the particles at the origin of the BAU, by employing the collision of heavy ions at the Large Hadron Collider, instead of the conventional protons: we demonstrated that for scenarios in which long-lived particles are produced in the decay of light particles, this search strategy can increase the number of observable events by several orders of magnitude.
Finally we provided predictions for the lepton number violating rate in the Standard Model extended with right-handed neutrinos, for all the 3-body decay channels of charged mesons and tau lepton, considering all the possible initial and final states; this study can help the experimental collaborations that are looking for right-handed neutrinos in the identification of the most suitable search strategies.