Periodic Reporting for period 1 - PheNUmenal (Phenomenological implications of neutrino effective theories)
Berichtszeitraum: 2022-09-01 bis 2024-08-31
Particle Physics is the branch of Physics that studies the fundamental components of our Universe—what they are and how they behave. In essence, it seeks to explain what the Universe is made of. Theoretical physics has developed the Standard Model of Particle Physics (SM), one of the most successful theories in Physics. However, the SM fails to account for certain experimental observations, such as those related to neutrino masses or the nature of dark matter in the Universe. Addressing these mysteries is the current driving force in particle physics.
Today, there is a multitude of new theories proposed to extend the SM into a more comprehensive framework capable of explaining these unresolved questions. This variety of theories is collectively referred to as Beyond the Standard Model (BSM) theories, and they often predict the existence of new particles or phenomena. Discovering these would be our best opportunity to validate which BSM theory accurately describes nature. Unfortunately, no current experiments have detected any new signals from these BSM theories, which in turn sets strong constraints on their viability.
The growing number of BSM proposals aimed at addressing these open questions, combined with the lack of new particle discoveries at the LHC, is motivating the use of effective field theories (EFTs) to explore new scenarios. This framework is appealing as it allows the exploration of multiple BSM theories simultaneously. However, this highly active field often overlooks the existence of new light particles, such as sterile neutrinos, which are predicted by many theories that attempt to explain the origin of neutrino masses—one of the most compelling indicators of new physics. As a result, the most widely used EFT extension of the SM, the SMEFT, cannot accommodate several well-motivated BSM scenarios.
In this context, the overarching aim of PheNUmenal was to develop a new framework incorporating sterile neutrinos within the EFT formalism and to identify and classify its most significant experimental implications.
Today, there is a multitude of new theories proposed to extend the SM into a more comprehensive framework capable of explaining these unresolved questions. This variety of theories is collectively referred to as Beyond the Standard Model (BSM) theories, and they often predict the existence of new particles or phenomena. Discovering these would be our best opportunity to validate which BSM theory accurately describes nature. Unfortunately, no current experiments have detected any new signals from these BSM theories, which in turn sets strong constraints on their viability.
The growing number of BSM proposals aimed at addressing these open questions, combined with the lack of new particle discoveries at the LHC, is motivating the use of effective field theories (EFTs) to explore new scenarios. This framework is appealing as it allows the exploration of multiple BSM theories simultaneously. However, this highly active field often overlooks the existence of new light particles, such as sterile neutrinos, which are predicted by many theories that attempt to explain the origin of neutrino masses—one of the most compelling indicators of new physics. As a result, the most widely used EFT extension of the SM, the SMEFT, cannot accommodate several well-motivated BSM scenarios.
In this context, the overarching aim of PheNUmenal was to develop a new framework incorporating sterile neutrinos within the EFT formalism and to identify and classify its most significant experimental implications.
The scientific focus of PheNUmenal followed two main paths. On one hand, it delved into the theoretical aspects of the SMEFT extension to include sterile neutrinos, the vSMEFT. In particular, the project explored the role of neutrino Yukawa couplings, which had largely been overlooked in previous vSMEFT studies, and computed the complete set of one-loop renormalization group evolution (RGE) equations of the theory, complementing and extending existing partial results.
On the other hand, PheNUmenal investigated a wide range of phenomenological implications related to neutrinos and effective field theories (EFTs). Considering the existence of heavy neutrinos, the project examined their impact on low-energy observables, conducting a global analysis to establish general constraints on their existence. It also explored their potential signals at high-energy colliders, such as the LHC. Regarding EFTs, PheNUmenal investigated rare processes forbidden in the Standard Model (SM), setting model-independent constraints on processes involving the emission of two photons. More broadly, it carried out the first global analysis of the lepton flavor violating (LFV) sector of the SMEFT. By integrating both neutrino and EFT frameworks, PheNUmenal analyzed the impact of incorporating bounds from neutrino non-standard interactions (NSI) into the global SMEFT framework, as well as deriving bounds for LFV vSMEFT operators due to the RGE effects from their Yukawa interactions.
Additionally, in parallel with its main objectives, PheNUmenal also examined the role of massive neutrinos in cosmology. This investigation was motivated by recent findings from the DESI collaboration, which set stringent constraints on the absolute neutrino mass scale, presenting a tension with the current understanding from neutrino oscillation experiments. The study offered a critical analysis of the status quo, highlighting the importance of cosmological models, statistical approaches, and the handling of systematics when setting cosmological bounds for neutrino masses.
As a result of this research, PheNUmenal published eight research articles in international journals and presented its findings at eight international conferences and workshops, also publishing two additional proceedings. All these contributions show the deep impact of current experimental facilities in the search of new physics in neutrino and EFT frameworks.
On the other hand, PheNUmenal investigated a wide range of phenomenological implications related to neutrinos and effective field theories (EFTs). Considering the existence of heavy neutrinos, the project examined their impact on low-energy observables, conducting a global analysis to establish general constraints on their existence. It also explored their potential signals at high-energy colliders, such as the LHC. Regarding EFTs, PheNUmenal investigated rare processes forbidden in the Standard Model (SM), setting model-independent constraints on processes involving the emission of two photons. More broadly, it carried out the first global analysis of the lepton flavor violating (LFV) sector of the SMEFT. By integrating both neutrino and EFT frameworks, PheNUmenal analyzed the impact of incorporating bounds from neutrino non-standard interactions (NSI) into the global SMEFT framework, as well as deriving bounds for LFV vSMEFT operators due to the RGE effects from their Yukawa interactions.
Additionally, in parallel with its main objectives, PheNUmenal also examined the role of massive neutrinos in cosmology. This investigation was motivated by recent findings from the DESI collaboration, which set stringent constraints on the absolute neutrino mass scale, presenting a tension with the current understanding from neutrino oscillation experiments. The study offered a critical analysis of the status quo, highlighting the importance of cosmological models, statistical approaches, and the handling of systematics when setting cosmological bounds for neutrino masses.
As a result of this research, PheNUmenal published eight research articles in international journals and presented its findings at eight international conferences and workshops, also publishing two additional proceedings. All these contributions show the deep impact of current experimental facilities in the search of new physics in neutrino and EFT frameworks.
PheNUmenal has significantly advanced the state of the art in neutrino physics and effective field theories through several key contributions:
1. It derived the most stringent bounds on the existence of sterile neutrinos with masses heavier than the electroweak scale.
2. It provided a comprehensive picture of the lepton flavor violating sector within the SMEFT framework.
3. It quantified the impact of neutrino non-standard interaction (NSI) bounds on the global SMEFT framework.
4. It computed the complete one-loop RGEs for the dimension-6 vSMEFT framework.
5. It established new bounds for lepton flavor violating vSMEFT operators.
6. It derived model-independent upper limits for lepton flavor violating diphoton processes.
7. It quantified the role of sterile neutrino mass splittings in the context of colliders and leptogenesis.
8. It performed a critical analysis of the cosmological bounds on the absolute neutrino mass scale following recent results from the DESI collaboration, quantifying how these bounds are modified when different statistical approaches or systematics are considered.
These results have a profound impact on the high-energy physics community, influencing both theorists and experimentalists working in neutrino physics, effective field theories, flavor physics, collider studies, and cosmology. The final contribution, in particular, is of great significance to the entire community, as determining the absolute neutrino mass scale remains one of the most critical challenges in high-energy physics today.
1. It derived the most stringent bounds on the existence of sterile neutrinos with masses heavier than the electroweak scale.
2. It provided a comprehensive picture of the lepton flavor violating sector within the SMEFT framework.
3. It quantified the impact of neutrino non-standard interaction (NSI) bounds on the global SMEFT framework.
4. It computed the complete one-loop RGEs for the dimension-6 vSMEFT framework.
5. It established new bounds for lepton flavor violating vSMEFT operators.
6. It derived model-independent upper limits for lepton flavor violating diphoton processes.
7. It quantified the role of sterile neutrino mass splittings in the context of colliders and leptogenesis.
8. It performed a critical analysis of the cosmological bounds on the absolute neutrino mass scale following recent results from the DESI collaboration, quantifying how these bounds are modified when different statistical approaches or systematics are considered.
These results have a profound impact on the high-energy physics community, influencing both theorists and experimentalists working in neutrino physics, effective field theories, flavor physics, collider studies, and cosmology. The final contribution, in particular, is of great significance to the entire community, as determining the absolute neutrino mass scale remains one of the most critical challenges in high-energy physics today.