Final Report Summary - NSFLHC (New Strong Forces at the Large Hadron Collider)
Summary
The Large Hadron Collider (LHC) has started to uncover some of the fundamental mysteries of particle physics. With the discovery of a new scalar boson at 126 GeV, announced the 4th of July 2012, a new era in the understanding of fundamental interactions and the elementary constituents has opened up. Yet, many questions remain unanswered: What is the origin of the observed asymmetry between electromagnetic and weak interactions? What is the origin of electron and quark masses?
What is the dark matter of the universe made of? What is the origin of the observed matter-antimatter asymmetry? In order to answer (some of) these questions from a theoretical standpoint severalmodels have been proposed. Among these the most thoroughly analyzed are the standard model and supersymmetry. A very intriguing possibility is that the symmetry between electromagnetic and weak interactions is broken dynamically by a new kind of strong force, known as Technicolor (TC).
Although very appealing, TC has received less attention than competing theories, because its strong nature makes it more difficult to analyze. However in the past few years a lot of progress has been made to understand strong dynamics, and we are in a position to make specific predictions about the signatures of TC at colliders. Based on the recent findings, we have aimed at analyzing the most relevant aspects of TC phenomenology at the LHC, and proposed new mechanisms for fermion mass generation in the context of TC theories.
The timing of the project could not have been more appropriate. In the midst of it a new boson has been discovered with properties similar to the scalar predicted in the SM. A full class of theories/models, such as those predicting no boson at all, has been excluded and the new data has been included in the model-building activity, the main activity of this project.
Objectives
The activity of the team has been aimed at uncovering properties of WTC and analyze its signatures at the LHC. First studies of WTC LHC signatures exist for the “strawman model”, which is based on topcolour dynamics, and the minimal Higgsless model. In this project the LHC analysis has been extended to the most recent models of pure WTC. The analysis of WTC phenomenology is based on effective theories, in which the bound states are treated as ordinary fields interacting with the known particles. Three main objectives are:
1) Analysis of the properties of technimesons and technibaryons in WTC and interactions with elementary particles
Analysis of this type includes:
Higgs phenomenology Composite Higgs production and decay has been studied in a systematic and complete way, including constraints from unitarity of pion-pion scattering, and by adding Lagrangian terms for decays into photons and gluons. The enhancement of Higgs producton in association with the W or the Z boson should be investigated in the simplest effective theory (with the smallest number of vector mesons) as in [13], but including the Higgs interactions with vector meson kinetic terms, which have proved to be important in TC dynamics. The associate Higgs production should also be investigated in nonminimal models, with a richer vector boson spectrum. If the composite spin-0 isospin-0 state is broad, and thus does not behave like the SM Higgs, the analysis for production and decay should be modified accordingly. Technipions phenomenology Several TC models feature technipions in their spectra. These are pseudoscalar bound states produced in the symmetry breaking mechanism, which are massless in certain limits. Thus technipions are expected to be lighter than other bound states, and their collider phenomenology is therefore relevant. Vector meson phenomenology Vector meson production and decay plays an important role in TC phenomenology, because of the mixing with the electroweak gauge bosons. The main results obtained in the literature can be extended by considering nonminimal vector meson sectors, and studying the interplay between “Drell-Yan” and vector boson fusion production for different values of the parameters. It is very important to find ways to discriminate TC from theories which can provide similar signatures in the spin-1 channels, like for example little-Higgs models.
Flavour physics in TC Effective field theory formalism allows the parametrization of flavour physics without knowing the details of the fermion mass generation mechanism. This can be done either by assuming minimal flavour violation or allowing for more general interactions. In either case the effect of flavour violation or heavy flavour (third generation fermions) can be analyzed in the effective theory. Particularly interesting is the question of CP violation, especially in light of the recently measured evidence for nonstandard sources at Tevatron.
2) Analysis of WTC signatures at the LHC
The effective Lagrangian for WTC theories has been implemented in FeynRules, a software for extracting the interaction vertices. These are then used for authomated computation of matrix elements (for example with MadGraph) to extract signal and background for the different processes. Full event generators (for example Pythia or MadEvent) are then employed to simulate LHC processes. This involves the most recently implemented techniques, like matching of matrix elements and parton showers. A complete analysis of this type is stil lacking for pure WTC theories (i.e. without additional mechanisms like top-color condensation).
Besides this “top-down” approach, it is also important to focus on the “inverse LHC problem”: learning from data back to the effective Lagrangian. The tools and implementation in the FeynRules/MadGraph/Pythia/detector-simulation chain and the idea of an effective Lagrangian allows to perfom also the up-stream learning process in collaboration with the experimentalists.
3) Model building and analysis for fermion mass generation
Ordinary ETC models and supersymmetric extensions have been studied. These will have an impact on the effective theories of TC, allowing specific predictions for flavour physics. This kind of work is more of a theoretical type, and is highly constrained by the peculiar pattern of flavour symmetry breaking in the quark and lepton sectors.
Results
The research activity performed in CP3 has lead to 5+2 publications also in collaborations with members of the research group, showing also the effective capability of Dr. Foadi to independently lead projects and collaborations.
The Large Hadron Collider (LHC) has started to uncover some of the fundamental mysteries of particle physics. With the discovery of a new scalar boson at 126 GeV, announced the 4th of July 2012, a new era in the understanding of fundamental interactions and the elementary constituents has opened up. Yet, many questions remain unanswered: What is the origin of the observed asymmetry between electromagnetic and weak interactions? What is the origin of electron and quark masses?
What is the dark matter of the universe made of? What is the origin of the observed matter-antimatter asymmetry? In order to answer (some of) these questions from a theoretical standpoint severalmodels have been proposed. Among these the most thoroughly analyzed are the standard model and supersymmetry. A very intriguing possibility is that the symmetry between electromagnetic and weak interactions is broken dynamically by a new kind of strong force, known as Technicolor (TC).
Although very appealing, TC has received less attention than competing theories, because its strong nature makes it more difficult to analyze. However in the past few years a lot of progress has been made to understand strong dynamics, and we are in a position to make specific predictions about the signatures of TC at colliders. Based on the recent findings, we have aimed at analyzing the most relevant aspects of TC phenomenology at the LHC, and proposed new mechanisms for fermion mass generation in the context of TC theories.
The timing of the project could not have been more appropriate. In the midst of it a new boson has been discovered with properties similar to the scalar predicted in the SM. A full class of theories/models, such as those predicting no boson at all, has been excluded and the new data has been included in the model-building activity, the main activity of this project.
Objectives
The activity of the team has been aimed at uncovering properties of WTC and analyze its signatures at the LHC. First studies of WTC LHC signatures exist for the “strawman model”, which is based on topcolour dynamics, and the minimal Higgsless model. In this project the LHC analysis has been extended to the most recent models of pure WTC. The analysis of WTC phenomenology is based on effective theories, in which the bound states are treated as ordinary fields interacting with the known particles. Three main objectives are:
1) Analysis of the properties of technimesons and technibaryons in WTC and interactions with elementary particles
Analysis of this type includes:
Higgs phenomenology Composite Higgs production and decay has been studied in a systematic and complete way, including constraints from unitarity of pion-pion scattering, and by adding Lagrangian terms for decays into photons and gluons. The enhancement of Higgs producton in association with the W or the Z boson should be investigated in the simplest effective theory (with the smallest number of vector mesons) as in [13], but including the Higgs interactions with vector meson kinetic terms, which have proved to be important in TC dynamics. The associate Higgs production should also be investigated in nonminimal models, with a richer vector boson spectrum. If the composite spin-0 isospin-0 state is broad, and thus does not behave like the SM Higgs, the analysis for production and decay should be modified accordingly. Technipions phenomenology Several TC models feature technipions in their spectra. These are pseudoscalar bound states produced in the symmetry breaking mechanism, which are massless in certain limits. Thus technipions are expected to be lighter than other bound states, and their collider phenomenology is therefore relevant. Vector meson phenomenology Vector meson production and decay plays an important role in TC phenomenology, because of the mixing with the electroweak gauge bosons. The main results obtained in the literature can be extended by considering nonminimal vector meson sectors, and studying the interplay between “Drell-Yan” and vector boson fusion production for different values of the parameters. It is very important to find ways to discriminate TC from theories which can provide similar signatures in the spin-1 channels, like for example little-Higgs models.
Flavour physics in TC Effective field theory formalism allows the parametrization of flavour physics without knowing the details of the fermion mass generation mechanism. This can be done either by assuming minimal flavour violation or allowing for more general interactions. In either case the effect of flavour violation or heavy flavour (third generation fermions) can be analyzed in the effective theory. Particularly interesting is the question of CP violation, especially in light of the recently measured evidence for nonstandard sources at Tevatron.
2) Analysis of WTC signatures at the LHC
The effective Lagrangian for WTC theories has been implemented in FeynRules, a software for extracting the interaction vertices. These are then used for authomated computation of matrix elements (for example with MadGraph) to extract signal and background for the different processes. Full event generators (for example Pythia or MadEvent) are then employed to simulate LHC processes. This involves the most recently implemented techniques, like matching of matrix elements and parton showers. A complete analysis of this type is stil lacking for pure WTC theories (i.e. without additional mechanisms like top-color condensation).
Besides this “top-down” approach, it is also important to focus on the “inverse LHC problem”: learning from data back to the effective Lagrangian. The tools and implementation in the FeynRules/MadGraph/Pythia/detector-simulation chain and the idea of an effective Lagrangian allows to perfom also the up-stream learning process in collaboration with the experimentalists.
3) Model building and analysis for fermion mass generation
Ordinary ETC models and supersymmetric extensions have been studied. These will have an impact on the effective theories of TC, allowing specific predictions for flavour physics. This kind of work is more of a theoretical type, and is highly constrained by the peculiar pattern of flavour symmetry breaking in the quark and lepton sectors.
Results
The research activity performed in CP3 has lead to 5+2 publications also in collaborations with members of the research group, showing also the effective capability of Dr. Foadi to independently lead projects and collaborations.