Effective Lagrangian for a light Higgs-like scalar (1303.3876v4)

Abstract: We reconsider the effective Lagrangian that describes a light Higgs-like boson and better clarify a few issues which were not exhaustively addressed in the previous literature. In particular we highlight the strategy to determine whether the dynamics responsible for the electroweak symmetry breaking is weakly or strongly interacting. We also discuss how the effective Lagrangian can be implemented into automatic tools for the calculation of Higgs decay rates and production cross sections.

• The paper introduces a refined effective Lagrangian framework to describe a light Higgs boson and its interactions beyond Standard Model expectations.
• It incorporates higher-dimensional (dimension-6) operators to capture anomalous couplings, enabling precise predictions for decay rates and production cross sections.
• By updating tools like HDECAY, the work offers actionable insights for distinguishing weak versus strong electroweak dynamics at collider experiments.

Overview of "Effective Lagrangian for a Light Higgs-Like Scalar"

This paper revisits the framework of effective Lagrangians to describe a light Higgs-like boson and focuses on refining the understanding of electroweak symmetry breaking (EWSB) dynamics. It does so by probing whether this process is underpinned by weakly or strongly interacting forces.

Given the discovery of a possible Higgs boson by the LHC, whose mass is approximately 125 GeV, the authors aim to extend the effective Lagrangian approach. This method, which is valid when new physics emerges at a scale much higher than this mass, allows the delineation of the properties of the discovered boson within a model-independent framework. The output of the paper provides formulae necessary for precision predictions of Higgs decay rates and production cross sections, enhancing automatic computation tools.

Contents of the Paper

1. Introduction: The foundational premise is the need for a flexible theoretical landscape to accommodate the new bosonic state found at the LHC. The absence of new particles beyond the Standard Model (SM) and agreement of this observed boson with SM predictions necessitates alternative theoretical formalisms beyond the SM predictions. Effective Lagrangians offer a viable path by parametrizing our lack of knowledge about new physics.
2. Effective Lagrangian Construction:
   • This section formalizes the structure of an effective Lagrangian that describes the interactions of the Higgs doublet with other SM fields beyond the simplest model. These extend to incorporating higher-dimensional operators, specifically dimension-6, to capture deviations in Higgs couplings.
   • The formulation accommodates potential anomalous couplings to fermions and electroweak gauge bosons, and the section also highlights operator effects varying by the mass scale (M) and coupling strength (g*).
3. Constraints and Parameters: Parameters impacting the precision of predictions include electroweak precision data and flavor constraints, particularly relevant for some specific operators like those inducing Flavor-Changing Neutral Currents (FCNC). The constraints imply a minimum threshold for masses of new particles beyond the SM.
4. Numerical Implementation and Simulation:
   • A notable contribution in this work is the adaptation of the widely used HDECAY software to include the extended set of possible Higgs scenarios. This involves updating existing code bases to encapsulate the dimension-6 operators described by the revised effective Lagrangian.
   • Also involved are discussions about renormalization group running and the intricacies surrounding numerical fidelity when the energy approaches the mass scale M.
5. Phenomenological Implications and Future Outlook: Thematic analysis includes juxtaposing scenarios with weak and strong coupling dynamics, notably contrasting these interactions within supersymmetric extensions and composite Higgs models. The utility of the parameter space explored in distinguishing these scenarios at collider experiments, such as the LHC, is stressed.
6. Concluding Discussion: The paper closes on the note that, given experimental findings continue to align with the observed rate patterns, paths beyond SM—theories like minimally extended SM or composite Higgs frameworks—might require reevaluation. Experimental searches for the modifications in cross-sections or angular distributions thus also become pivotal in confirming the effective Lagrangian's assumptions.

Implications and Future Developments

Practically, this model serves as a scaffold for interpreting future LHC results. Within the theoretical field, should the cross-sections calculated under this extended framework deviate from SM predictions, they may hint at phenomena related to strong coupling dynamics yet to be discovered.

Additionally, precision in separate multi-bosonic processes could provide further clues about the Higgs' role in the broader bosonic hierarchy, challenging the existing framework where the Higgs boson simply emerges as a low-energy phenomena typical within an effective potential limit.

In summary, this paper presents a nuanced view of the Higgs boson landscape, mapping and motivating significant alterations to the current theoretical toolbelt, necessitated by ongoing experimental revelations.