Light Top Partners for a Light Composite Higgs (1204.6333v2)

Abstract: Anomalously light fermionic partners of the top quark often appear in explicit constructions, such as the 5d holographic models, where the Higgs is a light composite pseudo Nambu-Goldstone boson and its potential is generated radiatively by top quark loops. We show that this is due to a structural correlation among the mass of the partners and the one of the Higgs boson. Because of this correlation, the presence of light partners could be essential to obtain a realistic Higgs mass. We quantitatively confirm this generic prediction, which applies to a broad class of composite Higgs models, by studying the simplest calculable framework with a composite Higgs, the Discrete Composite Higgs Model. In this setup we show analytically that the requirement of a light enough Higgs strongly constraints the fermionic spectrum and makes the light partners appear. The light top partners thus provide the most promising manifestation of the composite Higgs scenario at the LHC. Conversely, the lack of observation of these states can put strong restrictions on the parameter space of the model. A simple analysis of the 7-TeV LHC searches presently available already gives some non-trivial constraint. The strongest bound comes from the exclusion of the 5/3-charged partner. Even if no dedicated LHC search exists for this particle, a bound of 611 GeV is derived by adapting the CMS search of bottom-like states in same-sign dileptons.

• The paper demonstrates that achieving a light composite Higgs requires at least one sub-TeV top partner to generate the observed 120 GeV mass.
• It employs the Discrete Composite Higgs Model (DCHM) to analytically link the masses of fermionic resonances with electroweak symmetry breaking.
• The study emphasizes that the non-observation of such light top partners at the LHC would significantly constrain composite Higgs models and naturalness tuning.

Analysis of Light Top Partners for a Light Composite Higgs

This paper investigates the implications of light fermionic partners of the top quark in composite Higgs models, particularly focusing on their role in achieving a realistic Higgs mass. Through an analytical framework, the authors elucidate the correlation between the mass of these top partners and the Higgs boson within a broad class of composite Higgs models, particularly highlighting their analysis using the Discrete Composite Higgs Model (DCHM).

The authors begin by contextualizing the challenges facing the Standard Model (SM) Higgs, especially addressing naturalness concerns that could hint at a more intricate structure around the TeV scale. The composite Higgs, envisioned as a pseudo Nambu-Goldstone Boson (pNGB), emerges as a dynamic field offering a solution to these naturalness issues, attributed to its light mass in comparison to the strong sector resonances.

The core argument presented is that achieving a suitably light Higgs mass necessitates the presence of anomalously light top partners. These partners emanate from the composite sector and mix with the SM top quark, providing an interaction mechanism that is pivotal for generating both the Higgs potential and top quark mass. The paper articulates that these light top partners are not merely an incidental artifact of model building but result from the fundamental structural correlation between the Higgs boson mass and the mass of its fermionic partners.

Through the utilization of the Discrete Composite Higgs Model (DCHM), the paper provides a calculable framework to confirm these theoretical insights, illustrating the constraints imposed on the fermionic spectrum necessary for a light Higgs. The findings suggest that a minimum of one top partner must be within the sub-TeV range to ensure the Higgs mass conforms with the empirically observed values around 120 GeV. This correlation suggests that the composite Higgs scenario could manifest visibly at the LHC, offering an experimental avenue for validation or refutation.

From a theoretical standpoint, the paper asserts that the mass of these partners is integral in tuning the parameters to achieve realistic Electroweak Symmetry Breaking (EWSB). The paper employs the DCHM to articulate the interplay between the fermionic resonances and mixing angles that impose naturalness constraints demanding light partners. The framework's analytic nature allows for a robust confirmation of these theoretical assertions.

Moreover, the paper addresses the experimental implications, emphasizing how the lack of observation of such light top partners would significantly constrain the parameter space of composite Higgs models. Preliminary LHC analyses, as discussed in the paper, already exclude certain mass ranges, such as 5/3-charged partners below 611 GeV, by adapting searches for bottom-like states.

This research contributes to the theoretical landscape by enhancing our understanding of how structural constraints within the composite Higgs framework necessitate light, potentially detectable, top partners. The discussion opens up promising avenues for future experimental investigations at the LHC and guides the theoretical extension of composite Higgs models in seeking configurations that adhere to anticipated phenomenological outcomes.

In summary, this paper underscores the pivotal role of light top partners within the composite Higgs paradigm, firmly suggesting that their detection is crucial for verifying the predictive power and viability of such models in addressing the shortcomings of the SM. Future research could delve into varied embeddings of fermion representations or explore models allowing multiple mixing origins to assess the robustness of these conclusions across broader theoretical contexts.