[Paper Review] A Little KK Graviton at 750 GeV

Barry M. Dillon, Verónica Sanz|arXiv (Cornell University)|Mar 31, 2016

Cosmology and Gravitation Theories3 citations

TL;DR

This paper proposes a holographic Composite Higgs model with a Little Randall-Sundrum setup to explain the 750 GeV diphoton excess as a Kaluza-Klein graviton, resolving tensions with precision and vector resonance constraints by placing the Higgs and top quark in the IR of the extra dimension. The model requires a low UV scale (~1000 TeV), explaining the resonance's absence in direct searches, and suggests 4D gravity may not be fundamental in the strongly coupled sector.

ABSTRACT

The standard experimental interpretation of the diphoton excess as a Kaluza-Klein graviton faces issues of compatibility with other constraints, particularly precision tests and direct searches for vector resonances. In this work we explain how to successfully incorporate this interpretation in the context of a holographic Composite Higgs setup, with the Higgs and top localised in the IR region of the extra dimension. We find that successful scenarios fall in the category of the so-called Little Randall-Sundrum models, as they require a low UV-scale of around 1000 TeV, which could explain why the resonance has so far evaded other searches. The scenario we find has an interesting dual interpretation in terms of partial compositeness. In particular, 4D gravity may not necessarily be involved in the dynamics of the strongly coupled sector, from which the Higgs and a 750 GeV spin-2 state would arise as composites.

Motivation & Objective

• To resolve the tension between the 750 GeV diphoton excess and existing experimental constraints on precision tests and vector resonances.
• To embed the diphoton resonance as a Kaluza-Klein graviton in a holographic Composite Higgs framework with IR-localized Higgs and top quark.
• To show that a low UV scale (~1000 TeV) in a Little Randall-Sundrum setup naturally explains the resonance's absence in direct searches.
• To explore the dual interpretation in terms of partial compositeness, where 4D gravity may not be fundamental to the strongly coupled sector.

Proposed method

• Adopt a holographic realization of the Composite Higgs model with a warped extra dimension.
• Localize the Higgs and top quark in the IR region of the extra dimension to suppress flavor-changing processes.
• Implement a Kaluza-Klein graviton state at 750 GeV as the resonance observed in diphoton decays.
• Use the Little Randall-Sundrum mechanism to set a low UV cutoff (~1000 TeV), reducing coupling strength and evading direct detection.
• Analyze the model's compatibility with precision electroweak constraints and vector resonance searches.
• Employ the partial compositeness framework to interpret the Higgs and spin-2 state as composite states from a strongly coupled sector.

Experimental results

Research questions

• RQ1 Can the 750 GeV diphoton resonance be consistently interpreted as a Kaluza-Klein graviton within a holographic Composite Higgs model?
• RQ2 How can the model reconcile the resonance with stringent constraints from precision measurements and vector resonance searches?
• RQ3 What role does the UV scale play in suppressing the resonance's couplings and evading direct detection?
• RQ4 Does the model allow for a scenario where 4D gravity is not fundamental to the strongly coupled dynamics?
• RQ5 How does the partial compositeness framework reinterpret the origin of the Higgs and spin-2 state in this setup?

Key findings

• The 750 GeV diphoton resonance can be consistently interpreted as a Kaluza-Klein graviton in a holographic Composite Higgs model with IR-localized Higgs and top quark.
• The model requires a low UV scale of approximately 1000 TeV, which suppresses couplings and explains the resonance's absence in direct searches.
• The Little Randall-Sundrum mechanism successfully reconciles the resonance with precision electroweak constraints and vector resonance bounds.
• The scenario allows for a dual interpretation in terms of partial compositeness, where the Higgs and spin-2 state emerge as composites from a strongly coupled sector.
• 4D gravity may not be fundamental to the dynamics of the strongly coupled sector, as the composite states arise independently of fundamental gravity.