The scalar sector of the Randall–Sundrum model Original Research Article

We consider the scalar sector of the Randall–Sundrum model. We derive the effective potential for the Standard Model Higgs-boson sector interacting with Kaluza–Klein excitations of the graviton (hμνn) and the radion (φ) and show that only the Standard Model vacuum solution of ∂V(h)/∂h=0 (h is the Higgs field) is allowed. We then turn to our main focus: the consequences of the curvature-scalar mixing ξRH†H (where H is a Higgs doublet field on the visible brane), which causes the physical mass eigenstates h and φ to be mixtures of the original Higgs and radion fields. First, we discuss the theoretical constraints on the allowed parameter space. Next, we give precise procedures for computing the h and φ couplings given the physical eigenstate masses, mh and mφ, ξ and the new physics scales of the model. Relations among these new-physics scales are discussed and a set of values not far above the smallest values required by precision electroweak constraints and RunI data is chosen. A simple result for the sum of the ZZh and ZZφ squared couplings relative to the ZZhSM squared coupling is derived. We demonstrate that this sum rule in combination with LEP/LEP2 data implies that not both the h and φ can be light. We present explicit results for the still allowed region in the (mh,mφ) plane that remains after imposing the appropriate LEP/LEP2 upper limits coming from the Higgs-strahlung channel. In the remaining allowed region of parameter space, we examine numerically the couplings and branching ratios of the h and φ for several cases with mh=120 GeV and mφ⩽300 GeV. The resulting prospects for detection of the h and φ at the LHC, a future LC and a γγ collider are reviewed. For moderate |ξ|, both the anomalous h→gg coupling and (when mh>2mφ) the non-standard decay channel h→φφ can substantially impact h discovery. Presence of the latter is a direct signature for non-zero ξ. We find that BR(h→φφ) as large as 30–40% is possible when |ξ| is large. Conversely, if mφ>2mh then BR(φ→hh) is generally large. Sensitivity to the model-dependent magnitude of the cubic radion potential term is discussed. We find that detection of a light φ might require the LC. Detection of a heavy φ might need to take into account the φ→hh channel. The feasibility of experimentally measuring the anomalous gg and γγ couplings of the h and φ is examined.