Towards composite Higgs: minimal coset from a regular bottom-up holographic model

Abstract

We study a bottom-up, holographic description of a field theory yielding the spontaneous breaking of an approximate SO(5) global symmetry to its SO(4) subgroup. The weakly-coupled, sixdimensional gravity dual has regular geometry. One of the dimensions is compactified on a circle that shrinks smoothly to zero size at a finite value of the holographic direction, hence introducing a physical scale in a way that mimics the effect of confinement in the dual four-dimensional field theory. We study the spectrum of small fluctuations of the bulk fields carrying SO(5) quantum numbers, which can be interpreted as spin-0 and spin-1 bound states in the dual field theory. This work supplements an earlier publication, focused only on the SO(5) singlet states. We explore the parameter space of the theory, paying particular attention to composite states that have the right quantum numbers to be identified as pseudo-Nambu-Goldstone Bosons (PNGBs).We find that in this model the PNGBs are generally heavy, with masses of the same order as other bound states, indicating the presence of a sizeable amount of explicit symmetry breaking in the field theory side. But we also find a qualitatively new, unexpected result. When the dimension of the field-theory operator inducing SO(5) breaking is close to half of the space-time dimensionality, there exists a region of parameter space in which the PNGBs and the lightest scalar are both parametrically light in comparison to all other bound states of the field theory. Although this region is known to yield metastable classical backgrounds, this finding might be relevant to model building in the composite Higgs context.

Sp(2N) Lattice Gauge Theories and Extensions of the Standard Model of Particle Physics

“…and Refs. [69][70][71][72][73][74][75][76][77]), many of which also implement top (partial) compositeness [78] (see also Refs. [79][80][81]).…”

“…We must mention that an alternative way to study strongly coupled dynamics is based upon gauge-gravity dualities; special strongly-coupled field theories admit an equivalent description as weakly coupled theories of gravity living in higher dimensions [129][130][131][132]. Indeed, the recent revival of interest on CHMs started before the Higgs discovery, driven by extra-dimensional models inspired by gauge/gravity dualities, and based on the minimal SO(5)/SO(4) coset [69][70][71][72][73][74][75][76][77]. More recently, progress has been made towards building semi-realistic descriptions of the dynamics of the more complex CHMs that are amenable to lattice studies, but in the context of bottom-up holography [133][134][135][136].…”

Holographic Non-Abelian Flavour Symmetry Breaking

“…It is natural to also apply them to strongly coupled models of Beyond the Standard Model (BSM) physics. For example, holographic studies of technicolour and Composite Higgs were performed in [20,[25][26][27][28][29][30][31][32][33][34]. Recently, some of the authors of the present paper have used a bottom-up holographic approach that retains some essential features of the D3/D7 top-down probe brane model [12,14,35] to investigate the meson spectrum and the top partner baryons for a large class of Composite Higgs models presented in [36][37][38][39].…”