Light composite fermions from holography

Abstract

Motivated by Beyond the Standard Model theories of composite fermions or top partners, we propose a holographic mechanism that generates light baryonic states in a strongly coupled gauge theory. The starting point are the fermionic fluctuations of massive probe branes embedded into AdS 5 × S 5 . We first consider the D3/probe D7-brane system. We derive in detail the fermionic fluctuation equations and show the supersymmetric degeneracy of the mesinos with the mesons. Here we view the fermionic mesinos as potential realizations of composite fermions or top partners. We then add higher dimension operators and study their impact on the mesino spectrum. In particular we show that the ground state mesino mass can be pushed to an arbitrarily light value by a suitable choice of the coupling of the higher dimension operator, g. No matter the value of g, the masses of higher excited states never fall below the mass of the ground state at g = 0. We also present similar results for the supersymmetric D3/D3 and D3/D5 systems. arXiv:1907.09489v3 [hep-th]

Gauge/gravity dual dynamics for the strongly coupled sector of composite Higgs models

“…In this paper we have adapted the holographic model of [15] to describe composite Higgs models, including fermionic bound states as in [55], as well as multiple representations of matter. Our holographic approach is inspired by string theory realizations of gauge/gravity duality: the holographic gravity action is based on the top-down DBI action for a probe D7-brane.…”

“…Here we will investigate this dynamics using holography. The D7-brane action, extended to its fermionic sector, naturally describes baryons (super-partners of the mesons) consisting of three fermions (a quark an anti-quark and an adjoint fermion in the root N = 2 theory) as fermionic fields in the DBI action [34,[54][55][56]. We phenomenologically extend this description to describe the top partners which are also usually constructed from three constituents.…”

“…In the D3/probe D7 system some fermionic superpartners of the mesons are made of a quark, an anti-quark and a gaugino and are described by fermionic excitations of the D7 world volume theory [34,54]. Indeed in a preparatory paper we carefully worked through the D3/probe D7 system example [55] (see also [56]) and that work will lead us here. That a three fermion bound state can have such a description in a top down model suggests phenomenologically a proton made of 3 quarks in QCD or the top partners in the models we will discuss below could reasonable be modelled by simply placing a fermion in the bulk.…”

“…Note that we impose these boundary conditions at ρ = L IR rather than at ρ = 0 as in the supersymmetric case in [55,56].…”

Fermions and baryons as open-string states from brane junctions

“…With a formal understanding of the massive embedding in the D3/probe-D7 intersection being a motivation as well as some phenomenological applications of holography and JHEP12(2020)157 the use of fermions in bottom-up models, the authors in [32] studied the top-down massive picture in all probe brane systems in the presence of the D3 background and obtained the expressions for the supergravity states dual to these fermions and the corresponding mass spectra. The work of [33] is also a top-down approach that investigates the D4-D8 setup in Type IIA supergravity and it pertains to the Sakai-Sugimoto model [18].…”