Light custodians in natural composite Higgs models

Abstract

We present a class of composite Higgs models arising from a warped extra dimension that can satisfy all the electroweak precision tests in a significant portion of their parameter space. A custodial symmetry plays a crucial role in keeping the largest corrections to the electroweak observables below their experimental limits. In these models the heaviness of the top quark is not only essential to trigger the electroweak symmetry breaking, but it also implies that the lowest top resonance and its custodial partners, the custodians, are significantly lighter than the other resonances. These custodians are the trademark of these scenarios. They are exotic colored fermions of electromagnetic charges 5/3, 2/3 and −1/3, with masses predicted roughly in the range 500 − 1500 GeV. We discuss their production and detection at the LHC.

Study of the Electroweak Symmetry Breaking Sector for the LHC

“…This last global symmetry undergoes a second breaking to SU (2) L+R . Examples of this kind of models are the (Minimal) Composite Higgs Model (based on the coset SO(5)/SO(4) [78][79][80][81]), dilaton models [82,83],.... This would explain, in a natural way, the presence of a mass gap between the electroweak scale (light EWSBS constituents) and the new physics scale which is shown in fig.…”

“…The top quark is not represented here (M t ≈ 173 GeV). models consider that the EWSBS constituents are pseudo-Goldstone bosons coming from a global symmetry (like SO(5) for the MCHM [78][79][80][81]) which breaks to a global SO(4) ≈ SU (2) L × SU (2) R . This last global symmetry undergoes a second breaking to SU (2) L+R .…”

“…The mass gap between the M W , M Z and M h masses, all of O(100 GeV), and the new physics scale (if there is one within reach), suggests that the Higgs boson and the would-be Goldstone bosons ω ± and z could be (pseudo) Goldstone Boson [111][112][113][114][115][116][117][118], related with a global spontaneous symmetry breaking extending the SU (2) L × SU (2) R → SU (2) L+R global symmetry breaking of the SM. There are several models with specific implementations for the relevant global symmetry breaking pattern: the (Minimal) Composite Higgs Model based on the coset SO(5)/SO(4) [78][79][80][81], dilaton models [82,83] and others [119].…”

Single production of an exotic bottom partner at LHC

“…Partial compositeness gives an economical mechanism to naturally obtain the hierarchy in the fermionic spectrum of the SM (although flavor mixing require some extra ingredients), it also gives rise to a mild separation of scales in the composite sector. Within partial compositeness, the large top mass requires large mixing, simultaneously leading to some top partners with masses parametrically smaller than the composite scale, these are the components of the multiplet that do not mix with the top before EWSB and are usually called custodians [8,9,21]. These states, being usually the lightest new particles, are the leading candidates to direct searches at colliders.…”

“…On the other hand, other common prediction in most of these models of EWSB is the presence of partners of the quarks of the third generation which are lighter than the other new particles [6][7][8][9]. In particular, since the top coupling with the Higgs is order 1, the top quark partners need to be light to stabilize the Higgs potential and keep naturalness.…”