Accidental matter at the LHC

Abstract

We classify weak-scale extensions of the Standard Model which automatically preserve its accidental and approximate symmetry structure at the renormalizable level and which are hence invisible to low-energy indirect probes. By requiring the consistency of the effective field theory up to scales of Λ eff ≈ 10 15 GeV and after applying cosmological constraints, we arrive at a finite set of possibilities that we analyze in detail. One of the most striking signatures of this framework is the presence of new charged and/or colored states which can be efficiently produced in high-energy particle colliders and which are stable on the scale of detectors.

Lepton flavor violation in the inert scalar model with higher representations

“…From figure 8, we can see that, LFV processes in higher scalar representation are more constrained by the current and near-future experiments. In addition, this phenomenological result is complementary to the appearance of low scale Landau pole for higher representations [22,88,89].…”

What is the γγ resonance at 750 GeV?

“…On the other hand for heavy quarks and leptons with conventional charges, the compatibility with experimental data depends on their decay modes. We estimate that stable charged leptons must be heavier than 0.4 TeV in order to avoid excessive Drell-Yan production [34,35]: thereby they cannot be lighter than M/2. An exception is a vector-like lepton that fills a quasi-degenerate multiplet of SU(2) L with a neutral component (which could be the dark matter) as lightest state.…”

Radiative accidental matter

“…Since R should preserve the SM symmetries, as pointed out in [17] fermionic representations should be such that operators of the form …”

“…[22,23], once a lower cutoff scale is allowed (in this case related with neutrino physics constraints) the neutral component contained in the representation decays fast, with typical lifetimes amounting to µs. This observation combined with a lower perturbative scale enables nonvanishing hypercharge sextets, that otherwise would be forbidden [17]. Moreover, in our analysis we will not consider hypercharge-zero septets since their quartic scalar couplings reach Landau poles at rather low scales, ∼ 10 7 GeV [24].…”

“…In the lepton sector despite not being univocally implementable it leads to a consistent picture that in its minimal realizations entails quite a few predictions for lepton flavor-violating processes [16]. Accidental matter, is another interesting approach that although does not aim at addressing the EW hierarchy problem it enables for new order-TeV physics without invoking any special flavor structure [17]. The idea is that the new physics should preserve all the SM exact and approximate symmetries up to a cutoff scale Λ, above which these symmetries are presumably broken by a larger theory.…”