Resonances from QCD bound states and the 750 GeV diphoton excess

Abstract

Pair production of colored particles is in general accompanied by production of QCD bound states (onia) slightly below the pair-production threshold. Bound state annihilation leads to resonant signals, which in some cases are easier to see than the decays of the pair-produced constituents. In a previous paper (arXiv:1204.1119) we estimated the bound state signals, at leading order and in the Coulomb approximation, for particles with various spins, color representations and electric charges, and used 7 TeV ATLAS and CMS resonance searches to set rough limits. Here we update our results to include 8 and 13 TeV data. We find that the recently reported diphoton excesses near 750 GeV could indeed be due to a bound state of this kind. A narrow resonance of the correct size could be obtained for a color-triplet scalar with electric charge −4/3 and mass near 375 GeV, if (as a recent lattice computation suggests) the wave function at the origin is somewhat larger than anticipated. Pair production of this particle could have evaded detection up to now. Other candidates may include a triplet scalar of charge 5/3, a triplet fermion of charge −4/3, and perhaps a sextet scalar of charge −2/3.

Exotic colored scalars at the LHC

“…For example, as demonstrated by the non-degenerate quartet scenario (case B in section 5), the data still allow four colored states with m X 250 GeV. In this section we study another way to discover light colored scalars, which might go first through the observation of their QCD bound state [4,5,68]. Moreover, constraints derived from bound state searches are less model dependent, in the sense that they do not depend on the decay mode of X.…”

“…In section 4 we discuss mass splittings within SU(2) W multiplets and the implications for cascade decays. In section 5 we present a benchmark model. Section 6 deals with the unique phenomenology of SU(2) W multiplets, and the footprint it might leave in indirect probes such as electroweak precision measurements (EWPM), Higgs couplings and the renormalisation group evolution of various couplings.…”

“…For exotic states the consequent constraints are often less model dependent than continuum pair production searches (see e.g. [4,5]). …”

Vacuum stability and perturbativity of SU(3) scalars

“…The quartic self-couplings of all multiplets can be made perturbative up to the Planck scale, provided that the mass of S is chosen to be high enough. 10 The vacuum stability conditions allow for some quartic scalar self-couplings to be negative. Nevertheless, we find that λ S < 0 either does not noticeably change the position of the Landau poles or bring them lower.…”

“…There has also been an interest in the phenomenological signals of higher multiplets. The LHC signals have been studied for example for the sextuplet [8,9] which can give rise to a diphoton signal [10]. Both sextuplets [11] and octuplets [12][13][14] can arise in GUTs.…”