Interpretation of LHC excesses in ditop and ditau channels as a 400-GeV pseudoscalar resonance

ARGANDA, ERNESTO; DA ROLD, LEANDRO; DÍAZ, DANIEL A.; MEDINA, ANIBAL D.

JOURNAL OF HIGH ENERGY PHYSICS - (Online)

Springer

Año: 2021 vol. 2021

1029-8479

Since the discovery in 2012 of the Higgs boson at the LHC, as the last missing piece of theStandard Model of particle physics, any hint of new physics has been intensively searched for,with no confirmation to date. There are however slight deviations from the SM that are worthinvestigating. The CMS collaboration has reported, in a search for heavy resonances decayingin tt̄ with a 13-TeV center-of-mass energy and a luminosity of 35.9 fb −1 , deviations from theSM predictions at the 3.5σ level locally (1.9σ after the look-elsewhere effect).In addition,√in the ditau final state search performed by the ATLAS collaboration at s = 13 TeV andL = 139 fb −1 , deviations from the SM at the 2σ level have been also observed. Interestingly,both slight excesses are compatible with a new pseudoscalar boson with a mass around 400GeV that couples at least to fermions of the third generation and gluons. Starting from apurely phenomenological perspective, we inspect the possibility that a 400-GeV pseudoscalarcan account for these deviations and at the same time satisfy the constraints on the rest ofthe channels that it gives contributions to and that are analyzed by the ATLAS and CMSexperiments. After obtaining the range of effective couplings compatible with all experimentalmeasurements, we study the gauge invariant UV completions that can give rise to this type ofpseudoscalar resonance, which can be accommodated in an SO(6)/SO(5) model with consistencyat the 1σ level and in a SO(5)×U (1) P ×U (1) X /SO(4)×U (1) X at the 2σ level, while exceedinglylarge quartic couplings would be necessary to account for it in a general two Higgs doublet model.