## Journal Club

Seminar Room, Mondays at 14:00

### Monday 7th of March, 2016

# The Quantum Critical Higgs

(Submitted on 25 Nov 2015)

The appearance of the light Higgs boson at the LHC is difficult to explain, particularly in light of naturalness arguments in quantum field theory. However light scalars can appear in condensed matter systems when parameters (like the amount of doping) are tuned to a critical point. At zero temperature these quantum critical points are directly analogous to the finely tuned standard model. In this paper we explore a class of models with a Higgs near a quantum critical point that exhibits non-mean-field behavior. We discuss the parametrization of the effects of a Higgs emerging from such a critical point in terms of form factors, and present two simple realistic scenarios based on either generalized free fields or a 5D dual in AdS space. For both of these models we consider the processesgg→ZZ andgg→hh , which can be used to gain information about the Higgs scaling dimension and IR transition scale from the experimental data.

Presented by M. Perez-Victoria

# Diphoton and Diboson Probes of Fermiophobic Higgs Bosons at the LHC

(Submitted on 3 Mar 2016)

Extensions of the Standard Model Higgs sector with electroweak charged scalars can possess exotic `Higgs' bosons with vanishing or suppressed couplings to Standard Model fermions. These `fermiophobic' scalars, which cannot be produced via gluon fusion, are constrained by LHC measurements of the 125 GeV Higgs boson to have a small vacuum expectation value. This implies that vector boson fusion and associated vector boson production are in general suppressed rendering conventional Higgs searches insensitive. However, Drell-Yan Higgs pair production, which is not present in the SM, can be sizeable even in the limit of vanishing exotic Higgs vacuum expectation value. We utilize this to show that diphoton searches at 8 TeV LHC already rule out a large class of neutral fermiophobic Higgs bosons below around 110 GeV. This includes fermiophobic scalars found in two Higgs doublet as well as Higgs triplet and Georgi-Machacek type models. Our results extend the only relevant limit on fermiophobic Higgs bosons obtained by a recent CDF analysis of4γ+X Tevatron data. Furthermore, diphoton limits are independent of the decay of the second Higgs boson and thus apply even for degenerate masses in contrast to the CDF search. We also find that if the fermiophobic Higgs has very enhanced couplings to photons, masses as large as∼150 GeV can be ruled out while if these couplings are somehow highly suppressed, masses below∼90 GeV can still be ruled out. Finally, we show thatWW andZZ diboson searches may serve as complementary probes for masses above the diphoton limit up to∼250 GeV and discuss prospects at 13 TeV LHC.

Presented by (the authors)