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Register a new userThe Non-Linear Higgs Legacy of the LHC Run I
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In the recent paper on The Higgs Legacy of the LHC Run I we interpreted the LHC Higgs results in terms of an effective Lagrangian using the SFitter framework. For the on-shell Higgs analysis of rates and kinematic distributions we relied on a linear representation based on dimension-6 operators with a simplified fermion sector. In this addendum we describe how the extension of Higgs couplings modifications in a linear dimension-6 Lagrangian can be formally understood in terms of the non-linear effective field theory. It turns out that our previous results can be translated to the non-linear framework through a simple operator rotation.
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Based on Run I data we present a comprehensive analysis of Higgs couplings. For the first time this SFitter analysis includes independent tests of the Higgs-gluon and top Yukawa couplings, Higgs decays to invisible particles, and off-shell Higgs measurements. The observed Higgs boson is fully consistent with the Standard Model, both in terms of coupling modifications and effective field theory. Based only on Higgs total rates the results using both approaches are essentially equivalent, with the exception of strong correlations in the parameter space induced by effective operators. These correlations can be controlled through additional experimental input, namely kinematic distributions. Including kinematic distributions the typical Run I reach for weakly interacting new physics now reaches 300 to 500 GeV.
We present a comprehensive study of the electroweak interactions using the available Higgs and electroweak diboson production results from LHC Runs 1 and 2 as well as the electroweak precision data, in terms of the dimension-six operators. Under the assumption that no new tree level sources of flavor violation nor violation of universality of the weak current is introduced, the analysis involves 21 operators. We assess the impact of the data on kinematic distributions for the Higgs production at the LHC by comparing the results obtained including the simplified template cross section data with those in which only total Higgs signal strengths are considered. We also compare the results obtained when including the dimension-six anomalous contributions to order $1/Lambda^2$ and to order $1/Lambda^4$. As an illustration of the LHC potential to indirectly learn about specific forms of new physics, we adapt the analysis to constrain the parameter space for a few simple extensions of the standard model which generate a subset of the dimension-six operators at tree level.
We revisit the extraction of the triple electroweak gauge boson couplings from the Large Hadron Collider Run I data on the $W^+W^-$ and $W^pm Z$ productions when the analysis also contains additional operators that modify the couplings of the gauge bosons to light quarks and the gauge boson self-energies. We work in the framework of effective Lagrangians where we consider dimension-six operators and perform a global fit to consistently take into account the bounds on these additional operators originating from the electroweak precision data. We show that the constraints on the Wilson coefficients $f_B/Lambda^2$ and $f_W/Lambda^2$ are modified when we include the additional operators while the limits on $f_{WWW}/Lambda^2$ remain unchanged.
We investigate the prospects for Central Exclusive Production (CEP) of MSSM Higgs bosons at the LHC using forward proton detectors proposed to be installed at 220 m and 420 m distance around ATLAS and / or CMS. We summarize the situation after the first and very successful data taking period of the LHC. The discovery of a Higgs boson and results from searches for additional MSSM Higgs bosons from both the ATLAS and CMS experiments, based on data samples each corresponding to about 25 fb-1, have recently led to a proposal of new low-energy MSSM benchmark scenarios. The CEP signal cross section for the process H/h -> bb and its backgrounds are estimated in these new scenarios. We also make some comments about the experimental procedure if the proposed forward proton detectors are to be used to measure the CEP signal.
Two major problems call for an extension of the Standard Model (SM): the hierarchy problem in the Higgs sector and the dark matter in the Universe. The discovery of a Higgs boson with mass of about 125 GeV was clearly the most significant piece of news from CERNs Large Hadron Collider (LHC). In addition to representing the ultimate triumph of the SM, it shed new light on the hierarchy problem and opened up new ways of probing new physics. The various measurements performed at Run I of the LHC constrain the Higgs couplings to SM particles as well as invisible and undetected decays. In this thesis, the impact of the LHC Higgs results on various new physics scenarios is assessed, carefully taking into account uncertainties and correlations between them. Generic modifications of the Higgs coupling strengths, possibly arising from extended Higgs sectors or higher-dimensional operators, are considered. Furthermore, specific new physics models are tested. This includes, in particular, the phenomenological Minimal Supersymmetric Standard Model. While a Higgs boson has been found, no sign of beyond the SM physics was observed at Run I of the LHC in spite of the large number of searches performed by the ATLAS and CMS collaborations. The implications of the negative results obtained in these searches constitute another important part of this thesis. First, supersymmetric models with a dark matter candidate are investigated in light of the negative searches for supersymmetry at the LHC using a so-called simplified model approach. Second, tools using simulated events to constrain any new physics scenario from the LHC results are presented. Moreover, during this thesis the selection criteria of several beyond the SM analyses have been reimplemented in the MadAnalysis 5 framework and made available in a public database.
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