Rui Santos

Probing wrong-sign Yukawa couplings at the LHC and a future linear collider

We consider the two-Higgs-doublet model as a framework in which to evaluate the viability of scenarios in which the sign of the coupling of the observed Higgs boson to down-type fermions (in particular, b-quark pairs) is opposite to that of the Standard Model (SM), while at the same time all other tree-level couplings are close to the SM values. We show that, whereas such a scenario is consistent with current LHC observations, both future running at the LHC and a future e +e − linear collider could determine the sign of the Higgs coupling to b-quark pairs. Discrimination is possible for two reasons. First, the interference between the b-quark and the t-quark loop contributions to the ggh coupling changes sign. Second, the charged-Higgs loop contribution to the γγh coupling is large and fairly constant up to the largest charged-Higgs mass allowed by tree-level unitarity bounds when the b-quark Yukawa coupling has the opposite sign from that of the SM (the change in sign of the interference terms between the b-quark loop and the W and t loops having negligible impact).

Neutral minima in two-Higgs doublet models

We study the neutral minima of two-Higgs doublet models, showing that these potentials can have at least two such minima with different depths. We analyse the phenomenology of these minima for the several types of two-Higgs doublet potentials, where CP is explicitly broken, spontaneously broken or preserved. We discover that it is possible to have a neutral minimum in these potentials where the masses of the known particles have their standard values, with another deeper minimum where those same particles acquire different masses.

Wrong sign and symmetric limits and non-decoupling in 2HDMs

A bstractWe analyse the possibility that, in two Higgs doublet models, one or more of the Higgs couplings to fermions or to gauge bosons change sign, relative to the respective Higgs Standard Model couplings. Possible sign changes in the coupling of a neutral scalar to charged ones are also discussed. These wrong signs can have important physical consequences, manifesting themselves in Higgs production via gluon fusion or Higgs decay into two gluons or into two photons. We consider all possible wrong sign scenarios, and also the symmetric limit, in all possible Yukawa implementations of the two Higgs doublet model, in two different possibilities: the observed Higgs boson is the lightest CP-even scalar, or the heaviest one. We also analyse thoroughly the impact of the currently available LHC data on such scenarios. With all 8 TeV data analysed, all wrong sign scenarios are allowed in all Yukawa types, even at the 1σ level. However, we will show that B-physics constraints are crucial in excluding the possibility of wrong sign scenarios in the case where tan β is below 1. We will also discuss the future prospects for probing the wrong sign scenarios at the next LHC run. Finally we will present a scenario where the alignment limit could be excluded due to non-decoupling in the case where the heavy CP-even Higgs is the one discovered at the LHC.

Combined effects of strong and electroweak flavor changing neutral current effective operators in top quark physics at the CERN LHC

We study the combined effects of both strong and electroweak dimension six effective operators on flavor changing top quark physics at the CERN LHC. Analytic expressions for the cross sections and decay widths of several flavor changing processes will be presented, as well as an analysis of the feasibility of their observation at the LHC.

Dimension six FCNC operators and top production at the LHC

R.A. Coimbra , P.M. Ferreira , R.B. Guedes , O. Oliveira , A. Onofre , R. Santos ∗∗ and Miguel Won †† 1 LIPDepartamento de F́ısica, Universidade de Coimbra, 3004-516 Coimbra, Portugal; 2 Centro de F́ısica Computacional, Universidade de Coimbra, 3004-516 Coimbra, Portugal; 3 Instituto Superior de Engenharia de Lisboa, Rua Conselheiro Emı́dio Navarro 1, 1959-007 Lisboa, Portugal; 4 Centro de F́ısica Teórica e Computacional, Faculdade de Ciências, Universidade de Lisboa, Avenida Professor Gama Pinto, 2, 1649-003 Lisboa, Portugal; 5 NExT Institute and School of Physics and Astronomy, University of Southampton Highfield, Southampton SO17 1BJ, United Kingdom

Distinctive Higgs signals of a type II two-Higgs-doublet model at the LHC

We perform a numerical analysis of Higgs-to-Higgs decays within a type II two-Higgs-doublet model (2HDM), highlighting several channels that cannot occur in its supersymmetric version, thereby allowing one to possibly distinguish between these two scenarios. Our results are compliant with all available experimental bounds from both direct and indirect Higgs searches and with theoretical constraints from vacuum stability and perturbative unitarity.

Neutral Higgs boson pair production in photon-photon annihilation in the two Higgs doublet model

We study double Higgs production in photon-photon collisions as a probe of the new dynamics of Higgs interactions in the framework of two Higgs doublet models. We analyze neutral Higgs bosons production and decay in the fusion processes, {gamma}{gamma}{yields}S{sub i}S{sub j}, S{sub i}=h{sup 0}, H{sup 0}, A{sup 0}, and show that both h{sup 0}h{sup 0} and A{sup 0}A{sup 0} production can be enhanced by threshold effects in the region E{sub {gamma}}{sub {gamma}}{approx_equal}2m{sub H{+-}}. Resonant effects due to the heavy Higgs H{sup 0} can also play a role in the cross section enhancement when it is allowed to decay to two light CP-even h{sup 0} or to two light CP-odd A{sup 0} scalars. We have scanned the allowed parameter space of the two Higgs doublet model and found a vast region of the parameter space where the cross section is 2 orders of magnitude above the standard model cross section. We further show that the standard model experimental analysis can be used to discover or to constrain the two Higgs doublet model parameter space.

Very light Higgs Bosons in extended models at the LHC

The Large Electron-Positron (LEP) collider experiments have constrained the mass of the standard model (SM) Higgs boson to be above 114.4 GeV. This bound applies to all extensions of the SM where the coupling of a Higgs boson to the Z boson and also the Higgs decay profile do not differ much from the SM one. However, in scenarios with extended Higgs sectors, this coupling can be made very small by a suitable choice of the parameters of the model. In such cases, the lightest CP-even Higgs boson mass can in turn be made very small. Such a very light Higgs state, with a mass of the order of the Z boson one or even smaller, could have escaped detection at LEP. In this work we perform a detailed parton level study on the feasibility of the detection of such a very light Higgs particle at the Large Hadron Collider (LHC) in the production process pp{yields}hj{yields}{tau}{sup +{tau}-}j, where j is a resolved jet. We conclude that there are several models where such a Higgs state could be detected at the LHC with early data.

Higgs boson phenomenology in τ+τ− final states at the LHC

We perform a detailed parton level study on the feasibility of the detection of a Higgs boson in the gluon fusion process pp(gg + gq) → h + jet → τ+τ- + jet at the Large Hadron Collider (LHC) for √s = 14 TeV. The obtained results are applied to a few chosen Beyond the Standard Model (BSM) scenarios where the branching ratio of a Higgs boson decaying into a τ+τ− pair is enhanced as compared to the Standard Model (SM) case. We present the parameter space of the BSM scenarios that can be observed at the LHC and conclude that some regions of the parameter space can be probed with just a few fb−1 of integrated luminosity. Noticeably, our results are presented in a form which potentially allows their application to any generic model giving rise to a pp(gg + gq) → h + jet → τ+τ− + jet signature.

Dimension six flavor changing neutral current operators and top-quark production at the LHC

In this work we calculate the effects of the electroweak flavor changing neutral currents dimension six effective operators on single-top production at the LHC. These results are then combined with previous ones we have obtained for the strong sector. This allow us, for the first time, to perform a combined analysis of flavor changing neutral currents in top production with all contributing dimension six operators. Finally, we study the feasibility of their observation and characterization both at the Tevatron and at the LHC.