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Undoubtable signs of CP-violation in Higgs boson decays at the LHC run 2

Publication . Fontes, Duarte; Romão, Jorge C.; Santos, Rui; Silva, João P.

With the discovery of the Higgs boson at the Large Hadron Collider the high energy physics community's attention has now turned to understanding the properties of the Higgs boson, together with the hope of finding more scalars during run 2. In this work we discuss scenarios where using a combination of three decays, involving the 125 GeV Higgs boson, the Z boson and at least one more scalar, an indisputable signal of CP-violation arises. We use a complex two-Higgs doublet model as a reference model and present some benchmark points that have passed all current experimental and theoretical constraints, and that have cross sections large enough to be probed during run 2.

2015-09-11Journal article

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Scotogenic model for co-bimaximal mixing

Publication . Ferreira, Pedro Miguel; Grimus, W.; Jurciukonis, D.; Lavoura, L.

We present a scotogenic model, i.e. a one-loop neutrino mass model with dark right-handed neutrino gauge singlets and one inert dark scalar gauge doublet eta, which has symmetries that lead to co-bimaximal mixing, i.e. to an atmospheric mixing angle theta(23) = 45 degrees and to a CP-violating phase delta = +/-pi/2, while the mixing angle theta(13) remains arbitrary. The symmetries consist of softly broken lepton numbers L-alpha (alpha = e, mu, tau), a non-standard CP symmetry, and three L-2 symmetries. We indicate two possibilities for extending the model to the quark sector. Since the model has, besides eta, three scalar gauge doublets, we perform a thorough discussion of its scalar sector. We demonstrate that it can accommodate a Standard Model-like scalar with mass 125 GeV, with all the other charged and neutral scalars having much higher masses.

2016-07-04Journal article

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More about unphysical zeroes in quark mass matrices

Publication . Costa, David Emmanuel; Gonzalez Felipe, Ricardo

We look for all weak bases that lead to texture zeroes in the quark mass matrices and contain a minimal number of parameters in the framework of the standard model. Since there are ten physical observables, namely, six nonvanishing quark masses, three mixing angles and one CP phase, the maximum number of texture zeroes in both quark sectors is altogether nine. The nine zero entries can only be distributed between the up- and down-quark sectors in matrix pairs with six and three texture zeroes or five and four texture zeroes. In the weak basis where a quark mass matrix is nonsingular and has six zeroes in one sector, we find that there are 54 matrices with three zeroes in the other sector, obtainable through right-handed weak basis transformations. It is also found that all pairs composed of a nonsingular matrix with five zeroes and a nonsingular and nondecoupled matrix with four zeroes simply correspond to a weak basis choice. Without any further assumptions, none of these pairs of up- and down-quark mass matrices has physical content. It is shown that all non-weak-basis pairs of quark mass matrices that contain nine zeroes are not compatible with current experimental data. The particular case of the so-called nearest-neighbour-interaction pattern is also discussed.

2017-01-10Journal article

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The neutrino flavor puzzle

Publication . Felipe, Ricardo Gonzalez

A remarkable breakthrough in neutrino physics has been witnessed in recent years. Neutrino oscillation experiments have firmly established the existence of neutrino masses and leptonic mixing, which represents solid evidence of physics beyond the Standard Model. We present a brief overview of the neutrino flavor puzzle, with emphasis on a theoretical approach to address this problem. A possible path toward the solution of this puzzle consists in requiring some of the elements in the leptonic mass matrices to vanish. Such texture zeros can be enforced by means of Abelian symmetries. We present some examples of the implementation of maximally restrictive texture zeros in the leptonic sector in the context of two-Higgs-doublet models with Majorana neutrinos. The compatibility of these textures with current neutrino data and their low-energy predictions are briefly analyzed.

2017-12Journal article

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The C2HDM revisited

Publication . Fontes, Duarte; Muehlleitner, Milada Margarete; Romão, Jorge; Santos, Rui; Silva, Joao; Wittbrodt, Jonas

The complex two-Higgs doublet model is one of the simplest ways to extend the scalar sector of the Standard Model to include a new source of CP-violation. The model has been used as a benchmark model to search for CP-violation at the LHC and as a possible explanation for the matter-antimatter asymmetry of the Universe. In this work, we re-analyse in full detail the softly broken ℤ2 symmetric complex two-Higgs doublet model (C2HDM). We provide the code C2HDM_HDECAY implementing the C2HDM in the well-known HDECAY program which calculates the decay widths including the state-of-the-art higher order QCD corrections and the relevant off-shell decays. Using C2HDM_HDECAY together with the most relevant theoretical and experimental constraints, including electric dipole moments (EDMs), we review the parameter space of the model and discuss its phenomenology. In particular, we find cases where large CP-odd couplings to fermions are still allowed and provide benchmark points for these scenarios. We examine the prospects of discovering CP-violation at the LHC and show how theoretically motivated measures of CP-violation correlate with observables.

2018-02Journal article

Open access