
Arbelaez, C., Fonseca, R. M., Romao, J. C., & Hirsch, M. (2013). Supersymmetric SO(10)inspired GUTs with sliding scales. Phys. Rev. D, 87(7), 075010–19pp.
Abstract: We construct lists of supersymmetric models with extended gauge groups at intermediate steps, all of which are inspired by SO(10) unification. We consider three different kinds of setups: (i) the model has exactly one additional intermediate scale with a leftright (LR) symmetric group; (ii) SO(10) is broken to the LR group via an intermediate PatiSalam scale; and (iii) the LR group is broken into SU(3)(c) X SU(2)(L) X U(1)(R) X U(1)(BL), before breaking to the standard model (SM) group. We use sets of conditions, which we call the “sliding mechanism,” which yield unification with the extended gauge group(s) allowed at arbitrary intermediate energy scales. All models thus can have new gauge bosons within the reach of the LHC, in principle. We apply additional conditions, such as perturbative unification, renormalizability and anomaly cancellation and find that, despite these requirements, for the ansatz (i) with only one additional scale still around 50 different variants exist that can have a LR symmetry below 10 TeV. For the more complicated schemes (ii) and (iii) literally thousands of possible variants exist, and for scheme (ii) we have also found variants with very low PatiSalam scales. We also discuss possible experimental tests of the models from measurements of supersymmetry masses. Assuming mSugra boundary conditions we calculate certain combinations of soft terms, called “invariants,” for the different classes of models. Values for all the invariants can be classified into a small number of sets, which contain information about the class of models and, in principle, the scale of beyondminimal supersymmetric extension of the Standard Model physics, even in case the extended gauge group is broken at an energy beyond the reach of the LHC.



Arbelaez, C., Romao, J. C., Hirsch, M., & Malinsky, M. (2014). LHCscale leftright symmetry and unification. Phys. Rev. D, 89(3), 035002–19pp.
Abstract: We construct a comprehensive list of nonsupersymmetric standard model extensions with a lowscale leftright (LR)symmetric intermediate stage that may be obtained as simple lowenergy effective theories within a class of renormalizable SO(10) grand unified theories. Unlike the traditional “minimal” LR models many of our example settings support a perfect gauge coupling unification even if the LR scale is in the LHC domain at a price of only (a few copies of) one or two types of extra fields pulled down to the TeVscale ballpark. We discuss the main aspects of a potentially realistic model building conforming the basic constraints from the quark and lepton sector flavor structure, proton decay limits, etc. We pay special attention to the theoretical uncertainties related to the limited information about the underlying unified framework in the bottomup approach, in particular, to their role in the possible extraction of the LRbreaking scale. We observe a general tendency for the models without new colored states in the TeV domain to be on the verge of incompatibility with the proton stability constraints.



Bonilla, C., Romao, J. C., & Valle, J. W. F. (2016). Electroweak breaking and neutrino mass: `invisible' Higgs decays at the LHC (type II seesaw). New J. Phys., 18, 033033–21pp.
Abstract: Neutrino mass generation through the Higgs mechanism not only suggests the need to reconsider the physics of electroweak symmetry breaking from a new perspective, but also provides a new theoretically consistent and experimentally viable paradigm. We illustrate this by describing the main features of the electroweak symmetry breaking sector of the simplest typeII seesaw model with spontaneous breaking of lepton number. After reviewing the relevant `theoretical' and astrophysical restrictions on the Higgs sector, we perform an analysis of the sensitivities of Higgs Boson searches at the ongoing ATLAS and CMS experiments at the LHC, including not only the new contributions to the decay channels present in the standard model (SM) but also genuinely nonSM Higgs Boson decays, such as `invisible' Higgs Boson decays to majorons. We find sensitivities that are likely to be reached at the upcoming run of the experiments.



Bonilla, C., Romao, J. C., & Valle, J. W. F. (2015). Neutrino mass and invisible Higgs decays at the LHC. Phys. Rev. D, 91(11), 113015–7pp.
Abstract: The discovery of the Higgs boson suggests that neutrinos also get their mass from spontaneous symmetry breaking. In the simplest ungauged leptonnumber scheme, the Standard Model Higgs now has two other partners: a massive CPeven scalar, and the massless NambuGoldstone boson, called the Majoron. For weakscale breaking of lepton number the invisible decays of the CPeven Higgs bosons to the Majoron lead to potentially copious sources of events with large missing energy. Using LHC results, we study how the constraints on invisible decays of the Higgs boson restrict the relevant parameters, substantially extending those previously derived from LEP and potentially shedding light on the scale of spontaneous leptonnumber violation.



Esteves, J. N., Joaquim, F. R., Joshipura, A. S., Romao, J. C., Tortola, M., & Valle, J. W. F. (2010). A(4)based neutrino masses with Majoron decaying dark matter. Phys. Rev. D, 82(7), 073008–8pp.
Abstract: We propose an A(4) flavorsymmetric SU(3) circle times SU(2) circle times U(1) seesaw model where lepton number is broken spontaneously. A consistent twozero texture pattern of neutrino masses and mixing emerges from the interplay of typeI and typeII seesaw contributions, with important phenomenological predictions. We show that, if the Majoron becomes massive, such seesaw scenario provides a viable candidate for decaying dark matter, consistent with cosmic microwave background lifetime constraints that follow from current WMAP observations. We also calculate the subleading oneloopinduced decay into photons which leads to a monoenergetic emission line that may be observed in future xray missions such as Xenia.



Esteves, J. N., Romao, J. C., Hirsch, M., Porod, W., Staub, F., & Vicente, A. (2012). Dark matter and LHC phenomenology in a leftright supersymmetric model. J. High Energy Phys., 01(1), 095–33pp.
Abstract: Leftright symmetric extensions of the Minimal Supersymmetric Standard Model can explain neutrino data and have potentially interesting phenomenology beyond that found in minimal SUSY seesaw models. Here we study a SUSY model in which the leftright symmetry is broken by triplets at a high scale, but significantly below the GUT scale. Sparticle spectra in this model differ from the usual constrained MSSM expectations and these changes affect the relic abundance of the lightest neutralino. We discuss changes for the standard stau (and stop) coannihilation, the Higgs funnel and the focus point regions. The model has potentially large lepton flavour violation in both, left and right, scalar leptons and thus allows, in principle, also for flavoured coannihilation. We also discuss lepton flavour signals due to violating decays of the second lightest neutralino at the LHC, which can be as large as 20 fb(1) at root s = 14 TeV.



Esteves, J. N., Romao, J. C., Hirsch, M., Staub, F., & Porod, W. (2011). Supersymmetric typeIII seesaw mechanism: Lepton flavor violating decays and dark matter. Phys. Rev. D, 83(1), 013003–21pp.
Abstract: We study a supersymmetric version of the seesaw mechanism type III. The model consists of the minimal supersymmetric extension of the standard model particle content plus three copies of 24 superfields. The fermionic part of the SU(2) triplet contained in the 24 is responsible for the typeIII seesaw, which is used to explain the observed neutrino masses and mixings. Complete copies of 24 are introduced to maintain gauge coupling unification. These additional states change the beta functions of the gauge couplings above the seesaw scale. Using minimal Supergravity boundary conditions, we calculate the resulting supersymmetric mass spectra at the electroweak scale using full 2loop renormalization group equations. We show that the resulting spectrum can be quite different compared to the usual minimal Supergravity spectrum. We discuss how this might be used to obtain information on the seesaw scale from mass measurements. Constraints on the model space due to limits on lepton flavour violating decays are discussed. The main constraints come from the bounds on μ> e gamma but there are also regions where the decay tau > μgamma gives stronger constraints. We also calculate the regions allowed by the dark matter constraint. For the sake of completeness, we compare our results with those for the supersymmetric seesaw type II and, to some extent, with type I.



Esteves, J. N., Romao, J. C., Hirsch, M., Vicente, A., Porod, W., & Staub, F. (2010). LHC and lepton flavour violation phenomenology of a leftright extension of the MSSM. J. High Energy Phys., 12(12), 077–44pp.
Abstract: We study the phenomenology of a supersymmetric leftright model, assuming minimal supergravity boundary conditions. Both leftright and (BL) symmetries are broken at an energy scale close to, but significantly below the GUT scale. Neutrino data is explained via a seesaw mechanism. We calculate the RGEs for superpotential and soft parameters complete at 2loop order. At low energies lepton flavour violation (LFV) and small, but potentially measurable mass splittings in the charged scalar lepton sector appear, due to the RGE running. Different from the supersymmetric “pure seesaw” models, both, LFV and slepton mass splittings, occur not only in the leftbut also in the right slepton sector. Especially, ratios of LFV slepton decays, such as Br((tau) over bar (R) > μchi(0)(1))/Br((tau) over bar (L) > μchi(0)(1)) are sensitive to the ratio of (BL) and leftright symmetry breaking scales. Also the model predicts a polarization asymmetry of the outgoing positrons in the decay mu(+) > e(+)gamma, A similar to [0, 1], which differs from the pure seesaw “prediction” A = 1. Observation of any of these signals allows to distinguish this model from any of the three standard, pure (mSugra) seesaw setups.



Fontes, D., Romao, J. C., & Valle, J. W. F. (2019). Electroweak breaking and Higgs boson profile in the simplest linear seesaw model. J. High Energy Phys., 10(10), 245–28pp.
Abstract: We examine the simplest realization of the linear seesaw mechanism within the Standard Model gauge structure. Besides the standard scalar doublet, there are two leptonnumbercarrying scalars, a nearly inert SU(2)(L) doublet and a singlet. Neutrino masses result from the spontaneous violation of lepton number, implying the existence of a NambuGoldstone boson. Such “majoron” would be copiously produced in stars, leading to stringent astrophysical constraints. We study the profile of the Higgs bosons in this model, including their effective couplings to the vector bosons and their invisible decay branching ratios. A consistent electroweak symmetry breaking pattern emerges with a compressed spectrum of scalars in which the “Standard Model” Higgs boson can have a sizeable invisible decay into the invisible majorons.



Forero, D. V., Morisi, S., Romao, J. C., & Valle, J. W. F. (2013). Neutrino mixing with revamped A(4) flavor symmetry. Phys. Rev. D, 88(1), 016003–7pp.
Abstract: We suggest a minimal extension of the simplest A(4) flavor model that can induce a nonzero theta(13) value, as required by recent neutrino oscillation data from reactors and accelerators. The predicted correlation between the atmospheric mixing angle theta(23) and the magnitude of theta(13) leads to an allowed region substantially smaller than indicated by neutrinooscillation global fits. Moreover, the scheme correlates CP violation in neutrino oscillations with the octant of the atmospheric mixing parameter theta(23) in such a way that, for example, maximal mixing necessarily violates CP. We briefly comment on other phenomenological features of the model.

