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Boucenna, S. M., Fonseca, R. M., Gonzalez-Canales, F., & Valle, J. W. F. (2015). Small neutrino masses and gauge coupling unification. Phys. Rev. D, 91(3), 031702–5pp.
Abstract: The physics responsible for gauge coupling unification may also induce small neutrino masses. We propose a novel gauge-mediated radiative seesaw mechanism for calculable neutrino masses. These arise from quantum corrections mediated by new SU(3)(C) circle times SU(3)(L) circle times U(1)(X) (3-3-1) gauge bosons and the physics driving gauge coupling unification. Gauge couplings unify for a 3-3-1 scale in the TeV range, making the model directly testable at the LHC.
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Fonseca, R. M., & Hirsch, M. (2015). SU(5)-inspired double beta decay. Phys. Rev. D, 92(1), 015014–14pp.
Abstract: The short-range part of the neutrinoless double beta amplitude is generated via the exchange of exotic particles, such as charged scalars, leptoquarks and/or diquarks. In order to give a sizable contribution to the total decay rate, the masses of these exotics should be of the order of (at most) a few TeV. Here, we argue that these exotics could be the “light” (i.e., weak-scale) remnants of some B – L violating variants of SU(5). We show that unification of the standard model gauge couplings, consistent with proton decay limits, can be achieved in such a setup without the need to introduce supersymmetry. Since these nonminimal SU(5)-inspired models violate B – L, they generate Majorana neutrino masses and therefore make it possible to explain neutrino oscillation data. The light colored particles of these models can potentially be observed at the LHC, and it might be possible to probe the origin of the neutrino masses with Delta L = 2 violating signals. As particular realizations of this idea, we present two models, one for each of the two possible tree-level topologies of neutrinoless double beta decay.
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Bonilla, C., Fonseca, R. M., & Valle, J. W. F. (2015). Consistency of the triplet seesaw model revisited. Phys. Rev. D, 92(7), 075028–7pp.
Abstract: Adding a scalar triplet to the Standard Model is one of the simplest ways of giving mass to neutrinos, providing at the same time a mechanism to stabilize the theory's vacuum. In this paper, we revisit these aspects of the type-II seesaw model pointing out that the bounded-from-below conditions for the scalar potential in use in the literature are not correct. We discuss some scenarios where the correction can be significant and sketch the typical scalar boson profile expected by consistency.
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Fonseca, R. M., & Hirsch, M. (2016). Lepton number violation in 331 models. Phys. Rev. D, 94(11), 115003–16pp.
Abstract: Different models based on the extended SU(3)(C) x SU(3)(L) x U(1)(X) (331) gauge group have been proposed over the past four decades. Yet, despite being an active research topic, the status of lepton number in 331 models has not been fully addressed in the literature, and furthermore many of the original proposals can not explain the observed neutrino masses. In this paper we review the basic features of various 331 models, focusing on potential sources of lepton number violation. We then describe different modifications which can be made to the original models in order to accommodate neutrino (and charged lepton) masses.
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Fonseca, R. M., & Hirsch, M. (2017). Gauge vectors and double beta decay. Phys. Rev. D, 95(3), 035033–14pp.
Abstract: We discuss contributions to neutrinoless double beta (0 nu beta beta) decay involving vector bosons. The starting point is a list of all possible vector representations that may contribute to 0 nu beta beta decay via d = 9 or d = 11 operators at tree level. We then identify gauge groups which contain these vectors in the adjoint representation. Even though the complete list of vector fields that can contribute to 0 nu beta beta up to d = 11 is large (a total of 46 vectors), only a few of them can be gauge bosons of phenomenologically realistic groups. These latter cases are discussed in some more detail, and lower (upper) limits on gauge boson masses (mixing angles) are derived from the absence of 0 nu beta beta decay.
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