Barenboim, G., & Bosch, C. (2016). Composite states of two right-handed neutrinos. Phys. Rev. D, 94(11), 116019–10pp.
Abstract: In this work, we develop a model for Higgs-like composites based on two generations of right-handed neutrinos that condense. We analyze the spontaneous symmetry breaking of the theory with two explicit breakings, setting the different scales of the model and obtaining massive bosons as a result. Finally, we calculate the gravitational wave imprint left by the phase transition associated with the symmetry breaking of a generic potential dictated by the symmetries of the composites.
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Botella, F. J., Branco, G. C., Rebelo, M. N., & Silva-Marcos, J. I. (2016). What if the masses of the first two quark families are not generated by the standard model Higgs boson? Phys. Rev. D, 94(11), 115031–6pp.
Abstract: We point out that in the standard model there is meaningful quark mixing even in the extreme chiral (EC) limit, where only the third generation of quarks acquires mass. This mixing is in general expected to be of order 1 and the fact that |V-13|(2) + |V-23|(2) approximate to 1.6 x 10(-3) implies a novel fine-tuning problem in the SM which we point out for the first time. We propose a possible way of avoiding this fine-tuning by introducing a symmetry S which leads to V-CKM = 1, with only the third generation of quarks acquiring mass. We consider two scenarios for generating the mass of the first two quark generations and full quark mixing based on the assumption that the masses of the first two quark families are not generated by the standard Higgs. One consists of the introduction of a second Higgs doublet which is neutral under S. The second scenario consists of assuming new physics at a high energy scale, contributing to the masses of light quark generations, in an effective field theory approach. This last scenario leads to couplings of the Higgs particle to s (s) over bar and c (c) over tilde which are significantly enhanced with respect to those of the SM. In both schemes, one has scalar-mediated flavor-changing neutral currents which are naturally suppressed. Flavor-violating top decays are predicted in the second scenario at the level Br(t -> hc) >= 5 x 10(-5).
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Boucenna, S. M., Morisi, S., & Vicente, A. (2016). LHC diphoton resonance from gauge symmetry. Phys. Rev. D, 93(11), 115008–8pp.
Abstract: Motivated by what is possibly the first sign of new physics seen at the LHC, the diphoton excess at 750 GeV in ATLAS and CMS, we present a model that provides naturally the necessary ingredients to explain the resonance. The simplest phenomenological explanation for the diphoton excess requires a new scalar state, X(750), as well as additional vectorlike (VL) fermions introduced in an ad-hoc way in order to enhance its decays into a pair of photons and/or increase its production cross section. We show that the necessary VL quarks and their couplings can emerge naturally from a complete framework based on the SU(3)(L) circle times U(1)(X) gauge symmetry.
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Olmo, G. J., Rubiera-Garcia, D., & Sanchez-Puente, A. (2016). Impact of curvature divergences on physical observers in a wormhole space-time with horizons. Class. Quantum Gravity, 33(11), 115007–12pp.
Abstract: The impact of curvature divergences on physical observers in a black hole space-time, which, nonetheless, is geodesically complete is investigated. This space-time is an exact solution of certain extensions of general relativity coupled to Maxwell's electrodynamics and, roughly speaking, consists of two Reissner-Nordstrom (or Schwarzschild or Minkowski) geometries connected by a spherical wormhole near the center. We find that, despite the existence of infinite tidal forces, causal contact is never lost among the elements making up the observer. This suggests that curvature divergences may not be as pathological as traditionally thought.
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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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