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Deppisch, F. F., Desai, N., & Valle, J. W. F. (2014). Is charged lepton flavor violation a high energy phenomenon? Phys. Rev. D, 89(5), 051302–5pp.
Abstract: Searches for rare processes such as μ-> e gamma put stringent limits on lepton flavor violation expected in many beyond-the-Standard-Model physics scenarios. This usually precludes the observation of flavor violation at high energy colliders such as the LHC. We here discuss a scenario where right-handed neutrinos are produced via a Z' portal but which can only decay via small flavor violating couplings. Consequently, the process rate is unsuppressed by the small couplings and can be visible despite unobservably small μ-> e gamma rates.
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King, S. F., Morisi, S., Peinado, E., & Valle, J. W. F. (2013). Quark-lepton mass relation in a realistic A(4) extension of the Standard Model. Phys. Lett. B, 724(1-3), 68–72.
Abstract: We propose a realistic A(4) extension of the Standard Model involving a particular quark-lepton mass relation, namely that the ratio of the third family mass to the geometric mean of the first and second family masses are equal for down-type quarks and charged leptons. This relation, which is approximately renormalization group invariant, is usually regarded as arising from the Georgi-Jarlskog relations, but in the present model there is no unification group or supersymmetry. In the neutrino sector we propose a simple modification of the so-called Zee-Wolfenstein mass matrix pattern which allows an acceptable reactor angle along with a deviation of the atmospheric and solar angles from their bi-maximal values. Quark masses, mixing angles and CP violation are well described by a numerical fit.
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Ding, G. J., Morisi, S., & Valle, J. W. F. (2013). Bilarge neutrino mixing and Abelian flavor symmetry. Phys. Rev. D, 87(5), 053013–13pp.
Abstract: We explore two bilarge neutrino mixing Anzatze within the context of Abelian flavor symmetry theories: (BL1) sin theta(12) similar to lambda, sin theta(13) similar to lambda, sin theta(23) similar to lambda, and (BL2) sin theta(12) similar to lambda, sin theta(13) similar to lambda, sin theta(23) similar to 1 – lambda. The first pattern is proposed by two of us and is favored if the atmospheric mixing angle theta(23) lies in the first octant, while the second one is preferred for the second octant of theta(23). In order to reproduce the second texture, we find that the flavor symmetry should be U(1) x Z(m), while for the first pattern the flavor symmetry should be extended to U(1) x Z(m) x Z(n) with m and n of different parity. Explicit models for both mixing patterns are constructed based on the flavor symmetries U(1) x Z(3) x Z(4) and U(1) x Z(2). The models are extended to the quark sector within the framework of SU(5) grand unified theory in order to give a successful description of quark and lepton masses and mixing simultaneously. Phenomenological implications are discussed.
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Lavoura, L., Morisi, S., & Valle, J. W. F. (2013). Accidental stability of dark matter. J. High Energy Phys., 02(2), 118–17pp.
Abstract: We propose that dark matter is stable as a consequence of an accidental Z(2) that results from a flavour symmetry group which is the double-cover group of the symmetry group of one of the regular geometric solids. Although model-dependent, the phenomenology resembles that of a generic “inert Higgs” dark matter scheme.
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Bazzocchi, F., Morisi, S., Peinado, E., Valle, J. W. F., & Vicente, A. (2013). Bilinear R-parity violation with flavor symmetry. J. High Energy Phys., 01(1), 033–16pp.
Abstract: Bilinear R-parity violation (BRPV) provides the simplest intrinsically supersymmetric neutrino mass generation scheme. While neutrino mixing parameters can be probed in high energy accelerators, they are unfortunately not predicted by the theory. Here we propose a model based on the discrete flavor symmetry Lambda(4) with a single R-parity violating parameter, leading to (i) correct Cabbibo mixing given by the Gatto-Sartori-Tonin formula, and a successful unification-like b-tau mass relation, and (ii) a correlation between the lepton mixing angles theta(13) and theta(23) in agreement with recent neutrino oscillation data, as well as a (nearly) massless neutrino, leading to absence of neutrinoless double beta decay.
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De Romeri, V., Patel, K. M., & Valle, J. W. F. (2018). Inverse seesaw mechanism with compact supersymmetry: Enhanced naturalness and light superpartners. Phys. Rev. D, 98(7), 075014–15pp.
Abstract: We consider the supersymmetric inverse seesaw mechanism for neutrino mass generation within the context of a low-energy effective theory where supersymmetry is broken geometrically in an extra dimensional theory. It is shown that the effective scale characterizing the resulting compact supersymmetric spectrum can be as low as 500-600 GeV for moderate values of tan beta. The potentially large neutrino Yukawa couplings, naturally present in inverse seesaw schemes, enhance the Higgs mass and allow the superpartners to be lighter than in compact supersymmetry without neutrino masses. The inverse seesaw structure also implies a novel spectrum profile and couplings, in which the lightest supersymmetric particle can be an admixture of isodoublet and isosinglet sneutrinos. Dedicated collider as well as dark matter studies should take into account such specific features.
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Chen, P., Centelles Chulia, S., Ding, G. J., Srivastava, R., & Valle, J. W. F. (2018). Realistic tribimaximal neutrino mixing. Phys. Rev. D, 98(5), 055019–6pp.
Abstract: We propose a generalized version of the tribimaximal (TBM) ansatz for lepton mixing, leading to a nonzero reactor angle theta(13) and CP violation. The latter is characterized by two CP phases. The Dirac phase, affecting neutrino oscillations, is nearly maximal (delta(CP) similar to +/- pi/2), while the Majorana phase implies narrow allowed ranges for the neutrinoless double beta decay amplitude. The solar angle theta(12) lies nearly at its TBM value, while the atmospheric angle theta(23) has the TBM value for a maximal delta(CP). Neutrino oscillation predictions can be tested in present and upcoming experiments.
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Reig, M., Valle, J. W. F., & Wilczek, F. (2018). SO(3) family symmetry and axions. Phys. Rev. D, 98(9), 095008–6pp.
Abstract: Motivated by the idea of comprehensive unification, we study a gauged SO(3) flavor extension of the extended Standard Model, including right-handed neutrinos and a Peccei-Quinn symmetry with simple charge assignments. The model accommodates the observed fermion masses and mixings and yields a characteristic, successful relation among them. The Peccei-Quinn symmetry is an essential ingredient.
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Centelles Chulia, S., Srivastava, R., & Valle, J. W. F. (2018). Seesaw Dirac neutrino mass through dimension-six operators. Phys. Rev. D, 98(3), 035009–18pp.
Abstract: In this paper, a follow-up of [S. C. Chulia, R. Srivastava, and J. W. F. Valle, Phys. Lett. B 781, 122 (2018)], we describe the many pathways to generate Dirac neutrino mass through dimension-six operators. By using only the standard model Higgs doublet in the external legs, one gets a unique operator 1/Lambda(2) (L) over bar (Phi) over bar (Phi) over bar Phi nu(R). In contrast, the presence of new scalars implies new possible field contractions, which greatly increase the number of possibilities. Here, we study in detail the simplest ones, involving SU(2)(L) singlets, doublets, and triplets. The extra symmetries needed to ensure the Dirac nature of neutrinos can also be responsible for stabilizing dark matter.
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Srivastava, R., Ternes, C. A., Tortola, M., & Valle, J. W. F. (2018). Zooming in on neutrino oscillations with DUNE. Phys. Rev. D, 97(9), 095025–11pp.
Abstract: We examine the capabilities of the DUNE experiment as a probe of the neutrino mixing paradigm. Taking the current status of neutrino oscillations and the design specifications of DUNE, we determine the experiment's potential to probe the structure of neutrino mixing and CP violation. We focus on the poorly determined parameters theta(23) and delta(cp) and consider both two and seven years of run. We take various benchmarks as our true values, such as the current preferred values of theta(23) and delta(cp), as well as several theory-motivated choices. We determine quantitatively DUNE's potential to perform a precision measurement of theta(23), as well as to test the CP violation hypothesis in a model-independent way. We find that, after running for seven years, DUNE will make a substantial step in the precise determination of these parameters, bringing to quantitative test the predictions of various theories of neutrino mixing.
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