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Centelles Chulia, S., Doring, C., Rodejohann, W., & Saldana-Salazar, U. J. (2020). Natural axion model from flavour. J. High Energy Phys., 09(9), 137–29pp.
Abstract: We explore a common symmetrical origin for two long standing problems in particle physics: the strong CP and the fermion mass hierarchy problems. The Peccei-Quinn mechanism solves the former one with an anomalous global U(1)(PQ) symmetry. Here we investigate how this U(1)(PQ) could at the same time explain the fermion mass hierarchy. We work in the context of a four-Higgs-doublet model which explains all quark and charged fermion masses with natural, i.e. order 1, Yukawa couplings. Moreover, the axion of the model constitutes a viable dark matter candidate and neutrino masses are incorporated via the standard type-I seesaw mechanism. A simple extension of the model allows for Dirac neutrinos.
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Cepedello, R., Hirsch, M., & Helo, J. C. (2017). Loop neutrino masses from d=7 operator. J. High Energy Phys., 07(7), 079–21pp.
Abstract: We discuss the generation of small neutrino masses from d = 71 -loop diagrams. We first systematically analyze all possible d = 7 1 -loop topologies. There is a total of 48 topologies, but only 8 of these can lead to “genuine” d = 7 neutrino masses. Here, we define genuine models to be models in which neither d = 5 nor d = 7 tree -level masses nor a d = 5 1 -loop mass appear, such that the d = 7 1 -loop is the leading order contribution to the neutrino masses. All genuine models can then be organized w.r.t. their particle content. We find there is only one diagram with no representation larger than triplet, while there are 22 diagrams with quadruplets. We briefly discuss three minimal example models of this kind.
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Cepedello, R., Hirsch, M., & Helo, J. C. (2018). Lepton number violating phenomenology of d=7 neutrino mass models. J. High Energy Phys., 01(1), 009–24pp.
Abstract: We study the phenomenology of d = 7 1-loop neutrino mass models. All models in this particular class require the existence of several new SU(2)(L) multiplets, both scalar and fermionic, and thus predict a rich phenomenology at the LHC. The observed neutrino masses and mixings can easily be fitted in these models. Interestingly, despite the smallness of the observed neutrino masses, some particular lepton number violating (LNV) final states can arise with observable branching ratios. These LNV final states consists of leptons and gauge bosons with high multiplicities, such as 4/ + 4W, 6/ + 2W etc. We study current constraints on these models from upper bounds on charged lepton flavour violating decays, existing lepton number conserving searches at the LHC and discuss possible future LNV searches.
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Cepedello, R., Hirsch, M., Rocha-Moran, P., & Vicente, A. (2020). Minimal 3-loop neutrino mass models and charged lepton flavor violation. J. High Energy Phys., 08(8), 067–37pp.
Abstract: We study charged lepton flavor violation for the three most popular 3-loop Majorana neutrino mass models. We call these models “minimal” since their particle content correspond to the minimal sets for which genuine 3-loop models can be constructed. In all the three minimal models the neutrino mass matrix is proportional to some powers of Standard Model lepton masses, providing additional suppression factors on top of the expected loop suppression. To correctly explain neutrino masses, therefore large Yukawa couplings are needed in these models. We calculate charged lepton flavor violating observables and find that the three minimal models survive the current constraints only in very narrow regions of their parameter spaces.
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Cepedello, R., Fonseca, R. M., & Hirsch, M. (2018). Systematic classification of three-loop realizations of the Weinberg operator. J. High Energy Phys., 10(10), 197–34pp.
Abstract: We study systematically the decomposition of the Weinberg operator at three-loop order. There are more than four thousand connected topologies. However, the vast majority of these are infinite corrections to lower order neutrino mass diagrams and only a very small percentage yields models for which the three-loop diagrams are the leading order contribution to the neutrino mass matrix. We identify 73 topologies that can lead to genuine three-loop models with fermions and scalars, i.e. models for which lower order diagrams are automatically absent without the need to invoke additional symmetries. The 73 genuine topologies can be divided into two sub-classes: normal genuine ones (44 cases) and special genuine topologies (29 cases). The latter are a special class of topologies, which can lead to genuine diagrams only for very specific choices of fields. The genuine topologies generate 374 diagrams in the weak basis, which can be reduced to only 30 distinct diagrams in the mass eigenstate basis. We also discuss how all the mass eigenstate diagrams can be described in terms of only five master integrals. We present some concrete models and for two of them we give numerical estimates for the typical size of neutrino masses they generate. Our results can be readily applied to construct other d = 5 neutrino mass models with three loops.
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Chakraborty, K., Goswami, S., Gupta, C., & Thakore, T. (2019). Enhancing the hierarchy and octant sensitivity of ESS nu SB in conjunction with T2K, NO nu A and ICAL@INO. J. High Energy Phys., 05(5), 137–26pp.
Abstract: The main aim of the ESSSB proposal is the discovery of the leptonic CP phase (CP) with a high significance (5 sigma for 50% values of (CP)) by utilizing the physics at the second oscillation maxima of the P-e channel. It can achieve 3 sigma sensitivity to hierarchy for all values of (CP). In this work, we concentrate on the hierarchy and octant sensitivity of the ESSSB experiment. We show that combining the ESSSB experiment with the atmospheric neutrino data from the proposed India-based Neutrino Observatory (INO) experiment can result in an increased sensitivity to mass hierarchy. In addition, we also combine the results from the ongoing experiments T2K and NOa assuming their full run-time and present the combined sensitivity of ESSSB + ICAL@INO + T2K + NOA. We show that while by itself ESSSB can have up to 3 sigma hierarchy sensitivity, the combination of all the experiments can give up to 5 sigma sensitivity depending on the true hierarchy-octant combination. The octant sensitivity of ESSSB is low by itself. However the combined sensitivity of all the above experiments can give up to 3 sigma sensitivity depending on the choice of true hierarchy and octant. We discuss the various degeneracies and the synergies that lead to the enhanced sensitivity when combining different experimental data.
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Chala, M., Krause, C., & Nardini, G. (2018). Signals of the electroweak phase transition at colliders and gravitational wave observatories. J. High Energy Phys., 07(7), 062–29pp.
Abstract: If the electroweak phase transition (EWPT) is of strongly first order due to higher dimensional operators, the scale of new physics generating them is at the TeV scale or below. In this case the effective-field theory (EFT) neglecting operators of dimension higher than six may overlook terms that are relevant for the EWPT analysis. In this article we study the EWPT in the EFT to dimension eight. We estimate the reach of the future gravitational wave observatory LISA for probing the region in which the EWPT is strongly first order and compare it with the capabilities of the Higgs measurements via double-Higgs production at current and future colliders. We also match different UV models to the previously mentioned dimension-eight EFT and demonstrate that, from the top-down point of view, the double-Higgs production is not the best signal to explore these scenarios.
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Chang, Q., Li, X. Q., & Yang, Y. D. (2011). The effects of a family nonuniversal Z ' boson on B -> pi pi decays. Int. J. Mod. Phys. A, 26(7-8), 1273–1294.
Abstract: Motivated by the measured large branching ratio of (B) over bar (0) --> pi(0)pi(0) (the so-called pi pi puzzle), we investigate the effects of a family nonuniversal Z' model on the tree-dominated B --> pi pi decays. We find that the Z' coupling parameter zeta(LR)(d) similar to 0.05 with a nontrivial new weak phase phi(L)(d) similar to -50 degrees, which is relevant to the Z' contributions to the QCD penguin sector Delta C-5, is needed to reconcile the observed discrepancy. Combined with the recent fitting results from B --> pi K, pi K* and rho K decays, the Z' parameter spaces are severely reduced but still not excluded entirely, implying that both the “pi pi” and “pi K” puzzles could be accommodated simultaneously within such a family nonuniversal Z' model.
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Cheng, L., Eberhardt, O., & Murphy, C. W. (2019). Novel theoretical constraints for color-octet scalar models. Chin. Phys. C, 43(9), 093101–11pp.
Abstract: We study the theoretical constraints on a model whose scalar sector contains one color octet and one or two color singlet SU(2)(L) doublets. To ensure unitarity of the theory, we constrain the parameters of the scalar potential for the first time at the next-to-leading order in perturbation theory. Moreover, we derive new conditions guaranteeing the stability of the potential. We employ the HEPfit package to extract viable parameter regions at the electroweak scale and test the stability of the renormalization group evolution up to the multi-TeV region. Furthermore, we set upper limits on the scalar mass splittings. All results are given for both cases with and without a second scalar color singlet.
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Chowdhury, D., & Eberhardt, O. (2018). Update of global Two-Higgs-Doublet model fits. J. High Energy Phys., 05(5), 161–42pp.
Abstract: We perform global fits of Two-Higgs-Doublet models with a softly broken Z(2) symmetry to recent results from the LHC detectors CMS and ATLAS, that is signal strengths and direct search limits obtained at root s = 8 TeV and root s = 13 TeV. We combine all available ATLAS and CMS constraints with the other relevant theoretical and experimental bounds and present the latest limits on the model parameters. We obtain that deviations from the so-called alignment limit beta-alpha = pi/2 cannot be larger than 0.03 in type I and have to be smaller than 0.02 in the remaining three types. For the latter, we also observe lower limits on the heavy Higgs masses in the global fit. The splittings between these masses cannot exceed 200 GeV in the types I and X and 130 GeV in the types II and Y. Finally, we find that the decay widths of the heavy Higgs particles cannot be larger than 7% of their masses if they are lighter than 1.5 TeV.
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