Coloma, P., Donini, A., Fernandez-Martinez, E., & Hernandez, P. (2012). Precision on leptonic mixing parameters at future neutrino oscillation experiments. J. High Energy Phys., 06(6), 073–27pp.
Abstract: We perform a comparison of the different future neutrino oscillation experiments based on the achievable precision in the determination of the fundamental parameters theta(13) and the CP phase, delta, assuming that theta(13) is in the range indicated by the recent Daya Bay measurement. We study the non-trivial dependence of the error on delta on its true value. When matter effects are small, the largest error is found at the points where CP violation is maximal, and the smallest at the CP conserving points. The situation is different when matter effects are sizable. As a result of this effect, the comparison of the physics reach of different experiments on the basis of the CP discovery potential, as usually done, can be misleading. We have compared various proposed super-beam, beta-beam and neutrino factory setups on the basis of the relative precision of theta(13) and the error on delta. Neutrino factories, both high-energy or low-energy, outperform alternative beam technologies. An ultimate precision on theta(13) below 3% and an error on delta of <= 7 degrees at 1 sigma (1 d.o.f.) can be obtained at a neutrino factory.
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Cirigliano, V., Gisbert, H., Pich, A., & Rodriguez-Sanchez, A. (2020). Isospin-violating contributions to epsilon '/epsilon. J. High Energy Phys., 02(2), 032–44pp.
Abstract: The known isospin-breaking contributions to the K -> pi pi amplitudes are reanalyzed, taking into account our current understanding of the quark masses and the relevant non-perturbative inputs. We present a complete numerical reappraisal of the direct CP-violating ratio is an element of(')/is an element of, where these corrections play a quite significant role. We obtain the Standard Model prediction Re (is an element of(')/is an element of) = (14 +/- 5) <bold> </bold>10(-4), which is in very good agreement with the measured ratio. The uncertainty, which has been estimated conservatively, is dominated by our current ignorance about 1/N-C-suppressed contributions to some relevant chiral-perturbation-theory low-energy constants.
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Chen, P., Centelles Chulia, S., Ding, G. J., Srivastava, R., & Valle, J. W. F. (2018). Neutrino predictions from generalized CP symmetries of charged leptons. J. High Energy Phys., 07(7), 077–26pp.
Abstract: We study the implications of generalized CP transformations acting on the mass matrices of charged leptons in a model-independent way. Generalized e – mu, e – tau and μ- tau symmetries are considered in detail. In all cases the physical parameters of the lepton mixing matrix, three mixing angles and three CP phases can be expressed in terms of a restricted set of independent “theory parameters” that characterize a given choice of CP transformation. This leads to implications for neutrino oscillations as well as neutrinoless double beta decay experiments.
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Chen, P., Centelles Chulia, S., Ding, G. J., Srivastava, R., & Valle, J. W. F. (2019). CP symmetries as guiding posts: revamping tri-bi-maximal mixing. Part I. J. High Energy Phys., 03(3), 036–27pp.
Abstract: We analyze the possible generalized CP symmetries admitted by the Tri-Bi-Maximal (TBM) neutrino mixing. Taking advantage of these symmetries we construct in a systematic way other variants of the standard TBM Ansatz. Depending on the type and number of generalized CP symmetries imposed, we get new mixing matrices, all of which related to the original TBM matrix. One of such revamped TBM variants is the recently discussed mixing matrix of arXiv:1806.03367. We also briefly discuss the phenomenological implications following from these mixing patterns.
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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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Centelles Chulia, S., & Trautner, A. (2020). Asymmetric tri-bi-maximal mixing and residual symmetries. Mod. Phys. Lett. A, 35(35), 2050292–15pp.
Abstract: Asymmetric tri-bi-maximal mixing is a recently proposed, grand unified theory (GUT) based, flavor mixing scheme. In it, the charged lepton mixing is fixed by the GUT connection to down-type quarks and a T-13 flavor symmetry, while neutrino mixing is assumed to be tri-bi-maximal (TBM) with one additional free phase. Here we show that this additional free phase can be fixed by the residual flavor and CP symmetries of the effective neutrino mass matrix. We discuss how those residual symmetries can be unified with T-13 and identify the smallest possible unified flavor symmetries, namely (Z(13)xZ(13))(sic)D-12 and (Z(13)xZ(13))(sic)S-4. Sharp predictions are obtained for lepton mixing angles, CP violating phases and neutrinoless double beta decay.
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Celis, A., Fuentes-Martin, J., & Serodio, H. (2014). A class of invisible axion models with FCNCs at tree level. J. High Energy Phys., 12(12), 167–53pp.
Abstract: We build a class of invisible axion models with tree-level Flavor Changing Neutral Currents completely controlled by the fermion mixing matrices. The scalar sector of these models contains three-Higgs doublets and a complex scalar gauge singlet, with the same fermionic content as in the Standard Model. A horizontal Peccei-Quinn symmetry provides a solution to the strong CP problem and predicts the existence of a very light and weakly coupled pseudo-Goldstone boson, the invisible axion or familon. A phenomenological analysis is performed taking into account familon searches in rare kaon and muon decays, astrophysical considerations and axion searches via axion-photon conversion. Drastic differences are found in the axion properties of different models due to the strong hierarchy of the CKM matrix, making some of the models considered much more constrained than others. We also obtain that a rich variety of these models avoid the domain wall problem. A possible mechanism to protect the solution to the strong CP problem against gravitational effects is also discussed.
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Botella, F. J., Branco, G. C., & Nebot, M. (2012). The hunt for New Physics in the Flavour Sector with up vector-like quarks. J. High Energy Phys., 12(12), 040–34pp.
Abstract: We analyse the possible presence of New Physics (NP) in the Flavour Sector and evaluate its potential for solving the tension between the experimental values of A(J/Psi KS) and Br(B+ -> tau(+)v(tau)) with respect to the Standard Model (SM) expectations. Updated model independent analyses, where NP contributions are allowed in B-d(0) – (B) over bar (0)(d) and B-s(0) – (B) over bar (0)(s) transitions, suggest the need of New Physics in the bd sector. A detailed analysis of recent Flavour data is then presented in the framework of a simple extension of the SM, where a Q = 2/3 vector-like isosinglet quark is added to the spectrum of the SM. Special emphasis is given to the implications of this model for correlations among various measurable quantities. We include constraints from all the relevant quark flavour sectors and give precise predictions for selected rare processes. We find important deviations from the SM in observables in the bd sector like the semileptonic asymmetry A(SL)(d), B-d(0) -> mu(+)mu(-) and A(SL)(s) – A(SL)(d). Other potential places where NP can show up include A(J/Psi Phi), gamma, K-L(0) -> pi(0)v (v) over bar, t -> Zq and D-0 -> mu(+)mu(-) among others. The experimental data favours in this model the existence of an up vector-like quark with a mass below 600(1000) GeV at 1(2) sigma.
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Bordes, J., Chan, H. M., & Tsun, T. S. (2010). A solution to the strong CP problem transforming the theta angle to the KM CP-violating phase. Int. J. Mod. Phys. A, 25(32), 5897–5911.
Abstract: It is shown that in the scheme with a rotating fermion mass matrix (i.e. one with a scale-dependent orientation in generation space) suggested earlier for explaining fermion mixing and mass hierarchy, the theta angle term in the QCD action of topological origin can be eliminated by chiral transformations, while giving still nonzero masses to all quarks. Instead, the effects of such transformations get transmitted by the rotation to the CKM matrix as the KM phase giving, for theta of order unity, a Jarlskog invariant typically of order 10(-5), as experimentally observed. Strong and weak CP violations appear then as just two facets of the same phenomenon.
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Bordes, J., Chan, H. M., & Tsou, S. T. (2021). delta(CP) for leptons and a new take on CP physics with the FSM. Int. J. Mod. Phys. A, 36, 2150236–22pp.
Abstract: A bonus of the framed Standard Model (FSM), constructed initially to explain the mass and mixing patterns of quarks and leptons, is a solution (without axions) of the strong CP problem by cancelling the theta-angle term theta(I) Tr(H-mu v H-mu v*) in coloura by a chiral transformation on a quark zero mode which is inherent in FSM, and produces thereby a CP-violating phase in the CKM matrix similar in size to what is observed.' Extending here to flavour, one finds that there are two terms proportional to Tr(G(mu v) G(mu v)*): (a) in the action from flavour instantons with unknown coefficient, say theta(I)', (b) induced by the above FSM solution to the strong CP-problem with therefore known coefficient theta(C)'. Both terms can be cancelled in the FSM by a chiral transformation on the lepton zero mode to give a Jarlskog invariant J' in the PMNS matrix for leptons of order 10(-2), as is hinted by the experiment. But if, as suggested in Ref. 2, the term theta(I)' is to be cancelled by a chiral transformation in the predicted hidden sector to solve the strong CP problem therein, leaving only the term theta(C)' to be cancelled by the chiral transformation on leptons, then the following prediction results: J' similar to -0.012 (delta(CP)'similar to (1.11)pi) which is (i) of the right order, (ii) of the right sign and (iii) in the range favoured by the present experiment. Together with the earlier result for quarks, this offers an attractive unified treatment of all known CP physics.
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