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Boucenna, S. M., Celis, A., Fuentes-Martin, J., Vicente, A., & Virto, J. (2016). Phenomenology of an SU(2) x SU(2) x U(1) model with lepton-flavour non-universality. J. High Energy Phys., 12(12), 059–43pp.
Abstract: We investigate a gauge extension of the Standard Model in light of the observed hints of lepton universality violation in b -> clv and b -> sl(+) l(-) decays at BaBar, Belle and LHCb. The model consists of an extended gauge group SU(2)(1) x SU(2)(2) x U(l)(Y) which breaks spontaneously around the TeV scale to the electroweak gauge group. Fermion mixing effects with vector -like fermions give rise to potentially large new physics contributions in flavour transitions mediated by WI and Z' bosons. This model can ease tensions in B -physics data while satisfying stringent bounds from flavour physics, and electroweak precision data. Possible ways to test the proposed new physics scenario with upcoming experimental measurements are discussed. Among other predictions, the ratios RM =Gamma(B -> M mu(+)mu(-))/Gamma(B -> Me(+)e(-)), with M = K*, phi, are found to be reduced with respect to the Standard Model expectation R-M similar or equal to 1.
Keywords: Beyond Standard Model; Gauge Symmetry
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Botella, F. J., Branco, G. C., Carmona, A., Nebot, M., Pedro, L., & Rebelo, M. N. (2014). Physical constraints on a class of two-Higgs doublet models with FCNC at tree level. J. High Energy Phys., 07(7), 078–33pp.
Abstract: We analyse the constraints and some of the phenomenological implications of a class of two Higgs doublet models where there are flavour-changing neutral currents (FCNC) at tree level but the potentially dangerous FCNC couplings are suppressed by small entries of the CKM matrix V. This class of models have the remarkable feature that, as a result of a discrete symmetry of the Lagrangian, the FCNC couplings are entirely fixed in the quark sector by V and the ratio v(2)/v(1) of the vevs of the neutral Higgs. The discrete symmetry is extended to the leptonic sector, so that there are FCNC in the leptonic sector with their flavour structure fixed by the leptonic mixing matrix. We analyse a large number of processes, including decays mediated by charged Higgs at tree level, processes involving FCNC at tree level, as well as loop induced processes. We show that in this class of models one has new physical scalars beyond the standard Higgs boson, with masses reachable at the next round of experiments.
Keywords: Higgs Physics; Beyond Standard Model
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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.
Keywords: Beyond Standard Model; Rare Decays; CP violation
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Botella, F. J., Branco, G. C., Nebot, M., & Rebelo, M. N. (2011). Two-Higgs leptonic minimal flavour violation. J. High Energy Phys., 10(10), 037–21pp.
Abstract: We construct extensions of the Standard Model with two Higgs doublets, where there are flavour changing neutral currents both in the quark and leptonic sectors, with their strength fixed by the fermion mixing matrices V(CKM) and V(PMNS). These models are an extension to the leptonic sector of the class of models previously considered by Branco, Grimus and Lavoura, for the quark sector. We consider both the cases of Dirac and Majorana neutrinos and identify the minimal discrete symmetry required in order to implement the models in a natural way.
Keywords: Higgs Physics; Beyond Standard Model; Neutrino Physics
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Bordes, J., Hong-Mo, C., & Tsun, T. S. (2019). Accommodating three low-scale anomalies (g-2, Lamb shift, and Atomki) in the framed Standard Model. Int. J. Mod. Phys. A, 34(25), 1950140–27pp.
Abstract: The framed Standard Model (FSM) predicts a 0(+) boson with mass around 20 MeV in the “hidden sector,” which mixes at tree level with the standard Higgs hW and hence acquires small couplings to quarks and leptons which can be calculated in the FSM apart from the mixing parameter rho Uh. The exchange of this mixed state U will contribute to g – 2 and to the Lamb shift. By adjusting rho Uh alone, it is found that the FSM can satisfy all present experimental bounds on the g – 2 and Lamb shift anomalies for μand e, and for the latter for both hydrogen and deuterium. The FSM predicts also a 1(-) boson in the “hidden sector” with a mass of 17 MeV, that is, right on top of the Atomki anomaly X. This mixes with the photon at 1-loop level and couples thereby like a dark photon to quarks and leptons. It is however a compound state and is thought likely to possess additional compound couplings to hadrons. By adjusting the mixing parameter and the X's compound coupling to nucleons, the FSM can reproduce the production rate of the X in beryllium decay as well as satisfy all the bounds on X listed so far in the literature. The above two results are consistent in that the U, being 0(+), does not contribute to the Atomki anomaly if parity and angular momentum are conserved, while X, though contributing to g – 2 and Lamb shift, has smaller couplings than U and can, at first instance, be neglected there. Thus, despite the tentative nature of the three anomalies in experiment on the one hand and of the FSM as theory on the other, the accommodation of the former in the latter has strengthened the credibility of both. Indeed, if this FSM interpretation were correct, it would change the whole aspect of the anomalies from just curiosities to windows into a vast hitherto hidden sector comprising at least in part the dark matter which makes up the bulk of our universe.
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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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Bordes, J., Chan, H. M., & Tsou, S. T. (2021). Unified FSM treatment of CP physics extended to hidden sector giving (i) delta(CP) for leptons as prediction, (ii) new hints on the material content of the universe. Int. J. Mod. Phys. A, 36, 2150238–19pp.
Abstract: A unified treatment of CP physics for quarks and leptons in the framed Standard Model (FSM) is extended to include the predicted hidden sector giving as consequences: (i) that an earlier part estimate of the Jarlskog invariant J' for leptons is turned into a prediction for its actual value, i.e. J' similar to -0.012 (delta(CP)' similar to 1.11 pi), which is of the right order of magnitude, of the right sign, and in the range of values favoured by the present experiment, (ii) some novel twists to the effects of CP-violation on the material content of the universe.
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Bordes, J., Chan, H. M., & Tsou, S. T. (2023). A vacuum transition in the FSM with a possible new take on the horizon problem in cosmology. Int. J. Mod. Phys. A, 38(25), 2350124–32pp.
Abstract: The framed standard model (FSM), constructed to explain the empirical mass and mixing patterns (including CP phases) of quarks and leptons, in which it has done quite well, gives otherwise the same result as the standard model (SM) in almost all areas in particle physics where the SM has been successfully applied, except for a few specified deviations such as the W mass and the g-2 of muons, that is, just where experiment is showing departures from what SM predicts. It predicts further the existence of a hidden sector of particles some of which may function as dark matter. In this paper, we first note that the above results involve, surprisingly, the FSM undergoing a vacuum transition (VTR1) at a scale of around 17MeV, where the vacuum expectation values of the colour framons (framed vectors promoted into fields) which are all nonzero above that scale acquire some vanishing components below it. This implies that the metric pertaining to these vanishing components would vanish also. Important consequences should then ensue, but these occur mostly in the unknown hidden sector where empirical confirmation is hard at present to come by, but they give small reflections in the standard sector, some of which may have already been seen. However, one notes that if, going off at a tangent, one imagines colour to be embedded, Kaluza-Klein (KK) fashion, into a higher-dimensional space-time, then this VTR1 would cause 2 of the compactified dimensions to collapse. This might mean then that when the universe cooled to the corresponding temperature of 1011 K when it was about 10-3 s old, this VTR1 collapse would cause the three spatial dimensions of the universe to expand to compensate. The resultant expansion is estimated, using FSM parameters previously determined from particle physics, to be capable, when extrapolated backwards in time, of bringing the present universe back inside the then horizon, solving thus formally the horizon problem. Besides, VTR1 being a global phenomenon in the FSM, it would switch on and off automatically and simultaneously over all space, thus requiring seemingly no additional strategy for a graceful exit. However, this scenario has not been checked for consistency with other properties of the universe and is to be taken thus not as a candidate solution of the horizon problem but only as an observation from particle physics which might be of interest to cosmologists and experts in the early universe. For particle physicists also, it might serve as an indicator for how relevant this VTR1 can be, even if the KK assumption is not made.
Keywords: Framed standard model; phase transition; early Universe; cosmology
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Bordes, J., Chan, H. M., & Tsou, S. T. (2023). Search for new physics in semileptonic decays of K and B as implied by the g-2 anomaly in FSM. Int. J. Mod. Phys. A, 38, 2350177–24pp.
Abstract: The framed standard model (FSM), constructed to explain, with some success, why there should be three and apparently only three generations of quarks and leptons in nature falling into a hierarchical mass and mixing pattern,(10) suggests also, among other things, a scalar boson U, with mass around 17 MeV and small couplings to quarks and leptons,(11) which might explain(9) the g – 2 anomaly reported in experiment.(12) The U arises in FSM initially as a state in the predicted “hidden sector” with mass around 17 MeV, which mixes with the standard model (SM) Higgs h(W), acquiring thereby a coupling to quarks and leptons and a mass just below 17 MeV. The initial purpose of this paper is to check whether this proposal is compatible with experiment on semileptonic decays of Ks and Bs where the U can also appear. The answer to this we find is affirmative, in that the contribution of U to new physics as calculated in the FSM remains within the experimental bounds, but only if m(U) lies within a narrow range just below the unmixed mass. As a result from this, one has an estimate m(U) similar to 15-17 MeV for the mass of U, and from some further considerations the estimate Gamma(U) similar to 0.02 eV for its width, both of which may be useful for an eventual search for it in experiment. If found, it will be, for the FSM, not just the discovery of a predicted new particle, but the opening of a window into a whole “hidden sector” containing at least some, perhaps even the bulk, of the dark matter in the universe.
Keywords: Framed standard model; light scalar boson; meson decays
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Bordes, J., Hong-Mo, C., & Tsun, T. S. (2018). The Z boson in the framed standard model. Int. J. Mod. Phys. A, 33(32), 1850190–19pp.
Abstract: The framed standard model (FSM), constructed initially for explaining the existence of three fermion generations and the hierarchical mass and mixing patterns of quarks and leptons,(1,2) suggests also a “hidden sector” of particles(3) including some dark matter candidates. It predicts in addition a new vector boson G, with mass of order TeV, which mixes with the gamma and Z of the standard model yielding deviations from the standard mixing scheme, all calculable in terms of a single unknown parameter mG. Given that standard mixing has been tested already to great accuracy by experiment, this could lead to contradictions, but it is shown here that for the three crucial and testable cases so far studied (i) m(Z) – m(W), (ii) Gamma(Z -> l(+)l(-)), (iii) Gamma(Z -> hadrons), the deviations are all within the present stringent experimental bounds provided m(G) > 1 TeV, but should soon be detectable if experimental accuracy improves. This comes about because of some subtle cancellations, which might have a deeper reason that is not yet understood. By virtue of mixing, G can be produced at the LHC and appear as a l(+)l(-) anomaly. If found, it will be of interest not only for its own sake but serve also as a window on to the “hidden sector” into which it will mostly decay, with dark matter candidates as most likely products.
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