Bartl, A., Eberl, H., Herrmann, B., Hidaka, K., Majerotto, W., & Porod, W. (2011). Impact of squark generation mixing on the search for squarks decaying into fermions at LHC. Phys. Lett. B, 698(5), 380–388.
Abstract: We study the effect of squark generation mixing on squark production and decays at LHC in the Minimal Supersymmetric Standard Model (MSSM). We show that the effect can be very large despite the very strong constraints on quark-flavour violation (QFV) from experimental data on B mesons. We find that the two lightest up-type squarks (u) over bar (1.2) can have large branching ratios for the decays into c (chi) over bar (0)(1) and t (chi) over bar (0)(1) at the same time due to squark generation mixing, leading to QFV signals 'pp -> c (t) over bar (t (c) over bar) + missing-E-T + X' with a significant rate. The observation of this remarkable signature would provide a powerful test of supersymmetric QFV at LHC. This could have a significant impact on the search for squarks and the determination of the underlying MSSM parameters.
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Penalva, N., Hernandez, E., & Nieves, J. (2022). Visible energy and angular distributions of the charged particle from the tau-decay in b -> C tau (mu(nu)over-bar(mu)nu(tau), pi nu(tau), rho nu(tau))(nu)over-bar(tau) reactions. J. High Energy Phys., 04(4), 026–25pp.
Abstract: We study the d(2)Gamma(d)/(d omega d cos theta(d) ), d Gamma(d)/d cos theta(d) and d Gamma(d)/dE(d) distributions, which are defined in terms of the visible energy and polar angle of the charged particle from the tau-decay in b -> C tau (mu(nu) over bar (mu)nu(tau), pi nu(tau), rho nu(tau))(nu) over bar (tau), reactions. These differential decay widths could be measured in the near future with certain precision. The first two contain information on the transverse tau-spin, tau-angular and tau-angular-spin asymmetries of the H-b -> H-c tau(nu) over bar (tau) parent decay and, from a dynamical point of view, they are richer than the commonly used one, d(2)Gamma(d)/(d omega dE(d)), since the latter only depends on the tau longitudinal polarization. We pay attention to the deviations with respect to the predictions of the standard model (SM) for these new observables, considering new physics (NP) operators constructed using both right- and left-handed neutrino fields, within an effective field-theory approach. We present results for Lambda(b) -> Lambda(c)tau (mu(nu) over bar (mu)nu(tau), pi nu(tau), rho nu(tau))(nu) over bar (tau) and (B) over bar -> D-(*()) tau (mu(nu) over bar (mu)nu(tau), pi nu(tau), rho nu(tau))(nu) over bar (tau) sequential decays and discuss their use to disentangle between different NP models. In this respect, we show that d Gamma(d)/d cos theta(d) , which should be measured with sufficiently good statistics, becomes quite useful, especially in the tau -> pi nu(tau) mode. The study carried out in this work could be of special relevance due to the recent LHCb measurement of the lepton flavor universality ratio R Lambda(c) in agreement with the SM. The experiment identified the tau using its hadron decay into pi(-)pi(+)pi(-)nu(tau), and this result for R Lambda(c )which is in conflict with the phenomenology from the b-meson sector, needs confirmation from other tau reconstruction channels.
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Botella, F. J., Branco, G. C., & Rebelo, M. N. (2010). Minimal flavour violation and multi-Higgs models. Phys. Lett. B, 687(2-3), 194–200.
Abstract: We propose an extension of the hypothesis of Minimal Flavour Violation (MFV) to general multi-Higgs models without the assumption of Natural Flavour Conservation (NFC) in the Higgs sector. We study in detail under what conditions the neutral Higgs couplings are only functions of V-CKM and propose a MFV expansion for the neutral Higgs couplings to fermions.
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Bonilla, C., Lamprea, J. M., Peinado, E., & Valle, J. W. F. (2018). Flavour-symmetric type-II Dirac neutrino seesaw mechanism. Phys. Lett. B, 779, 257–261.
Abstract: We propose a Standard Model extension with underlying A(4) flavour symmetry where small Dirac neutrino masses arise from a Type-II seesaw mechanism. The model predicts the “golden” flavour-dependent bottom-tau mass relation, requires an inverted neutrino mass ordering and non-maximal atmospheric mixing angle. Using the latest neutrino oscillation global fit[ 1] we derive restrictions on the oscillation parameters, such as a correlation between delta(CP) and m(nu lightest).
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Carcamo Hernandez, A. E., Vishnudath, K. N., & Valle, J. W. F. (2023). Linear seesaw mechanism from dark sector. J. High Energy Phys., 09(9), 046–18pp.
Abstract: We propose a minimal model where a dark sector seeds neutrino mass generation radiatively within the linear seesaw mechanism. Neutrino masses are calculable, since treelevel contributions are forbidden by symmetry. They arise from spontaneous lepton number violation by a small Higgs triplet vacuum expectation value. Lepton flavour violating processes e.g. μ-> e gamma can be sizeable, despite the tiny neutrino masses. We comment also on dark-matter and collider implications.
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Centelles Chulia, S., Cepedello, R., & Medina, O. (2022). Absolute neutrino mass scale and dark matter stability from flavour symmetry. J. High Energy Phys., 10(10), 080–23pp.
Abstract: We explore a simple but extremely predictive extension of the scotogenic model. We promote the scotogenic symmetry Z(2) to the flavour non-Abelian symmetry sigma(81), which can also automatically protect dark matter stability. In addition, sigma(81) leads to striking predictions in the lepton sector: only Inverted Ordering is realised, the absolute neutrino mass scale is predicted to be m(lightest)approximate to 7.5x10(-4) eV and the Majorana phases are correlated in such a way that vertical bar m(ee)vertical bar approximate to 0.018 eV. The model also leads to a strong correlation between the solar mixing angle theta(12) and delta(CP), which may be falsified by the next generation of neutrino oscillation experiments. The setup is minimal in the sense that no additional symmetries or flavons are required.
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Bernigaud, J., Blanke, M., de Medeiros Varzielas, I., Talbert, J., & Zurita, J. (2022). LHC signatures of tau-flavoured vector leptoquarks. J. High Energy Phys., 08(8), 127–31pp.
Abstract: We consider the phenomenological signatures of Simplified Models of Flavourful Leptoquarks, whose Beyond-the-Standard Model (SM) couplings to fermion generations occur via textures that are well motivated from a broad class of ultraviolet flavour models (which we briefly review). We place particular emphasis on the study of the vector leptoquark Delta(mu) with assignments (3, 1, 2/3) under the SM's gauge symmetry, SU(3)(C) x SU(2)(L) x U(1)(Y), which has the tantalising possibility of explaining both R-K(*) and R-D(*) anomalies. Upon performing global likelihood scans of the leptoquark's coupling parameter space, focusing in particular on models with tree-level couplings to a single charged lepton species, we then provide confidence intervals and benchmark points preferred by low(er)-energy flavour data. Finally, we use these constraints to further evaluate the (promising) Large Hadron Collider (LHC) detection prospects of pairs of tau-flavoured Delta(mu), through their distinct (a)symmetric decay channels. Namely, we consider direct third-generation leptoquark and jets plus missing-energy searches at the LHC, which we find to be complementary. Depending on the simplified model under consideration, the direct searches constrain the Delta(mu), mass up to 1500-1770 GeV when the branching fraction of Delta(mu), is entirely to third-generation quarks (but are significantly reduced with decreased branching ratios to the third generation), whereas the missing-energy searches constrain the mass up to 1150-1700 GeV while being largely insensitive to the third-generation branching fraction.
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Drewes, M., Georis, Y., Hagedorn, C., & Klaric, J. (2022). Low-scale leptogenesis with flavour and CP symmetries. J. High Energy Phys., 12(12), 044–113pp.
Abstract: We consider a type-I seesaw framework endowed with a flavour symmetry, belonging to the series of non-abelian groups increment (3 n(2)) and increment (6 n(2)), and a CP symmetry. Breaking these symmetries in a non-trivial way results in the right-handed neutrinos being degenerate in mass up to possible (further symmetry-breaking) splittings kappa and lambda, while the neutrino Yukawa coupling matrix encodes the entire flavour structure in the neutrino sector. For a fixed combination of flavour and CP symmetry and residual groups, this matrix contains five real free parameters. Four of them are determined by the light neutrino mass spectrum and by accommodating experimental data on lepton mixing well, while the angle theta(R) is related to right-handed neutrinos. We scrutinise for all four lepton mixing patterns, grouped into Case 1) through Case 3 b.1), the potential to generate the baryon asymmetry of the Universe through low-scale leptogenesis numerically and analytically. The main results are: a) the possible correlation of the baryon asymmetry and the Majorana phases, encoded in the Pontecorvo-Maki-Nakagawa-Sakata mixing matrix, in certain instances; b) the possibility to generate the correct amount of baryon asymmetry for vanishing splittings kappa and lambda among the right-handed neutrinos as well as for large kappa, depending on the case and the specific choice of group theory parameters; c) the chance to produce sufficient baryon asymmetry for large active-sterile mixing angles, enabling direct experimental tests at current and future facilities, if theta(R) is close to a special value, potentially protected by an enhanced residual symmetry. We elucidate these results with representative examples of flavour and CP symmetries, which all lead to a good agreement with the measured values of the lepton mixing angles and, possibly, the current indication of the CP phase delta. We identify the CP-violating combinations relevant for low-scale leptogenesis, and show that the parametric dependence of the baryon asymmetry found in the numerical study can be understood well with their help.
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de Adelhart Toorop, R., Bazzocchi, F., & Morisi, S. (2012). Quark mixing in the discrete dark matter model. Nucl. Phys. B, 856(3), 670–681.
Abstract: We consider a model in which dark matter is stable as it is charged under a Z(2) symmetry that is residual after an A(4) flavour symmetry is broken. We consider the possibility to generate the quark masses by charging the quarks appropriately under A(4). We find that it is possible to generate the CKM mixing matrix by an interplay of renormalisable and dimension-six operators. In this set-up, we predict the third neutrino mixing angle to be large and the dark matter relic density to be in the correct range. Low energy observables – in particular meson-antimeson oscillations – are hard to facilitate. We find that only in a situation where there is a strong cancellation between the Standard Model contribution and the contribution of the new Higgs fields, B meson oscillations are under control.
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Penalva, N., Flynn, J. M., Hernandez, E., & Nieves, J. (2024). Study of new physics effects in (B)over-bars → Ds(*) τ-(ν)over-bar τ semileptonic decays using lattice QCD form factors and heavy quark effective theory. J. High Energy Phys., 01(1), 163–33pp.
Abstract: We benefit from the lattice QCD determination by the HPQCD of the Standard Model (SM) form factors for the (B) over bar (s) -> D-s [Phys. Rev. D101(2020) 074513] and the SM and tensor ones for the (B) over bar (s) -> D-s* (arXiv:2304.03137[hep-lat]) semileptonic decays, and the heavy quark effective theory (HQET) relations for the analogous B -> D-(*()) decays obtained by F.U. Bernlochner et al. in Phys. Rev. D95(2017) 115008, to extract the leading and sub-leading Isgur-Wise functions for the (B) over bar (s) -> D-s(()*()) decays. Further use of the HQET relations allows us to evaluate the corresponding scalar, pseudoscalar and tensor form factors needed for a phenomenological study of new physics (NP) effects on the (B) over bar (s) -> D-s(()*()) semileptonic decay. At present, the experimental values for the ratios R-D(*) = Gamma[ (B) over bar -> D-(*())(tau- (nu) over bar tau)]/Gamma[(B) over bar -> D-(*())e(-)(mu(-)) (nu) over bar (e(mu))]are the best signal in favor of lepton flavor universality violation (LFUV) seen in charged current (CC) b -> c decays. In this work we conduct a study of NP effects on the (B) over bar (s) -> D-s(()*()) tau(-)(tau) semileptonic decays by comparing tau spin, angular and spin-angular asymmetry distributions obtained within the SM and three different NP scenarios. As expected from SU(3) light-flavor symmetry, we get results close to the ones found in a similar analysis of the (B) over bar -> D-(*()) case. The measurement of the (B) over bar (s) -> D-s(()*())(l (nu) over bar tau) semileptonic decays, which is within reach of present experiments, could then be of relevance in helping to establish or rule out LFUV in CC b -> c transitions.
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