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Husek, T., Monsalvez-Pozo, K., & Portoles, J. (2021). Lepton-flavour violation in hadronic tau decays and mu-tau conversion in nuclei. J. High Energy Phys., 01(1), 059–48pp.
Abstract: Within the Standard Model Effective Field Theory framework, with operators up to dimension 6, we perform a model-independent analysis of the lepton-flavour-violating processes involving tau leptons. Namely, we study hadronic tau decays and l-tau conversion in nuclei, with l = e, mu. Based on available experimental limits, we establish constraints on the Wilson coefficients of the operators contributing to these processes. Our work paves the way to extract the related information from Belle II and foreseen future experiments.
Keywords: Beyond Standard Model; Effective Field Theories
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Krause, C., Pich, A., Rosell, I., Santos, J., & Sanz-Cillero, J. J. (2019). Colorful imprints of heavy states in the electroweak effective theory. J. High Energy Phys., 05(5), 092–51pp.
Abstract: We analyze heavy states from generic ultraviolet completions of the Standard Model in a model-independent way and investigate their implications on the low-energy couplings of the electroweak effective theory. We build a general effective Lagrangian, implementing the electroweak symmetry breaking SU(2)(L) circle times SU(2)(R) SU(2)(L+R) with a non-linear Nambu-Goldstone realization, which couples the known particles to the heavy states. We generalize the formalism developed in previous works [1, 2] to include colored resonances, both of bosonic and fermionic type. We study bosonic heavy states with J(P) = 0(+/-) and J(P) = 1(+/-), in singlet or triplet SU(2)(L+R) representations and in singlet or octet representations of SU(3)(C) , and fermionic resonances with that are electroweak doublets and QCD triplets or singlets. Integrating out the heavy scales, we determine the complete pattern of low-energy couplings at the lowest non-trivial order. Some specific types of (strongly- and weakly-coupled) ultraviolet completions are discussed to illustrate the generality of our approach and to make contact with current experimental searches.
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Liem, S., Bertone, G., Calore, F., Ruiz de Austri, R., Tait, T. M. P., Trotta, R., et al. (2016). Effective field theory of dark matter: a global analysis. J. High Energy Phys., 09(9), 077–22pp.
Abstract: We present global fits of an effective field theory description of real, and complex scalar dark matter candidates. We simultaneously take into account all possible dimension 6 operators consisting of dark matter bilinears and gauge invariant combinations of quark and gluon fields. We derive constraints on the free model parameters for both the real (five parameters) and complex (seven) scalar dark matter models obtained by combining Planck data on the cosmic microwave background, direct detection limits from LUX, and indirect detection limits from the Fermi Large Area Telescope. We find that for real scalars indirect dark matter searches disfavour a dark matter particle mass below 100 GeV. For the complex scalar dark matter particle current data have a limited impact due to the presence of operators that lead to p-wave annihilation, and also do not contribute to the spin-independent scattering cross-section. Although current data are not informative enough to strongly constrain the theory parameter space, we demonstrate the power of our formalism to reconstruct the theoretical parameters compatible with an actual dark matter detection, by assuming that the excess of gamma rays observed by the Fermi Large Area Telescope towards the Galactic centre is entirely due to dark matter annihilations. Please note that the excess can very well be due to astrophysical sources such as millisecond pulsars. We find that scalar dark matter interacting via effective field theory operators can in principle explain the Galactic centre excess, but that such interpretation is in strong tension with the non-detection of gamma rays from dwarf galaxies in the real scalar case. In the complex scalar case there is enough freedom to relieve the tension.
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Murgui, C., Peñuelas, A., Jung, M., & Pich, A. (2019). Global fit to b -> c tau nu transitions. J. High Energy Phys., 09(9), 103–45pp.
Abstract: We perform a general model-independent analysis of b -> c tau(nu) over bar (tau) transitions, including measurements of R-D, R-D*, their q(2) differential distributions, the recently measured longitudinal D* polarization F-L(D)*, and constraints from the B-c -> tau(nu) over bar (tau) lifetime, each of which has significant impact on the fit. A global fit to a general set of Wilson coefficients of an effective low-energy Hamiltonian is presented, the solutions of which are interpreted in terms of hypothetical new-physics mediators. From the obtained results we predict selected b -> c tau(nu) over bar (tau) observables, such as the baryonic transition Lambda(b) -> Lambda(c)tau(nu) over bar (tau), the ratio R-J/psi, the forward-backward asymmetries A(FB)(D()*()), the tau polarization asymmetries P-tau(D()*()), and the longitudinal D* polarization fraction F-L(D)*. The latter shows presently a slight tension with any new-physics model, such that an improved measurement could have an important impact. We also discuss the potential change due the very recently announced preliminary R-D(*) measurement by the Belle collaboration.
Keywords: Beyond Standard Model; Effective Field Theories
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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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