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Hernandez, P., Kekic, M., Lopez-Pavon, J., Racker, J., & Salvado, J. (2016). Testable baryogenesis is in seesaw models. J. High Energy Phys., 08(8), 157–29pp.
Abstract: We revisit the production of baryon asymmetries in the minimal type I seesaw model with heavy Majorana singlets in the GeV range. In particular we include “washout” effects from scattering processes with gauge bosons, Higgs decays and inverse decays, besides the dominant top scatterings. We show that in the minimal model with two singlets, and for an inverted light neutrino ordering, future measurements from SHiP and neutrinoless double beta decay could in principle provide sufficient information to predict the matter-antimatter asymmetry in the universe. We also show that SHiP measurements could provide very valuable information on the PMNS CP phases.
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ATLAS Collaboration(Aaboud, M. et al), Alvarez Piqueras, D., Barranco Navarro, L., Cabrera Urban, S., Castillo Gimenez, V., Cerda Alberich, L., et al. (2016). Search for resonances in diphoton events at root s=13 TeV with the ATLAS detector. J. High Energy Phys., 09(9), 001–50pp.
Abstract: Searches for new resonances decaying into two photons in the ATLAS experiment at the CERN Large Hadron Collider are described. The analysis is based on protonproton collision data corresponding to an integrated luminosity of 3.2 fb(-1) at root s = 13TeV recorded in 2015. Two searches are performed, one targeted at a spin-2 particle of mass larger than 500 GeV, using Randall-Sundrum graviton states as a benchmark model, and one optimized for a spin-0 particle of mass larger than 200 GeV. Varying both the mass and the decay width, the most significant deviation from the background-only hypothesis is observed at a diphoton invariant mass around 750 GeV with local significances of 3.8 and 3.9 standard deviations in the searches optimized for a spin-2 and spin-0 particle, respectively. The global significances are estimated to be 2.1 standard deviations for both analyses. The consistency between the data collected at 13TeV and 8TeV is also evaluated. Limits on the production cross section times branching ratio to two photons for the two resonance types are reported.
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Anamiati, G., Hirsch, M., & Nardi, E. (2016). Quasi-Dirac neutrinos at the LHC. J. High Energy Phys., 10(10), 010–19pp.
Abstract: Lepton number violation is searched for at the LHC using same-sign leptons plus jets. The standard lore is that the ratio of same-sign lepton to opposite-sign lepton events, R-ll, is equal to R-ll = 1 (R-ll = 0) for Majorana (Dirac) neutrinos. We clarify under which conditions the ratio Rll can assume values different from 0 and 1, and we argue that the precise value 0 < R-ll < 1 is controlled by the mass splitting versus the width of the quasi-Dirac resonances. A measurement of R-ll not equal 0, 1 would then contain valuable information about the origin of neutrino masses. We consider as an example the inverse seesaw mechanism in a left-right symmetric scenario, which is phenomenologically particularly interesting since all the heavy states in the high energy completion of the model could be within experimental reach. A prediction of this scenario is a correlation between the values of R-ll and the ratio between the rates for heavy neutrino decays into standard model gauge bosons, and into three body final states ljj mediated by off-shell W-R exchange.
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Herrero-Garcia, J., Rius, N., & Santamaria, A. (2016). Higgs lepton flavour violation: UV completions and connection to neutrino masses. J. High Energy Phys., 11(11), 084–45pp.
Abstract: We study lepton violating Higgs (HLFV) decays, first from the effective field theory (EFT) point of view, and then analysing the different high-energy realizations of the operators of the EFT, highlighting the most promising models. We argue why two Higgs doublet models can have a BR(h -> tau mu) similar to 0:01, and why this rate is suppressed in all other realizations including vector-like leptons. We further discuss HLFV in the context of neutrino mass models: in most cases it is generated at one loop giving always BR (h -> tau mu) < 10(-4) and typically much less, which is beyond experimental reach. However, both the Zee model and extended left-right symmetric models contain extra SU(2) doublets coupled to leptons and could in principle account for the observed excess, with interesting connections between HLFV and neutrino parameters.
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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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Fuentes-Martin, J., Portoles, J., & Ruiz-Femenia, P. (2016). Integrating out heavy particles with functional methods: a simplified framework. J. High Energy Phys., 09(9), 156–26pp.
Abstract: We present a systematic procedure to obtain the one-loop low-energy effective Lagrangian resulting from integrating out the heavy fields of a given ultraviolet theory. We show that the matching coefficients are determined entirely by the hard region of the functional determinant involving the heavy fields. This represents an important simplification with respect the conventional matching approach, where the full and effective theory contributions have to be computed separately and a cancellation of the infrared divergent parts has to take place. We illustrate the method with a descriptive toy model and with an extension of the Standard Model with a heavy real scalar triplet. A comparison with other schemes that have been put forward recently is also provided.
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Gonzalez, L., Helo, J. C., Hirsch, M., & Kovalenko, S. G. (2016). Scalar-mediated double beta decay and LHC. J. High Energy Phys., 12(12), 130–15pp.
Abstract: The decay rate of neutrinoless double beta (0 nu beta beta) decay could be dominated by Lepton Number Violating (LNV) short-range diagrams involving only heavy scalar intermediate particles, known as “topology-II” diagrams. Examples are diagrams with diquarks, leptoquarks or charged scalars. Here, we compare the LNV discovery potentials of the LHC and 0 nu beta beta-decay experiments, resorting to three example models, which cover the range of the optimistic-pessimistic cases for 0 nu beta beta decay. We use the LHC constraints from dijet as well as leptoquark searches and find that already with 20/fb the LHC will test interesting parts of the parameter space of these models, not excluded by the current limits on 0 nu beta beta-decay.
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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.
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Rocha-Moran, P., & Vicente, A. (2016). Lepton Flavor Violation in the singlet-triplet scotogenic model. J. High Energy Phys., 07(7), 078–25pp.
Abstract: We investigate lepton flavor violation (LFV) in the the singlet-triplet scotogenic model in which neutrinos acquire non-zero masses at the 1-loop level. In contrast to the most popular variant of this setup, the singlet scotogenic model, this version includes a triplet fermion as well as a triplet scalar, leading to a scenario with a richer dark matter phenomenology. Taking into account results from neutrino oscillation experiments, we explore some aspects of the LFV phenomenology of the model. In particular, we study the relative weight of the dipole operators with respect to other contributions to the LFV amplitudes and determine the most constraining observables. We show that in large portions of the parameter space, the most promising experimental perspectives are found for LFV 3-body decays and for coherent mu-e conversion in nuclei.
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Escudero, M., Rius, N., & Sanz, V. (2017). Sterile neutrino portal to Dark Matter I: the U(1)(B-L) case. J. High Energy Phys., 02(2), 045–27pp.
Abstract: In this paper we explore the possibility that the sterile neutrino and Dark Matter sectors in the Universe have a common origin. We study the consequences of this assumption in the simple case of coupling the dark sector to the Standard Model via a global U(1)(B-L), broken down spontaneously by a dark scalar. This dark scalar provides masses to the dark fermions and communicates with the Higgs via a Higgs portal coupling. We find an interesting interplay between Dark Matter annihilation to dark scalars – the CP-even that mixes with the Higgs and the CP-odd which becomes a Goldstone boson, the Majoron and heavy neutrinos, as well as collider probes via the coupling to the Higgs. Moreover, Dark Matter annihilation into sterile neutrinos and its subsequent decay to gauge bosons and quarks, charged leptons or neutrinos lead to indirect detection signatures which are close to current bounds on the gamma ray flux from the galactic center and dwarf galaxies.
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