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de Medeiros Varzielas, I., Neder, T., & Zhou, Y. L. (2018). Effective alignments as building blocks of flavor models. Phys. Rev. D, 97(11), 115033–21pp.
Abstract: Flavor models typically rely on flavons-scalars that break the family symmetry by acquiring vacuum expectation values in specific directions. We develop the idea of effective alignments, i.e., cases where the contractions of multiple flavons give rise to directions that are hard or impossible to obtain directly by breaking the family symmetry. Focusing on the example where the symmetry is S-4, we list the effective alignments that can be obtained from flavons vacuum expectation values that arise naturally from S-4. Using those effective alignments as building blocks, it is possible to construct flavor models, for example by using the effective alignments in constrained sequential dominance models. We illustrate how to obtain several of the mixing schemes in the literature, and explicitly construct renormalizable models for three viable cases, two of which lead to trimaximal mixing scenarios.
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Hirsch, M., Srivastava, R., & Valle, J. W. F. (2018). Can one ever prove that neutrinos are Dirac particles? Phys. Lett. B, 781, 302–305.
Abstract: According to the “Black Box” theorem the experimental confirmation of neutrinoless double beta decay (0 nu 2 beta) would imply that at least one of the neutrinos is a Majorana particle. However, a null 0 nu 2 beta signal cannot decide the nature of neutrinos, as it can be suppressed even for Majorana neutrinos. In this letter we argue that if the null 0 nu 2 beta decay signal is accompanied by a 0 nu 2 beta quadruple beta decay signal, then at least one neutrino should be a Dirac particle. This argument holds irrespective of the underlying processes leading to such decays.
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Gonzalez, M., Hirsch, M., & Kovalenko, S. G. (2018). Neutrinoless double beta decay and QCD running at low energy scales. Phys. Rev. D, 97(11), 115005–6pp.
Abstract: There is a common belief that the main uncertainties in the theoretical analysis of neutrinoless double beta (0 nu beta beta) decay originate from the nuclear matrix elements. Here, we uncover another previously overlooked source of potentially large uncertainties stemming from nonperturbative QCD effects. Recently perturbative QCD corrections have been calculated for all dimension 6 and 9 effective operators describing 0 nu beta beta-decay and their importance for a reliable treatment of 0 nu beta beta-decay has been demonstrated. However, these perturbative results are valid at energy scales above similar to 1 GeV, while the typical 0 nu beta beta scale is about similar to 100 MeV. In view of this fact we examine the possibility of extrapolating the perturbative results towards sub-GeV nonperturbative scales on the basis of the QCD coupling constant “freezing” behavior using background perturbation theory. Our analysis suggests that such an infrared extrapolation does modify the perturbative results for both short-range and long-range mechanisms of 0 nu beta beta-decay in general only moderately. We also discuss that the tensor circle times tensor effective operator cannot appear alone in the low energy limit of any renormalizable high-scale model and then demonstrate that all five linearly independent combinations of the scalar and tensor operators, which can appear in renormalizable models, are infrared stable.
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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. (2018). Measurement of the Soft-Drop Jet Mass in pp Collisions at root s=13 TeV with the ATLAS Detector. Phys. Rev. Lett., 121(9), 092001–21pp.
Abstract: Jet substructure observables have significantly extended the search program for physics beyond the standard model at the Large Hadron Collider. The state-of-the-art tools have been motivated by theoretical calculations, but there has never been a direct comparison between data and calculations of jet substructure observables that are accurate beyond leading-logarithm approximation. Such observables are significant not only for probing the collinear regime of QCD that is largely unexplored at a hadron collider, but also for improving the understanding of jet substructure properties that are used in many studies at the Large Hadron Collider. This Letter documents a measurement of the first jet substructure quantity at a hadron collider to be calculated at next-to-next-to-leading-logarithm accuracy. The normalized, differential cross section is measured as a function of log(10)rho(2), where rho is the ratio of the soft-drop mass to the ungroomed jet transverse momentum. This quantity is measured in dijet events from 32.9 fb(-1) of root s = 13 TeV proton-proton collisions recorded by the ATLAS detector. The data are unfolded to correct for detector effects and compared to precise QCD calculations and leading-logarithm particle-level Monte Carlo simulations.
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Boggia, M., Cruz-Martinez, J. M., Frellesvig, H., Glover, N., Gomez-Ambrosio, R., Gonella, G., et al. (2018). The HiggsTools handbook: a beginners guide to decoding the Higgs sector. J. Phys. G, 45(6), 065004–152pp.
Abstract: This report summarises some of the activities of the HiggsTools initial training network working group in the period 2015-2017. The main goal of this working group was to produce a document discussing various aspects of state-of-the-art Higgs physics at the large hadron collider (LHC) in a pedagogic manner The first part of the report is devoted to a description of phenomenological searches for new physics (NP) at the LHC. All of the available studies of the couplings of the new resonance discovered in 2012 by the ATLAS and CMS experiments (Aad et al (ATLAS Collaboration) 2012 Phys. Lett. B 716 1-29; Chatrchyan et al (CMS Collaboration) 2012 Phys. Lett. B 716 30-61) conclude that it is compatible with the Higgs boson of the standard model (SM) within present precision. So far the LHC experiments have given no direct evidence for any physical phenomena that cannot be described by the SM. As the experimental measurements become more and more precise, there is a pressing need for a consistent framework in which deviations from the SM predictions can be computed precisely. Such a framework should be applicable to measurements in all sectors of particle physics, not only LHC Higgs measurements but also electroweak precision data, etc. We critically review the use of the k-framework, fiducial and simplified template cross sections, effective field theories, pseudoobservables and phenomenological Lagrangians. Some of the concepts presented here are well known and were used already at the time of the large electron-positron collider (LEP) experiment. However, after years of theoretical and experimental development, these techniques have been refined, and we describe new tools that have been introduced in order to improve the comparison between theory and experimental data. In the second part of the report, we propose Phi(eta)* as a new and complementary observable for studying Higgs boson production at large transverse momentum in the case where the Higgs boson decays to two photons. The Phi(eta)* variable depends on measurements of the angular directions and rapidities of the two Higgs decay products rather than the energies, and exploits the information provided by the calorimeter in the detector. We show that, even without tracking information, the experimental resolution for Phi(eta)* is better than that of the transverse momentum of the photon pair, particularly at low transverse momentum. We make a detailed study of the phenomenology of the Phi(eta)* variable, contrasting the behaviour with the Higgs transverse momentum distribution using a variety of theoretical tools including event generators and fixed order perturbative computations. We consider the theoretical uncertainties associated with both p TH and Phi(eta)* distributions. Unlike the transverse momentum distribution, the Phi(eta)* distribution is well predicted using the Higgs effective field theory in which the top quark is integrated out-even at large values of Phi(eta)*-thereby making this a better observable for extracting the parameters of the Higgs interaction. In contrast, the potential of the Phi(eta)* distribution as a probe of NP is rather limited, since although the overall rate is affected by the presence of additional heavy fields, the shape of the Phi(eta)* distribution is relatively insensitive to heavy particle thresholds.
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Liang, W. H., Dias, J. M., Debastiani, V. R., & Oset, E. (2018). Molecular Omega(b) states. Nucl. Phys. B, 930, 524–532.
Abstract: Motivated by the recent finding of five Omega(c) states by the LHCb collaboration, and the successful reproduction of three of them in a recent approach searching for molecular states of meson-baryon with the quantum numbers of Omega(c), we extend these ideas and make predictions for the interaction of meson-baryon in the beauty sector, searching for poles in the scattering matrix that correspond to physical states. We find several Omega(b) states: two states with masses 6405 MeV and 6465 MeV for J(P) = 1/2(-) ; two more states with masses 6427 MeV and 6665 MeV for 3/4(-) ; and three states between 6500 and 6820 MeV, degenerate with J(P) = 1/2(-), 3/4(-), stemming from the interaction of vector-baryon in the beauty sector.
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Casas, J. A., Gomez Vargas, G. A., Moreno, J. M., Quilis, J., & Ruiz de Austri, R. (2018). Extended Higgs-portal dark matter and the Fermi-LAT Galactic Center Excess. J. Cosmol. Astropart. Phys., 06(6), 031–16pp.
Abstract: In the present work, we show that the Galactic Center Excess (GCE) emission, as recently updated by the Fermi-LAT Collaboration, could be explained by a mixture of Fermi bubbles-like emission plus dark matter (DM) annihilation, in the context of a scalar-singlet Higgs portal scenario (SHP). In fact, the standard SHP, where the DM particle, S, only has renormalizable interactions with the Higgs, is non-operational due to strong constraints, especially from DM direct detection limits. Thus we consider the most economical extension, called ESHP (for extended SHP), which consists solely in the addition of a second (more massive) scalar singlet in the dark sector. The second scalar can be integrated-out, leaving a standard SHP plus a dimension-6 operator. Mainly, this model has only two relevant parameters (the DM mass and the coupling of the dim-6 operator). DM annihilation occurs mainly into two Higgs bosons, SS -> hh. We demonstrate that, despite its economy, the ESHP model provides an excellent fit to the GCE (with p-value similar to 0.6-0.7) for very reasonable values of the parameters, in particular, ms similar or equal to 130 GeV. This agreement of the DM candidate to the GCE properties does not clash with other observables and keep the S – particle relic density at the accepted value for the DM content in the universe.
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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. (2018). Search for top-squark pair production in final states with one lepton, jets, and missing transverse momentum using 36 fb(-1) of root s=13 TeV pp collision data with the ATLAS detector. J. High Energy Phys., 06(6), 108–96pp.
Abstract: The results of a search for the direct pair production of top squarks, the supersymmetric partner of the top quark, in final states with one isolated electron or muon, several energetic jets, and missing transverse momentum are reported. The analysis also targets spin-0 mediator models, where the mediator decays into a pair of dark-matter particles and is produced in association with a pair of top quarks. The search uses data from proton-proton collisions delivered by the Large Hadron Collider in 2015 and 2016 at a centre-of-mass energy of root s = 13TeV and recorded by the ATLAS detector, corresponding to an integrated luminosity of 36 fb(-1). A wide range of signal scenarios with different mass-splittings between the top squark, the lightest neutralino and possible intermediate supersymmetric particles are considered, including cases where the W bosons or the top quarks produced in the decay chain are off-shell. No significant excess over the Standard Model prediction is observed. The null results are used to set exclusion limits at 95% confidence level in several supersymmetry benchmark models. For pair-produced top-squarks decaying into top quarks, top-squark masses up to 940 GeV are excluded. Stringent exclusion limits are also derived for all other considered top-squark decay scenarios. For the spin-0 mediator models, upper limits are set on the visible cross-section.
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Bhattacharyya, G., Das, D., Jay Perez, M., Saha, I., Santamaria, A., & Vives, O. (2018). Can measurements of 2HDM parameters provide hints for high scale supersymmetry? Phys. Rev. D, 97(9), 095018–9pp.
Abstract: Two-Higgs-doublet models (2HDMs) arc minimal extensions of the Standard Model (SM) that may still be discovered at the LHC. The quartic couplings of their potentials can be determined from the measurement of the masses and branching ratios of their extended scalar sectors. We show that the evolution of these couplings through renormalization group equations can determine whether the observed 2HDM is a low energy manifestation of a more fundamental theory, as for instance, supersymmetry, which fixes the quartic couplings in terms of the gauge couplings. At leading order, the minimal supersymmetric extension of the SM (MSSM) dictates all the quartic couplings, which can be translated into a predictive structure for the scalar masses and mixings at the weak scale. Running these couplings to higher scales, one can check if they converge to their MSSM values, and more interestingly, whether one can infer the supersymmetry breaking scale. Although we study this question in the context of supersymmetry, this strategy could be applied to any theory whose ultraviolet completion unambiguously predicts all scalar quartic couplings.
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Barenboim, G., Ternes, C. A., & Tortola, M. (2018). Neutrinos, DUNE and the world best bound on CPT invariance. Phys. Lett. B, 780, 631–637.
Abstract: CPT symmetry, the combination of Charge Conjugation, Parity and Time reversal, is a cornerstone of our model building strategy and therefore the repercussions of its potential violation will severely threaten the most extended tool we currently use to describe physics, i.e. local relativistic quantum fields. However, limits on its conservation from the Kaon system look indeed imposing. In this work we will show that neutrino oscillation experiments can improve this limit by several orders of magnitude and therefore are an ideal tool to explore the foundations of our approach to Nature. Strictly speaking testing CPT violation would require an explicit model for how CPT is broken and its effects on physics. Instead, what is presented in this paper is a test of one of the predictions of CPT conservation, i.e., the same mass and mixing parameters in neutrinos and antineutrinos. In order to do that we calculate the current CPT bound on all the neutrino mixing parameters and study the sensitivity of the DUNE experiment to such an observable. After deriving the most updated bound on CPT from neutrino oscillation data, we show that, if the recent T2K results turn out to be the true values of neutrino and antineutrino oscillations, DUNE would measure the fallout of CPT conservation at more than 3 sigma. Then, we study the sensitivity of the experiment to measure CPT invariance in general, finding that DUNE will be able to improve the current bounds on Delta(Delta m(31)(2)) by at least one order of magnitude. We also study the sensitivity to the other oscillation parameters. Finally we show that, if CPT is violated in nature, combining neutrino with antineutrino data in oscillation analysis will produce imposter solutions.
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