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  • Di Chiara, Stefano; Tuominen, Kimmo (2015)
    We study an extension of the Standard Model featuring a hidden sector that consists of a new scalar charged under a new SU(N)(D) gauge group, singlet under all Standard Model gauge interactions, and coupled with the Standard Model only via a Higgs portal. We assume that the theory is classically conformal, with electroweak symmetry breaking dynamically induced via the Coleman-Weinberg mechanism operating in the hidden sector. Due to the symmetry breaking pattern, the SU(N)(D) gauge group is completely Higgsed and the resulting massive vectors of the hidden sector constitute a stable dark matter candidate. We perform a thorough scan over the parameter space of the model at different values of N = 2, 3, and 4, and investigate the phenomenological constraints. We find that N = 2, 3 provide the most appealing model setting in light of present data from colliders and dark matter direct search experiments. We expect a heavy Higgs to be discovered at LHC by the end of Run II or the N = 3 model to be ruled out.
  • The CMS collaboration; Sirunyan, A. M.; Eerola, P.; Kirschenmann, H.; Pekkanen, J.; Voutilainen, M.; Havukainen, J.; Heikkilä, J. K.; Järvinen, T.; Karimäki, V.; Kinnunen, R.; Lampén, T.; Lassila-Perini, K.; Laurila, S.; Lehti, S.; Lindén, T.; Luukka, P.; Mäenpää, T.; Siikonen, H.; Tuominen, E.; Tuominiemi, J.; Tuuva, T. (2018)
    A measurement is presented of the effective leptonic weak mixing angle (sin(2) theta(effl))using the forward- backward asymmetry of Drell-Yan lepton pairs (mu mu and ee) produced in proton-proton collisions at N root s = 8 TeV at the CMS experiment of the LHC. The data correspond to integrated luminosities of 18.8 and 19.6 fb(-1) in the dimuon and dielectron channels, respectively, containing 8.2 million dimuon and 4.9 million dielectron events. With more events and new analysis techniques, including constraints obtained on the parton distribution functions from the measured forward-backward asymmetry, the statistical and systematic uncertainties are significantly reduced relative to previous CMS measurements. The extracted value of sin(2) theta(effl) from the combined dilepton data is sin(2) theta(effl) = 0.23101 +/- 0.00036 (stat) +/- 0.00018 (syst) 0.00016 (theo) +/- 0.00031 (parton distributions in proton) = 0.23101 +/- 0.00053.
  • Bandyopadhyay, Priyotosh; Di Chiara, Stefano; Huitu, Katri; Keceli, Asli Sabanci (2014)
  • Niemi, Lauri; Schicho, Philipp; Tenkanen, Tuomas V. (2021)
    We investigate the electroweak phase transition in the real-singlet extension of the Standard Model at two-loop level, building upon existing one-loop studies. We calculate the effective potential in the high-temperature approximation and detail the required resummations at two-loop order. In typical strongtransition scenarios, we find deviations of order 20%-50% from one-loop results in transition strength and critical temperature for both one- and two-step phase transitions. For extremely strong transitions, the discrepancy with one-loop predictions is even larger, presumably due to sizable scalar couplings in the tree-level potential. Along the way, we obtain a dimensionally reduced effective theory applicable for nonperturbative lattice studies of the model.