The complex scalar dark matter (DM) candidate in the gauged two-Higgs-doublet model, stabilized by a peculiar hidden parity (h parity), is studied in detail. We explore the parameter space for the DM candidate by taking into account the most recent DM constraints from various experiments, in particular, the PLANCK relic density measurement and the current DM direct detection limit from XENON1T. We separate our analysis in three possible compositions for the mixing of the complex scalar. We first constrain our parameter space with the vacuum stability and perturbative unitarity conditions for the scalar potential, LHC Higgs measurements, plus Drell-Yan and electroweak precision test constraints on the gauge sector. We find that DM dominated by composition of the inert doublet scalar is completely excluded by further combining the previous constraints with both the latest results from PLANCK and XENON1T. We also demonstrate that the remaining parameter space with two other DM compositions can be further tested by indirect detection like the future Cherenkov Telescope Array gamma-ray telescope.
Taking a phenomenological approach, we study a color sextet scalar at the LHC. We focus on the QCD production of a color sextet pair Φ 6Φ6 through gg fusion and qq annihilation. Its unique coupling toψ c ψ allows the color sextet scalar to decay into same-sign diquark states, such as Φ 6 → tt/tt * . We propose a new reconstruction in the multijet plus same sign dilepton with missing transverse energy samples (bb + ℓ ± ℓ ± + E T + N j, N ≥ 6) to search for on-shell tttt final states from sextet scalar pair production. Thanks to the large QCD production, the search covers the sextet mass range up to 1 TeV for 100 fb −1 integrated luminosity.
We study a scenario that a hidden gauge boson constitutes the dominant
component of dark matter and decays into the standard model particles through a
gauge kinetic mixing. Interestingly, gamma rays and positrons produced from the
decay of hidden gauge boson can explain both the EGRET excess of diffuse gamma
rays and the HEAT anomaly in the positron fraction. The spectra of the gamma
rays and the positrons have distinctive features; the absence of line emission
of the gamma ray and a sharp peak in the positron fraction. Such features may
be observed by the GLAST and PAMELA satellites.Comment: 16 pages, 4 figures, adding PAMELA data, the version accepted by PL
The forward-backward asymmetry for top quarks measured in proton-antiproton collisions at the Tevatron shows an interesting deviation from standard model expectations. Among possible interpretations, the exchange of a non-universal, flavor-changing Z ′ is of some interest as it naturally predicts a top quark in the forward region of rapidity. To reproduce the size of the Tevatron asymmetry, the couplings of the Z ′ to standard model quarks must be large, inevitably leading to production of same-sign top quark pairs at the Tevatron and at the Large Hadron Collider (LHC). We discuss the constraints on this model from (a) the Tevatron t t cross section, (b) the Tevatron t t invariant mass distribution, and the limits at the Tevatron on the same sign top quark pair cross section. We explore the discovery potential for tt and ttj production in early LHC experiments at 7 TeV and conclude that if a tt signal is not observed with 1 fb −1 of integrated luminosity, then a non-universal Z ′ alone cannot explain the Tevatron forward-backward asymmetry. Limits on the same sign cross section at the LHC from the CMS collaboration already disfavor this interpretation of the reported asymmetry.
We investigate the production of beyond-the-standard-model color-sextet vector bosons at the Large Hadron Collider and their decay into a pair of same-sign top quarks. We demonstrate that the energy of the charged lepton from the top quark semi-leptonic decay serves as a good measure of the top-quark polarization, which, in turn determines the quantum numbers of the boson and distinguishes vector bosons from scalars.
New heavy gauge bosons exist in many models of new physics beyond the standard model of particle physics. Discovery of these W ′ and Z ′ resonances and the establishment of their spins, couplings, and other quantum numbers would shed light on the gauge structure of the new physics.The measurement of the polarization of the SM fermions from the gauge boson decays would decipher the handedness of the coupling of the new states, an important relic of the primordial new physics symmetry. Since the top quark decays promptly, its decay preserves spin information.We show how decays of new gauge bosons into third generation fermions (W ′ → tb, Z ′ → tt) can be used to determine the handedness of the couplings of the new states and to discriminate among various new physics models.
Higgs bosons pair production is well known for its sensitivity to probing the sign and size of Higgs boson self coupling, providing a way to determine whether there is an extended Higgs sector. The Georgi-Machacek (GM) model extends the Standard Model (SM) with an SU(2) L triplet scalar field that has one real and one complex components. The Higgs self coupling now has a wider range than that in the SM, with even the possibility of a sign flip. The new heavy singlet Higgs boson H 0 1 can contribute to s-channel production of the hh pairs. In this work, we study non-resonant/resonant Higgs boson pair productions pp → hh and pp → H 0 1 → hh, focusing exclusively on the contribution of H 0 1 . We show the sensitivity for Higgs boson pair production searches at the 13-TeV LHC with the luminosities of 3.2, 30 and 100 fb −1 .
We provide a scenario in which a hidden U (1) gauge boson constitutes dark matter of the Universe and decays into the standard-model particles through a kinetic mixing with an U (1) B−L gauge boson. Interestingly, our model can naturally account for the steep rise in the positron fraction recently reported by PAMELA. Moreover, we find that due to the charge assignment of U (1) B−L , only a small amount of antiprotons are produced in the decay, which is also consistent with the PAMELA and other observational data.
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