Signatures of Extra Gauge Bosons in the Littlest Higgs Model with T-parity at Future Colliders

We study the collider signatures of a T-odd gauge boson $W_{H}$ pair production in the Littlest Higgs Model with T-parity (LHT) at Large Hadron Collider (LHC) and Linear Collider (LC). At the LHC, we search for the $W_{H}$ boson using its leptonic decay, i.e. $pp\to W_{H}^{+}W_{H}^{-}\to A_{H}A_{H}\ell^{+}\nu_{\ell}\ell^{\prime-}\bar{\nu}_{\ell^{\prime}}$, which gives rise to a collider signature of \ell^{+}\ell^{\prime-}+\met. We demonstrate that the LHC not only has a great potential of discovering the $W_{H}$ boson in this channel, but also can probe enormous parameter space of the LHT. Due to four missing particles in the final state, one cannot reconstruct the mass of $W_{H}$ at the LHC. But such a mass measurement can be easily achieved at the LC in the process of $e^{+}e^{-}\to W_{H}^{+}W_{H}^{-}\to A_{H}A_{H}W^{+}W^{-}\to A_{H}A_{H}jjjj$. We present an algorithm of measuring the mass and spin of the $W_{H}$ boson at the LC. Furthermore, we illustrate that the spin correlation between the $W$ boson and its mother particle ($W_{H}$) can be used to distinguish the LHT from other new physics models.Comment: version to appear in PRD (a few references added

Resummation Effects in the Search of SM Higgs Boson at Hadron Colliders

We examine the soft-gluon resummation effects, including the exact spin correlations among the final state particles, in the search of the Standard Model Higgs boson, via the process $gg\to H\to WW/ZZ \to 4 leptons, at the Tevatron and the LHC. A comparison between the resummation and the Next-to-Leading order (NLO) calculation is performed after imposing various kinematics cuts suggested in the literature for the Higgs boson search. For the$H\to ZZ$mode, the resummation effects increase the acceptance of the signal events by about 25various kinematics distributions of the final state leptons. For the$H\to WW$ mode, the acceptance rates of the signal events predicted by the resummation and NLO calculations are almost the same, but some of the predicted kinematical distributions are quite different. Thus, to precisely determine the properties of the Higgs boson at hadron colliders, the soft-gluon resummation effects have to be taken into account.Comment: The version to appear in PR

Same-Sign Dilepton Excesses and Vector-like Quarks

Multiple analyses from ATLAS and CMS collaborations, including searches for ttH production, supersymmetric particles and vector-like quarks, observed excesses in the same-sign dilepton channel containing b-jets and missing transverse energy in the LHC Run 1 data. In the context of little Higgs theories with T parity, we explain these excesses using vector-like T-odd quarks decaying into a top quark, a W boson and the lightest T-odd particle (LTP). For heavy vector-like quarks, decay topologies containing the LTP have not been searched for at the LHC. The bounds on the masses of the T-odd quarks can be estimated in a simplified model approach by adapting the search limits for top/bottom squarks in supersymmetry. Assuming a realistic decay branching fraction, a benchmark with a 750 GeV T-odd b-prime quark is proposed. We also comment on the possibility to fit excesses in different analyses in a common framework.Comment: 1+17 pages and 11 figure

Implications of the Little Higgs Dark Matter and T-odd Fermions

We study the phenomenology of dark matter in the Littlest Higgs model with T-parity after the discovery of Higgs boson. We analyze the relic abundance of dark matter, focusing on the effects of coannihilaitons with T-odd fermions. After determining the parameter space that predicts the correct relic abundance measured by WMAP and Planck collaborations, we evaluate the elastic scattering cross section between dark matter and nucleon. In comparison with experimental results, we find that the lower mass of dark matter is constrained mildly by LUX 2013 while the future XENON experiment has potential to explore most of the parameter space for both T-odd lepton and T-odd quark coannihilation scenarios. We also study the collider signatures of T-odd fermion pair production at the LHC. Even though the production cross sections are large, it turns out very challenging to search for these T-odd fermions directly at the collider because the visible charged leptons or jets are very soft. Furthermore, we show that, with an extra hard jet radiated out from the initial state, the T-odd quark pair production can contribute significantly to mono-jet plus missing energy search at the LHC

Interpretations and Implications of the Top Quark Rapidity Asymmetries AFBtA_{FB}^t and AFBℓA_{FB}^{\ell}

Forward-backward asymmetries $A_{FB}^t$ and $A_{FB}^\ell$ are observed in the top quark $t$ rapidity distribution and in the rapidity distribution of charged leptons $\ell$ from top quark decay at the Tevatron proton-antiproton collider, and a charge asymmetry $A_C$ is seen in proton-proton collisions at the Large Hadron Collider (LHC). In this paper, we update our previous studies of the Tevatron asymmetries using the most recent data. We provide expectations for $A_C$ at the LHC based first on model independent extrapolations from the Tevatron, and second based on new physics models that can explain the Tevatron asymmetries. We examine the relationship of the two asymmetries $A_{FB}^t$ and $A_{FB}^\ell$. We show their connection through the $(V-A)$ spin correlation between the charged lepton and the top quark with different polarization states. We show that the ratio of the two asymmetries provides independent insight into new physics models that are invoked to fit the top quark asymmetry. We emphasize the value of the measurement of both asymmetries, and we conclude that a model which produces more right-handed than left-handed top quarks is favored by the present Tevatron data.Comment: Some figures changed. A typo in appendix fixed. Published in Physical Review