We explore the potential for discovery of an exotic color sextet scalar in same-sign top quark pair production in early running at the LHC. We present the first phenomenological analysis at colliders of color sextet scalars with full top quark spin correlations included. We demonstrate that one can measure the scalar mass, the top quark polarization, and confirm the scalar resonance with 1 fb⁻¹ of integrated luminosity. The top quark polarization can distinguish gauge triplet and singlet scalars.
The Cryogenic Dark Matter Search recently announced the observation of two signal events with a 77% confidence level. Although statistically inconclusive, it is nevertheless suggestive. In this work we present a model-independent analysis on the implication of direct and indirect searches for the dark matter using effective operator approach. Assuming that the interactions between (scalar, fermion or vector) dark matter and the standard model are mediated by unknown new physics at the scale Λ, we examine various dimension-6 tree-level induced operators and constrain them using the current experimental data, including the WMAP data of the relic abundance, CDMS II direct detection of the spin-independent scattering, and indirect detection data (Fermi LAT cosmic gamma-ray). Finally, the LHC search is also explored.
We explicitly show that split-universal extra dimension (split-UED), a recently suggested extension of universal extra dimension (UED) model, can nicely explain recent anomalies in cosmic-ray positrons and electrons observed by PAMELA and ATIC/PPB-BETS. Kaluza-Klein (KK) dark matters mainly annihilate into leptons because the hadronic branching fraction is highly suppressed by large KK quark masses and the antiproton flux agrees very well with the observation where no excess is found . The flux of cosmic gamma-rays from pion decay is also highly suppressed and hardly detected in low energy region (E γ 20 GeV). Collider signatures of colored KK particles at the LHC, especially q 1 q 1 production, are studied in detail. Due to the large split in masses of KK quarks and other particles, hard p T jets and missing E T are generated, which make it possible to suppress the standard model background and discover the signals. Recent observations by PAMELA [1] and ATIC/PPB-BETS [2, 3] consistently suggest a new primary source of energetic cosmic electrons and positrons in the neighborhood of our solar system, since high energy electrons/positrons lose their energy quickly within about 1 kpc. These resutls have attracted enormous attentions and stimulated many interpretations of the primary electric source from both astrophysics and particle physics, for example, the nearby pulsars [4] and dark matter decay [5] or annihilation [6]. The existing data of cosmic electrons and positrons cannot distinguish among these possibilities, and we expect that future data from cosmic-ray and accelerator experiments such as Fermi and Large Hadron Collider (LHC) will give us some clues on which interpretation is more promising and ultimately correct. In this paper, we consider one of the most attractive models of dark matter, universal extra dimension (UED) with its minimal realization (mUED)[7, 8] and a recently suggested variety split-UED [9]. When the reflection symmetry (dubbed Kaluza-Klein parity) about the mid point of the orbifold extra dimension is exact, the lightest Kaluza-Klein particle (LKP), which is odd under the parity operation, is absolutely stable and is a good candidate of dark matter [10]. It turns out that in most cases of universal extra dimension scenarios the LKP is the first Kaluza-Klein (KK) photon (B 1 ), and a pair of charged leptons is produced in the annihilation process of B 1 . Interestingly enough, the mass of dark matter suggested by the ATIC/PPB-BETS data (∼ 600 − 700 GeV) exactly coincides with the one that gives the right relic density for the LKP dark matter after taking co-annihilation channels into account [11].On the other hand, the measured data of the cosmic ray antiproton-to-proton flux ratio between 1 and 100 GeV by PAMELA follow the expectations from secondary production and strongly constrain contributions from dark matter particle annihilation [12]. Therefore it is required to naturally reduce antiproton flux in any dark matter model. Split-UED is promising in the sense that production of ant...
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