123243656
CONSTRAINTS ON THE OPERA SUPERLUMINAL NEUTRINOS
The OPERA collaboration has recently reported the superluminal neutrinos with velocity of (vν - c)/c ~ 2.5 × 10-5. This result can be explained in the Lorentz invariance violation (LIV) models. The modified dispersion relation of neutrino lead to modified kinematics of the processes the neutrinos involved. For processes that neutrinos in the final states the processes are suppressed. We find to allow the neutrino production process π → μ + νμ, the neutrino energy should be less than about 5 GeV if taking a large LIV parameter ~ O(10-5) implied by OPERA data. For the processes that neutrinos in the initial states new processes that are forbidden in the LI scenario may open, such as the ν → ν + γ or ν → ν + e+ + e-, which lead neutrinos to lose energy quickly. As the atmospheric neutrino spectrum agrees well with expectation without LIV we find it can constrain the neutrino LIV parameter to ~ O(10-12), which is 7 orders smaller than the value measured at OPERA. We further propose to study the astrophysical neutrino spectra, which can constrain the neutrino LIV parameter down to O(10-15).
118840081
Constraining the interaction strength between dark matter and visible matter: II. Scalar, vector and spin-3/2 dark matter
We investigate the constraints on the scalar, vector and spin-3/2 dark matter interaction with the standard model particles, from the observations of dark matter relic density, the direct detection experiments of COMS and XENON, and the indirect detection of the (p) over bar /p ratio by PAMELA. A model independent way is adopted by constructing general 4-particle operators up to dimension 6 for the effective interaction between dark matter and standard model particles. We find that the constraints from different experiments are complementary with each other. Comparison among these constraints may exclude some effective models of dark matter and limit some parameters of others. The spin-independent direct detection gives strong constraints for some operators, while the indirect detection of (p) over bar /p data can be more sensitive than direct detection or relic density for light dark matter (whose mass less than or similar to 70 GeV) in some cases. The constraints on some operators for spin-3/2 dark matter are shown to be similar to those on their analogous operators for Dirac fermionic dark matter. There are still some operators not sensitive to the current dark matter direct and indirect search experiments. (C) 2012 Elsevier B.V. All rights reserved.
119303268
Detecting light stop pairs in coannihilation scenarios at the LHC
In this work, we study the light stop pair signals at the Large Hadron Collider (LHC) in three coannihilation scenarios, where the neutralino can coannihilate with the stop, chargino and stau, respectively, so as to yield the desired dark matter relic density. Signatures of the first scenario can be probed at the LHC via the associated jet production processes pp -> j + (t) over tilde(t) over tilde* by tagging an energetic monojet and a large missing transverse energy. The signatures of the other two scenarios can be searched via the pair production process pp -> (t) over tilde(t) over tilde* by tagging energetic b jets in the final states and a large missing transverse energy. We find that the LHC results at 7 TeV with 5 fb(-1) of data can exclude the stop mass up to 220, 380, and 220 GeV for these three scenarios, respectively. While the 20 fb(-1) data set at 8 TeV is considered, the LHC can be expected to exclude the stop mass up to 340, 430, and 370 GeV. DOI: 10.1103/PhysRevD.87.055007
119245716
Constraining the interaction strength between dark matter and visible matter: I. Fermionic dark matter
In this work we study the constraints on the dark matter interaction with the standard model particles, from the observations of dark matter relic density, the direct detection experiments of CDMS and XENON, and the indirect detection of the (p) over bar /p ratio by PAMELA. A model independent way is adopted in the study by constructing the effective interaction operators between dark matter and standard model particles. The most general 4-fermion operators are investigated. We find that the constraints from different observations are complementary with each other. Especially the spin independent scattering gives very strong constraints for corresponding operators. In some cases the indirect detection of (p) over bar /p data can actually be more sensitive than the direct detection or relic density for light dark matter (less than or similar to 70 GeV). (C) 2011 Elsevier B.V. All rights reserved.
119244329
QCD NLO and EW NLO corrections to $t\bar{t}H$ production with top quark decays at hadron collider
Higgs boson production associated with a top quark pair is an important process in studying the nature of the newly discovered Higgs boson at the LHC. In this letter, we report on our calculations including the next-to-leading order (NLO) QCD and NLO electroweak corrections to the pp → tt̄H process in the standard model. We present the integrated cross sections at the 14 TeV LHC and even at the future proton-proton colliders with √ s = 33 and 100 TeV. Our calculation includes the top quark subsequent decays by adopting the narrow width approximation. The kinematic distributions of Higgs boson and top quark decay products at the LHC are provided. We find that the O(α2sα2ew) corrections are quantitatively comparable with the O(α3sαew) corrections in some kinematic region.
119275234
Electroweak radiative corrections to $W^+W^-\gamma$ production at the ILC
We provide and discuss the precision predictions for the $W^+W^-\gamma$ production at the ILC including the full electroweak (EW) one-loop corrections and high order initial state radiation (ISR) contributions in the Standard Model. The dependence of the leading order (LO) and EW corrected cross sections on the colliding energy is investigated. We find that the EW correction suppresses the LO cross section significantly, and the ISR effect beyond ${\cal O}(\alpha)$ is important near the threshold, but is negligible in the high energy region. We provide the LO and EW corrected distributions of the transverse momenta and rapidities of final $W^-$-boson and photon as well as the $W$-pair invariant mass. From the various kinematic distributions, we find that EW correction strongly depends on the final state phase space. We investigate the leptonic decays of the final W-boson pair by adopting the narrow width approximation (NWA), and find that the final produced photon and leptons can be well separated from each other.