118441224
Probing light stop pairs at the LHC
In this work, we study the light stop pair signals at the LHC. We explore the supersymmetry parameter space with nonuniversal gaugino and third-generation masses at the grand unified theory scale. Recent LHC supersymmetry search results based on 35 pb(-1) and 1 fb(-1) of data are implemented to put the limits on stop pair events. The dark matter relic density and direct detection constraints are also taken into account. Detailed simulations on the signals and background for some benchmark points are performed, and it is found that the stop pair signals usually escape the LHC search if the present cut conditions are used. We also explore the potential and sensitivity of ILC to probe such scenarios. It is found that the ILC can detect them with an integrated luminosity of a few tens of fb(-1).
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).
49215683
PAMELA data and leptonically decaying dark matter
Recently PAMELA released their first results on the positron and antiproton ratios. Stimulated by the new data, we studied the cosmic ray propagation models and calculated the secondary positron and antiproton spectra. The low energy positron ratio can be consistent with data in the convection propagation model. Above similar to 10 GeV PAMELA data shows a clear excess on the positron ratio. However, the secondary antiproton is roughly consistent with the data. The positron excess may be evidence of dark matter annihilation or decay. We compare the positron and antiproton spectra with the data by assuming that dark matter annihilates or decays into different final states. The PAMELA data actually excludes quark pairs being the main final states, and disfavors gauge boson final states. Only in the case of leptonic final states can the positron and antiproton spectra be explained simultaneously. We also compare the decaying and annihilating dark matter scenarios which can account for the PAMELA results and find that the decaying dark matter is preferred. Finally, we consider a decaying neutralino dark matter model in the frame of supersymmetry with R-parity violation. The PAMELA data is well fitted with a neutralino mass of 600 similar to 2000 GeV and a lifetime of similar to 10(26) seconds. We also demonstrate that a neutralino with mass around 2 TeV can fit PAMELA and ATIC data simultaneously.
119243402
Neutrino emission of Fermi supernova remnants
The Fermi gamma-ray space telescope reported the observation of several Galactic supernova remnants recently, with the gamma-ray spectra well described by hadronic pp collisions. The possible neutrino emissions from these Fermi detected supernova remnants are discussed in this work, assuming the hadronic origin of the gamma-ray emission. The muon event rates induced by the neutrinos from these supernova remnants on typical km(3) neutrino telescopes, such as the IceCube and the KM3NeT, are calculated. The results show that for most of these supernova remnants the neutrino signals are too weak to be detected by the on-going or up-coming neutrino experiment. Only for the TeV bright sources RX J1713.7-3946 and possibly W28 the neutrino signals can be comparable with the atmospheric background in the TeV region, if the protons can be accelerated to very high energies. The northern hemisphere based neutrino telescope might detect the neutrinos from these two sources. (C) 2011 Elsevier B.V. All rights reserved.
118368892
Light stop/sbottom pair production searches in the NMSSM
In this work, we study the constraints on the scenario of light stops and sbottoms in the next-to-minimal supersymmetric standard model ( NMSSM), especially by a 125 GeV Higgs boson discovery and the LHC bounds on supersymmetry. The constraints from dark matter detections are also taken into account. From the parameter scan, we find that the NMSSM can well accommodate a light Higgs boson around 125 GeV and decay patterns. We would like to stress that the LHC direct supersymmetry searches with b tagging are very powerful and can set strong bounds on many NMSSM parameter points with light stops and sbottoms. We find (t) over tilde -> b (chi) over tilde (+)(1) is a very promising channel for light stop detection if the mass splitting between (chi) over tilde (+)(1) and (chi) over tilde (0)(1) is very small. It is also pointed out that in order to close the parameter space of light stops and sbottoms, new search strategies for signal channels such as pp -> (t) over tilde (1) -> (t) over tilde (1) -> t (t) over bar hh (chi) over tilde (0)(1)(chi) over tilde (0)(1) and pp -> (b) over tilde (1)(b) over tilde (1) -> t (t) over barW(+)W(-)(chi) over tilde (0)(1)(chi) over tilde (0)(1) may be necessary. DOI: 10.1103/PhysRevD. 87.035007
119110704
Tau portal dark matter models at the LHC
Motivated by the Galactic Center gamma-ray excess in the Fermi-LAT data, we study the signatures of a class of tau portal dark matter (DM) models where DM particles preferentially couple to tau leptons at the LHC. We consider the constraints from the DM direct detection and investigate the sensitivity of the LHC to di-tau plus missing energy signatures. We find that the LHC with a high luminosity of 3000 fb(-1) can test the tau portal DM models with fermionic mediators in the mass range of 120 similar to 450 GeV.
118693296
Three-body force effect on neutrino emissivities of neutron stars within the framework of the Brueckner-Hartree-Fock approach
The three-body force (TBF) effect on the neutrino emissivity in neutron star matter and the total neutrino emissivity of neutron stars have been investigated within the framework of the Brueckner-Hartree-Fock approach by adopting the AV18 two-body interaction plus a microscopic TBF. The neutrino emissivity from the direct Urca process turns out to be much larger than that from the modified Urca process. Inclusion of the TBF reduces strongly the density thresholds of the direct Urca processes involving electrons and muons. The TBF effect on the total neutrino emissivity of neutron stars is shown to be negligibly weak for neutron stars with small masses. For neutron stars with large masses, the TBF effect becomes visible and inclusion of the TBF may enhance the total neutrino emissivity by about 50% for neutron stars with a given mass of M = 1.6M(circle dot).