2,838 research outputs found
Fermionic semi-annihilating dark matter
No full textAbstract: Semi-annihilation is a generic feature of dark matter theories with symmetries larger than ℤ2. We investigate two examples with multi-component dark sectors comprised of an SU(2)L singlet or triplet fermion besides a scalar singlet. These are respectively the minimal fermionic semi-annihilating model, and the minimal case for a gauge-charged fermion. We study the relevant dark matter phenomenology, including the interplay of semi-annihilation and the Sommerfeld effect. We demonstrate that semi-annihilation in the singlet model can explain the gamma ray excess from the galactic center. For the triplet model we scan the parameter space, and explore how signals and constraints are modified by semi-annihilation. We find that the entire region where the model comprises all the observed dark matter is accessible to current and planned direct and indirect searches. © 2016, The Author(s)9911Nsciescopu
A systematic effective operator analysis of semi-annihilating dark matter
No full textSemi-annihilation is a generic feature of dark matter theories stabilized by symmetries larger than a ℤ2. It contributes to thermal freeze out, but is irrelevant for direct and collider searches. This allows semi-annihilating dark matter to avoid those limits in a natural way. We use an effective operator approach to make the first model-independent study of the associated phenomenology. We enumerate all possible operators that contribute to 2 → 2 semi-annihilation up to dimension 6, plus leading terms at dimension 7. We find that when the only light states charged under the dark symmetry are dark matter, the model space is highly constrained. Only fifteen operators exist, and just two for single-component dark sectors. If there can be additional light, unstable “dark partner” states the possible phenomenology greatly increases, at the cost of additional model dependence in the dark partner decay modes. We also derive the irreducible constraints on models with single-component dark matter from cosmic ray searches and astrophysical observations. We find that for semi-annihilation to electrons and light quarks, the thermal relic cross sections can be excluded for dark matter masses up to 100 GeV. However, significant model space for semi-annihilating dark matter remains. © 2017, The Author(s)2111Nsciescopu
Low-temperature enhancement of semi-annihilation and the AMS-02 positron anomaly
No full textAbstract Semi-annihilation is a generic feature of particle dark matter that is most easily probed by cosmic ray experiments. We explore models where the semi-annihilation cross section is enhanced at late times and low temperatures by the presence of an s-channel resonance near threshold. The relic density is then sensitive to the evolution of the dark matter temperature, and we compute expressions for the associated Boltzmann equation valid in general semi-annihilating models. At late times, a self-heating effect warms the dark matter, allowing number-changing processes to remain effective long after kinetic decoupling of the dark and visible sectors. This allows the semi-annihilation signal today to be enhanced by up to five orders of magnitude over the thermal relic cross section. As a case study, we apply this to a dark matter explanation of the positron excess seen by AMS-02. We see that unlike annihilating dark matter, our model has no difficulty fitting the data while also giving the correct relic density. However, constraints from the CMB and γ-rays from the galactic centre do restrict the preferred regions of parameter space
The galactic center excess from Z3 scalar semi-annihilations
No full textWe investigate the possibility of theZ3scalar singlet model explaining the Fermi galactic centre excess. We find a good fit to the measured spectral excess in the region where the dark matter mass is comparable to the Higgs and the Higgs portal coupling λHS∼0.04. This preferred region is consistent with constraints from vacuum stability and current dark matter experiments, and will be discovered or falsified soon by future dark matter direct detection experiment. (c) The Authors.2411Nsciescopu
Electroweak multiplet dark matter at future lepton colliders
No full textAbstract An electroweak multiplet stable due to a new global symmetry is a simple and well-motivated candidate for thermal dark matter. We study how direct searches at a future linear collider, such as the proposed CLIC, can constrain scalar and fermion triplets, quintets and septets, as well as a fermion doublet. The phenomenology is highly sensitive to charged state lifetimes and thus the mass splitting between the members of the multiplet. We include both radiative corrections and the effect of non-renormalisable operators on this splitting. In order to explore the full range of charged state lifetimes, we consider signals including long-lived charged particles, disappearing tracks, and monophotons. By combining the different searches we find discovery and exclusion contours in the mass-lifetime plane. In particular, when the mass splitting is generated purely through radiative corrections, we can exclude the pure-Higgsino doublet below 310 GeV, the pure-wino triplet below 775 GeV, and the minimal dark matter fermion quintet below 1025 GeV. The scenario where the thermal relic abundance of a Higgsino accounts for the whole dark matter of the Universe can be excluded if the mass splitting between the charged and neutral states is less than 230 MeV. Finally, we discuss possible improvements to these limits by using associated hard leptons to idenify the soft visible decay products of the charged members of the dark matter multiplet
Long-lived, colour-triplet scalars from unnaturalness
No full textAbstract: Long-lived, colour-triplet scalars are a generic prediction of unnatural, or split, composite Higgs models where the spontaneous global-symmetry breaking scale f ≳ 10 TeV and an unbroken SU(5) symmetry is preserved. Since the triplet scalars are pseudo NambuGoldstone bosons they are split from the much heavier composite-sector resonances and are the lightest exotic, coloured states. This makes them ideal to search for at colliders. Due to discrete symmetries the triplet scalar decays via a dimension-six term and given the large suppression scale f is often metastable. We show that existing searches for collider-stable R-hadrons from Run-I at the LHC forbid a triplet scalar mass below 845 GeV, whereas with 300 fb−1 at 13 TeV triplet scalar masses up to 1.4 TeV can be discovered. For shorter lifetimes displaced-vertex searches provide a discovery reach of up to 1.8 TeV. In addition we present exclusion and discovery reaches of future hadron colliders as well as indirect limits that arise from modifications of the Higgs couplings. © 2016, The Author(s)6511Nsciescopu
Police using batons and capsicum spray push rioters back through the gates at Cronulla Railway Station during the race riots in Cronulla, 11 December 2005 [picture] /
No full textTitle devised by cataloguer from acquisition documentation.; "Police using batons and capsicum spray push rioters back through the gates at Cronulla Railway Station after men of Middle Eastern appearance were attacked by dozens of rioters on a train."--Taken from photogapher's notes.; Part of the collection: Cronulla riots, New South Wales, 2005.; Acquired in digital format; access copy available online.; Mode of access: Online
Efficacy and safety of fentanyl pectin nasal spray compared with immediate-release morphine sulfate tablets in the treatment of breakthrough cancer pain: A multicenter, randomized, controlled, double-blind, double-dummy multiple-crossover study
No full textBackground: Immediate-release morphine sulfate (IRMS) remains the standard treatment for breakthrough cancer pain (BTCP), but its onset of effect does not match the rapid onset and short duration of most BTCP episodes. Objective: This study will evaluate the efficacy/tolerability of fentanyl pectin nasal spray (FPNS) compared with IRMS for BTCP. Methods: Patients (n = 110) experiencing one to four BTCP episodes/day while taking ≥60 mg/day oral morphine (or equivalent) for background cancer pain entered a double-blind, double-dummy (DB/DD), multiple-crossover study. Patients completing a titration phase (n = 84) continued to a DB/DD phase: 10 episodes of BTCP were randomly treated with FPNS and oral capsule placebo (five episodes) or IRMS and nasal spray placebo (5 episodes). The primary end point was pain intensity (P < .05 FPNS vs. IRMS) difference from baseline at 15 minutes (PID 15). Secondary end points were onset of pain intensity (PI) decrease (≥1-point) and time to clinically meaningful pain relief (CMPR, ≥2-point PI decrease). Safety and tolerability were evaluated by adverse events (AEs) and nasal assessments. By-patient and by-episode analyses were completed. Results: Compared with IRMS, FPNS significantly improved mean PID 15 scores. 57.5% of FPNS-treated episodes significantly demonstrated onset of PI improvement by 5 minutes and 95.7% by 30 minutes. CMPR (≥2-point PI decrease) was seen in 52.4% of episodes by 10 minutes. Only 4.7% of patients withdrew from titration (2.4% in DB/DD phase) because of AEs; no significant nasal effects were reported. Conclusion: FPNS was efficacious and well tolerated in the treatment of BTCP and provided faster onset of analgesia and attainment of CMPR than IRMS. © 2011
Spray simulation of diesel fuel under different ambient pressures and temperatures
No full textThis study investigates the impact of ambient pressure and temperature on the spray behaviour of diesel fuel. Spray
simulation tests were conducted using Ansys Forte in a 45-degree sector of a diesel engine under different ambient pressures (1, 4 and 8 bar) and different ambient temperatures (400, 600 and 800 K). Non-reactive conditions were used as they allow calibration of the model for predicting correct spray dynamics. The simulation results of diesel fuel showed that the spray penetration decreased with increased ambient pressure. However, the spray penetration region became longer and wider for diesel fuel because of increased ambient air temperature. With higher ambient temperature the evaporation rate increased
Rioters at Cronulla Railway Station yell abuse at their victims following their attack on a small group of men of Middle Eastern appearance during the race riots in Cronulla, 11 December 2005 [picture] /
No full textTitle devised by cataloguer from acquisition documentation.; "Rioters at Cronulla Railway Station yell abuse at their victims following their attack on a small group of men of Middle Eastern appearance who had been travelling on a train. Moments later a small group of Police officers broke up the crowd with batons and capsicum spray."--Taken from photogapher's notes.; Part of the collection: Cronulla riots, New South Wales, 2005.; Acquired in digital format; access copy available online.; Mode of access: Online
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