53540874
Dark matter induced nucleon decay: model and signatures
A bstractIf dark matter (DM) carries anti-baryon number, a DM particle may annihilate with a nucleon by flipping to anti-DM. Inspired by Hylogenesis models, we introduce a single component DM model where DM is asymmetric and carries B and L as -1/2. It can annihilate with a nucleon to an anti-lepton and an anti-DM at leading order or with an additional meson at sub-leading order. Such signals may be observed in proton decay experiments. If DM is captured in the Sun, the DM induced nucleon decay can generate a large flux of anti-neutrinos, which could be observed in neutrino experiments. Furthermore, the anti-DM particle in the final state obtains a relatively large momentum (few hundred MeV), and escapes the Sun. These fast-moving anti-DM particles could also induce interesting signals in various underground experiments.
117991499
Zero and one jet combined next-to-leading order analysis of the top quark forward-backward asymmetry
We present an analysis of the forward{backward asymmetry in the production of top quark pairs at the Tevatron collider. We use novel Monte Carlo methods for merging matrix elements and parton showers to combine NLO QCD predictions fort t andt t+jet production. Theoretical uncertainties are quantied in detail. We nd agreement with experimental data on the transverse momentum dependence of the asymmetry. t t events with large invariant mass, mt t 450 GeV. The inclusive parton-level asymmetry was measured as 0:164 0:047 considering all pair masses, and 0:295 0:067 for mt t 450 GeV. This needs to be compared to theoretical predictions from various event generators in the unrestricted and high t t mass region: 0:067 0:020 and 0:089 0:027 from MC@NLO (6, 7), 0:066 0:020 and 0:100 0:030 from POWHEG (8, 9), and 0:073 0:022 and 0:110 0:033 from MCFM (4, 10). In all cases, electroweak corrections had been applied. The linear behavior of AFB with increasing y and mt t persists,
118612347
Collisions of Jets of Particles from Active Galactic Nuclei with Neutralino Dark Matter
We examine the possibility that energetic Standard Model particles contained in the jets produced by active galactic nuclei (AGN) may scatter off of the dark matter halo which is expected to surround the AGN. In particular, if there are nearby states in the dark sector which can appear resonantly in the scattering, the cross section can be enhanced and a distinctive edge feature in the energy spectrum may appear. We examine bounds on supersymmetric models which may be obtained from the Fermi Gamma-ray Space Telescope observation of the nearby AGN Centaurus A.
12644662
Observation of thundercloud-related gamma rays and neutrons in Tibet
During the 2010 rainy season in Yangbajing (4300 m above sea level) in Tibet, China, a long-duration count enhancement associated with thunderclouds was detected by a solar-neutron telescope and neutron monitors installed at the Yangbajing Comic Ray Observatory. The event, lasting for similar to 40 min, was observed on July 22, 2010. The solar-neutron telescope detected significant gamma-ray signals with energies >40 MeV in the event. Such a prolonged high-energy event has never been observed in association with thunderclouds, clearly suggesting that electron acceleration lasts for 40 min in thunderclouds. In addition, Monte Carlo simulations showed that >10 MeV gamma rays largely contribute to the neutron monitor signals, while >1 keV neutrons produced via a photonuclear reaction contribute relatively less to the signals. This result suggests that enhancements of neutron monitors during thunderstorms are not necessarily clear evidence for neutron production, as previously thought.
119100961
Tree amplitudes of noncommutative U(N) Yang–Mills theory
Following the spirit of the S-matrix program, we propose a modified Britto?Cachazo?Feng?Witten recursion relation for tree amplitudes of noncommutative U(N) Yang?Mills theory. Starting from three-point amplitudes, one can use this modified BCFW recursion relation to compute or analyze color-ordered tree amplitudes without relying on any detailed information of noncommutative Yang?Mills theory. After clarifying the color structure of noncommutative tree amplitudes, we write down the noncommutative analogies of Kleiss?Kuijf and Bern?Carrasco?Johansson relations for color-ordered tree amplitudes and prove them using the modified BCFW recursion relation. This checks the consistency of the relation.
121088924
Chemical Composition and Maximum Energy of Galactic Cosmic Rays
A model of the cosmic-ray energy spectrum is proposed that assumes various acceleration limits at multiple sources. The model describes the broken power-law energy spectrum of cosmic rays by superposition of multiple sources; a diffusive shock acceleration mechanism plays an essential role. The maximum energy of galactic cosmic rays is discussed based on a comparison of experimental data with calculations done using the proposed model. The model can describe the energy spectrum at very high energies of up to several times 1018 eV, but the observed highest-energy cosmic rays deviate from the model predictions, indicating a different origin, such as an extragalactic source. This model describes the steepening of the power index at the so-called knee. However, it was found that additional assumptions are needed to explain the sharpness of the knee. Two possible explanations for the structure of the knee are discussed in terms of nearby source(s) and the hard energy spectrum suggested by nonlinear effects of cosmic-ray acceleration mechanisms.
121252165
PROTON--PROTON ELASTIC SCATTERING AT HIGH ENERGIES AND LARGE ANGLES, AND THE INCOHERENT DROPLET MODEL.
A study has been made of the elastic proton-proton scattering at high energies and large angles, using a model first proposed by K. Huang. This model decomposes a proton during collision into $N$ subunits and recombines them after collision in an incoherent combinatorial manner. The technique used is more general than the asymptotic methods used by Huang in obtaining the probabilities for the final states. The new procedure allows us to extend the range of validity for the model, since asymptotic expansions are no longer used. The analysis is limited to spinless protons, and to regions of high energy where there exists no discontinuity in the shape of the angular distribution such as was found by Allaby et al. around ${P}_{L}=8 \mathrm{to} 11$ BeV/c. The theoretical curves are in good agreement with the experimental results from ${\ensuremath{\theta}}_{\mathrm{c}.\mathrm{m}.}=65\ifmmode^\circ\else\textdegree\fi{} \mathrm{to} 90\ifmmode^\circ\else\textdegree\fi{}$ and ${P}_{L}=14 \mathrm{to} 27$ BeV/c, while the asymptotic expressions are in good agreement only from around 76\ifmmode^\circ\else\textdegree\fi{} to 90\ifmmode^\circ\else\textdegree\fi{}. The experimentally observed quenching of large-momentum-transfer states as the energy increases is reproduced.