122395245
Chiral symmetry breaking in QED for weak coupling
The authors examine the procedure for studying chiral symmetry breaking for weak coupling in QED. They note that while the lowest non-trivial order calculations using numerical solutions to the Schwinger-Dyson equation indicate a breaking of chiral symmetry, the neglected higher-order contributions to the effective potential have imaginary values which can indicate possible instabilities in the theory.
121477317
Neutrinos in a Robertson-Walker universe
A solution to the Einstein-Dirac system of equations in a Robertson-Walker spacetime is presented using the separation of variables method. With an axially symmetric and a non-axially symmetric boundary conditions, we find that there are no solutions for the massless fermions and only null or `ghost' solutions for the massive fermions. The `ghost' solutions carry a current but have a vanishing energy-momentum tensor and correspond to the special case when the Robertson-Walker spacetime reduces to flat spacetime.
122685473
Ladder approximation, scalar-exchange mesons, and Bethe--Salpeter scattering states
120766753
Stability of the electron in the SU(5) and GWS models
Within the framework of the SU(5) model and by using non-zero vacuum expectation values for both charged and neutral Higgs fields, the lifetime of the electron ( tau e) can be expressed in terms of the photon mass (mgamma ). Using the upper limit of 10-24 GeV for mgamma given by studies of Jupiter's magnetic field, a lower limit of 1027 years is obtained for tau e, while the upper limit of 10-36 GeV for mgamma given by studies of galactic magnetic fields yielded a lower limit of 1051 years for tau e. The values for tau e can be obtained without giving rise to light Higgs particles. In contrast, the standard GWS model with two Higgs doublets gave rise to comparable values for tau e, but yielded a light Higgs particle with masses similar to mgamma .
122132298
On the Green's Functions for the Bethe‐Salpeter Equation
Considering the Bethe‐Salpeter equation as a relativistic equation, we have studied the free particle Green's functions for unequal mass scalar bosons, interacting via a translationally invariant potential. The scattering Green's function found by Huang and DeFacio (HD) is presented for all possible Ω‐plane contours for the unequal masses case. Only two k‐plane contours are found to be physically interesting. The causal, advanced, and retarded Green's functions are listed in an appendix for unequal masses for the physical contour. The timelike Green's functions again require severe restrictions on the interaction potential as found by HD, and possible Bethe‐Salpeter bound states are briefly discussed.
122140676
SPIN-1 AND SPIN-2 GAUGE FIELDS IN UNIFIED SL(2N,C) MODELS
124505729
NLO merging in $t\bar{t}$+jets
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.
119211995
A Monte Carlo study to check the hadronic interaction models by a new EAS hybrid experiment in Tibet
A new EAS hybrid experiment has been designed by constructing a YAC (Yangbajing Air shower Core) detector array inside the existing Tibet- III air shower array. The first step of YAC, called "YAC-I", consists of 16 plastic scintillator units (4 rows times 4 columns) each with an area of 40 cm◊50 cm which is used to check hadronic interaction models used in AS simulations. A Monte Carlo study shows that YAC-I can record high energy electromagnetic component in the core region of air showers induced by primary particles of several tens TeV energies where the primary composition is directly measured by space experiments. It may provide a direct check of the hadronic interaction models currently used in the air shower simulations in the corresponding energy region. In present paper, the method of the observation and the sensitivity of the characteristics of the observed events to the different interaction models are discussed.
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.
119301023
Lifting slepton masses with a non-universal, non-anomalous U(1)NAF′ in Anomaly Mediated SUSY Breaking
Abstract We extend the Minimum Supersymmetry Standard Model by a non-anomalous family (NAF) U ( 1 ) NAF ′ gauge symmetry. All gauge anomalies are cancelled with no additional exotics other than the three right-handed neutrinos. The FI D-terms associated with the U ( 1 ) NAF ′ symmetry lead to additional positive contributions to slepton squared masses. In a RG invariant way, this thus solves the tachyonic slepton mass problem in Anomaly Mediated Supersymmetry Breaking. In addition, the U ( 1 ) NAF ′ symmetry naturally gives rise to the fermion mass hierarchy and mixing angles, and determines the mass spectrum of the sparticles.