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.
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.
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.
121710663
SPIN-2 GLUON - GRAVITON MODEL WITH BARYON NUMBER NONCONSERVATION
We have shown how a weak-strong gravity model with Higgs fields can contain a baryon-number-violating mechanism. If more than one set of Higgs particles are allowed, the Higgs-fermion coupling will generate the violation of baryon-number symmetry spontaneously. To illustrate our point, we present some numerical examples on quark and nucleon decay. We find that some of the quarks can decay into leptons, antileptons, and pions with very short lifetimes. The proton is found to be much more stable than the neutron and both have possible baryon-number-violating modes of decay with very long lifetimes.
122140676
SPIN-1 AND SPIN-2 GAUGE FIELDS IN UNIFIED SL(2N,C) MODELS
16233799
Bulge formation in very late-type galaxies
The dynamical evolution of super star clusters (SSCs) moving in the background of a dark matter halo has been investigated as a possible event responsible for the formation of bulges in late-type spirals. The underlying physical processes include sinking of SSCs due to the dynamical friction and stripping of SSCs on their way to the center. Based on the assumption of a universal density profile for the dark matter halo, and an isothermal model for the SSCs, our simulations have yielded bulges that are similar in many aspects to the observational ones. In particular, the derived surface density profiles can be well fitted by an exponential structure with nuclear cusps, which is consistent with HST observations.The preliminary simulations with the Burkert density profile yield very instructive predictions on the bulge formation, which is surely worth further investigating.
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.
121270760
The complex EAS hybrid arrays in Tibet
The Tibet hybrid experiment is an extensive air shower experiment that operated at Yangbajing (E90°31', N30°06'; 4300 m above sea level) in Tibet, China, since 1996. This multi-detector system is used to observe air showers of high energy celestial gamma-ray origin and that of nuclear-component origin. Both observations aim to investigate the origin of cosmic rays using different methods. In this paper, based on the energy spectrum of the nuclear component and its chemical composition around the knee, we would like to discuss whether they could be described by the theoretical picture of the diffusive shock acceleration at SNRs. The consistency of the experimental data with rigidity dependent cutoff spectrum of CRs is examined using Tibet data and KASCADE data. It is found that both experimental data cannot be fully interpreted by such a simple approach. The sharp knee observed by Tibet experiment suggests the contribution of nearby source(s).
119331816
An Equilibrium Dark Matter Halo with the Burkert Profile
In this paper a prescription for generating an equilibrium spherical system depicted with cuspy density profiles is extended to a core density profile, the Burkert profile, which is observationally more suitable to dwarfs. By using a time-saving Monte Carlo method instead of N-body simulations, we show that the Burkert halo, which is initialized with a distribution function that depends only on energy, is in a practically stable equilibrium. The one generated with the local Maxwellian approximation is unstable, where the flat core density structure tends to steepen. This is fundamentally different from a previous study on a halo with a cuspy density profile. The deviation of the unstable “Burkert” from the initial Burkert profile is found to be closely related to taking a Gaussian as the velocity distribution at any given point. The significance of not using the local Maxwellian approximation is further demonstrated by exploring the dynamical evolution of compact super star clusters (SSCs) in the Burkert halo. In particular, the local Maxwellian approximation results in underestimating the dynamical friction and overestimating sinking time scale. Accordingly, this leads to a lower probability of forming massive bulges and young nuclear star clusters in bulgeless galaxies.