Precursors and postcursors (PPCs) are rare emission components detected in a handful of pulsars that appear beyond the main pulse emission, in some cases far away from it. In this paper we attempt to characterize the PPC emission in relation to the p
ulsar main pulse geometry. In our analysis we find that PPC components have properties very different from that of outer conal emission. The separation of the PPC components from the main pulse center remains constant with frequency. In addition the beam opening angles corresponding to the separation of PPC components from the pulsar center are much larger than the largest encountered in conal emission. Pulsar radio emission is believed to originate within the magnetic polar flux tubes due to the growth of instabilities in the outflowing relativistic plasma. Observationally, there is strong evidence that the main pulse emission originates at altitudes of about 50 neutron star radii for a canonical pulsar. Currently, the most plausible radio emission model that can explain main pulse emission is the coherent curvature radiation mechanism, wherein relativistic charged solitons are formed in a non-stationary electron-positron-pair plasma. The wider beam opening angles of PPC require the emission to emanate from larger altitudes as compared to the main pulse, if both these components originate by the same emission mechanism. We explore this possibility and find that this emission mechanism is probably inapplicable at the height of the PPC emission. We propose that the PPC emission represents a new type of radiation from pulsars with a mechanism different from that of the main pulse.
We present a NLO calculation of prompt photon production in DIS. The calculation involves direct, fragmentation and resolved contributions. It is performed in the virtual-photon proton center-of-mass system. A comparison of the theoretical results with HERA data is carried out.
We discuss, in the framework of perturbative QCD at next to leading order, two related observables which are usually considered to provide tests of the BFKL dynamics : jet-jet correlations at Tevatron energies and forward particle-jet correlations at
HERA. In the first case we study the rapidity gap dependence of the azimuthal correlations and find slightly too strong correlations at large gap. In the second case we discuss the cross section as well as the azimuthal correlations over a rapidity gap range of 5 units. We find that the requirement of a forward particle imposes strong kinematical constraints which distort the distributions, notably at small rapidity gaps. We also show that the decorrelation is stronger in electroproduction than in hadron-hadron collisions. Unfortunately no data are yet available for comparison.
We study the production of the lightest neutralinos in the radiative process $e^+e^- to tildechi^0_1 tildechi^0_1gamma$ in low energy supersymmetric models for the International Linear Collider energies. This includes the minimal supersymmetric stand
ard model as well as its extension with an additional chiral Higgs singlet superfield, the nonminimal supersymmetric standard model. We compare and contrast the dependence of the signal cross section on the parameters of the neutralino sector of the minimal and nonminimal supersymmetric standard model. We also consider the background to this process coming from the Standard Model process $e^+e^- to u bar u gamma$, as well as from the radiative production of the scalar partners of the neutrinos (sneutrinos) $e^+e^- to tilde u tilde u^ast gamma$, which can be a background to the radiative neutralino production when the sneutrinos decay invisibly. In low energy supersymmetric models radiative production of the lightest neutralinos may be the only channel to study supersymmetric partners of the Standard Model particles at the first stage of a linear collider, since heavier neutralinos, charginos and sleptons may be too heavy to be pair-produced at a $e^+ e^-$ machine with $sqrt{s} =500GeV$.
We extend next-to-leading logarithmic threshold and joint resummation for prompt photon production to include leading collinear effects. The impact of these effects is assessed for both fixed-target and collider kinematics. We find them in general to be small, but noticeable.
