Absorption of High Energy Gamma-Rays by Low Energy Intergalactic Photons

Following our previously proposed technique, we have used the recent gamma-ray observations of Mrk 421 to place theoretically significant constraints on and possible estimates of the intergalactic infrared radiation field (IIRF) which are consistent with normal galactic IR production by stars and dust and rule out exotic mechanisms proposed to produce a larger IIRF. Using models for the low energy intergalactic photon spectrum from microwave to UV energies, we calculate the opacity of inter- galactic space to gamma-rays as a function of energy and redshift. These calculations indicate that the GeV gamma-ray burst recently observed by the EGRET experiment on CGRO originates at a redshift less than approximately 1.5.Comment: 12 pg., uuencoded, Z-compressed ps file (includes figures), To be published in Space Sci. Re

Flavor decomposition of the elastic nucleon electromagnetic form factors

The u- and d-quark contributions to the elastic nucleon electromagnetic form factors have been determined using experimental data on GEn, GMn, GpE, and GpM. Such a flavor separation of the form factors became possible up to 3.4 GeV2 with recent data on GEn from Hall A at JLab. At a negative four-momentum transfer squared Q2 above 1 GeV2, for both the u- and d-quark components, the ratio of the Pauli form factor to the Dirac form factor, F2/F1, was found to be almost constant, and for each of F2 and F1 individually, the d-quark portions of both form factors drop continuously with increasing Q2.Comment: 4 pages, 3 figure

Are higher education institutions delivering customer satisfaction?

Higher education institutions are realising the importance of a customer centred approach to survival in the face of increased domestic competition and the globalisation of higher education. The objective of the study is to determine the impact of different variables on customer satisfaction in the higher education sector. More explicitly, this study aims to identify the effects of: support facilities and infrastructure; location and access; and image and marketing on customer satisfaction. A random sample of 390 students was chosen. A review of the structural model indicates that only the causal link between ‘support facilities and infrastructure’ and customer satisfaction can be supported statistically

HESS J1507-622: an unique unidentified source off the Galactic Plane

Galactic very high energy (VHE, > 100 GeV) gamma ray sources in the inner Galaxy H.E.S.S. survey tend to cluster within 1 degree in latitude around the Galactic plane. HESS J1507-622 instead is unique, since it is located at latitude of ~3.5 degrees. HESS J1507-622 is slightly extended over the PSF of the instrument and hence its Galactic origin is clear. The search for counterparts in other wavelength regimes (radio, infrared and X-rays) failed to show any plausible counterparts; and given its position off the Galactic plane and hence the absorption almost one order of magnitude lower, it is very surprising to not see any counterparts especially at X-rays wavelengths (by ROSAT, XMM Newton and Chandra). Its latitude implies that it is either rather close, within about 1 kpc, or is located well off the Galactic plane. And also the models reflect the uniqueness of this object: a leptonic PWN scenario would place this source due to its quite small extension to multi-kpc distance whereas a hadronic scenario would preferentially locate this object at distances of < 1 kpc where the density of target material is higher

Neutrinos from the pulsar wind nebulae

In the recent paper we calculated the $\gamma$-ray spectra from pulsar wind nebulae (PWNe), assuming that a significant amount of the pulsar rotational energy is converted into relativistic nuclei. These nuclei accelerate leptons which are responsible for most of the observed electromagnetic emission from PWNe. Small part of nuclei also interact with the matter of the supernova producing $\gamma$-rays, which can also contribute to the observed spectra of young nebulae. Here we calculate the spectra of neutrinos from the interaction of nuclei inside the nebula and the expected neutrino event rates in the 1 km$^2$ neutrino detector from: the Crab Nebula (PSR 0531+21), the Vela SNR (PSR 0833-45), G 343.1-2.3 (PSR 1706-44), MSH15-52 (PSR 1509-58), 3C58 (PSR J0205+6449), and CTB80 (PSR 1951+32). It is shown that only the Crab Nebula can produce the neutrino event rate above the sensitivity limit of the 1 km$^2$ neutrino detector, provided that nuclei take most of the rotational energy lost by the pulsar. The neutrino event rate expected from the Vela SNR is comparable to that from the Crab Nebula but these neutrinos are less energetic and emitted from a much larger region on the sky. Therefore it may be difficult to subtract the Vela SNR signal from the higher background of the atmospheric neutrinos.Comment: 7 pages, 3 figures, A&A style, accepted to A&

Testing the Color Charge and Mass Dependence of Parton Energy Loss with Heavy-to-light Ratios at RHIC and LHC

The ratio of nuclear modification factors of high-pT heavy-flavored mesons to light-flavored hadrons (``heavy-to-light ratio'') in nucleus-nucleus collisions tests the partonic mechanism expected to underlie jet quenching. Heavy-to-light ratios are mainly sensitive to the mass and color-charge dependences of medium-induced parton energy loss. Here, we assess the potential for identifying these two effects in D and B meson production at RHIC and at the LHC. To this end, we supplement the perturbative QCD factorized formalism for leading hadron production with radiative parton energy loss. For D meson spectra at high but experimentally accessible transverse momentum (10 < pT < 20 GeV) in Pb-Pb collisions at the LHC, we find that charm quarks behave essentially like light quarks. However, since light-flavored hadron yields are dominated by gluon parents, the heavy-to-light ratio of D mesons is a sensitive probe of the color charge dependence of parton energy loss. In contrast, due to the larger b quark mass, the medium modification of B mesons in the same kinematical regime provides a sensitive test of the mass dependence of parton energy loss. At RHIC energies, the strategies for identifying and disentangling the color charge and mass dependence of parton energy loss are more involved because of the smaller kinematical range accessible. We argue that at RHIC, the kinematical regime best suited for such an analysis of D mesons is 7 < pT < 12 GeV, whereas the study of lower transverse momenta is further complicated due to the known dominant contribution of additional, particle species dependent, non-perturbative effects.Comment: 21 pages RevTex, 9 Figure