Grand Unification Signal from Ultra High Energy Cosmic Rays?

The spectrum of ultrahigh energy (above \approx 10^{9} GeV) cosmic rays is consistent with the decay of GUT scale particles. The predicted mass is m_X=10^b GeV, where b=14.6_{-1.7}^{+1.6}.Comment: 4 pages, 3 figures one figure removed, one table added, conclusions essentially remained the same within errorbar

Taxing the Informal Economy: The Current State of Knowledge and Agendas for Future Research

This paper reviews the literature on taxation of the informal economy, taking stock of key debates and drawing attention to recent innovations. Conventionally, the debate on whether to tax has frequently focused on the limited revenue potential, high cost of collection, and potentially adverse impact on small firms. Recent arguments have increasingly emphasised the more indirect benefits of informal taxation in relation to economic growth, broader tax compliance, and governance. More research is needed, we argue, into the relevant costs and benefits for all, including quasi-voluntary compliance, political and administrative incentives for reform, and citizen-state bargaining over taxation

Probing Grand Unified Theories with Cosmic Ray, Gamma-Ray and Neutrino Astrophysics

We explore scenarios where the highest energy cosmic rays are produced by new particle physics near the grand unification scale. Using detailed numerical simulations of extragalactic nucleon, gamma-ray, and neutrino propagation, we show the existence of an interesting parameter range for which such scenarios may explain part of the data and are consistent with all observational constraints. A combination of proposed observatories for ultra-high energy cosmic rays, neutrino telescopes of a few kilometer scale, and gamma-ray astrophysics instruments should be able to test these scenarios. In particular, for neutrino masses in the eV range, exclusive neutrino decay modes of superheavy particles can give rise to neutrino fluxes comparable to those predicted in models of active galactic nuclei.Comment: 15 latex pages, 5 postscript figures included, uses revtex.sty and psfig.sty. Submitted to Physical Review

Signatures of Topological Defects

We argue that due to various restrictions cosmic strings and monopole-string networks are not likely to produce the observed flux of ultra-high energy cosmic rays (UHECR). Among the topological defects studied so far, the most promising UHECR sources are necklaces and monopolonia. Other viable sources which are similar to topological defects are relic superheavy particles. All these sources have an excess of pions (and thus photons) over nucleons at production. We demonstrate that in the case of necklaces the diffuse proton flux can be larger than photon flux, due to absorption of the latter on radiobackground, while monopolonia and relic particles are concentrated in the Galactic halo, and the photon flux dominates. Another signature of the latter sources is anisotropy imposed by asymmetric position of the sun in the Galactic halo. In all cases considered so far, including necklaces, photons must be present in ultra-high energy radiation observed from topological defects, and experimental discrimination between photon-induced and proton-induced extensive air showers can give a clue to the origin of ultra-high energy cosmic rays.Comment: version accepted for publication in Phys. Rev. D. No changes in the conclusions and in figure

TeV and Superheavy Mass-Scale Particles from Supersymmetric Topological Defects, the Extragalactic Gamma-ray Background, and the Highest Energy Cosmic Rays

Cosmic topological defects in a wide class of supersymmetric theories can simultaneously be sources of higgs particles of mass comparable to the supersymmetry breaking scale $\sim$ TeV, as well as superheavy gauge bosons of mass $\sim\eta$, where $\eta$ (>> 1 TeV) denotes the associated gauge symmetry breaking scale. For cosmic strings with $\eta\sim 10^{14}$ GeV, the higgs decay can account for the extragalactic diffuse gamma ray background above $\sim$ 10 GeV, while the gauge boson decay may explain the highest energy cosmic ray flux above $\sim 10^{11}$ GeV, provided that particle production is the dominant energy loss mechanism for cosmic strings, as recent simulations suggest. By the same token, cosmic strings with $\eta$ much above $\sim 10^{14}$ GeV will be ruled out.Comment: 4 pages, Revtex, includes 1 figure, major changes in text, arguments made more general, main conclusions unchanged, version accepted for publication in PR

Cosmic Topological Defects, Highest Energy Cosmic Rays, and the Baryon Asymmetry of the Universe

It is pointed out that the observed extremely high energy cosmic rays (EHECR) above $10^{11}$ GeV and the observed baryon asymmetry of the Universe (BAU), both may have a common origin in baryon number violating decays of supermassive ``X'' particles released from cosmic topological defects (TDs) such as cosmic strings and monopoles. The X particles produced by TDs in the recent epochs produce the EHECR, while the BAU is created by X particles released from TDs mainly in the very early Universe. In this scenario the EHECR is predicted to contain baryons as well as antibaryons with a small asymmetry between the two.Comment: 4 pages, RevTex, no figures, discussions and references added, other minor changes, version to appear in Phys. Rev. Let

Observations of the unidentified gamma-ray source TeV J2032+4130 by VERITAS

TeV J2032+4130 was the first unidentified source discovered at very high energies (VHE; E $>$ 100 GeV), with no obvious counterpart in any other wavelength. It is also the first extended source to be observed in VHE gamma rays. Following its discovery, intensive observational campaigns have been carried out in all wavelengths in order to understand the nature of the object, which have met with limited success. We report here on a deep observation of TeV J2032+4130, based on 48.2 hours of data taken from 2009 to 2012 by the VERITAS (Very Energetic Radiation Imaging Telescope Array System) experiment. The source is detected at 8.7 standard deviations ($\sigma$) and is found to be extended and asymmetric with a width of 9.5$^{\prime}$$\pm$1.2$^{\prime}$ along the major axis and 4.0$^{\prime}$$\pm$0.5$^{\prime}$ along the minor axis. The spectrum is well described by a differential power law with an index of 2.10 $\pm$ 0.14$_{stat}$ $\pm$ 0.21$_{sys}$ and a normalization of (9.5 $\pm$ 1.6$_{stat}$ $\pm$ 2.2$_{sys}$) $\times$ 10$^{-13}$TeV$^{-1}$ cm$^{-2}$ s$^{-1}$ at 1 TeV. We interpret these results in the context of multiwavelength scenarios which particularly favor the pulsar wind nebula (PWN) interpretation

Investigating the TeV Morphology of MGRO J1908+06 with VERITAS

We report on deep observations of the extended TeV gamma-ray source MGRO J1908+06 made with the VERITAS very high energy (VHE) gamma-ray observatory. Previously, the TeV emission has been attributed to the pulsar wind nebula (PWN) of the Fermi-LAT pulsar PSR J1907+0602. We detect MGRO J1908+06 at a significance level of 14 standard deviations (14 sigma) and measure a photon index of 2.20 +/- 0.10_stat +/- 0.20_sys. The TeV emission is extended, covering the region near PSR J1907+0602 and also extending towards SNR G40.5--0.5. When fitted with a 2-dimensional Gaussian, the intrinsic extension has a standard deviation of sigma_src = 0.44 +/- 0.02 degrees. In contrast to other TeV PWNe of similar age in which the TeV spectrum softens with distance from the pulsar, the TeV spectrum measured near the pulsar location is consistent with that measured at a position near the rim of G40.5--0.5, 0.33 degrees away.Comment: To appear in ApJ, 8 page