The Telescope Array (TA) experiment, located in the western desert of Utah, USA, is designed for the observation of extensive air showers from extremely high energy cosmic rays. The experiment has a surface detector array surrounded by three fluorescence detectors to enable simultaneous detection of shower particles at ground level and fluorescence photons along the shower track. The TA surface detectors and fluorescence detectors started full hybrid observation in March, 2008. In this article we describe the design and technical features of the TA surface detector.close372

We investigate constraints on primordial black holes (PBHs) as dark matter candidates that arise from their capture by neutron stars (NSs). If a PBH is captured by a NS, the star is accreted onto the PBH and gets destroyed in a very short time. Thus, mere observations of NSs put limits on the abundance of PBHs. High DM densities and low velocities are required to constrain the fraction of PBHs in DM. Such conditions may be realized in the cores of globular clusters if the latter are of a primordial origin. Assuming that cores of globular clusters possess the DM densities exceeding several hundred $\mathrm{GeV}/{\mathrm{cm}}^{3}$ would imply that PBHs are excluded as comprising all of the dark matter in the mass range $3\ifmmode\times\else\texttimes\fi{}{10}^{18}$\lesssim${}{m}_{\mathrm{BH}}$\lesssim${}{10}^{24}\text{ }\text{ }\mathrm{g}$. At the DM density of $2\ifmmode\times\else\texttimes\fi{}{10}^{3}\text{ }\text{ }\mathrm{GeV}/{\mathrm{cm}}^{3}$ that has been found in simulations in the corresponding models, less than 5% of the DM may consist of PBH for these PBH masses.

We take advantage of the wealth of rotation measures data contained in the NRAO VLA Sky Survey catalog to derive new, statistically robust, upper limits on the strength of extragalactic magnetic fields. We simulate the extragalactic magnetic field contribution to the rotation measures for a given field strength and correlation length, by assuming that the electron density follows the distribution of Lyman-$\alpha$ clouds. Based on the observation that rotation measures from distant radio sources do not exhibit any trend with redshift, while the extragalactic contribution instead grows with distance, we constrain fields with Jeans’ length coherence length to be below 1.7 nG at the $2\sigma$ level, and fields coherent across the entire observable Universe below 0.65 nG. These limits do not depend on the particular origin of these cosmological fields.