The leaky-box model and the attendant concept of path-length distribution of cosmic rays were invented in the mid-1960s. Even though versatile computational packages such as GALPROP and DRAGON with the diffusion approach are now available for analyzing cosmic-ray data, the concepts of the leaky box and path-length distribution continue to be adopted extensively. We show here mathematically that there is a close correspondence between the two approaches: the path lengths or resident times of the leaky-box models are similar to the “impulse response functions” of complex dynamical systems and are intuitively transparent. The results provided by the leaky-box model are valid when used judiciously.

The recent measurements of the spectral intensities of cosmic-ray nuclei have suggested that the ratio of boron to carbon nuclei, R ( E ) , comprises two components, R 1 ( E ) which carries all of the energy dependence and the other R A , a constant independent of energy per nucleon. This finding supports the earlier theoretical expectations and results of gamma-ray astronomy that one of these components is attributable to spallation in a cocoon like region surrounding the sources and the other in the general interstellar medium before cosmic rays leak away from the Galaxy. A new model-independent way of analyzing cosmic-ray spectra is presented here to shed light on the recent findings: Imposing the single constraint that the source function of B nuclei is minimal we use a cascade of rate equations to map point by point the observed cosmic-ray spectra of p, B, C, O, and Fe onto their source spectra and the two lifetimes of cosmic rays rG G in the Galaxy and rS S in the cocoons surrounding the sources. The model-independent results show that the appropriate choice rS(E) S ( E ) is responsible for R 1 ( E ) and the source spectra are power laws with indices of similar to - 2.7.

We take a phenomenological approach in a minimal model to understand the spectral intensity of secondary cosmicray particles like positrons, antiprotons, Lithium, Beryllium and Boron.Our analysis shows that cosmic rays at ∼ GeV energies pass through a significant amount of matter in regions surrounding the sources.This grammage decreases with increasing cosmic-ray energy and becomes negligible beyond ∼ 100 GeV.During the subsequent propagation in the interstellar medium cosmic rays of all energies up to ∼ 10 5 GeV/n pass through about 1-2 g cm -2 of matter before leaking into the intergalactic medium.It is in the interstellar medium that the bulk of the positrons and antiprotons are generated.Also cosmic-ray nuclei like C, N, and O at all energies generate additional amounts of Li, Be and B nuclei with a spectrum similar to those of C, O etc.The implications of these findings of the minimal model to the observations of gamma rays and also the importance of spatial and temporal discreteness of cosmic-ray sources for modeling cosmic-ray propagation are briefly pointed out.

We have developed a torsion balance with a sensitivity about ten times better than those of previously operating balances for the study of long range forces coupling to baryon and lepton numbers. We present here the details of the design and expected characteristics of this balance. Operation of this balance for a year will also result in improved bounds on long range interactions of dark matter violating Einstein's equivalence principle.

M. G. K. Menon, referred to as Goku, was an outstanding particle physicist and an extraordinary statesman of science. He made his major contributions to particle physics during the tortuous years of the unravelling of the full complexity of the families of elementary particles. It was an exciting but perplexing period, and the elucidation of the complexities of the world of elementary particles took the combined efforts of the experimentalists and the theorists. Goku's contributions were central to establishing what was eventually to become the standard picture of elementary particles. He will be remembered for his studies of the two- and three-body decay modes of the charged kaon that gave rise to the ‘τ–θ’ puzzle signalling non-conservation of parity. He coined the evocative phrase ‘associated production’ to describe the creation of kaons and hyperons together in high-energy interactions. He led a team that carried out experiments at great depths underground, and in 1965 they detected an event in which a cosmic-ray neutrino interacted with rock, producing an energetic muon. In the 1980s, with a large detector, also deployed underground, he set a lower bound on the lifetime for the decay of the proton. Menon was a great builder of academic and scientific institutions and a pre-eminent advocate for science. Accordingly, he stimulated and participated actively in building up the scientific and technological infrastructure in independent India, initially as the secretary of the Government of India and subsequently as the minister of state for science and technology. As the president of the International Council of Scientific Unions, he spearheaded its participation in the policymaking body of the United Nations. He was at various times the president of the three leading academies of sciences in India and a founding member and vice-president of the World Academy of Sciences. He was a gentle and loving family man and an energetic and engaged scientific colleague.

Baron Roland von Eötvös performed amazing experiments on the equivalence of inertial and gravitational mass. Since his work experiments have become progressively more refined. The $G^{\epsilon\epsilon}$ Lab at Washington University in St. Louis has built a new experiment in the hopes of refining these tests even further. We have operated a prototype of this experiment by continuously monitoring the angular orientation of a torsion balance for over 115 days and the results we have obtained are promising. The experience we have gained from this experiment suggest the need for improved thermal and magnetic shielding; it also gives us confidence that long-period torsion balances have the ability to significantly improve the bounds on violation of the Equivalence Principle. Here we describe our instrument and how these experiences will be used to improve our next generation torsion balance.

We report here the results of operation of a torsion balance with a period of $\sim 1.27 \times 10^4$ s. The analysis of data collected over a period of $\sim$115 days shows that the difference in the accelerations towards the Galactic Center of test bodies made of aluminum and quartz was $(0.61 \pm 1.27) \times 10^{-15} \, \mathrm{ m \, s}^{-2}$. This sets a bound on the violation of the equivalence principle by forces exerted by Galactic dark matter which is expressed by the Eotvos parameter $\eta_{DM} = (1.32 \pm 2.68) \times 10^{-5}$, a significant improvement upon earlier bounds.

I consider the impact of recent measurements of positron and antiproton spectra in cosmic rays on our understanding of the origins and propagation of cosmic rays, as well as on the annihilation and decay characteristics of particles of Galactic dark matter, from the perspective of current models postulating energy-dependent leakage of cosmic rays from the Galaxy and of the nested leaky-box model, in which the leakage from the Galaxy is independent of energy. The nested leaky-box model provides a straightforward and consistent explanation of the observed spectral intensities, and finds no compelling need for a contribution from the annihilation or decay of Galactic dark matter. Improved observations and modeling efforts are needed to probe the properties of dark matter deeply enough to be significant to particle physics and cosmology.

This paper describes the Polarization Spectroscopic Telescope Array (PolSTAR), a mission proposed to NASA's 2014 Small Explorer (SMEX) announcement of opportunity. PolSTAR measures the linear polarization of 3-50 keV (requirement; goal: 2.5-70 keV) X-rays probing the behavior of matter, radiation and the very fabric of spacetime under the extreme conditions close to the event horizons of black holes, as well as in and around magnetars and neutron stars. The PolSTAR design is based on the technology developed for the Nuclear Spectroscopic Telescope Array (NuSTAR) mission launched in June 2012. In particular, it uses the same X-ray optics, extendable telescope boom, optical bench, and CdZnTe detectors as NuSTAR. The mission has the sensitivity to measure similar to 1% linear polarization fractions for X-ray sources with fluxes down to similar to 5 mCrab. This paper describes the PolSTAR design as well as the science drivers and the potential science return. (C) 2015 Elsevier B.V. All rights reserved.

The observation of neutrons turning into antineutrons would constitute a discovery of fundamental importance for particle physics and cosmology. Observing the n–n̄ transition would show that baryon number (B) is violated by two units and that matter containing neutrons is unstable. It would provide a clue to how the matter in our universe might have evolved from the B=0 early universe. If seen at rates observable in foreseeable next-generation experiments, it might well help us understand the observed baryon asymmetry of the universe. A demonstration of the violation of B–L by 2 units would have a profound impact on our understanding of phenomena beyond the Standard Model of particle physics. Slow neutrons have kinetic energies of a few meV. By exploiting new slow neutron sources and optics technology developed for materials research, an optimized search for oscillations using free neutrons from a slow neutron moderator could improve existing limits on the free oscillation probability by at least three orders of magnitude. Such an experiment would deliver a slow neutron beam through a magnetically-shielded vacuum chamber to a thin annihilation target surrounded by a low-background antineutron annihilation detector. Antineutron annihilation in a target downstream of a free neutron beam is such a spectacular experimental signature that an essentially background-free search is possible. An authentic positive signal can be extinguished by a very small change in the ambient magnetic field in such an experiment. It is also possible to improve the sensitivity of neutron oscillation searches in nuclei using large underground detectors built mainly to search for proton decay and detect neutrinos. This paper summarizes the relevant theoretical developments, outlines some ideas to improve experimental searches for free neutron oscillations, and suggests avenues both for theoretical investigation and for future improvement in the experimental sensitivity.

ABSTRACT In this paper we note that the spectral intensities of antiprotons observed in Galactic cosmic rays in the energy range ∼1–300 GeV by BESS, PAMELA, and AMS instruments display nearly the same spectral shape as that generated by primary cosmic rays through their interaction with matter in the interstellar medium, without any significant modifications. More importantly, a constant residence time of ∼2.3 ± 0.7 million years in the Galactic volume, independent of the energy of cosmic rays, matches the observed intensities. A small additional component of secondary antiprotons in the energy range below 10 GeV, generated in cocoon-like regions surrounding the cosmic-ray sources, seems to be present. We discuss this result in the context of observations of other secondary components such as positrons and boron, and the bounds on anisotropy of cosmic rays. In the nested leaky-box model the spectral intensities of antiprotons and positrons can be interpreted as secondary products of cosmic-ray interactions.

X-ray polarimetry promises to give qualitatively new information about high-energy astrophysical sources, such as binary black hole systems, micro-quasars, active galactic nuclei, and gamma-ray bursts. We designed, built and tested a hard X-ray polarimeter, X-Calibur, to be used in the focal plane of the balloon-borne InFOCμS grazing incidence X-ray telescope with the goal of observing astrophysical sources. X-Calibur combines a low-Z Compton scatterer with a CZT detector assembly to measure the polarization of 20–60 keV X-rays making use of the fact that polarized photons Compton scatter preferentially perpendicular to the electric field orientation. A 1-day test flight of the instrument was performed from Ft.Sumner, NM, in fall 2014. The sensitivity, performance and first results form the flight will be presented.