arXiv subjects

John Swain

Publications and source records attributed to John Swain.

35 records · Page 2Linked to original sources

arXiv2003

The Pierre Auger Observatory

One of the most fascinating puzzles in particle astrophysics today is that of the origin and nature of the highest energy cosmic rays. The Pierre Auger Observatory (PAO), currently under construction in Province of Mendoza, Argentina, and with another site planned in the Northern hemisphere, is a major international effort to make precise, high statistics studies of the highest energy cosmic rays. It is the first experiment designed to work in a hybrid mode incorporating both a ground-based array of 1600 particle detectors spread over 3000 km$^2$ with fluorescence telescopes placed on the boundaries of the surface array. The current status of the observatory is presented and prospects for the future discussed.

astro-ph↗

arXiv2003

Full-Sky Search for Ultra High Energy Cosmic Ray Anisotropies

Using data from the SUGAR and the AGASA experiments taken during a 10 yr period with nearly uniform exposure to the entire sky, we search for large-scale anisotropy patterns in the arrival directions of cosmic rays with energies > 10^{19.6} eV. We determine the angular power spectrum from an expansion in spherical harmonics for modes out to \ell=5. Based on available statistics, we find no significant deviation from isotropy. We compare the rather modest results which can be extracted from existing data samples with the results that should be forthcoming as new full-sky observatories begin operation.

astro-ph↗

arXiv2003

The Pauli Exclusion Principle and SU(2) vs. SO(3) in Loop Quantum Gravity

Recent attempts to resolve the ambiguity in the loop quantum gravity description of the quantization of area has led to the idea that j=1 edges of spin-networks dominate in their contribution to black hole areas as opposed to j=1/2 which would naively be expected. This suggests that the true gauge group involved might be SO(3) rather than SU(2) with attendant difficulties. We argue that the assumption that a version of the Pauli principle is present in loop quantum gravity allows one to maintain SU(2) as the gauge group while still naturally achieving the desired suppression of spin-1/2 punctures. Areas come from j=1 punctures rather than j=1/2 punctures for much the same reason that photons lead to macroscopic classically observable fields while electrons do not.

gr-qc↗

arXiv2002

Ultrahigh Energy Cosmic Rays: The state of the art before the Auger Observatory

In this review we discuss the important progress made in recent years towards understanding the experimental data on cosmic rays with energies $\agt 10^{19}$ eV. We begin with a brief survey of the available data, including a description of the energy spectrum, mass composition, and arrival directions. At this point we also give a short overview of experimental techniques. After that, we introduce the fundamentals of acceleration and propagation in order to discuss the conjectured nearby cosmic ray sources. We then turn to theoretical notions of physics beyond the Standard Model where we consider both exotic primaries and exotic physical laws. Particular attention is given to the role that TeV-scale gravity could play in addressing the origin of the highest energy cosmic rays. In the final part of the review we discuss the potential of future cosmic ray experiments for the discovery of tiny black holes that should be produced in the Earth's atmosphere if TeV-scale gravity is realized in Nature.

hep-ph↗

arXiv2001

The Mysterious Ultrahigh Energy Cosmic Ray Clustering

We examine the correlation between compact radio quasars (redshifts in the range $z = 0.3 - 2.2$) and the arrival direction of ultrahigh energy cosmic rays forming clusters. Our Monte Carlo simulation reveals a statistically significant correlation on the AGASA sample: the chance probability of this effect being less than 1%. The implications of this result on the origin of ultrahigh energy cosmic rays are discussed.

astro-ph↗

arXiv2001

Extragalactic Sources for Ultra High Energy Cosmic Ray Nuclei

In this article we examine the hypothesis that the highest energy cosmic rays are complex nuclei from extragalactic sources. Under reasonable physical assumptions, we show that the nearby metally rich starburst galaxies (M82 and NGC 253) can produce all the events observed above the ankle. This requires diffusion of particles below $10^{20}$ eV in extragalactic magnetic fields $B \approx 15$ nG. Above $10^{19}$ eV, the model predicts the presence of significant fluxes of medium mass and heavy nuclei with small rate of change of composition. Notwithstanding, the most salient feature of the starburst-hypothesis is a slight anisotropy induced by iron debris just before the spectrum-cutoff.

hep-ph↗

arXiv2001

Hadronic interactions, precocious unification, and cosmic ray showers at Auger energies

At Auger energies only model predictions enable us to extract primary cosmic ray features. The simulation of the shower evolution depends sensitively on the first few interactions, necessarily related to the quality of our understanding of high energy hadronic collisions. Distortions of the standard ``soft semi-hard'' scenario include novel large compact dimensions and a string or quantum gravity scale not far above the electroweak scale. Na\"ıvely, the additional degrees of freedom yield unification of all forces in the TeV range. In this article we study the influence of such precocious unification during atmospheric cascade developments by analyzing the most relevant observables in proton induced showers.

hep-ph↗

arXiv2001

Extensive air showers with TeV-scale quantum gravity

One of the possible consequences of the existence of extra degrees of freedom beyond the electroweak scale is the increase of neutrino-nucleon cross sections ($σ_{νN}$) beyond Standard Model predictions. At ultra-high energies this may allow the existence of neutrino-initiated extensive air showers. In this paper, we examine the most relevant observables of such showers. Our analysis indicates that the future Pierre Auger Observatory could be potentially powerful in probing models with large compact dimensions.

hep-ph↗

arXiv2000

Echoes of the fifth dimension?

In this article we examine the question of whether the highest energy cosmic ray primaries could be ultra relativistic magnetic monopoles. The analysis is performed within the framework of large compact dimensions and TeV scale quantum gravity. Our study indicates that while this hypothesis must be regarded as highly speculative it cannot be ruled out with present data.

hep-ph↗

arXiv2000

Scalable Parallel Implementation of Geant4 Using Commodity Hardware and Task Oriented Parallel C

We describe a scalable parallelization of Geant4 using commodity hardware in a collaborative effort between the College of Computer Science and the Department of Physics at Northeastern University. The system consists of a Beowulf cluster of 32 Pentium II processors with 128 MBytes of memory each, connected via ATM and fast Ethernet. The bulk of the parallelization is done using TOP-C (Task Oriented Parallel C), software widely used in the computational algebra community. TOP-C provides a flexible and powerful framework for parallel algorithm development, is easy to learn, and is available at no cost. Its task oriented nature allows one to parallelize legacy code while hiding the details of interprocess communications. Applications include fast interactive simulation of computationally intensive processes such as electromagnetic showers. General results motivate wider applications of TOP-C to other simulation problems as well as to pattern recognition in high energy physics.

hep-ph↗

arXiv1999

Effects of anomalous charged current dipole moments of the tau on the decay $τ^-\toν_τπ^-π^0$

We analyse the process $τ^-\toν_τπ^-π^0$ allowing for anomalous weak charged current magnetic and electric dipole moment interactions and determine the effects on the differential and total decay rates. Using recent experimental data we determine the following values for the anomalous magnetic and electric dipole moment parameters, respectively: $κ= 0.16 \pm 0.08; and |\tildeκ| = 0.88^{+0.25}_{-0.35}.$

hep-ph↗

arXiv1999

Sensitivities of one-prong tau branching fractions to tau neutrino mass, mixing, and anomalous charged current couplings

We analyse the sensitivities of exclusive one-prong tau branching fractions to: the tau neutrino mass; its mixing with a fourth generation neutrino; the weak charged current magnetic and electric dipole moments of the tau; and the Michel parameter $η$. Quantitative constraints are derived from current experimental data and the future constraints derivable from tau-charm factory measurements are estimated. The anomalous coupling constraints are used to constrain the tau compositeness scale and the allowed parameter space for Higgs doublet models.

hep-ph↗

arXiv1997

First unitarity-independent determination of the CKM matrix elements $V_{td}$, $V_{ts}$, and ${V_{tb}$ and the implications for unitarity

The magnitudes of the CKM matrix elements $V_{td}$, $V_{ts}$, and $V_{tb}$ are determined for the first time without any assumptions of unitarity. The implications for the unitarity of the CKM matrix as a whole are discussed.

hep-ph↗

arXiv1997

First determination of the quark mixing matrix element Vtb independent of assumptions of unitarity

We present a new method for the determination of the Cabibbo-Kobayashi-Maskawa quark mixing matrix element $|V_{tb}|$ from electroweak loop corrections, in particular those affecting the process $Z\to b\bar{b}$. From a combined analysis of results from the LEP, SLC, Tevatron, and neutrino scattering experiments we determine $|V_{tb}| = 0.77^{+0.18}_{-0.24}$. This is the first determination of $|V_{tb}|$ which is independent of unitarity assumptions.

hep-ph↗

arXiv1997

New constraints on the tau neutrino mass and fourth generation mixing

We present new constraints on the mass $m_{ν_τ}$ of the tau neutrino and its mixing with a fourth generation neutrino. From an analysis of the partial widths of tau lepton decays we obtain the following bounds at the 90% confidence level: $m_{ν_τ} < 32$ MeV and $\sin^2θ< 0.007$, where $θ$ describes the Cabibbo-like mixing of the third and fourth generation neutrinos.

hep-ph↗

arXiv1997

Anomalous charged current couplings of the tau and implications for tau compositeness and two-Higgs doublet models

The leptonic branching fractions of the tau lepton are sensitive to anomalous charged current interactions. We use recent experimental measurements to determine the weak charged current magnetic and electric dipole moments and the Michel parameter $η$ with unprecedented precision. These results are then used to constrain the tau compositeness scale and the allowed parameter space for Higgs doublet models.

hep-ph↗

arXiv1996

Constraints on the tau neutrino mass and mixing from precise measurements of tau decay rates

We have derived constraints on the tau neutrino mass and fourth generation mixing from an analysis of the partial widths of tau lepton decays, in particular: tau -> e nu nu_tau, tau -> mu nu nu_tau, tau -> pi nu_tau, tau -> K nu_tau. We present predictions for the tau decay widths, allowing for a non-zero tau neutrino mass, m(nu_tau), and for mixing with a neutrino of mass m(nu_L) > M_Z/2, which is parametrised using a Cabibbo-like mixing angle, theta_L. By comparison of these theoretical predictions with the experimental measurements, we obtain the following bounds at the 90% confidence level: m(nu_tau) < 42 MeV and sin^2(theta_L) < 0.014.

hep-ph↗