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Articles 1 - 15 of 15

Full-Text Articles in Physics

Electric Dipole Moments And Polarizability In The Quark-Diquark Model Of The Neutron, Y. N. Srivastava, A. Widom, J. Swain, O. Panella Feb 2011

Electric Dipole Moments And Polarizability In The Quark-Diquark Model Of The Neutron, Y. N. Srivastava, A. Widom, J. Swain, O. Panella

John Swain

For a bound state internal wave function respecting parity symmetry, it can be rigorously argued that the mean electric dipole moment must be strictly zero. Thus, both the neutron, viewed as a bound state of three quarks, and the water molecule, viewed as a bound state of ten electrons two protons and an oxygen nucleus, both have zero mean electric dipole moments. Yet, the water molecule is said to have a nonzero dipole moment strength $d=e\Lambda $ with $\Lambda_{H_2O} \approx 0.385\ \dot{A}$. The neutron may also be said to have an electric dipole moment strength with ...


Entropy And Area In Loop Quantum Gravity, John Swain Feb 2011

Entropy And Area In Loop Quantum Gravity, John Swain

John Swain

Black hole thermodynamics suggests that the maximum entropy that can be contained in a region of space is proportional to the area enclosing it rather than its volume. I argue that this follows naturally from loop quantum gravity and a result of Kolmogorov and Bardzin' on the the realizability of networks in three dimensions. This represents an alternative to other approaches in which some sort of correlation between field configurations helps limit the degrees of freedom within a region. It also provides an approach to thinking about black hole entropy in terms of states inside rather than on its surface ...


Effects Of Anomalous Charged Current Dipole Moments Of The Tau On The Decay $\Tau^-\To\Nu_\Tau\Pi^-\Pi^0$, Maria-Teresa Dova, Pablo Lacentre, John Swain, Lucas Taylor Feb 2011

Effects Of Anomalous Charged Current Dipole Moments Of The Tau On The Decay $\Tau^-\To\Nu_\Tau\Pi^-\Pi^0$, Maria-Teresa Dova, Pablo Lacentre, John Swain, Lucas Taylor

John Swain

We analyse the process $\tau^-\to\nu_\tau\pi^-\pi^0$ 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: $\kappa = 0.16 \pm 0.08; and |\tilde\kappa| = 0.88^{+0.25}_{-0.35}.$


Echoes Of The Fifth Dimension?, Luis A. Anchordoqui, Thomas P. Mccauley, Stephen Reucroft, John Swain Feb 2011

Echoes Of The Fifth Dimension?, Luis A. Anchordoqui, Thomas P. Mccauley, Stephen Reucroft, John Swain

John Swain

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.


Effect Of The 3k Background Radiation On Ultrahigh Energy Cosmic Rays, L. A. Anchordoqui, M. T. Dova, L. N. Epele, J. D. Swain Feb 2011

Effect Of The 3k Background Radiation On Ultrahigh Energy Cosmic Rays, L. A. Anchordoqui, M. T. Dova, L. N. Epele, J. D. Swain

John Swain

In this work we re-examine the opacity of the cosmic background radiation to the propagation of extremely high energy cosmic rays. We use the continuous energy loss approximation to provide spectral modification factors for several hypothesized cosmic ray sources. Earlier problems with this approximation are resolved including the effects of resonances other than the $\Delta$.


Air Shower Simulation Using Geant4 And Commodity Parallel Computing, L. A. Anchordoqui, G. Cooperman, V. Grinberg, T. P. Mccauley, T. Paul, S. Reucroft, J. D. Swain, G. Alverson Jan 2011

Air Shower Simulation Using Geant4 And Commodity Parallel Computing, L. A. Anchordoqui, G. Cooperman, V. Grinberg, T. P. Mccauley, T. Paul, S. Reucroft, J. D. Swain, G. Alverson

John Swain

We present an evaluation of a simulated cosmic ray shower, based on GEANT4 and TOP-C, which tracks all the particles in the shower. TOP-C (Task Oriented Parallel C) provides a framework for parallel algorithm development which makes tractable the problem of following each particle. This method is compared with a simulation program which employs the Hillas thinning algorithm.


A Pot Of Gold At The End Of The Cosmic "Raynbow"?, L. A. Anchordoqui, M. T. Dova, T. P. Mccauley, T. Paul, S. Reucroft, J. D. Swain Jan 2011

A Pot Of Gold At The End Of The Cosmic "Raynbow"?, L. A. Anchordoqui, M. T. Dova, T. P. Mccauley, T. Paul, S. Reucroft, J. D. Swain

John Swain

We critically review the common belief that ultrahigh energy cosmic rays are protons or atomic nuclei with masses not exceeding that of iron. We find that heavier nuclei are indeed possible, and discuss possible sources and acceleration mechanisms for such primaries. We also show detailed simulations of extensive air showers produced by "superheavy" nuclei, and discuss prospects for their detection in future experiments.


Constraints On The Tau Neutrino Mass And Mixing From Precise Measurements Of Tau Decay Rates, J. Swain, L. Taylor Jan 2011

Constraints On The Tau Neutrino Mass And Mixing From Precise Measurements Of Tau Decay Rates, J. Swain, L. Taylor

John Swain

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: τ¯→e¯ν⁻eντ, τ¯→μ¯ν⁻μντ, τ →π¯ντ, and τ →K¯ντ. We present predictions for the tau decay widths, allowing for a non-zero tau neutrino mass, mντ, and for mixing with a neutrino of mass mνL > MZ/2, which is parametrised using a Cabibbo-like mixing angle, θL. By comparison of these theoretical predictions with the experimental measurements, we obtain the following bounds at the 90% confidence level: mντ < 42 MeV ...


Asymptotic Infrared Fractal Structure Of The Propagator For A Charged Fermion, S. Gulzari, J. Swain, A. Widom Jan 2011

Asymptotic Infrared Fractal Structure Of The Propagator For A Charged Fermion, S. Gulzari, J. Swain, A. Widom

John Swain

It is well known that the long-range nature of the Coulomb interaction makes the definition of asymptotic "in" and "out" states of charged particles problematic in quantum field theory. In particular, the notion of a simple particle pole in the vacuum charged particle propagator is untenable and should be replaced by a more complicated branch cut structure describing an electron interacting with a possibly infinite number of soft photons. Previous work suggests a Dirac propagator raised to a fractional power dependent upon the fine structure constant, however the exponent has not been calculated in a unique gauge invariant manner. It ...


Anomalous Charged Current Couplings Of The Tau And Implications For Tau Compositeness And Two-Higgs Doublet Models, Maria-Teresa Dova, John Swain, Lucas Taylor Jan 2011

Anomalous Charged Current Couplings Of The Tau And Implications For Tau Compositeness And Two-Higgs Doublet Models, Maria-Teresa Dova, John Swain, Lucas Taylor

John Swain

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 with unprecedented precision. These results are then used to constrain the tau compositeness scale and the allowed parameter space for Higgs doublet models.


Constraints On Anomalous Charged Current Couplings, Tau Neutrino Mass And Fourth Generation Mixing From Tau Leptonic Branching Fractions, Maria Teresa Dova, John Swain, Lucas Taylor Jan 2011

Constraints On Anomalous Charged Current Couplings, Tau Neutrino Mass And Fourth Generation Mixing From Tau Leptonic Branching Fractions, Maria Teresa Dova, John Swain, Lucas Taylor

John Swain

We use recent experimental measurements of tau branching fractions to determine the weak charged current magnetic and electric dipole moments of the tau 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. We also present new constraints on the mass of the tau neutrino and its mixing with a fourth generation neutrino.


A Depression Before A Bump In The Highest Energy Cosmic Ray Spectrum, L. A. Anchordoqui, M. T. Dova, L. N. Epele, J. D. Swain Jan 2011

A Depression Before A Bump In The Highest Energy Cosmic Ray Spectrum, L. A. Anchordoqui, M. T. Dova, L. N. Epele, J. D. Swain

John Swain

We re-examine the interaction of ultra high energy nuclei with the microwave background radiation. We find that the giant dipole resonance leaves a new signature in the differential energy spectrum of iron sources located around 3 Mpc: A depression before the bump which is followed by the expected cutoff.


A New Way To Detect The Higgs, S. Reucroft, Y. Srivastava, J. Swain, A. Widom Jan 2011

A New Way To Detect The Higgs, S. Reucroft, Y. Srivastava, J. Swain, A. Widom

John Swain

We describe a new technique to look for evidence of the Higgs mechanism. The usual method involves seeking evidence for the Higgs boson either directly or via the indirect effect that a virtual Higgs boson would have on a variety of Standard Model parameters. The new technique looks for Higgs field effects that are predicted to reduce the masses of heavy particles when they are in the presence of other heavy particles.


Anisotropies In Ultrahigh Energy Cosmic Rays, John Swain Jan 2011

Anisotropies In Ultrahigh Energy Cosmic Rays, John Swain

John Swain

The present status of anisotropy studies for the highest energy cosmic rays is presented including the first full sky survey. Directions and prospects for the future are also discussed in light of new statistical methods and the last quantities of data expected in the near future from the Pierre Auger Observatory.


A Method To Determine The Tau Neutrino Helicity Using Polarized Taus, M.-T. Dova, L. N. Epele, H. Fanchiotti, C.A. García Canal, P. E. Lacentre, J. D. Swain Jan 2011

A Method To Determine The Tau Neutrino Helicity Using Polarized Taus, M.-T. Dova, L. N. Epele, H. Fanchiotti, C.A. García Canal, P. E. Lacentre, J. D. Swain

John Swain

A method is presented to extract the tau neutrino helicity, or equivalently, the chirality parameter γVA, independent of any tau polarization which may be present. The method is thus well-suited to measurements using taus produced from the Z⁰ and is complementary to analyses using tau correlations since it provides the sign of the chirality parameter which is otherwise unavailable without recourse to lower energy experiments where taus are unpolarized. Results of Monte Carlo studies and comments regarding the use of technique in experiments are also included.