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John P. Ralston

Publications and source records attributed to John P. Ralston.

At least 73 records · Page 4Linked to original sources
arXiv2000

Radio Detection of High Energy Particles: Coherence Versus Multiple Scales

Radio Cherenkov emission underlines detection of high energy particles via a signal growing like the particle-energy-squared. Cosmic ray-induced electromagnetic showers are a primary application. While many studies have treated the phenomenon approximately, none have attempted to incorporate all the physical scales involved in problems with time- or spatially- evolving charges. We find it is possible to decompose the calculated fields into the product of a form factor, characterizing a moving charge distribution, multiplying a general integral which depends on the charge evolution. In circumstances of interest for cosmic ray physics, the resulting expressions can be evaluated explicitely in terms of a few parameters obtainable from shower codes. The classic issues of Frauhofer and Fresnel zones play a crucial role in the coherence.

astro-ph↗
arXiv1999

Hadronic electromagnetic form factors and color transparency

We review the current status of electromagnetic form factor calculations in perturbative QCD. There is growing evidence that factorization prescriptions involving a transverse coordinate integration, such as that of Li and Sterman, are more appropriate than the prescription of LePage and Brodsky. Color transparency is naturally described within the formalism. We report the first explicit calculations of color transparency and nuclear filtering as perturbatively calculable phenomena.

hep-ph↗
arXiv1999

Core, Mantle, Crust: Imaging the Earth's Interior with Ultra-High Energy Neutrino Tomography

We report on the feasibility of using an isotropic flux of cosmic neutrinos in the energy range of 10 to 10,000 TeV to study the interior geophysical structure of the Earth. The angular distribution of events in a $\sim {\rm km}^3$-scale neutrino telescope can be inverted to yield the Earth's nucleon density distribution. The approach is independent of previous seismic methods. The energy spectrum of the neutrino primaries can also be determined from consistency with the angular distribution. Depending on neutrino flux, a reasonable density determination can be obtained with a few hundred receivers operating for a few years.

astro-ph↗
arXiv1999

New Results on Perturbative Color Transparency in Quasi-Exclusive Electroproduction

We review the perturbative QCD formalism of hadronic electromagnetic form factors and the color transparency ratio for quasi-exclusive electroproduction of the proton and pion from nuclear targets. We have completed the first full calculations including all leading order quark subprocesses and integrations over distribution amplitudes, including Sudakov effects. For the case of the proton, the calculated result shows scaling beyond $Q^2=10$ GeV$^2$. The calculation incorporating filtering due to the nuclear medium is cleaner than the corresponding calculation in free space because of attenuation of large distance amplitudes. We find that the color transparency ratio is rather insensitive to theoretical uncertainties inherent in the perturbative formalism, such as the choice of the hadron distribution amplitude.

hep-ph↗
arXiv1999

Neutrino Absorption Tomography of the Earth's Interior using Isotropic Ultra-high Energy Flux

We study the feasibility of using an isotropic flux of cosmic neutrinos in the energy range of 10 to 10000 TeV to study the interior structure of Earth. The angular distribution of events in a $\sim {\rm km}^3$-scale neutrino telescope can be inverted to yield information on the Earth's mass distribution that is independent of other methods. The energy spectrum of the neutrino primaries is also determined from consistency with the angular distribution. It is possible to make a model independent determination of the density profile of Earth's interior, separate from the absolute normalization of the incident cosmic neutrinos.

hep-ph↗
arXiv1998

Covariant Symmetry Classifications for Observables of Cosmological Birefringence

Polarizations of electromagnetic waves from distant galaxies are known to be correlated with the source orientations. These quantities have been used to search for signals of cosmological birefringence. We review and classify transformation properties of the polarization and source orientation observables. The classifications give a firm foundation to certain practices which have sprung up informally in the literature. Transformations under parity play a central role, showing that parity violation in emission or in the subsequent propagation is an observable phenomenon. We also discuss statistical measures, correlations and distributions which transform properly and which can be used for systematic data analysis.

astro-ph↗
arXiv1997

The Corkscrew Effect

We discuss a new mechanism which could cause a rotation of polarization of electromagnetic waves due to magnetic fields on cosmological scales. The effect is due to the geometrical phase of Pancharatnam and Berry, and causes a corkscrew twisting of the plane of polarization. The new effect represents an additional tool that allows possible intergalactic and cosmological magnetic fields to be studied using radio propagation.

astro-ph↗
arXiv1997

Response to Leahy's Comment on the Data's Indication of Cosmological Birefringence

Recently, J. P. Leahy commented (astro-ph/9704285) on the indication of anisotropy in the propagation of radio waves over cosmological distances, published by Nodland and Ralston (B. Nodland and J. P. Ralston, Phys. Rev. Lett. 78, 3043 (1997); astro-ph/9704196). Unfortunately, Leahy ignores the need for a statistical comparison, egregiously selects data, compares incompatible measures, uses a variable incapable of resolving birefringence, and makes mistakes in the calculations he presents.

astro-ph↗
arXiv1997

Response to Eisenstein and Bunn's Null Hypothesis Comment on Cosmological Birefringence

Eisenstein and Bunn have widely circulated a Comment (astro-ph/9704247) suggesting a non-standard null hypothesis in a test for cosmological birefringence. The Comment misrepresents the procedure used by Nodland and Ralston (B. Nodland and J. P. Ralston, Phys. Rev. Lett. 78, 3043 (1997); astro-ph/9704196) and lacks statistical basis; no calculations were reported, but sweeping conclusions were drawn from eyeballing a single scatter plot. The results of the suggested procedure range from an underestimate of the statistical significance of well-correlated data, to a failure of detecting a perfect correlation in the limit of strong cuts. We verified these faults by performing the actual calculation which EB suggested, but neglected to carry out themselves. Furthermore, the calculation showed that the original correlation remains statistically significant, with the lego-plot of 1/P versus s showing a persistent bump, and the anisotropy direction s remaining in the same direction as previously reported.

astro-ph↗
arXiv1997

Cosmologically Screwy Light

We present evidence for a new phenomenon in the propagation of electromagnetic radiation across the Universe, a corkscrew rotation of the plane of polarization not accounted for by conventional physics.

astro-ph↗
arXiv1997

Indication of Anisotropy in Electromagnetic Propagation over Cosmological Distances

We report a systematic rotation of the plane of polarization of electromagnetic radiation propagating over cosmological distances. The effect is extracted independently from Faraday rotation, and found to be correlated with the angular positions and distances to the sources. Monte Carlo analysis yields probabilistic P-values of order 10^(-3) for this to occur as a fluctuation. A fit yields a birefringence scale of order 10^(25) meters. Dependence on redshift z rules out a local effect. Barring hidden systematic bias in the data, the correlation indicates a new cosmological effect.

astro-ph↗
arXiv1996

The Ultra High Energy Neutrino-Nucleon Cross Section

The ultra-high energy neutrino nucleon cross section grows at a surprising rate with energy due to QCD effects in the target. Recent electroproduction data allows an update of earlier predictions. We compare the results of our own calculations with those of other groups, and critically review the foundation and reliability of the calculations. The question of the `new physics' potential of neutrino telescopes sensitive to the total cross section in multi-PeV energy domain is considered. We point out a loophole in the arguments which might be an important consideration in extrapolating the cross section to extremely high energies.

astro-ph↗
arXiv1996

Toward Radio Detection of PeV Neutrinos on the Cubic Kilometer Scale

Interactions of ultrahigh energy neutrinos of cosmological origin in large volumes of radio-transparent South Polar ice can be detected via coherent Cherenkov emission from accompanying electromagnetic showers. A pilot experiment employing buried radio receivers has been successfully deployed at the South Pole and data are now being collected. The physics of coherent radio emission together with the properties of radio-pulse propagation in Antarctic ice clearly distinguishes the radio method from phototube detection. In the context of the proposed km^3-scale neutrino telescope, these two detection modes provide complementary information on UHE neutrino interactions.

astro-ph↗
arXiv1995

Quantum Color Transparency and Nuclear Filtering

Color transparency is the proposal that under certain circumstances the strong interactions can be reduced in magnitude. We give a comprehensive review of the physics, which hinges on the interface of perturbative QCD with non--perturbative strong interactions. Color transparency is complementary to {\it nuclear filtering}, which is the conversion of quark wave functions in hadrons to small transverse space dimensions by interaction with a nuclear medium. We review current approaches, including pictures based on modeling the time evolution of hadronic wave--packets as well as the use of light cone matrix elements. Spin plays an intrinsic role in testing and understanding the physics and is discussed at length. We emphasize the use of data analysis procedures which have minimal model dependence. We also review existing experimental data and the experimental program planned at various facilities. The subject has strong scientific complementarity and potential to make progress in exploring hadron physics at current and future facilities.

hep-ph↗
arXiv1995

On Radio Detection of Ultra-High Energy Neutrinos in Antarctic Ice

Interactions of ultrahigh energy neutrinos of cosmological origin in large volumes of dense, radio-transparent media can be detected via coherent Cherenkov emission from accompanying electromagnetic showers. Antarctic ice meets the requirements for an efficient detection medium for a radio frequency neutrino telescope. We carefully estimate the sensitivity of realistic antennas embedded deep in the ice to 100 MHz - 1 GHz signals generated by predicted neutrino fluxes from active galactic nuclei. Our main conclusion is that a {\it single radio receiver} can probe a $\sim 1$ ${\rm km}^3$ volume for events with primary energy near 2 PeV and that the total number of events registered would be roughly 200 to 400 ${\rm year}^{-1}$ in our most conservative estimate. An array of such receivers would increase sensitivity dramatically. A radio neutrino telescope could directly observe and test our understanding of the most powerful particle accelerators in the universe, simultaneously testing the standard theory of particle physics at unprecedented energies.

astro-ph↗