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Pankaj Jain

Publications and source records attributed to Pankaj Jain.

At least 145 records · Page 8Linked to original sources
arXiv2002

Electromagnetic Form Factors and the Localization of Quark Orbital Angular Momentum in the Proton

A new picture is given of generalized parton distributions probed in experiments in which the probe scale $Q^{2}$ and the momentum transfer $\DD^{2}$ are well separated. Application of this picture to the $Q^{2}$ dependence of the form factors $F_{1}, F_{2}$ shows that gauge invariant quark orbital angular momentum can be measured and indeed {\it localized} in the transverse profile of the proton. A previous prediction that $\sqrt{Q^{2}}F_{2}(Q^{2})/F_{1}(Q^{2}) \sim const. $ is generalized to GPD language. This prediction appears to have been confirmed by recent CEBAF data.

hep-ph↗
arXiv2002

Universality and Scale Invariance in Hourly Rainfall

We show that the hourly rainfall rate distribution can be described by a simple power law to a good approximation. We show that the exponent of the distribution in tropics is universal and is equal to $1.13\pm 0.11$. At higher latitudes the exponent increases and is found to lie in the range 1.3-1.6.

physics.ao-ph↗
arXiv2001

Spectral Dependence of Polarized Radiation due to Spatial Correlations

We study the polarization of light emitted by spatially correlated sources. We show that in general polarization acquires nontrivial spectral dependence due to spatial correlations. The spectral dependence is found to be absent only for a special class of sources where the correlation length scales as the wavelength of light. We further study the cross correlations between two spatially distinct points that are generated due to propagation. It is found that such cross correlation leads to sufficiently strong spectral dependence of polarization which can be measured experimentally.

physics.optics↗
arXiv2001

Cosmic Birefringence within the Framework of Heterotic String Theory

Low energy string theory predicts the existence of an axion field which can lead to cosmic birefringence. We solve the electromagnetic wave equations in the presence of such an axion and a dilaton field in order to determine their effect on the polarization of light. We find that the presence of dilaton field leads to a nontrivial modification of the final result. We comment on the possibility of discovering such an effect by observations of radio wave polarizations from distant radio galaxies and quasars. We have also determined the limits on the string theory parameters that are imposed by the current polarization data from distant quasars and radio galaxies.

hep-ph↗
arXiv2001

Neutrino-Induced Giant Air Showers in Large Extra Dimension Models

In models based on large extra dimensions where massive spin 2 exchange can dominate at high energies, the neutrino-proton cross section can rise to typical hadronic values at energies above 10^20 eV. The neutrino then becomes a candidate for the primary that initiates the highest energy cosmic ray showers. We investigate characteristics of neutrino-induced showers compared to proton-induced showers. The comparison includes study of starting depth, profile with depth, lateral particle distribution at ground and muon lateral distribution at ground level. We find that for cross sections above 20 mb there are regions of parameter space where the two types of showers are essentially indistinguishable. We conclude that the neutrino candidate hypothesis cannot be ruled out on the basis of shower characteristics.

hep-ph↗
arXiv2000

Correlation of Ultra High Energy Cosmic Rays with Compact Radio Loud Quasars

Angular correlations of ultra-high energy cosmic rays with cosmologically distant sources may provide clues to these mysterious events. We compare cosmic ray tracks with energies above $ 10^{20}eV$ to a compilation of radio-loud compact QSO positions. The statistical method emphasizes invariant quantities and a test of {\it statistical independence} of track and source distributions. Statistical independence is ruled out by several independent statistics at confidence levels of less that $10^{-3}$ ($99.9% $.), indicating that track directions and QSO source positions are correlated at a highly significant level.

astro-ph↗
arXiv2000

Progress in Perturbative Color Transparency

A brief overview of the status of color transparency experiments is presented. We report on the first complete calculations of color transparency within a perturbative QCD framework. We also comment on the underlying factorization method and assumptions. Detailed calculations show that the slope of the transparency ratio with $Q^2$, and the effective attenuation cross sections extracted from color transparency experiments depend on the $x$ distribuition of wave functions.

hep-ph↗
arXiv2000

A Circular Statistical Method for Extracting Rotation Measures

We propose a new method for the extraction of Rotation Measure from spectral polarization data. The method is based on maximum likelihood analysis and takes into account the circular nature of the polarization data. The method is unbiased and statistically more efficient than the standard $χ^2$ procedure. We also find that the method is computationally much faster than the standard $χ^2$ procedure if the number of data points are very large.

astro-ph↗
arXiv2000

Perturbative Color Transparency in Electroproduction Experiments

We calculate quasi-exclusive scattering of a virtual photon and a proton or pion in nuclear targets. This is the first complete calculation of ``color transparency" and "nuclear filtering " in perturbative QCD. The calculation includes full integrations over hard interaction kernels and distribution amplitudes in Feynman -x fractions and transverse spatial separation space $b$. Sudakov effects depending on $b$ and the momentum transfer $Q^2$ are included. Attenuation of the hadronic states propagating through the medium is calculated using an eikonal Glauber formalism. Nuclear correlations are included explicitly. We find that the color transparency ratio is comparatively insensitive to theoretical uncertainties inherent in perturbative formalism, such as choice of infrared cutoff scales. However, the $Q^2$ dependence of the transparency ratio is found to depend sensitively on the model of the distribution amplitude, with endpoint-dominated models failing to be dominated by short-distance. Color transparency experiments should provide an excellent test of the underlying theoretical assumptions used in the pQCD calculations.

hep-ph↗
arXiv2000

Oscillating Color Transparency in $πA\to πp (A-1)$ and $γA\to πN (A-1)$

The energy dependence of $90^o$ $cm$ fixed angle scattering of $πp \to π' p'$ and $γp\to π^+ n$ at large momentum transfer are found to be well described in terms of interfering short and long distance amplitudes with dynamical phases induced by Sudakov effects. We calculate the color transparency ratio for the corresponding processes in nuclear environments $πA\to π'p(A-1)$ and $γA\to πN (A-1)$ taking nuclear filtering into account. A prediction that the transparency ratio for these reactions will oscillate with energy provides an important test of the Sudakov phase shift and nuclear filtering hypothesis which is testable in upcoming experiments.

hep-ph↗
arXiv2000

Polarized Electromagnetic Radiation from Spatially Correlated Sources

We consider the effect of spatial correlations on sources of polarized electromagnetic radiation. The sources, assumed to be monochromatic, are constructed out of dipoles aligned along a line such that their orientation is correlated with their position. In one representative example, the dipole orientations are prescribed by a generalized form of the standard von Mises distribution for angular variables such that the azimuthal angle of dipoles is correlated with their position. In another example the tip of the dipole vector traces a helix around the symmetry axis of the source, thereby modelling the DNA molecule. We study the polarization properties of the radiation emitted from such sources in the radiation zone. For certain ranges of the parameters we find a rather striking angular dependence of polarization. This may find useful applications in certain biological systems as well as in astrophysical sources.

physics.optics↗
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

Dynamical Gauge Symmetry Breaking in $SU(3)_L\otimes U(1)_X$ Extension of the Standard Model

We study the $SU(3)_L\otimes U(1)_X$ extension of the Standard model with a strong U(1) coupling. We argue that current experiments limit this coupling to be relatively large. The model is dynamically broken to the Standard $SU(2)_L \otimes U(1)$ model at the scale of a few TeV with all the extra gauge bosons and the exotic quarks acquiring masses much larger than the scale of electroweak symmetry breaking. Furthermore we find that the model leads to large dynamical mass of the top quark and hence also breaks the electroweak gauge symmetry. It therefore leads to large dynamical effects within the Standard model and can partially replace the Higgs interactions.

hep-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↗