620 research outputs found
Hypothesis of path integral duality: Applications to QED
We use the modified propagator for quantum field based on a ``principle of
path integral duality" proposed earlier in a paper by Padmanabhan to
investigate several results in QED. This procedure modifies the Feynman
propagator by the introduction of a fundamental length scale. We use this
modified propagator for the Dirac particles to evaluate the first order
radiative corrections in QED. We find that the extra factor of the modified
propagator acts like a regulator at the Planck scales thereby removing the
divergences that otherwise appear in the conventional radiative correction
calculations of QED. We find that:(i) all the three renormalisation factors
, , and pick up finite corrections and (ii) the modified
propagator breaks the gauge invariance at a very small level of
. The implications of this result to generation of the
primordial seed magnetic fields are discussed.Comment: 15 pages, LaTeX2e (uses ijmpd.sty); To appear in IJMP-D; References
adde
Can Maxwell's equations be obtained from the continuity equation?
We formulate an existence theorem that states that given localized scalar and
vector time-dependent sources satisfying the continuity equation, there exist
two retarded fields that satisfy a set of four field equations. If the theorem
is applied to the usual electromagnetic charge and current densities, the
retarded fields are identified with the electric and magnetic fields and the
associated field equations with Maxwell's equations. This application of the
theorem suggests that charge conservation can be considered to be the
fundamental assumption underlying Maxwell's equations.Comment: 14 pages. See the comment: "O. D. Jefimenko, Causal equations for
electric and magnetic fields and Maxwell's equations: comment on a paper by
Heras [Am. J. Phys. 76, 101 (2008)].
Scattering of Gravitational Waves by the Weak Gravitational Fields of Lens Objects
We consider the scattering of the gravitational waves by the weak
gravitational fields of lens objects. We obtain the scattered gravitational
waveform by treating the gravitational potential of the lens to first order,
i.e. using the Born approximation. We find that the effect of scattering on the
waveform is roughly given by the Schwarzschild radius of the lens divided by
the wavelength of gravitational wave for a compact lens object. If the lenses
are smoothly distributed, the effect of scattering is of the order of the
convergence field along the line of sight to the source. In the short
wavelength limit, the amplitude is magnified by , which is consistent
with the result in weak gravitational lensing.Comment: 4 pages, 2 figures, A&A Letters, in press, minor changes, references
adde
Prediction and measurement of radiation damage to CMOS devices on board spacecraft
The CMOS Radiation Effects Measurement (CREM) experiment is presently being flown on the Explorer-55. The purpose of the experiment is to evaluate device performance in the actual space radiation environment and to correlate the respective measurements to on-the-ground laboratory irradiation results. The experiment contains an assembly of C-MOS and P-MOS devices shielded in front by flat slabs of aluminum and by a practically infinite shield in the back. Predictions of radiation damage to C-MOS devices are based on standard environment models and computational techniques. A comparison of the shifts in CMOS threshold potentials, that is, those measured in space to those obtained from the on-the-ground simulation experiment with Co-60, indicates that the measured space damage is smaller than predicted by about a factor of 2-3 for thin shields, but agrees well with predictions for thicker shields
RELATION OF RHEUMATIC-LIKE CARDIAC LESIONS OF THE MOUSE TO LOCALIZATION OF GROUP A STREPTOCOCCAL CELL WALLS
Mice injected intraperitoneally with isolated cell wall fragments of Group A streptococci develop a carditis similar to that previously observed in mice injected with crude extracts of this organism. Neither the soluble cytoplasmic components of Group A streptococcal cells nor the nonfragmented cell walls produced carditis in this experimental model. Fluorescein and 125I-labeled antibodies specific for Group A streptococcal cell wall antigens were used to demonstrate that, for 5 wk after injection, cell wall material is localized around the sites of active lesions in the heart. In addition, the cell wall antigen accumulates in the liver, spleen, mediastinal lymph nodes, and the adjacent loose connective tissue, where it persists for at least 10 wk
Post-Newtonian Parameters from Alternative Theories of Gravity
Alternative theories of gravity have been recently studied in connection with
their cosmological applications, both in the Palatini and in the metric
formalism. The aim of this paper is to propose a theoretical framework (in the
Palatini formalism) to test these theories at the solar system level and
possibly at the galactic scales. We exactly solve field equations in vacuum and
find the corresponding corrections to the standard general relativistic
gravitational field. On the other hand, approximate solutions are found in
matter cases starting from a Lagrangian which depends on a phenomenological
parameter. Both in the vacuum case and in the matter case the deviations from
General Relativity are controlled by parameters that provide the Post-Newtonian
corrections which prove to be in good agreement with solar system experiments.Comment: 17 pages, no figure
Exact solutions of a particle in a box with a delta function potential: The factorization method
We use the factorization method to find the exact eigenvalues and
eigenfunctions for a particle in a box with the delta function potential
. We show that the presence of the potential
results in the discontinuity of the corresponding ladder operators. The
presence of the delta function potential allows us to obtain the full spectrum
in the first step of the factorization procedure even in the weak coupling
limit .Comment: 8 pages, 2 figures, to appear in American Journal of Physic
Using the Uncharged Kerr Black Hole as a Gravitational Mirror
We extend the study of the possibility to use the Schwarzschild black hole as
a gravitational mirror to the more general case of an uncharged Kerr black
hole. We use the null geodesic equation in the equatorial plane to prove a
theorem concerning the conditions the impact parameter has to satisfy if there
shall exist boomerang photons. We derive an equation for these boomerang
photons and an equation for the emission angle. Finally, the radial null
geodesic equation is integrated numerically in order to illustrate boomerang
photons.Comment: 11 pages Latex, 3 Postscript figures, uufiles to compres
Biomass Vertical Distribution in a Grazed Grassland Under Monoespecific and Mixed Grazing
Mixed grazing is defined as the use of the same forage resource for more than one herbivore species. It has been shown that different herbivore species have specific grazing modalities (Black and Kenney, 1984), which may differentially modify the structure of the pasture. The aim of this study was to evaluate the biomass vertical distribution in a sward with mixed grazing
Gravitational coupling to two-particle bound states and momentum conservation in deep inelastic scattering
The momentum conservation sum rule for deep inelastic scattering (DIS) from
composite particles is investigated using the general theory of relativity. For
two 1+1 dimensional examples, it shown that covariant theories automatically
satisy the DIS momentum conservation sum rule provided the bound state is
covariantilly normalized. Therefore, in these cases the two DIS sum rules for
baryon conservation and momentum conservation are equivalent
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