32 research outputs found
Non-linear general relativistic effects in the observed redshift
We present the second-order expression for the observed redshift, accounting
for all the relativistic effects from the light propagation and from the frame
change at the observer and the source positions. We derive the generic
gauge-transformation law that any observable quantities should satisfy, and we
verify our second-order expression for the observed redshift by explicitly
checking its gauge transformation property. This is the first time an explicit
verification is made for the second-order calculations of observable
quantities. We present our results in popular gauge choices for easy use and
discuss the origin of disagreements in previous calculations.Comment: 44 pages, 1 figure, Version published in JCA
Galaxy Two-Point Correlation Function in General Relativity
We perform theoretical and numerical studies of the full relativistic
two-point galaxy correlation function, considering the linear-order scalar and
tensor perturbation contributions and the wide-angle effects. Using the
gauge-invariant relativistic description of galaxy clustering and accounting
for the contributions at the observer position, we demonstrate that the
complete theoretical expression is devoid of any long-mode contributions from
scalar or tensor perturbations and it lacks the infrared divergences in
agreement with the equivalence principle. By showing that the gravitational
potential contribution to the correlation function converges in the infrared,
our study justifies an IR cut-off in computing the
gravitational potential contribution. Using the full gauge-invariant
expression, we numerically compute the galaxy two-point correlation function
and study the individual contributions in the conformal Newtonian gauge. We
find that the terms at the observer position such as the coordinate lapses and
the observer velocity (missing in the standard formalism) dominate over the
other relativistic contributions in the conformal Newtonian gauge such as the
source velocity, the gravitational potential, the integrated Sachs-Wolf effect,
the Shapiro time-delay and the lensing convergence. Compared to the standard
Newtonian theoretical predictions that consider only the density fluctuation
and redshift-space distortions, the relativistic effects in galaxy clustering
result in a few percent-level systematic errors beyond the scale of the
baryonic acoustic oscillation. Our theoretical and numerical study provides a
comprehensive understanding of the relativistic effects in the galaxy two-point
correlation function, as it proves the validity of the theoretical prediction
and accounts for effects that are often neglected in its numerical evaluation.Comment: 35 pages, 9 figures, submitted to JCA
Galaxy Power Spectrum in General Relativity
We present the galaxy power spectrum in general relativity. Using a novel
approach, we derive the galaxy power spectrum taking into account all the
relativistic effects in observations. In particular, we show independently of
survey geometry that relativistic effects yield no divergent terms
(proportional to or on all scales) that would
mimic the signal of primordial non-Gaussianity. This cancellation of such
divergent terms is indeed expected from the equivalence principle, meaning that
any perturbation acting as a uniform gravity on the scale of the experiment
cannot be measured. We find that the unphysical infrared divergence obtained in
previous calculations occurred only due to not considering all general
relativistic contributions consistently. Despite the absence of divergent
terms, general relativistic effects represented by non-divergent terms alter
the galaxy power spectrum at large scales (smaller than the horizon scale). In
our numerical computation of the full galaxy power spectrum, we show the
deviations from the standard redshift-space power spectrum due to these
non-divergent corrections. We conclude that, as relativistic effects
significantly alter the galaxy power spectrum at , they need
to be taken into account in the analysis of large-scale data.Comment: 29 pages, 10 figures, accepted for publication in JCA
Human Genotoxic Study Carried Out Two Years after Oil Exposure during the Clean-up Activities Using Two Different Biomarkers
Micronuclei, comet and chromosome alterations assays are the most widely used biomarkers for determining the genotoxic damage in a population exposed to genotoxic chemicals. While chromosome alterations are an excellent biomarker to detect short- and long-term genotoxic effects, the comet assay only measures early biological effects, and furthermore it is unknown whether nuclear abnormalies, such as those measured in the micronucleus test, remain detectable long-term after an acute exposure. In our previous study, an increase in structural chromosome alterations in fishermen involved in the clean-up of the Prestige oil spill, two years after acute exposure, was detected. The aim of this study is to investigate whether, in lymphocytes from peripheral blood, the nuclear abnormalies (micronucleus, nucleoplasmic bridges and nuclear buds) have a similar sensitivity to the chromosome damage analysis for genotoxic detection two years after oil exposure in the same non-smoker individuals and in the same peripheral blood extraction. No significant differences in nuclear abnormalies frequencies between exposed and non-exposed individuals were found (p > 0.05). However, chromosome damage, in the same individuals, was higher in exposed vs. non-exposed individuals, especially for chromosome lesions (p < 0.05). These findings, despite the small sample size, suggest that nuclear abnormalities are probably less-successful biomarkers than are chromosome alterations to evaluate genotoxic effects two or more years after an exposure to oil. Due to the great advantage of micronucleus automatic determination, which allows for a rapid study of hundreds of individuals exposed to genotoxic chemical exposure, further studies are needed to confirm whether this assay is or is not useful in long-term genotoxic studies after the toxic agent is no longer present
Human genotoxic study carried out two years after oil exposure during the clean-up activities using two different biomarkers
Micronuclei, comet and chromosome alterations assays are the most widely used biomarkers for determining the genotoxic damage in a population exposed to genotoxic chemicals. While chromosome alterations are an excellent biomarker to detect short- and long-term genotoxic effects, the comet assay only measures early biological effects, and furthermore it is unknown whether nuclear abnormalies, such as those measured in the micronucleus test, remain detectable long-term after an acute exposure. In our previous study, an increase in structural chromosome alterations in fishermen involved in the clean-up of the Prestige oil spill, two years after acute exposure, was detected. The aim of this study is to investigate whether, in lymphocytes from peripheral blood, the nuclear abnormalies (micronucleus, nucleoplasmic bridges and nuclear buds) have a similar sensitivity to the chromosome damage analysis for genotoxic detection two years after oil exposure in the same non-smoker individuals and in the same peripheral blood extraction. No significant differences in nuclear abnormalies frequencies between exposed and non-exposed individuals were found (p > 0.05). However, chromosome damage, in the same individuals, was higher in exposed vs. non-exposed individuals, especially for chromosome lesions (p < 0.05). These findings, despite the small sample size, suggest that nuclear abnormalities are probably less-successful biomarkers than are chromosome alterations to evaluate genotoxic effects two or more years after an exposure to oil. Due to the great advantage of micronucleus automatic determination, which allows for a rapid study of hundreds of individuals exposed to genotoxic chemical exposure, further studies are needed to confirm whether this assay is or is not useful in long-term genotoxic studies after the toxic agent is no longer present