9 research outputs found
Cosmological parameter estimation and the spectral index from inflation
Accurate estimation of cosmological parameters from microwave background
anisotropies requires high-accuracy understanding of the cosmological model.
Normally, a power-law spectrum of density perturbations is assumed, in which
case the spectral index can be measured to around using
microwave anisotropy satellites such as MAP and Planck. However, inflationary
models generically predict that the spectral index of the density
perturbation spectrum will be scale-dependent. We carry out a detailed
investigation of the measurability of this scale dependence by Planck,
including the influence of polarization on the parameter estimation. We also
estimate the increase in the uncertainty in all other parameters if the scale
dependence has to be included. This increase applies even if the scale
dependence is too small to be measured unless it is assumed absent, but is
shown to be a small effect. We study the implications for inflation models,
beginning with a brief examination of the generic slow-roll inflation
situation, and then move to a detailed examination of a recently-devised hybrid
inflation model for which the scale dependence of may be observable.Comment: 6 pages LaTeX file with one figure incorporated (uses mn.sty and
epsf). Important modifications to result
On the reliability of inflaton potential reconstruction
If primordial scalar and tensor perturbation spectra can be inferred from
observations of the cosmic background radiation and large-scale structure, then
one might hope to reconstruct a unique single-field inflaton potential capable
of generating the observed spectra. In this paper we examine conditions under
which such a potential can be reliably reconstructed. For it to be possible at
all, the spectra must be well fit by a Taylor series expansion. A complete
reconstruction requires a statistically-significant tensor mode to be measured
in the microwave background. We find that the observational uncertainties
dominate the theoretical error from use of the slow-roll approximation, and
conclude that the reconstruction procedure will never insidiously lead to an
irrelevant potential.Comment: 16 page LaTeX file with eight postscript figures embedded with epsf;
no special macros neede
Accurate determination of inflationary perturbations
We use a numerical code for accurate computation of the amplitude of linear
density perturbations and gravitational waves generated by single-field
inflation models to study the accuracy of existing analytic results based on
the slow-roll approximation. We use our code to calculate the coefficient of an
expansion about the exact analytic result for power-law inflation; this
generates a fitting function which can be applied to all inflationary models to
obtain extremely accurate results. In the appropriate limit our results confirm
the Stewart--Lyth analytic second-order calculation, and we find that their
results are very accurate for inflationary models favoured by current
observational constraints.Comment: 9 pages LaTeX file with 3 figures incorporated, using RevTeX and eps
Cosmological Parameter Estimation and the Spectral Index From Inflation
Accurate estimation of cosmological parameters from microwave background anisotropies requires high-accuracy understanding of the cosmological model. Normally, a power-law spectrum of density perturbations is assumed, in which case the spectral index n can be measured to around \Sigma0:004 using microwave anisotropy satellites such as MAP and Planck. However, inflationary models generically predict that the spectral index n of the density perturbation spectrum will be scale-dependent. We carry out a detailed investigation of the measurability of this scale dependence by Planck, including the influence of polarization on the parameter estimation. We include an estimate of the increase in the uncertainty in all other parameters if the scale dependence has to be included. The expected uncertainty on n is increased by a factor of ten; note that this applies even if the scale dependence is too small to be measured, unless it is assumed absent. Other parameters are much more mildly affected..
Prevalence and Clinical Outcomes of Poor Immune Response Despite Virologically Suppressive Antiretroviral Therapy Among Children and Adolescents With Human Immunodeficiency Virus in Europe and Thailand: Cohort Study
BACKGROUND: In human immunodeficiency virus (HIV)-positive adults, low CD4 cell counts despite fully suppressed HIV-1 RNA on antiretroviral therapy (ART) have been associated with increased risk of morbidity and mortality. We assessed the prevalence and outcomes of poor immune response (PIR) in children receiving suppressive ART. METHODS: Sixteen cohorts from the European Pregnancy and Paediatric HIV Cohort Collaboration (EPPICC) contributed data. Children <18 years at ART initiation, with sustained viral suppression (VS) (≤400 copies/mL) for ≥1 year were included. The prevalence of PIR (defined as World Health Organization advanced/severe immunosuppression for age) at 1 year of VS was described. Factors associated with PIR were assessed using logistic regression. Rates of acquired immunodeficiency syndrome (AIDS) or death on suppressive ART were calculated by PIR status. RESULTS: Of 2318 children included, median age was 6.4 years and 68% had advanced/severe immunosuppression at ART initiation. At 1 year of VS, 12% had PIR. In multivariable analysis, PIR was associated with older age and worse immunological stage at ART start, hepatitis B coinfection, and residing in Thailand (all P ≤ .03). Rates of AIDS/death (95% confidence interval) per 100 000 person-years were 1052 (547, 2022) among PIR versus 261 (166, 409) among immune responders; rate ratio of 4.04 (1.83, 8.92; P < .001). CONCLUSIONS: One in eight children in our cohort experienced PIR despite sustained VS. While the overall rate of AIDS/death was low, children with PIR had a 4-fold increase in risk of event as compared with immune responders
Prevalence and Clinical Outcomes of Poor Immune Response Despite Virologically Suppressive Antiretroviral Therapy Among Children and Adolescents With Human Immunodeficiency Virus in Europe and Thailand: Cohort Study
International audienceIn human immunodeficiency virus (HIV)-positive adults, low CD4 cell counts despite fully suppressed HIV-1 RNA on antiretroviral therapy (ART) have been associated with increased risk of morbidity and mortality. We assessed the prevalence and outcomes of poor immune response (PIR) in children receiving suppressive ART