arXiv subjects

Hannu Kurki-Suonio

Publications and source records attributed to Hannu Kurki-Suonio.

27 records · Page 2Linked to original sources

arXiv2000

Limits on isocurvature fluctuations from Boomerang and MAXIMA

We present the constraints on isocurvature fluctuations for a flat universe implied by the Boomerang and Maxima-1 data on the anisotropy of the cosmic microwave background. Because the new data defines the shape of the angular power spectrum in the region of the first acoustic peaks much more clearly than earlier data, even a tilted pure isocurvature model is now ruled out. However, a mixed model with a sizable isocurvature contribution remains allowed. We consider primordial fluctuations with different spectral indices for the adiabatic and isocurvature perturbations, and find that the 95% C.L. upper limit to the isocurvature contribution to the low multipoles is $α\leq 0.63$. The upper limit to the contribution in the $ł\sim 200$ region is $α_{200} \leq 0.13$.

astro-ph↗

arXiv2000

Antimatter Regions in the Early Universe and Big Bang Nucleosynthesis

We have studied big bang nucleosynthesis in the presence of regions of antimatter. Depending on the distance scale of the antimatter region, and thus the epoch of their annihilation, the amount of antimatter in the early universe is constrained by the observed abundances. Small regions, which annihilate after weak freezeout but before nucleosynthesis, lead to a reduction in the 4He yield, because of neutron annihilation. Large regions, which annihilate after nucleosynthesis, lead to an increased 3He yield. Deuterium production is also affected but not as much. The three most important production mechanisms of 3He are 1) photodisintegration of 4He by the annihilation radiation, 2) pbar-4He annihilation, and 3) nbar-4He annihilation by "secondary" antineutrons produced in anti-4He annihilation. Although pbar-4He annihilation produces more 3He than the secondary nbar-4He annihilation, the products of the latter survive later annihilation much better, since they are distributed further away from the annihilation zone.

astro-ph↗

arXiv2000

Alternative Solutions to Big Bang Nucleosynthesis

Standard big bang nucleosynthesis (SBBN) has been remarkably successful, and it may well be the correct and sufficient account of what happened. However, interest in variations from the standard picture come from two sources: First, big bang nucleosynthesis can be used to constrain physics of the early universe. Second, there may be some discrepancy between predictions of SBBN and observations of abundances. Various alternatives to SBBN include inhomogeneous nucleosynthesis, nucleosynthesis with antimatter, and nonstandard neutrino physics.

astro-ph↗

arXiv2000

Constraining Antimatter Domains in the Early Universe with Big Bang Nucleosynthesis

We consider the effect of a small-scale matter-antimatter domain structure on big bang nucleosynthesis and place upper limits on the amount of antimatter in the early universe. For small domains, which annihilate before nucleosynthesis, this limit comes from underproduction of He-4. For larger domains, the limit comes from He-3 overproduction. Most of the He-3 from antiproton-helium annihilation is annihilated also. The main source of He-3 is photodisintegration of He-4 by the electromagnetic cascades initiated by the annihilation.

astro-ph↗

arXiv1999

Constraining Isocurvature Fluctuations with the Planck Surveyor

We consider the detection possibilities of isocurvature fluctuations in the future CMB satellite experiments MAP and Planck for different cosmological reference models. We present a simultaneous 10 parameter fit (8 for the case of open model) to determine the correlations between the cosmological parameters, including isocurvature cold dark matter contribution to the anisotropy. Assuming that polarization information can be fully exploited, we find that an isocurvature perturbation can be detected by the Planck Surveyor if the ratio of the initial isocurvature and adiabatic perturbation amplitude is larger than 0.07. In the absence of polarization data, the signal from isocurvature perturbations can be confused with tensor perturbations or early reionization effects, and the limit is larger by almost an order of magnitude.

astro-ph↗

arXiv1996

Stochastic Isocurvature Baryon Fluctuations, Baryon Diffusion, and Primordial Nucleosynthesis

We examine effects on primordial nucleosynthesis from a truly random spatial distribution in the baryon-to-photon ratio ($η$). We generate stochastic fluctuation spectra characterized by different spectral indices and root-mean-square fluctuation amplitudes. For the first time we explicitly calculate the effects of baryon diffusion on the nucleosynthesis yields of such stochastic fluctuations. We also consider the collapse instability of large-mass-scale inhomogeneities. Our results are generally applicable to any primordial mechanism producing fluctuations in $η$ which can be characterized by a spectral index. In particular, these results apply to primordial isocurvature baryon fluctuation (PIB) models. The amplitudes of scale-invariant baryon fluctuations are found to be severely constrained by primordial nucleosynthesis. However, when the $η$ distribution is characterized by decreasing fluctuation amplitudes with increasing length scale, surprisingly large fluctuation amplitudes on the baryon diffusion scale are allowed.

astro-ph↗

arXiv1994

Statistical Constraints on the Inflation Effective Potential from the COBE DMR Results

We explore constraints on various forms for the effective potential during inflation based upon a statistical comparison between inflation-generated fluctuations in the cosmic microwave background temperature and the COBE DMR results. Fits to the first year 53 A + B x 90 A + B cross correlation function using an effective potential of the form V(phi) = lambda*phi^x/x!, yield upper limits of x le 107 and x le 397 at the 1 sigma and 2 sigma confidence levels, while the same analysis produces a power law of index of n = 1.10 ^{+0.47}_{-0.64} which would imply an underestimate of x le 63 from the simple analytic relation between x and n . We also quantify new limits on the parameters for polynomial effective potentials. This work highlights the importance of a careful statistical treatment when seeking constraints on the inflation-generating effective potential.

astro-ph↗

arXiv1993

Constraints on Chaotic Inflation from the COBE DMR results

We explore constraints on various forms for the effective potential during inflation based upon a statistical comparison between inflation-generated fluctuations in the cosmic microwave background temperature and the COBE DMR results. Fits to the COBE 53A+B x 90A+B angular correlation function are obtained using simple analytic forms for the effective potential in chaotic inflation models. Not surprisingly, these fits are optimized for a nearly scale-free fluctuation power spectrum. However, from the chi^2 distribution for the fits we can set upper limits of n le 1.2 and n le 7 at the 1 sigma and 2 sigma confidence levels, respectively, for a V(phi) = lambda phi^n effective potential. Similarly, new limits on parameters for polynomial effective potentials can be determined at the 1 sigma and 2 sigma confidence levels. The most stringent constraint, however, is on the overall magnitude of the effective potential.

astro-ph↗

arXiv1993

Inhomogeneous Inflation: Numerical Evolution

We describe our 3-dimensional numerical relativity code for the evolution of inhomogeneous cosmologies. During the evolution the constraint equations are monitored but not solved. The code has been tested against perturbation theory with good results. We present some runs of inhomogeneous inflation with strongly inhomogeneous initial data.

astro-ph↗