Karsten Jedamzik

Limit on primordial small-scale magnetic fields from cosmic microwave background distortions

Spatially varying primordial magnetic fields may be efficiently dissipated prior to the epoch of recombination due to the large viscosity of the baryon-photon fluid. We show that this dissipation may result in observable chemical potential &mgr; and Compton y distortions in the cosmic microwave background spectrum. Current upper limits on &mgr; and y from FIRAS constrain magnetic fields to have strength B0<3x10(-8) G (scaled to the present) between comoving coherence length approximately 400 pc and approximately 0.6 Mpc. These represent the strongest upper limits on small-scale primordial magnetic fields to date.

Dynamics of primordial black hole formation

We present a numerical investigation of the gravitational collapse of horizon-size density fluctuations to primordial black holes (PBHs) during the radiation-dominated phase of the early Universe. The collapse dynamics of three different families of initial perturbation shapes, imposed at the time of horizon crossing, is computed. The perturbation threshold for black hole formation, needed for estimations of the cosmological PBH mass function, is found to be

Near-Critical Gravitational Collapse and the Initial Mass Function of Primordial Black Holes

{ensuremath{delta}}_{mathrm{c}}ensuremath{approx}0.7

Lithium 6: A Probe of the early universe

rather than the generally employed

B-ball dark matter and baryogenesis

{ensuremath{delta}}_{mathrm{c}}ensuremath{approx}1/3

Damped Lya systems at high redshift and models of protogalactic discs

if

Systematic uncertainties in the determination of the primordial He-4 abundance

ensuremath{delta}

On metric preheating

is defined as

Inhomogeneous big bang nucleosynthesis: Upper limit on Omega(b) and production of lithium, beryllium, and boron

ensuremath{Delta}{M/M}_{mathrm{h}},

Big bang nucleosynthesis with matter / antimatter domains

the relative excess mass within the initial horizon volume. In order to study the accretion onto the newly formed black holes, we use a numerical scheme that allows us to follow the evolution for long times after formation of the event horizon. In general, small black holes (compared to the horizon mass at the onset of the collapse) give rise to a fluid bounce that effectively shuts off accretion onto the black hole, while large ones do not. In both cases, the growth of the black hole mass owing to accretion is insignificant. Furthermore, the scaling of black hole mass with the distance from the formation threshold, known to occur in near-critical gravitational collapse, is demonstrated to apply to primordial black hole formation.