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We study spherically symmetric bubble growth and droplet decay in first order cosmological phase transitions, using a numerical code including both the complete hydrodynamics of the problem and a phenomenological model for the microscopic entropy producing mechanism at the phase transition surface. The small-scale effects of finite wall width and surface tension are thus consistently incorporated. We verify the existence of the different hydrodynamical growth modes proposed recently and investigate the problem of a decaying quark droplet in the QCD phase transition. We find that the decaying droplet leaves behind no rarefaction wave, so that any baryon number inhomogeneity generated previously should survive the decay., Comment: 10 pages (revtex), 10 figures as uuencoded postscript

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., Comment: 18 pages, 20 figures available on request, plain TeX, HU-TFT-93-31

We have investigated inhomogeneous cosmic nucleosynthesis with extremely high contrasts (up to $R={10}^{4}$) in baryon-number density. Because those models develop sharp structure at the boundaries between the high- and low-density regions, accurate results require a high resolution. We have carried out such high-resolution numerical simulations and find that inhomogeneity in a closure density (${\ensuremath{\Omega}}_{b}=1$) model cannot bring the $^{4}\mathrm{He}$ yields down to fit observational constraints. Investigation of the detailed process dynamics shows that neutrons diffuse so rapidly during nucleosynthesis that they cannot effectively be separated from protons for long enough times to significantly suppress $^{4}\mathrm{He}$.

Department of Physics, University of Oslo, N-0316 Oslo, Norway(Dated: February 2, 2008)The dark energy in the Universe is described in the context of modified Friedmann equations asa fluid parameterized by the density of dark matter and undergoing an adiabatic expansion. Thisformulation is applied to the Cardassian model. Choosing then parameters consistent with the su-pernova observations, it gives a background expansion in which the cosmic temperature fluctuationsare calculated. The resulting spectrum is quite similar to what is obtained in the standard concor-dance model. If the Cardassian fluid is interpreted as a new kind of interacting dark matter, itsoverdensities are driven into oscillations when the interaction energy is rising in importance. Thisdoes not occur in a description of the Cardassian fluctuations motivated by theories of modifiedgravity. There the energy of the underlying matter is also conserved, which requires appearance ofeffective shear stress in the late Universe. In both approaches that allow fluctuations the thermalpower spectrum at large scales is much too strongly enhanced by the late integrated Sachs-Wolfeeffect. With the interacting dark matter assumption, we conclude that the Cardassian model isruled out by observations, expect in a small neighbourhood of the ΛCDM limit.Introduction

We use cosmic microwave background (CMB) and large scale structure data to constrain cosmological models where the primordial perturbations have both an adiabatic and a cold dark matter (CDM) isocurvature component. We allow for a possible correlation between the adiabatic and isocurvature modes, and for different spectral indices for the power in each mode and for their correlation. We do a likelihood analysis with 11 independent parameters and discuss the effect of choosing the pivot scale for the definition of amplitude parameters. The upper limit to the isocurvature fraction is 18% around a pivot scale $k=0.01\text{ }\text{ }{\mathrm{M}\mathrm{p}\mathrm{c}}^{\ensuremath{-}1}$. For smaller pivot wavenumbers the limit stays about the same. For larger pivot wavenumbers, very large values of the isocurvature spectral index are favored, which makes the analysis problematic, but larger isocurvature fractions seem to be allowed. For large isocurvature spectral indices ${n}_{\mathrm{i}\mathrm{s}\mathrm{o}}g2$ a positive correlation between the adiabatic and isocurvature mode is favored, and for ${n}_{\mathrm{i}\mathrm{s}\mathrm{o}}l2$ a negative correlation is favored. The upper limit to the nonadiabatic contribution to the CMB temperature variance is 7.5%. Of the standard cosmological parameters, determination of the CDM density ${\ensuremath{\omega}}_{c}$ and the sound horizon angle $\ensuremath{\theta}$ (or the Hubble constant ${H}_{0}$) are affected most by a possible presence of a correlated isocurvature contribution. The baryon density ${\ensuremath{\omega}}_{b}$ nearly retains its ``adiabatic value''.

The recent Boomerang and MAXIMA data on the cosmic microwave background suggest a large value for the baryonic matter density of the universe, omega_b = 0.03. This density is larger than allowed by standard big bang nucleosynthesis theory and observations on the abundances of the light elements. We explore here the possibility of accommodating this high density in inhomogeneous big bang nucleosynthesis (IBBN). It turns out that in IBBN the observed D and Y_p values are quite consistent with this high density. However, IBBN is not able to reduce the 7Li yield by more than about a factor of two. For IBBN to be the solution, one has to accept that the 7Li plateau in population II halo stars is depleted from the primordial abundance by at least a factor of two., Comment: 6 pages, 4 figures, submitted to PRD

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., Comment: 6 pages, 4 figures, revtex

We consider inhomogeneous big bang nucleosynthesis in light of the present observational situation. Different observations of He-4 and D disagree with each other, and depending on which set of observations one uses, the estimated primordial He-4 corresponds to a lower baryon density in standard big bang nucleosynthesis than what one gets from deuterium. Recent Kamiokande results rule out a favorite particle physics solution to this tension between He-4 and D. Inhomogeneous nucleosynthesis can alleviate this tension, but the more likely solution is systematics in the observations. The upper limit to Omega_b from inhomogeneous nucleosynthesis is higher than in standard nucleosynthesis, given that the distance scale of the inhomogeneity is near the optimal value, which maximizes effects of neutron diffusion. Possible sources of baryon inhomogeneity include the QCD and electroweak phase transitions. The distance scale of the inhomogeneities arising from the electroweak transition is too small for them to have a large effect on nucleosynthesis, but the effect may still be larger than some of the other small corrections recently incorporated to SBBN codes., 12 pages, 8 figures, REVTeX

We have simulated the onset of the inflationary era of the early Universe numerically, starting with inhomogeneous initial data for the Higgs field. Our computer code is fully general relativistic, including the gravitational effect of the Higgs field, and simulates a spacetime inhomogeneous in one space direction. According to our results, large initial fluctuations of the Higgs field do not prevent inflation, if the potential has the right shape. In a Coleman-Weinberg-type model with sigma = 0.1m/sub Pl/ inflation is realized for lambdaapprox.

Self-focusing of an intense optical beam in a plasma is studied, including the nonlinear effects of both the relativistic electron mass and the ponderomotive potential due to the electromagnetic wave. An exact steady-state asymptotic solution of beam propagation in a localized solitary waveform is obtained in slab geometry. Amplitude-width scaling relations are obtained, which imply that the width is limited to be less than the square root of three collisionless skin depths. In the weakly relativistic limit our solution reduces to the solution obtained by Schmidt and Horton (Comm. Plasma Phys. Controlled Fusion E 9, 85 (1985)). Solutions where the beam profile is of oscillatory nature, which correspond to the presence of the steady-state solution of a multiple-beamlet profile, are also presented. Finally, the asymptotic nature of the solitary wave is tested using a recently developed numerical particle simulation code.

It was recently proposed that a critical, i.e., closure, baryon density could be compatible with helium and deuterium observations, if this baryon density were suitably inhomogeneous during cosmic nucleosynthesis. In this scenario, neutrons would diffuse out of the high-density regions, which would lead to a nonstandard nucleosynthesis, with reduced helium production and improved deuterium survival, and could restore the agreement with observations, which is lost in homogeneous closure models. We have used a numerical model which shows that this proposal is not viable. Our model combines inhomogeneous nucleosynthesis and neutron diffusion self-consistently to study element formation in inhomogeneous situations in which diffusion is important. We find that the proposal fails: it is very difficult to lower the helium production significantly or to raise the final deuterium abundance, because the neutrons diffuse back to the high-density region once nucleosynthesis begins there.

An improved numerical model on primordial nucleosynthesis in an anisotropic cosmology is used to calculate the produced mass fractions of /sup 2/H, /sup 3/He, /sup 4/He, /sup 7/Li. The results are presented as a function of two parameters: B/sub 0/, the anisotropy/radiation energy density ratio at T = 5 x 10/sup 10/ K, and eta, the present baryon/photon ratio. The anisotropic results show that for fixed eta there is practically no decrease with anisotropy in any of the abundances considered, and most increase. The relative increases found are for /sup 2/H: B/sub 0/ x 1%; /sup 3/He: 0; /sup 4/He: B/sub 0/ x 3%; /sup 7/Li: B/sub 0/ x 6% for eta 5 x 10/sup -10/. This linear approximation is good for moderate values of B/sub 0/. Larger anisotropy (B/sub 0/ > owig5) is unrealistic because of excess /sup 4/He production.

We have studied the generation of inhomogeneity in the baryon-number density during the cos- mic quark-hadron phase transition. We use a simple model with thin-wall phase boundaries and ideal-gas equations of state. The result depends on the unknown nucleation scale ${r}_{0}$. Large-amplitude inhomogeneities can be created if ${r}_{0}$ is small and ${T}_{c}$ is low. The distance scale of this inhomogeneity is then the bubble coalescence scale. It seems unlikely that the inhomogeneity could have significantly affected the light element abundances produced in the cosmic nucleosynthesis.