Triviality of λϕ4 theory in 3+1-dimensional spatially flat Robertson-Walker space in Gaussian approximation

We investigate λϕ⁴ theory within the Gaussian approximation in spatially flat Robertson-Walker space in 3+1 dimensions. After having performed an adiabatic expansion for one of the ansatz functions we find that the renormalization of the energy-momentum tensor provides two additional constraints which have to be satisfied by bare couplings. These conditions force the theory to be trivial after renormalization.     

Quantum string theory in curved space-times

A general method to quantize strings in curved space-times is exposed. It treats the space-time metric exactly and the string excitations small as compared with the energy scale of the geometry. The method is applied to cosmological (de Sitter) and black-hole (Schwarzschild) geometries. The critical dimension decreases in one for de Sitter and stays unaltered for black-holes as compared with flat space-time values. Bogoliubov transformations in the context of string theory are derived and the Bogoliubov coefficients describing elastic and inelastic scattering and excitation of modes are computed explicitely. The string-black-hole cross section is derived and a pair mode creation phenomena is found. The quantization and scattering of strings in shockwave geometries (ultrarelativistic boosted black-holes or Aichelburg-Sexl space time) is found to be exactly solvable.     

Paralleltransport and geodesic deviation in static spherically symmetric space-times

Tetrads which are parallelpropagated along time-like geodesics in static spherically symmetric spce-times are constructed. Its connection with the geodesic precession is explained. Moreover, we express the solution of the equations of geodesic deviation in terms of the Killing vectors and the fourvelocity.     

Mini-inflation prior to the cosmic confinement transition?

The onset of the confinement transition in the early universe is studied within the Friedmann model. Exploiting a bag model equation of state for the deconfined matter, which is generalized to include also metastable states, the possibility of a mini-inflationary epoch is demonstrated. A criterion of metastability is derived to estimate parameters of this mini-inflation.     

Can the ten-dimensional phase prior to Calabi-Yau splitting of the super-string phase generate the primordial entropy of the universe?

It is shown that the primordial entropy of the universe can be generated in the residual phase prior to Calabi-Yau splitting and following the passing to the field theory limit of the heterotic super-string in ten space-time dimensions, wherein matter is represented by either a radiative equation of state or the equation of state for stiff matter.     

Equilibrium flavor dynamics during the cosmic confinement transition

In einem thermodynamischen Modell wird die Flavor-Zusammensetzung der stark wechselwirkenden Materie während des kosmischen Confinement-Übergangs behandelt. Thermisches, mechanisches und chemisches Gleichgewicht vorausgesetzt, kann der Anteil von strange-Teilchen analysiert werden. Aufgrund des Gleichgewichts in Hinblick auf ΔS = 0 und ΔS = 1 schwache Wechselwirkungen hängen die verschiedenen Flavor-Anteile stark von dem wenig bekannten Leptonenüberschuß ab. Im Falle einer Leptonendichte (Antileptonendichte) in der Größenordnung der Baryonendichte wird der Anteil der strange-Quarks unterdrückt (hoch). In der Hadronenphase tragen die strange-Baryonen bis zu 50% des Baryonenüberschusses.     

宇宙黎明和再电离时期低频全天总功率探测实验现状

宇宙黎明和再电离时期探测是目前宇宙学最前沿科学研究方向之一.对这一时期的直接探测只能依赖于观测来自这一时期红移后的中性氢21 cm信号,其3种主要探测方式之一是21 cm信号全天总功率测量.在此回顾已有和正在计划中的探测宇宙黎明和再电离时期的低频全天总功率测量实验及其进展,包括地面射电望远镜如BIGHORNS¹、EDGES²、LACE³、LEDA⁴、MIST⁵、REACH⁶、SARAS⁷ 3、SCI-HI⁸、PRI^ZM⁹以及空间低频总功率相关实验如DARE¹⁰、DAPPER¹¹、FARSIDE¹²、鸿蒙计划.其中, EDGES实验是目前唯一声称观测到疑似宇宙黎明信号的实验,然而其实验结果与标准宇宙学模型(Λ Cold Dark Matter,ΛCDM)有不符之处.如果该探测结果被证实,那么这将是人类第1次...     

Higher order curvature terms in theories with creation

In two theories involving continuous creation higher order curvature terms are added to the field equations. At high gravitational curvatures the creation of matter depends critically on these extra terms.     

Phase transitions in perturbed stiff-fluid Friedmann-Robertson-Walker cosmological models

We consider one-soliton perturbations of a flat Friedmann-Robertson-Walker (FRW) cosmological model, with an ideal fluid with pressure equal to the energy density (stiff fluid), in the case where the “pole trajectory” parameter is negative, introducing thereby singularities along certain null hypersurfaces. Starting with a metric that approaches asymptotically the FR W background, we show that it is possible to construct an extension through these hypersurfaces such that the energy momentum tensor T_ab is finite and satisfies the energy conditions. The extension is only C₁, providing a sort of “shock front” with continuity in T_ab, that has an associated phase transition from null dust to stiff fluid, the transition being of the form described by CHANDRASEKHAR and XANTHOPOULOS.     

Spectral index determination between 408 MHz and 5 GHz in the northern sky

We present the joint analysis of two 5-GHz interferometric surveys of the northern sky, taken with different baselines. The two surveys were carried out on the Jodrell Bank 5-GHz interferometer based at Manchester. The Maximum Entropy Method is used to check the consistency of the two surveys and the final two-dimensional maps are used, together with low-frequency full sky surveys, to put constraints on the Galactic spectral index. It is found that synchrotron emission is the dominant process at high Galactic latitudes below 5 GHz.