arXiv subjects

Neil Turok

Publications and source records attributed to Neil Turok.

130 records · Page 8Linked to original sources

arXiv1993

$Π$ in the Sky ? Microwave Anisotropies from Cosmic Defects

High resolution maps of the anisotropy of the microwave sky will yield invaluable clues as to the mechanisms involved in cosmic structure formation. One fundamental question they should answer is whether the fluctuations were Gaussian random noise, as predicted in inflationary models, or were nonGaussian as in theories based on symmetry breaking and cosmic defects. In the latter case there is the prospect of obtaining information regarding symmetry breaking at high energy scales, specifically the homotopy classes $Π_n$ of the vacuum manifold. In this paper we report on detailed calculations of the degree scale anisotropies predicted in the cosmic string, monopole texture and nontopological texture theories of structure formation, emphasising their distinct character from those predicted by inflation, and the bright prospects for experimental tests.

hep-ph↗

arXiv1993

A Simple Test for Non-Gaussianity in CMBR Measurements

We propose a set of statistics $S_q$ for detecting non-gaussianity in CMBR anisotropy data sets. These statistics are both simple and, according to calculations over a space of linear combinations of three-point functions, nearly optimal at detecting certain types of non-gaussian features. We apply $S_3$ to the UCSB SP91 experiment and find that the mean of the four frequency channels is by this criterion strongly non-gaussian. Such an observation would be highly unlikely in a gaussian theory with a small coherence angle, such as standard ($n=1$, $Ω_b = .05$, $h = .5$) inflation. We cannot conclude that the non-gaussianity is cosmological in origin, but if we assume it due instead to foreground contamination or instrumental effects, and remove the points which are clearly responsible for the non-gaussian behavior, the rms of the remaining fluctuations is too small for consistency with standard inflation. Further data are needed before definitive conclusions may be drawn. Finally, we generalize the ideas behind this statistic to other types of non-gaussian behavior that might be detected in other experimental schemes.

hep-ph↗

arXiv1993

Degree Scale Microwave Anisotropies in NonGaussian Theories of Cosmic Structure Formation

The COBE satellite's maps of the cosmic microwave background (CMB) anisotropy do not have the resolution to discriminate between theories of cosmic structure formation based on inflation, and those based on field ordering following a symmetry breaking phase transition. For this purpose it is critical to resolve the CMB anisotropy on degree scales. In this paper we report on detailed calculations of the degree scale anisotropies predicted in the global string, monopole, texture and nontopological texture scenarios of structure formation, emphasising their distinct character from those predicted by inflation, and commenting on the prospects of their detection in the near future.

hep-ph↗

arXiv1993

Family Symmetry, Fermion Mass Matrices and Cosmic Texture

The observed replication of fermions in three families is undoubtedly a reflection of a deeper symmetry underlying the standard model. In this paper we investigate one very elementary possibility, that physics above the grand unification scale is described by the symmetry group $G\timesSU(3)_{fam}$ with $G$ a gauged grand unified group, and $SU(3)_{fam}$ a global family symmetry. The breaking of this symmetry at the GUT scale produces global texture, providing a mechanism for structure formation in the universe, and sets strong constraints on the low energy fermion mass matrix. With the addition of a ${\bf 45}$ Higgs and certain assumptions about the relative strength of Higgs couplings, the simplest $SU(5)$ theory yields an eight parameter form for the fermion mass matrices, which we show is consistent with the thirteen observable masses and mixing angles. We discuss the natural suppression of flavour changing neutral currents (FCNCs) and emphasise the rich low energy Higgs sector. With minor assumptions, the theory unifies consistently with the recent LEP data. We consider the extension to $G=SO(10)$, where some simplification and further predictiveness emerges. Finally we discuss the dynamics of $SU(3)_{fam}$ texture and show that the known constraints on unification `predict' a GUT symmetry breaking scale of the order required for cosmic structure formation, and by the recent detection of cosmic microwave anisotropy by COBE.

hep-ph↗