Study on our early Universe

Inflation and the ‘fine-structure’ of the early Universe.
 
One of the greatest mysteries in cosmology is the origin of the structures of the Universe. If the Universe started with some tiny inhomogeneities in an otherwise perfectly smooth background, the collapse of matter due to gravity would over time be enough to produce the galaxies and larger clusters of galaxies that we observe today. But how did those tiny inhomogeneities arise in the first place?
In the inflationary picture, these ‘primordial’ inhomogeneities begin as the tiny fluctuations of a quantum field. The accelerating expansion of space during inflation stretches these small fluctuations to truly vast sizes and thereafter they become the seeds for the formation of structures. Through this simple mechanism, inflation gives a definite prediction for the pattern of these primordial ripples in space - a prediction that agrees nicely with what has been inferred from measurements of the cosmic microwave background. Also here the Planck satellite will probe this question with incredible accuracy. The DISCOVERY center will, through its participating Danish Planck team, be at an optimal situation when these new data begin to roll in.
Although there is not yet one single observation that uniquely proves it, fluctuations in the cosmic microwave background give support to the idea that the Universe experienced some sort of inflationary epoch. The elegance of inflation lies in its reliance on just two simple ingredients—a fluctuating quantum field and a stage of accelerating expansion. However, it is also fair to say that inflation has some inelegant features as well. Any model for implementing inflation invariably requires very precisely setting of its parameters for it to work properly. And even the role of the field driving the expansion, when considered as part of a larger theory of particle physics, remains a mystery.
The DISCOVERY center will investigate the constraints from Planck satellite data that map the distribution of matter in the Universe over large scales. Do different ways of resolving these problems yield unique experimental signals? How are they affected by the properties of Nature at small scales? Answering such questions will test the inflationary idea. A milestone within three years will be a major publication on this matter.
 
After the analysis of the temperature anisotropy of WMAP it is widely accepted that tests of primordial non-Gaussianity offer a unique probe of the early Universe. The non-Gaussianity of the CMB anisotropy and polarization plays a crucial role in the analysis of the physical properties of matter at the beginning of the cosmological expansion and provides a unique opportunity to detect fundamental properties of space and time, such as non-trivial topology and global asymmetry of the Universe [12]. Although the non-Gaussianity in the simplest inflation models is very small, a large class of more general models predict substantially higher levels. Current calculations suggest that primordial non-Gaussianity could be a powerful tool for discriminating between the models mentioned above and standard slow-roll inflation.
The search for primordial non-Gaussianity is one of the primary goals of the Planck mission. The Danish Planck team has been involved in tackling some of the key problems of the WMAP data and in developing the most robust methods of extracting the signal of non-Gaussianity in the CMB fluctuations from the observational data. In particular the method of Pavel Naselsky and Poul Olesen phase analysis reveals a significant departure from the anisotropy in vacuum quantum fluctuations predicted by the simplest theories of inflation. A milestone within three years is to take an internationally leading role in this research using the much more accurate Planck data.
 
 
 
The ionization history of the cosmic plasma.
 
During the epoch of inflation, particle physics and cosmology were intertwined in a very direct way. But there are also later epochs where fundamental relics of the past could have played a major role. This influence would play out through the baryonic content of the cosmic plasma (4% of the present matter of the Universe) at the time of recombination. Remarkably, the lumpiness of baryonic matter at cosmological small scales can be tested though the distortion of the kinetics of the cosmological hydrogen and helium recombination just at the time of the formation of the CMB.
The ionization history of the cosmic plasma is one of the most important parts of modern cosmology. Based on well known principles of atomic physics, the theory of recombination provides remarkably accurate information about other fundamental particles around at the time through the anisotropy and polarization of the CMB. Early sources of photons like primordial black holes or meta-stable massive particles may lead to observable deviations. Small size clusters of baryonic matter can accelerate the process of hydrogen recombination and hereby change the dark matter and dark energy density. WMAP data clearly demonstrate the accelerated character of the recombination [13]. A major milestone for the first three years is to pursue this question with the much more accurate Planck data.
 
 
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