1,525 research outputs found
Renormalisation group improvement in the stochastic formalism
We investigate compatibility between the stochastic infrared (IR) resummation
of light test fields on inflationary spacetimes and renormalisation group
running of the ultra-violet (UV) physics. Using the Wilsonian approach, we
derive improved stochastic Langevin and Fokker-Planck equations which
consistently include the renormalisation group effects. With the exception of
stationary solutions, these differ from the naive approach of simply replacing
the classical potential in the standard stochastic equations with the
renormalisation group improved potential. Using this new formalism, we
exemplify the IR dynamics with the Yukawa theory during inflation, illustrating
the differences between the consistent implementation of the UV running and the
naive approach.Comment: 18 pages, 1 figure, 1 appendix, matches accepted version in JCA
Coupled dark energy and dark matter from dilatation anomaly
Cosmological runaway solutions may exhibit an exact dilatation symmetry in
the asymptotic limit of infinite time. In this limit, the massless dilaton or
cosmon could be accompanied by another massless scalar field - the geon. At
finite time, small time-dependent masses for both the cosmon and geon are still
present due to imperfect dilatation symmetry. For a sufficiently large mass the
geon will start oscillating and play the role of dark matter, while the cosmon
is responsible for dark energy. The common origin of the mass of both fields
leads to an effective interaction between dark matter and dark energy.
Realistic cosmologies are possible for a simple form of the effective
cosmon-geon-potential. We find an inverse geon mass of a size where it could
reduce subgalactic structure formation.Comment: 4 pages, 2 figure
Kahler potentials for the MSSM inflation and the spectral index
Recently it has been argued that some of the fine-tuning problems of the MSSM
inflation associated with the existence of a saddle point along a flat
direction may be solved naturally in a class of supergravity models. Here we
extend the analysis and show that the constraints on the Kahler potentials in
these models are considerably relaxed when the location of the saddle point is
treated as a free variable. We also examine the effect of supergravity
corrections on inflationary predictions and find that they can slightly alter
the value of the spectral index. As an example, for flat direction field values
we find while the
prediction of the MSSM inflation without any corrections is .Comment: 13 pages, one figure. Typos corrected and a reference adde
Shell-like structures in our cosmic neighbourhood
Signatures of the processes in the early Universe are imprinted in the cosmic
web. Some of them may define shell-like structures characterised by typical
scales. We search for shell-like structures in the distribution of nearby rich
clusters of galaxies drawn from the SDSS DR8. We calculate the distance
distributions between rich clusters of galaxies, and groups and clusters of
various richness, look for the maxima in the distance distributions, and select
candidates of shell-like structures. We analyse the space distribution of
groups and clusters forming shell walls. We find six possible candidates of
shell-like structures, in which galaxy clusters have maxima in the distance
distribution to other galaxy groups and clusters at the distance of about 120
Mpc/h. The rich galaxy cluster A1795, the central cluster of the Bootes
supercluster, has the highest maximum in the distance distribution of other
groups and clusters around them at the distance of about 120 Mpc/h among our
rich cluster sample, and another maximum at the distance of about 240 Mpc/h.
The structures of galaxy systems causing the maxima at 120 Mpc/h form an almost
complete shell of galaxy groups, clusters and superclusters. The richest
systems in the nearby universe, the Sloan Great Wall, the Corona Borealis
supercluster and the Ursa Major supercluster are among them. The probability
that we obtain maxima like this from random distributions is lower than 0.001.
Our results confirm that shell-like structures can be found in the distribution
of nearby galaxies and their systems. The radii of the possible shells are
larger than expected for a BAO shell (approximately 109 Mpc/h versus
approximately 120 Mpc/h), and they are determined by very rich galaxy clusters
and superclusters with high density contrast while BAO shells are barely seen
in the galaxy distribution. We discuss possible consequences of these
differences.Comment: Comments: 9 pages, 10 figures, Astronomy and Astrophysics, in pres
Supergravity origin of the MSSM inflation
We consider the supergravity origin of the recently proposed MSSM
inflationary model, which relies on the existence of a saddle point along a
dimension six flat direction. We derive the conditions that the Kahler
potential has to satisfy for the saddle point to exist irrespective of the
hidden sector vevs. We show that these conditions are satisfied by a simple
class of Kahler potentials, which we find to have a similar form as in various
string theory compactifications. For these potentials, slow roll MSSM inflation
requires no fine tuning of the soft supersymmetry breaking parameters.Comment: v3: 10 pages, no figures; version accepted for publication. Typos
correcte
Sievin Kiurunkankaan kaivausten kvartsilöytöjen alkuperän kartoitus
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