- January 22
Rose Lerner (Lancaster University): A minimal approach to inflation and dark matter with non-minimally coupled scalars
Abstract: In this talk I will give an overview of S-inflation, which uses scalar Dark Matter (non-minimally coupled to gravity) as the inflaton. I will begin with an overview of Higgs inflation – concentrating on the basic idea rather than the technical details. I will then generalise to include dark matter. I show the available parameter space in terms of the Higgs mass and DM mass and discuss the spectral index. I then discuss the possibilities for detection at LHC and with Planck. Finally I will attempt to explain and address the questions of ‘naturalness’ raised in the literature.
- February 19
Jussi Valiviita (University of Oslo): Initial conditions of perturbations and observational constraints for an interacting dark energy model
Abstract: I review a systematic way to derive initial conditions for cosmological
perturbations deep in the radiation dominated era. This 'matrix' method is
designed to ensure that one does not miss any important growing modes. The
initial conditions are needed in calculating the theoretical predictions
for today's temperature anisotropies (by solving the Boltzmann hierarchy
e.g. with CAMB) and the matter power spectrum. I apply the derived initial
conditions to interacting dark energy, and discuss observational
constrains for a phenomenological model where dark energy and dark matter
are treated as interacting fluids. It turns out that the CMB data alone
(even with the Planck accuracy) would allow for a relatively large
interaction rate of the order of today's expansion rate (H_0) of the
Universe. But when jointly analysed with the CMB, the supernovae (SN) or
baryon acoustic oscillation (BAO) data constrain the interaction
indirectly by restricting the allowed value of today's dark energy
density. CMB & SN & BAO limit the interaction rate to 20% of H_0 at 95%
C.L.
- March 26
Elina Keihanen (University of Helsinki): WMAP 7-year results
Abstract: WMAP 7 year results were published in January. The new results are consistent with
previous ones, but have improved due to reduced noise and improved data analysis
procedure. The TT spectrum now extends to l=1200 (previously l=1000). I discuss some
selected aspects of the new results. These include the first direct detection of
primordial 4He.
- May 14
Daniel G. Figueroa (Universidad Autonoma de Madrid): Gravitational Waves from Global Phase Transitions
Abstract: We will discuss the production of a new Gravitational Wave (GW)
Background on scales which are superhorizon at the time of production, as
expected from the self-ordering dynamics of fields present after a global
phase transition. If the source is active until a given initial
superhorizon mode enters the horizon, the resulting GW energy density
spectrum is frequency independent, i.e. scale invariant. Moreover, its
amplitude for a GUT scale scenario turns out to be within the range and
sensitivity of the GW detectors like LIGO, LISA, BBO and DECIGO. This new
GW background can indeed overtake the one generated during inflation (for
the same energy scale), so distinguishing both through the CMB B-mode
polarization signal will become crucial if evetually B-modes are measured
by Planck.
References:
L. M. Krauss et al, PRL 100:131302,2008, arXiv:0712.0778 [astro-ph]
Fenu et al., JCAP 0910:005,2009 ; arXiv:0908.0425 [astro-ph.CO]
Garcia-Bellido et al. ; arXiv:1003.0299 [astro-ph.CO]
Blas et al. ; arXiv:1004.XXXX [astro-ph.CO]
- June 11 at 15:15!!!
Syksy Rasanen (University of Helsinki): Beyond Newtonian cosmology
Abstract: It is common lore that Newtonian gravity is sufficient in cos- mology
for all scales smaller than the horizon, away from the vicinity of
very dense objects. However, strictly speaking there is no Newtonian
cosmology, only a family of cosmological generalisations of the
Newtonian theory. I will discuss problems of the usual generalisations
and an attempt towards a consistent post-Newtonian-like limit of
general relativity in the cosmological setting.
- June 18
Tomi Koivisto (Utrecht University): Three-form cosmology
Abstract: The cosmological dynamics of a three-form field is described. Such a field can provide, without noncanonical terms or slow-roll, a cosmological constant, dynamical dark energy or inflation. Stability properties, perturbations and observational signatures are discussed.
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December 3, 14:15 in A315 Mikko Kaasalainen (Tampere University of Technology)
Mapping dark matter with phase-space tomography
I discuss the inverse problem of inferring the dynamical characteristics (such as the potential field) of large gravitationally bound systems from kinematic observations. For a class of steady-state systems, the solution is unique even with fragmentary data, dark matter, or selection (bias) functions. Thus one can deduce the distribution of dark matter by subtracting the observed luminous matter from the mass distribution derived from the potential. One method of finding the potential involves the construction of invariant manifolds and the tomographic determination of distribution functions in phase space.
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September 10, 14:15 in A315 Teppo Mattsson (University of Canterbury)
On the role of shear in cosmological averaging
Due to the nonlinear backreaction of the cosmological structures, the evolution of the average expansion of the universe does not follow a homogeneous Friedmann model. The backreaction is determined by the variance of the expansion rate minus the non-negative average shear. A way to estimate the backreaction is to evaluate the variance of the expansion rate over different Friedmann models, but this method neglects the shear. Using the exact LTB solution of the Einstein equation for a void-wall configuration, we demonstrate how the shear can suppress the backreaction by the squared ratio of the void size to the horizon size. Albeit improving the estimation of the backreaction by including the shear, the LTB-based void-wall models considered here still contain various simplifications that may not be good approximations for the real universe.
Based on preprint 1007.2939.
