The High Energy/Cosmology Friday Seminar is a non-formal, interactive meeting
The presentations need not be advanced nor even on one's own subject of research, and students are encouraged to give talks. The only demand is: be interesting!
The cosmology group meeting (also known as "cosmocoffee") takes place on Wednesdays - if you wish to be informed about these meetings, please send mail to Olli Taanila (olli dot taanila at helsinki dot fi)
Fridays at 14:15, HIP Lecture Room A315
September 18
Pravabati Chingangbam (Korea Institute for Advanced Study):From cubic order primordial perturbations to non-Gaussian CMB temperature fluctuations
Abstract: We study the statistical nature of deviations from Gaussianity
of the CMB temperature fluctuations induced by cubic order primordial
perturbations. The study is motivated by recent inflationary models which
predict that the cubic order perturbations can be as important as,
or possibly even more important than, the quadratic order perturbations.
We present simulations of CMB maps which include the
cubic order perturbations encoded in the parameter g_{NL}.
Then we show how the genus, which is the the number of hot spots
minus the number of cold spots in the CMB maps, and other observables
that are derived from it, can sensitively measure the level of non-Gaussianity
and also distinguish between cubic and quadratic order perturbations.
September 25
Elina Keihanen (University of Helsinki):First results from Planck
Abstract: ESA's Planck satellite to study the CMB anisotropy was launched on 14 May.
Planck started to survey the sky on 13 August, after cooling and tuning of the
instruments. The first observation period, the "First Light Survey" (FLS) lasted two
weeks. The aim of the first survey was to verify the stability of the instrument. Maps
from the FLS period have now been released, and they indicate that the data quality is
excellent. The maps show a strip of the CMB sky, at each of the nine frequency channels
of Planck. The Planck team in Helsinki is responsible for map-making for the
Low-Frequency Instrument (LFI).
October 16
Kimmo Kainulainen (University of Jyvaskyla):Impact of cosmic inhomogeneities on observations, a new stochastic approach to cumulative weak lensing
Abstract: We will present a simple formalism to model the weak gravitational lensing
effects caused by a stochastic distribution of dark matter halos. Our method
can be used to compute the observable magnitude probability distribution
function including different selection biases and initial dispersions for
an arbitrary data sample. Our model can also generate effective PDFs for
arbitrarily binned data sets. We will introduce a very fast and simple,
publicly available, mathematica package "turboGL", which computes the
various PDF's based on our model. We then build a toy model for an
inhomogeneous universe, which combines a relatively small local void, that
gives apparent acceleration at low redshifts, with a meatball model that
gives sizeable lensing (dimming) at high redshifts. This model can confront
supernova data and yet is reasonably well compatible with the Copernican
Principle.
October 23
Sergey Dyadechkin (Finnish Meteorological Institute):Simulation of relativistic jet creation driven by a rotational
black hole
Abstract: It is generally believed that the magnetic field plays a key role
for relativistic jet generation in the vicinity of black holes. In
comparison with stationary processes which were suggested during
the last few decades we developed a non-stationary mechanism which
is build on the interaction of a spinning black hole with a
magnetic flux tube/string. Using the Lagrangian approach we can
consider the magnetized plasma as a set of flux tubes/strings that
allowing us to simplify the problem significantly. Numerical
simulation demonstrated how the energy can be extracted from the
Kerr black hole and showed the process of relativistic jet
formation. A magnetic flux tube falling onto a black hole is
involved into the differential rotation around the hole. This
leads to string braking and to the generation of negative energy
and momentum. According to conservation laws, positive energy and
momentum is generated and redistributed along the string
extracting the spinning energy from the black hole. This is a
non-local variant of the Penrose process, but now we don't need to
consider the particles decay. The energy extraction is accompanied
by the relativistic jet producing. The parts of the flux tube with
abundance of energy and momentum leave the ergosphere producing
helical jet structure which is propagating along the rotation axis
with relativistic speed.
November 20
Philip Stephens (Lancaster University):A unified source for BAU & DM
Abstract: I will discuss whether it is possible to construct a unified thermal history of
the universe based on a simple extension to the SM. In particular I will discuss a
phenomenological model based on arXiv 0907.0622, which attempts to unify observations of
DM, PAMELA/ATIC, and the BAU.