Seminars

Graduate Seminar, 15th April

Speaker: Artur Miroszewski

Title: Early universe cosmology and the coherent states

Abstract: The theory of General Relativity seems to be a well chosen tool to describe the evolution of the universe. Starting from very simplified model of the universe, Friedmann-Lemaître-Robertson-Walker spacetime, we are able to explain most of the observable phenomena on the cosmic scale. On the other hand the cosmological solutions in GR tend to contain past-incomplete geodesics, also know as singularities. The singularities occur in the very early universe regimes, where apart from the GR we should take into account quantum effects. Although the theory of Quantum Gravity seems to be far from invented and understood, the semi-classical approach may be able to point us to some features of it. During my talk I will present the semi-classical approach based on the coherent states, leading to the Big Bang singularity avoidance scenario- the Big Bounce.

Graduate Seminar, 8th April

Author: Chetan Bavdhankar

Title: Peculiar Velocities – a very important probe of cosmology

Abstract: Peculiar velocity of galaxies is one of the very important probes of the cosmological model (Strauss and Willick (1995)). Since peculiar velocities are induced by gravity only, they can be used to obtain various cosmological parameters such as mean matter density or the growth of structure (Nusser and Davis (2011)). The large-scale fluctuations of the matter distribution can be determined using bulk flows where a given volume of the sample shows the net peculiar motion of galaxies. To study these velocity dependent properties, I have started with estimating observers motion using the radial peculiar velocities of the galaxies in observers frame. In this analysis, I have simulated 1000 galaxies in a volume of a sphere of radius 350Mpc. These galaxies have peculiar velocities in random directions with gaussian magnitudes. Then we try to recover the observer’s motion from the observer frame updated data using chi-squared analysis. With real data, this type of analyses can be used to estimate the motion of the Local Group, bulk flows in at different scales, local voids, etc.

Graduate Seminar, 1st April

Speaker: Jakub Sierchuła

Title: Determination of the liquid eutectic metal fuel Dual Fluid Reactor (DFRm) design – steady state calculations

Abstract: The Dual Fluid Reactor (DFR) is a novel concept of a very high-temperature (fast) reactor which falls-off the classification of Generation IV International Forum (GIF). DFR makes best of the two previous designs: Molten Salt Reactor (MSR) and Lead-cooled Fast Reactor (LFR). During the presentation a novel reactor design (DFRm) with the liquid eutectic U-Cr metal fuel composition and the lead coolant will be present. By performing the first steady state neutronic calculations for such a reactor it will be shown that this 250 MWth reactor is critical, and that it can operate almost 20 years without refuelling. The geometry (reflector thickness, fuel tubes pin pitch) was optimise with respect to the multiplication factor. The optimisation together with some other opportunities for the liquid metal fuel design (e.g the use of electromagnetic pumps to circulate the medium) allows DFRm to be of a small size. This rises economy of the construction as expressed nicely in terms of the Energy Return on Invested (EROI) factor which is even higher than for the molten salt fuel design (DFRs). Last but not least, DFRm has all the (fuel, coolant, reflector) temperature coefficients negative, which is an important factor of the passive safety.

Graduate Seminar, 25th March

Speaker: Szymon Nakoneczny

Title: Catalog of quasars from the Kilo-Degree Survey Data Release 3

Abstract: Broad spectroscopic lines, large redshift range and variety of properties make quasar detection in photometric surveys a particularly difficult task. I will present a quasar detection method based on photometric ugri data in Kilo-Degree Survey (KIDS) – an imaging deep and wide field survey covering 447 sq. deg. on the sky. The KiDS third data release contains 49 millions of sources among which, however, a vast majority does not have any spectroscopically confirmed identification. We successfully trained a Random Forest classifier based on the KIDS data and a set of known quasars identified by the SDSS spectroscopic survey. The presented catalog consists of 190,000 quasar candidates, and its training purity equals 91%. Additional validation of the catalog was made by the means of comparison with GAIA second data release, other already existing quasar catalogs and WISE photometric data.

Graduate Seminar, 11th March

Speaker: Paritosh Verma

Title: Gravitational waves in the Jordan-Brans-Dicke theory

Abstract: I shall talk about gravitational waves in Jordan Brans Dicke (JBD) theory. There are two tensor polarization states in the General theory of relativity but there can also be vector and scalar polarization states in alternative theories of gravity. The JBD theory is one of the attempts to modify general theory of relativity by varying gravitational constant G and it has three polarization states. The first two states are the same as in GR and the third one is the scalar polarization.

Venue: Pasteura 7, Room 404.

Graduate Seminar, 28th January

Speaker: Grzegorz Żarnecki

Title: T2K results on CP violation in the neutrino sector

Abstract: Each of the three flavour states of neutrinos is a superposition of mass eigenstates. The flavour-mass mixing matrix may have an irreducible imaginary component resulting in possible CP symmetry violation in neutrino oscillations, i.e. asymmetries between neutrino and antineutrino oscillations. In the T2K experiment the CP is probed by the measurement of appearance probability of electron (anti)neutrinos originating from accelerator-produced muon (anti)neutrinos beam. Current T2K results indicates CP violation at 2 sigma confidence level.

Graduate Seminar, 15th October

Speaker: Anatolii Koval

Title: Exploration of thermosphere wave field planetary structure via in-situ satellite measurements

Abstract: The Earth’s atmosphere is in the process of dynamic adaptation and global movements striving to equilibrium. Development of new models requires a generation of much more precise numerical models of geo-space. Plenty of observations and theoretical estimations exposes the importance of atmospheric gravity waves (AGW) in an understanding of energy and impulse balance of a geo-space. Even nowadays giving numerical characteristics of AGW is problematic, since most of the data obtained from distant observations which can not give precise information for this processes. The only source of precise numerical characteristics can be in situ satellite measurements. Last and the most advanced satellite mission measuring required parameters was DE 2. It was operating in the period of 1980-1983 yy. Through digital signal analysis and complex procedure of AGW selection were identified quantitative properties of the planetary structure of a thermosphere wave field.

Graduate Seminar, 1st October 2018

Speaker:  Krzysztof Jodłowski

Title: R(D) (R(D*)) anomaly in B(B*)\to D\tau\nu decay vs 1-loop leptonic corrections in MSSM

Abstract: Quotient of branching ratios for different final lepton states – R(D) (R(D*)) – measured by LHCb, Belle and BaBar, deviates from predictions of Standard Model by \sim 2\sigma (4\sigma). One loop corrections in leptonic sector were calculated in Minimal Supersymmetric Standard Model.  Scan over parameter space was done and it was found that MSSM corrections
do not provide significant enhancement of R(D) (R(D*)), contrary to result given in https://arxiv.org/abs/1604.03416. In second part of the talk, brief review of dark matter physics will be given, focusing on work done in BayesFITS group.

Graduate Seminar, 4th June

Speaker: Viktor Svensson

Title: Tensor Network techniques for many-body systems

Abstract: In quantum many-body systems of even moderate sizes, Hilbert space is far too large to fit on a computer. This makes numerical calculations a challenge. With the use of tensor networks, certain classes of quantum states can be efficiently represented and computed. In this talk, I will give an introduction to tensor networks and what they are good for.

 

Graduate Seminar, 28th May

Speaker:  Oleksandr Kovalenko

Title: Experimental tests of perturbative Quantum Chromodynamics

Abstract:  The Deep Inelastic Scattering and Drell-Yan processes can’t be directly calculated. The factorization concept assumes that the cross sections of these processes can be expressed as a convolution of parton distribution functions and fragmentation functions (FFs). These functions can’t be obtained from the theory and require an input form the experiment. The seminar will be focused on the techniques that are used to extract the FFs for pp and ep collisions. The comparison of theoretical estimates of FFs and the most recent experimental results on neutral meson spectra will be given.