Topic: 
tba 
Date: 
08.05.17 
Time: 
16:15 
Place: 
H6 
Guest: 

Fritz Haber Institut and FU Berlin 

Abstract: 

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Topic: 
tba 
Date: 
21.04.17 
Time: 
16:15 
Place: 
V2210/216 
Guest: 
Yan Fodorov 
King's College London 

Abstract: 

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Topic: 
fNL Constraints from the Galaxy Power Spectrum 
Date: 
04.04.17 
Time: 
14:15 
Place: 
D6135 
Guest: 

Portsmouth 

Abstract: 
A way to learn about cosmic inflation is constraining the primordial nonGaussianity parameter fNL from the galaxy power spectrum. I demonstrate how systematic effects, such as obscuration of galaxies in angular directions with high stellar densities, can mimic a false detection of fNL. I assess and develop techniques to remove such contaminants when calculating the 3D galaxy power spectrum. Separating the process into three separate stages: (i) removing the contaminant signal, (ii) estimating the uncontaminated cosmological power spectrum and (iii) debiasing the resulting estimates. For (i), we showed in a recent paper that removing the bestfitting contaminant (mode subtraction) and setting the contaminated components of the covariance to be infinite (mode deprojection) are mathematically equivalent. For (ii), performing a quadratic maximum likelihood (QML) estimate after mode deprojection gives an optimal unbiased solution, although it requires the manipulation of large matrices, which is unfeasible for recent 3D galaxy surveys. Measuring a binned average of the modes for (ii) as proposed by Feldman, Kaiser \& Peacock (FKP) is faster and simpler, but is suboptimal and gives rise to a biased solution. We present a method to debias the resulting FKP measurements that does not require any large matrix calculations. We argue that the suboptimality of the FKP estimator compared with the QML estimator, caused by contaminants, is less severe than that commonly ignored due to the survey window. I present how I am applying the debiased FKP estimator on BOSS DR12 data. I finish with an outlook of how fNL constraints will improve in the future. 
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Topic: 
Connecting Spin Hamiltonians from DFT Calculations to Experiment 
Date: 
06.04.17 
Time: 
14:15 
Place: 
D5153 
Guest: 
Shadan Ghassemi 
TU Berlin 

Abstract: 

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Topic: 
Induced QCD 
Date: 
02.02.17 
Time: 
16:00 
Place: 
D5153 
Guest: 
Robert Lohmeyer 
University of Regensburg 

Abstract: 
We explore an alternative discretization of continuum SU(Nc) YangMills theory on a Euclidean spacetime lattice, originally introduced by Budzcies and Zirnbauer. In this discretization the selfinteractions of the gauge field are induced by a path integral over Nb auxiliary boson fields, which are coupled linearly to the gauge field. The main progress compared to earlier approaches is that Nb can be as small as Nc. In the main part of this talk we (i) extend the proof that the continuum limit of the new discretization reproduces YangMills theory in two dimensions from gauge group U(Nc) to SU(Nc), (ii) derive refined bounds on Nb for noninteger values, and (iii) perform a perturbative calculation to match the bare parameter of the induced gauge theory to the standard lattice coupling. Furthermore, we will present some numerical evidence in support of the conjecture that the induced gauge theory reproduces YangMills theory also in more than two dimensions. 
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Topic: 
Matrix product ensembles of Hermitetype 
Date: 
26.04.17 
Time: 
16:15 
Place: 
V3201 
Guest: 
DangZheng Liu 
Institute of Science and Technology Austria & University of Science and Technology of China 

Abstract: 
We investigate spectral properties of a Hermitised random matrix product which, contrary to previous product ensembles, allows for eigenvalues on the full real line. We find an explicit expression of the joint probability density function as a biorthogonal ensemble. As an interesting example, we focus on the product of GUE and LUE matrices and provide explicit expressions both for the biorthogonal functions and the correlation kernel. Then a new doubleside kernel is found at the origin, which is slightly different from the Bessel kernel. This talk is based on joint work with P. J. Forrester and J. R. Ipsen. 
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