Hintergrund-oben
Home | Studies | Research | Facilities | Highlights | People | 
  
change language

Upcoming Events

 

Colloquium

Topic:

tba

Date:

08.05.17

Time:

16:15

Place:

H6

Guest:

Dr. Tobias Kampfrath

Fritz Haber Institut and FU Berlin

Abstract:

Contact person:

M. Meinert

Colloquium Mathematical Physics

Topic:

tba

Date:

21.04.17

Time:

16:15

Place:

V2-210/216

Guest:

Yan Fodorov

King's College London

Abstract:

Contact person:

G. Akemann

Seminar High Energy Physics

Topic:

fNL Constraints from the Galaxy Power Spectrum

Date:

04.04.17

Time:

14:15

Place:

D6-135

Guest:

Benedikt Kalus

Portsmouth

Abstract:

A way to learn about cosmic inflation is constraining the primordial non-Gaussianity 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 best-fitting 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 sub-optimal 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.

Contact person:

D. Schwarz

Seminar Condensed Matter

Topic:

Connecting Spin Hamiltonians from DFT Calculations to Experiment

Date:

06.04.17

Time:

14:15

Place:

D5-153

Guest:

Shadan Ghassemi

TU Berlin

Abstract:

Contact person:

Jürgen Schnack

Seminar Mathematical Physics

Topic:

Induced QCD

Date:

02.02.17

Time:

16:00

Place:

D5-153

Guest:

Robert Lohmeyer

University of Regensburg

Abstract:

We explore an alternative discretization of continuum SU(Nc) Yang-Mills theory on a Euclidean spacetime lattice, originally introduced by Budzcies and Zirnbauer. In this discretization the self-interactions 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 Yang-Mills theory in two dimensions from gauge group U(Nc) to SU(Nc), (ii) derive refined bounds on Nb for non-integer 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 Yang-Mills theory also in more than two dimensions.

Contact person:

Gernot Akemann

Seminar AG Zufallsmatrizen

Topic:

Matrix product ensembles of Hermite-type

Date:

26.04.17

Time:

16:15

Place:

V3-201

Guest:

Dang-Zheng 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 bi-orthogonal ensemble. As an interesting example, we focus on the product of GUE and LUE matrices and provide explicit expressions both for the bi-orthogonal functions and the correlation kernel. Then a new double-side 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.

Contact person:

Gernot Akemann



  • @ 2008 Uni Bielefeld
  • | Letzte Änderung: 23.11.2011
  •  
  • | Kontakt
  • | Impressum
  • | Druckansicht PDF