Cluster PhD Meeting 2016

29 Sept 2016, 09:00 → 30 Sept 2016, 19:00 Europe/Berlin

New seminar room (MPE Garching)

Andreas Mueller (Excellence Cluster Universe), Ivan Vorobyev (Excellence Cluster Universe, TUM), Laura Morselli (Excellence Cluster Universe, TUM), Nicolas Guillard (ESO)

The Excellence Cluster PhD Meeting is a traditional event that aims to gather the Excellence Cluster PhD students in a two-days socializing event. The 2016 event will be organized in two days: the first day will be dedicated to meet up, to present current/past work to each other through talks, and to attend talks given by senior scientists. On the second day we plan to go hiking in the Bavarian Alps and visit the Wendelstein Observatory. The meeting intends to be informal to foster lively discussions and to create a productive atmosphere to share our results and experiences. Update 19 Sep: Timetable with titles and abstracts online Organizers: Ivan Vorobyev (PhD student, Excellence Cluster Universe, TU Muenchen) Laura Morselli (PhD student, Excellence Cluster Universe, TU Muenchen) Nicolas Guillard (PhD student, Excellence Cluster Universe, European Southern Observatory) Dr. Andreas Müller (Excellence Cluster Universe, Scientific Manager)

Program flyer Cluster_PhD_Meeting_2016_prg.pdf

Thursday 29 September

1 Welcome

Speaker: Organizers

2 Introduce yourself

Speaker: Participants

3 Overview Excellence Cluster Universe

Speaker: Andreas Müller (TU München)

4 Entanglement and topological Interfaces (RA-A)

In this talk the basic concepts of conformal field theories (CFTs), defects and entanglement entropy will be introduced. Further Daniel will give some applications of our research results.

Speaker: Daniel Jaud (LMU)

5 Background studies of rare decays at Belle II (RA-B)

Rare unobserved meson decays provide an excellent opportunity to probe the limits of the standard model of particle physics. At the Belle II experiment in Tsukuba, Japan, beginning in 2018, B meson pairs will be produced in larger volumes than ever before opening the door to many of these unobserved rare processes. This talk introduces the challenges in understanding and suppressing the backgrounds of such rare processes in the face of such high statistics in the context of one specific decay channel analysis.

Speaker: James Kahn (LMU)

6 Electroweak Precision calculations in two Higgs doublet Models (RA-B)

Precision calculations are a powerful tool to test physic beyond the Standard Model (SM). The theoretical prediction of precisely measured observables receives higher-order corrections from undetected particles in extensions of the SM. The comparison with the measured value allows to restrict the parameters of such extended models. In this talk Stephan will present results of electroweak precision calculations in the Two-Higgs-doublet-model (THDM), which is an extension of the SM by a second doublet. This extension leads to five Higgs states instead of just the one Higgs boson in the SM. One of these particles can be identified with the resonance found at the LHC in 2012. Electroweak precision calculations can constrain the properties of the additional scalars.

Speaker: Stephan Hessenberger (MPP)

10:40 Coffee break

7 From Physics to Science Journalism – A Writer's Perspective (Highlight talk)

Marlene Weiß who is a journalist at Süddeutsche Zeitung in Munich is going tell us about her career, science journalism and its future.

Speaker: Marlene Weiß (Süddeutsche Zeitung, München)

12:00 Lunch break (IPP canteen)

8 Global Analyses of Composite Higgs Models (RA-C)

We know that the Standard Model of particle physics cannot be everything. Therefore, it is well motivated to investigate models that go beyond it. One important class of such models assumes the Higgs bosons to be a composite object of some new strongly interacting New Physics sector. In this talk Christoph will introduce the basic ideas of such Composite Higgs Models and show ways to numerically test them against recent experimental data.

Speaker: Christoph Niehoff (TUM)

9 Measurement of low-mass dielectrons with ALICE Experiment at the LHC (RA-D)

Measurements of low-mass dielectrons with ALICE Experiment at the LHC Low-mass dielectrons (i.e. electron-positron pairs) are an excellent experimental probe to investigate the properties of hot and dense matter created in high-energy heavy ion collisions. Since they are produced during all stages of collision and do not interact strongly, their spectra reflects the whole space-time evolution of the system. In such collisions hadronic matter undergoes a phase transition to the state of quark-gluon plasma, in which quarks are not confined inside hadrons anymore, but move freely across the medium. The Universe is believed to be in such state of matter during the very first moments after the Big Bang. The ALICE (A Large Ion Collider Experiment) at CERN LHC is dedicated to the study of high energy heavy-ion collisions. Its excellent tracking and particle identification capabilities down to very low momenta make it well suited for low-mass dielectron measurements. In this talk the current status of dielectron measurement in proton-proton, proton-ion and heavy ions collisions at different energies will be presented. Measurements in proton-proton collisions serve as a medium-free baseline while the measurements in proton-ion collisions help to separate cold nuclear matter effects from those of the hot and dense medium. Future prospects of the low-mass dielectron measurements in ALICE during third period of LHC operation will be discussed as well.

Speaker: Ivan Vorobyev (TUM)

10 Leptogenesis from Oscillations of Heavy Neutrinos with Large Mixing Angles (RA-D)

The extension of the Standard Model by heavy right-handed neutrinos can simultaneously explain the observed neutrino masses via the seesaw mechanism and the baryon asymmetry of the Universe via leptogenesis. If the mass of the heavy neutrinos is below the electroweak scale, they may be found at LHCb, BELLE II, the proposed SHiP experiment or a future high-energy collider. In this mass range, the baryon asymmetry is generated via CP-violating oscillations of the heavy neutrinos during their production. We study the generation of the baryon asymmetry of the Universe in this scenario from first principles of non-equilibrium quantum field theory, including spectator processes and feedback effects. We eliminate several uncertainties from previous calculations and find that the baryon asymmetry of the Universe can be explained with larger heavy neutrino mixing angles, increasing the chance for an experimental discovery. For the limiting cases of fast and strongly overdamped oscillations of right-handed neutrinos, the generation of the baryon asymmetry can be calculated analytically up to corrections of order one.

Speaker: Dario Güter (TUM, MPP)

11 The luminous – dark matter interplay with halo lenses in rescaled cosmological simulations (RA-E)

Galaxy-galaxy lensing profiles are cross-correlations between shape distortions of remote galaxies and the presence of intermediate foreground objects, galaxies and their halos, along the line-of-sight. Given by the field equations of general relativity, these cross-correlations reveal the mass of the foreground sample, allowing us to investigate the relation between galaxy properties, such as stellar mass and color, and the mass and shape of the host halos. On larger scales, galaxy-galaxy lensing with additional clustering information yields an almost model-independent toolkit to explore the bias of visible tracers with respect to the overall matter distribution. The signal is present in the linear, weakly nonlinear and nonlinear regime which makes it an interesting testing ground to investigate the validity of different analytical theories of structure growth. To quantify the small-scale physics impact on large-scale structure observables in upcoming surveys, extensive (and expensive) simulations must be run. By matching the variance of the linear matter field over different smoothing scales and redshifts in simulated fiducial and target ΛCDM cosmologies, we identify sets of rescaling parameters which determine an accurate mapping between the two. With this improved fast and flexible algorithm, percent to subpercent-level agreement can be reached for the halo mass function and tangential shear profiles with respect to direct N-body simulations. This will reduce the required number of simulations for future surveys. Malin will show how the residual bias affects the concentration-mass-redshift relation in 2D and 3D and that the observed offsets can be predicted from the collapsed mass history of halos, which has been found to be a potent description in both cold and mildly warm dark models, given by excursion set theory (extended Press-Schechter). Moreover, she will discuss how these profiles can constrain MCMC samplings of galaxy evolution parameters in semi-analytical models in the L-Galaxies suite to probe the connection to cosmology. Specifically, Malin will demonstrate how we can add observational input with foreground lenses from the GAMA galaxy survey and background source galaxies taken from lensing catalogues from the Kilo-Degree Survey (KiDS) interpreted via halo occupation distribution models.

Speaker: Malin Renneby (LMU)

14:40 Coffee break

12 A bias to CMB lensing measurements from the bispectrum of large-scale structure (RA-E)

The tremendously improving precision of (cosmic microwave background) CMB lensing measurements demands for an increasing accuracy in its analysis. This involves questioning some of the simplifying assumptions that go into the lensing reconstruction. In the work presented, we drop the assumption of Gaussianity of the lensing potential and quantify the effect of a Non-Gaussianity induced by non-linear structure formation on measurements of the CMB lensing power spectrum.

Speaker: Vanessa Böhm

13 The Origin of Giant Clumps in High-Z Galaxies (RA-F)

Giant clumps are a characteristic feature of observed high-redshift disk galaxies. We propose that these kpc-sized clumps have a complex substructure and are the result of many smaller clumps self-organising themselves into clump clusters (CCs). This bottom-up scenario is in contrast to the common top-down view that these giant clumps form first and then sub- fragment. Using a high-resolution (~3pc) hydrodynamical simulation of an isolated, fragmenting massive gas disk and mimicking the observations from Genzel et al. at z~2, we find remarkable agreement in many details.

Speaker: Manuel Behrendt (MPE)

14 Formation of Nuclear Clusters (RA-F)

Nuclear Clusters (NCs) have been observed in a major fraction of galaxies of all Hubble types. A variety of formation scenarios have been suggested but the associated physical processes are still debated. Potential NCs progenitors start on a bumpy road due to the paramount role of the galactic environment of young star clusters in their infancy and teenage-hood (through their formation, the associated feedback and possible dissolution). This complex evolutionary track decides whether or not these 'seeds' evolve into bona fide NC. So far, such processes have been studied numerically at resolutions from 100 to 50 pc, leaving out the galaxy scale coupling leading to the main nuclear structures (e.g., nuclear discs below the 50 pc scale). Using state of the art hydrodynamical simulations of dwarf galaxies at parsec resolution, Nicolas will present the main processes involved in the formation of stellar clusters, emphasizing the importance of the early build-up for NCs. He will further focus on the impact of star formation, stellar driven feedback and galactic environment, and finally provide a context view of the formation and evolution of NCs.

Speaker: Nicolas Guillard (ESO)

15 Tracer-bias around voids in Magneticum simulations (RA-E)

The large-scale structure of the universe can only be observed directly via luminous tracers of the underlying distribution of dark matter. However, the clustering statistics of tracers are biased and depend on various properties of the tracers themselves, such as their host-halo mass and formation history. On very large scales, where density fluctuations are within the linear regime, this tracer bias results in a constant offset in the clustering amplitude, which is known as linear bias. Towards smaller semi-linear and non-linear scales, this is no longer the case and tracer bias becomes an unknown function of scale and time. We focus on tracer bias centered on cosmic voids, depressions of the density field in the large-scale structure that spatially dominate the universe. We find that void- tracer cross-correlations are successfully described by a linear bias-relation within voids. The tracer-density profile of voids can thus be related to their matter-density profile by a single number. We show that this number coincides with the linear tracer bias extracted from the large-scale auto-correlation function and expectations from theory, if sufficiently large voids are considered in the sample. For smaller voids we observe a shift towards higher values.

Speaker: Giorgia Pollina (LMU/USM)

16 Breakthrough in Physics: Direct Measurements of Gravitational Waves (Highlight talk)

Senior scientists Ewald Mueller (MPI for Astrophysics in Garching) will report on the physics of gravitational waves which were predicted by Einstein in 1916 and directly measured with the LIGO laser interferometers in September 2015. After a careful analysis the detection was announced on 11th February 2016.

Speaker: Ewald Müller (MPA)

17 Discussions

Speaker: Organizers

18:30 Social Dinner at Indian restaurant Moti Mahal, Garching City Center

Friday 30 September

18 Outdoor activity: Hiking in Bavarian Alps and visit Wendelstein Observatory (bad weather option: tba)