לוח שנה משולב

The knowledge of all correlation functions of a system is equivalent to solving the corresponding quantum many-body problem. If one can identify the relevant degrees of freedom, the knowledge of a finite set of correlation functions is in many cases sufficient to determine a sufficiently accurate solution of the corresponding field theory. Complete factorization is equivalent to identifying the relevant degrees of freedom where the Hamiltonian becomes diagonal. I will give examples how one can apply this powerful theoretical concept in experiment.

Work performed in collaboration with E.Demler (Harvard), Th. Gasenzer und J. Berges (Heidelberg). Supported by the Wittgenstein Prize, the Austrian Science Foundation (FWF): SFB FoQuS: F40-P10 and the EU: ERC-AdG QuantumRelax
[1] M. Gring et al., Science, 337, 1318 (2012);
[2] T. Langen et al., Science 348 207-211 (2015).
[3] T. Schweigler et al., Nature 545, 323 (2017), arXiv:1505.03126

Alternative splicing (AS) is a mechanism that increases transcriptomic and proteomic diversity by allowing the generation of multiple mRNA products from a single gene. A strong connection was established between AS and carcinogenesis. We recently developed a method that integrates all known physical interaction (protein-DNA, protein-RNA, protein-protein), gene expression and AS data to construct the largest map of transcriptomic and proteomic interactions leading to cancerous splicing aberrations defined to date and identify driver pathways therein. The method was already applied to colon adenocarcinoma and non-small-cell lung carcinoma. I will also talk about the link between chromatin organization and epigenetics markers and how they are related to the appearance of warm-blooded organisms and exon selection.

Neighboring neurons in motor cortex exhibit diverse selectivity during sensation, movement preparation, and movement execution. Neuronal selectivity could emerge from diverse mechanisms, including selective connectivity and nonlinear interactions of synaptic inputs in dendrites. We studied dendritic integration in the anterior motor cortex of mice performing a tactile discrimination task with a delayed response (Guo and Li et al., 2014). We constructed a two-photon microscope that allows rapid (~15 Hz) imaging of up to 300 µm of contiguous dendrite while resolving calcium transients in individual dendritic spines. Two galvanometers and a remote focusing mirror (Botcherby et al., 2008) steer 16 kHz lines (24 µm extent) produced by a resonant mirror arbitrarily in three dimensions. Pyramidal neurons were labeled sparsely with GCaMP6f in transgenic mice. We imaged spine and dendritic calcium transients, as well as somatic calcium transients associated with action potentials. We developed methods to computationally remove the influence of backpropagating action potentials (bAPs), which allowed us to quantify the selectivity of spines and dendritic segments during sensation, movement preparation, and movement execution. Nearby spines and dendritic segments share similar selectivity (length constant of signal correlation, ~30 µm). This clustering was more often seen in distal than in proximal dendrites. Using a measure of local autocorrelation, we also found that this reflects distinct “hotspot” locations on the dendrite where nearby dendrite and spines are co-active in time. Hotspot selectivity was correlated with the behavioral selectivity of somatic spikes, suggesting that these locations may have privileged influence over the output of the cell.

: The properties of the Higgs resonance discovered at the LHC are in good agreement with those of the Standard Model Higgs boson. Current measurements of the couplings of the Higgs to third generation quarks, however, carry large uncertainties, and deviations of the order of a few tens of percent may still be present. I will discuss the possibility of obtaining departures of these couplings from the Standard Model values in Minimal Supersymmetric Models, and also the difference of this situation with the alignment condition, for which the tree-level Higgs boson properties remain SM-like, independently of the masses of the additional Higgs bosons in the theory. Finally, I will discuss the impact of light Higgs bosons on Dark Matter direct detection in the Minimal Supersymmetric Standard Model with heavy superpartners.

Comparison of the properties of matter and antimatter is an important basic physics problem. Measurements of energy transitions in trapped antihydrogen and their comparison to the transitions in hydrogen atoms can be used as a sensitive test of CPT symmetry. The ALPHA collaboration in CERN first demonstrated trapping of cold antihydrogen atoms in 2010 [1], demonstrating later long time capture of 15 minutes and more. As a first demonstration of introducing resonant transitions between levels of trapped antihydrogen atoms [2], ALPHA used microwave radiation (2012) to induce transitions between the hyperfine levels of the ground state of the antiatoms. Last year (2016) we performed the first ever measurement of the resonant transition 1S→2S in antihydrogen, using two-photon laser excitation with 243 nm light [3]. These initial measurements indicated that the antihydrogen 1S→2S transition energy is equal to its hydrogen counterpart at the level of about 2×10-10. With improved techniques that enable us now to trap on average 14 antiatoms per trial, ALPHA plans to perform increasingly precise spectroscopy CPT tests. A new system is also being constructed to enable measurements of the gravitational free fall of antihydrogen.

[1] Trapped Antihydrogen, Nature 468,673 (2010).
[2] Resonant quantum transitions in trapped antihydrogen atoms, Nature, 483, 439 (2012).
[3] Observation of the 1S–2S transition in trapped antihydrogen, Nature, 541, 506 (2017).