Sommerfeld Theory Colloquium (ASC) LudwigMaximiliansUniversität München

 Science
The Arnold Sommerfeld Center for Theoretical Physics organizes regular colloquia about topics of current interest in the field of theoretical physics.

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Precision at the LHC: why and how
With Run II, the LHC experiment already reached an unprecedented
level of precision compared to previous hadron colliders. The amount
of data collected in Run III and the HighLuminosity run will increase
quickly and dramatically. I will discuss specific challenges to theorists
that must be overcome to provide predictions that have the precision
necessary to match the accuracy of data. A few novel ideas to exploit
this precision directly or indirectly will also be discussed. 
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Topological phases of matter: From classification to detection in experiments
Condensed matter is found in a variety of phases, the vast majority of which are characterized in terms of symmetry breaking. For example, magnets spontaneously break timereversal and spin rotation symmetries. A notable exception was provided by the discovery of the quantum Hall effects which exhibit new kinds of topological orders not associated with any symmetry breaking. One of the characterizing features of topological order is the existence of excitations with
exotic properties. These socalled anyonic excitations might make topologically ordered systems ideal building blocks of faulttolerant quantum computers. In this colloquium, I will start by giving a general introduction to the concept of topological order and then address some of the recent developments. In particular, I will introduce theoretical frameworks that allow us to classify topological phases and discuss dynamical signatures that are useful to experimentally detect them in experiments. 
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Quantum Gravity and the Swampland
String theory seems to offer an enormous number of possibilities for low energy physics. The huge set of solutions is often known as the String Theory Landscape. In recent years, however, it has become clear that not all quantum field theories can be consistently coupled to gravity. Theories that cannot be ultraviolet completed in quantum gravity are said to be in the Swampland. In this talk, I'll discuss some conjectured properties of quantum gravity, evidences for them, and their applications to cosmology and particle physics.

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Functional renormalization group approach to correlated fermion systems
The functional renormalization group (RG) is an ideal tool for dealing with the diversity of energy scales and competition of instabilities in interacting fermion systems. Starting point is an exact flow equation which yields the gradual evolution from a microscopic model action to the effective lowenergy action as a function of a continuously decreasing energy scale. Expanding in powers of the fields yields an exact hierarchy of flow equations for vertex functions. Truncations of this hierarchy have led to powerful new approximation schemes [1].
Applications reviewed in the colloqium include: (i) dwave superconductivity and other instabilities in the twodimensional Hubbard model, and (ii) transport through a barrier and resonant tunneling in a onedimensional Luttinger liquid metal. Recently, the functional RG has been upgraded from a weakcoupling method to a computational tool for strongly interacting fermion systems [2,3].
[1] W. Metzner et al., Rev. Mod. Phys. 84, 299 (2012).
[2] C. Taranto et al., Phys. Rev. Lett. 112, 196402 (2014).
[3] D. Vilardi et al., Phys. Rev. B 99, 104501 (2019). 
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Strange effects in the neutrino oscillations
Although the neutrino oscillations are well established phenomenon, new and unusual oscillation effects in matter are still emerging. I will describe three such effects which have applications to the solar, supernova and low energy atmospheric neutrinos: (i) Parametric resonance for neutrinos propagating in a flux of background neutrinos. (ii) Oscillation waves emitted from borders between layers in a multilayer medium, like in the Earth. (iii) The attenuation effect related to the energy uncertainty in oscillation setup.

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Particle Scattering and Number Theory
From the softest of interactions of a magnetic field with an electron, to the most violent collisions at the Large Hadron Collider, precision quantum field theory produces numbers and functions with interesting numbertheoretic properties. In many examples a coaction principle holds, an invariance under a ”cosmic” Galois group. I will provide several arenas in which this principle can be seen at work, including perhaps the richest set of theoretical data, scattering amplitudes in planar N = 4 superYangMills theory.