Oberseminar Mathematische Physik

Until further notice, the seminar will be held as an online seminar. Please contact Ms. Kabagema-Bilan if you would like to be added to the mailing list for the link to the weekly zoom meeting.

Abstract for Sascha Lill: The talk is about a rigorous derivation showing that in suitable quantum theories, particle detectors on a Cauchy surface Sigma in Minkowski space-time will find a |psi_Sigma|^2-distributed configuration.

Abstract for Philippe Droz-Vincent: We start from a covariant relativistic canonical formalism, for n point particles, in terms of unconstrained phase space of 8n dimensions and n "Hamiltonian generators" in involution. The No Go theorem is circumvented by accepting that positions are no more canonical coordinates. Evolution equations involve all proper times (or suitable generalizations of them). Two-body examples are given. Quantization is formulated, replacing Poisson brackets by commutators; n coupled wave equations involve the n "Hamiltonian" operators interpreted as half-squared-mass operators. A two-body simple example illustrates how to obtain a spectrum. Evolution formalism, Scattering and Second Quantization will be briefly sketched.

Abstract for Thibaut Demaerel: We consider a simplified model of quantum gravity using a mini-superspace description of an isotropic and homogeneous universe with dust. We derive the corresponding Friedmann equations for the scale factor, which now contain a dependence on the wave function. We identify wave functions for which the quantum effects lead to a period of accelerated expansion that is in agreement with the apparent evolution of our universe, without introducing a cosmological constant.

Abstract for Tom Wessel: Based on a result by Yarotsky (J. Stat. Phys. 118, 2005), we prove that localized but otherwise arbitrary perturbations of weakly interacting quantum spin systems with uniformly gapped on-site terms change the ground state of such a system only locally, even if they close the spectral gap. We also extend this strong LPPL-principle to Hamiltonians that have the appropriate structure of gapped on-site terms and weak interactions only locally in some region of space.

Abstract for Sahand Tokasi: In this talk I will explain how the shape degrees of freedom of a quantum system evolve, and which equation do they satisfy. Prior to that we will discuss under which circumstances an equation of motion for just relational degrees of freedom of a system (fully decoupled from it's absolute degrees of freedom) can be expected, and why a full decoupling of relational and absolute degrees of freedom of a system must first be established. This last point brings us to the deficiencies of current theories of nature in regards to appearance of highly tuned "fundamental constants of nature" whose values are not derivable from the first principles of the respective theories. These deficiencies would be used by us for the implementation of relational ideas in physics, which would also be empirically justified.