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BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230516T160000
DTEND;TZID=Europe/Berlin:20230516T160000
DTSTAMP:20260505T035640
CREATED:20250707T131600Z
LAST-MODIFIED:20250829T135335Z
UID:10000097-1684252800-1684252800@www.trr352.de
SUMMARY:Non-Perturbative Results on the Mass Shell in Nelson-Type Models
DESCRIPTION:We consider the infrared problem in translation-invariant Nelson-type models describing a single quantum mechanical particle linearly coupled to a field of scalar bosons at fixed total momentum. Physical examples include the non- and semi-relativistic Nelson models. If the bosons are massless\, then the model is infrared divergent and the infimum of the spectrum is not an eigenvalue for any total momentum\, i.e.\, no ground state exists. Applying an appropriate dressing transformation\, dependent on the total momentum\, one obtains an infrared-renormalized representation of the model\, which exhibits a ground state. Previously\, this situation has been investigated using perturba tive methods\, i.e.\, for small total momenta and (possibly dependent on the total momentum) small coupling constants. In this talk\, we discuss non-perturbative proofs both for the absence of ground states in the usual Fock space representation of Nelson-type models (for all total momenta) and the existence of ground states in the non-equivalent representation (for almost all physically relevant total momenta). We emphasize that our results hold for all values of the coupling constants\, due to the non-perturbative nature of their proofs. The talk is based on joint work with Thomas Norman Dam\, David Hasler and Oliver Siebert.
URL:https://www.trr352.de/event/non-perturbative-results-on-the-mass-shell-in-nelson-type-models/
LOCATION:Seminar room C4H33\, An der Morgenstelle 10\, Tübingen\, 72076\, Germany
CATEGORIES:Talks
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BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230526T141500
DTEND;TZID=Europe/Berlin:20230526T141500
DTSTAMP:20260505T035640
CREATED:20250707T131434Z
LAST-MODIFIED:20250829T135309Z
UID:10000096-1685110500-1685110500@www.trr352.de
SUMMARY:Observation of hole ordering mediated by antiferromagnetic correlations in mixed-dimensional Hubbard models
DESCRIPTION:Unraveling the origin of unconventional superconductivity is one of the driving forces behind quantum simulations with Fermions in optical lattices. In these strongly correlated materials\, the necessary pairing of charge carriers is often assumed to be related to the interplay of antiferromagnetic correlations and dopant motion. Despite impressive recent progress in the numerical treatment of the Hubbard model[1\,2\,9]\, many open questions remain in particular about the pseudo-gap regime and the relation of striped phases to superconductivity. \nWith our Lithium-6 quantum gas microscope\, we can image strongly correlated many-body Fermi systems with full spin and density resolution and study individual holes’ local distribution and spin environment [3\,4]. In addition\, the microscope and a new phase-stable superlattice enable us to engineer large classes of Hubbard-like Hamiltonians with control on the level of individual sites. \nIn antiferromagnets with weak doping\, individual holes form magnetic polarons whose motion is strongly reduced due to the magnetic background. Pairs of dopants can overcome the frustrating effect but we find strong competition between this magnetically mediated hole-hole attraction and repulsion due to Pauli blocking [5\,6]. The binding energy for hole pairing in normal two-dimensional Hubbard models is thus strongly reduced below the magnetic energy scale J. \nHowever\, in a mixed-dimensional system [7]\, where we restrict the hole motion to one dimension while keeping the spin order two-dimensional\, we directly image tightly bound pairs of holes and find binding energies on the order of the spin exchange energy J [5]. Upon increased doping\, we observe repulsion between hole pairs in one spatial direction and currently investigate the formation of stripes [8]\, which we expect to form already at our current experimental temperatures in the mixD configuration. Such stripes form the ground state of the normal Hubbard model [1] and recent numerical results show that with a diagonal hopping term\, they support the emergence of d-wave superconductivity [9].
URL:https://www.trr352.de/event/observation-of-hole-ordering-mediated-by-antiferromagnetic-correlations-in-mixed-dimensional-hubbard-models/
LOCATION:Room B 349\, Theresienstr. 39\, Munich\, 80333\, Germany
CATEGORIES:Talks
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230530T143000
DTEND;TZID=Europe/Berlin:20230530T143000
DTSTAMP:20260505T035640
CREATED:20250707T130900Z
LAST-MODIFIED:20250829T135232Z
UID:10000095-1685457000-1685457000@www.trr352.de
SUMMARY:Bulk-edge correspondence for unbounded Dirac-Landau operators
DESCRIPTION:We consider two-dimensional unbounded magnetic Dirac operators\, either defined on the whole plane\, or with infinite mass boundary conditions on a half-plane. Our main results use techniques from elliptic PDEs and integral operators\, while their topological consequences are presented as corollaries of some more general identities involving magnetic derivatives of local traces of fast decaying functions of the bulk and edge operators. One of these corollaries leads to the so-called Streda formula: if the bulk operator has an isolated compact spectral island\, then the integrated density of states of the corresponding bulk spectral projection varies linearly with the magnetic field as long as the gaps between the spectral island and the rest of the spectrum are not closed\, and the slope of this variation is given by the Chern character of the projection. The same bulk Chern character is related to the number of edge states which appear in the gaps of the bulk operator. This is joint work with M. Moscolari and K. Sørensen.
URL:https://www.trr352.de/event/bulk-edge-correspondence-for-unbounded-dirac-landau-operators/
LOCATION:Room C3N16\, An der Morgenstelle 10\, Tübingen\, 72076\, Germany
CATEGORIES:Talks
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=Europe/Berlin:20230530T160000
DTEND;TZID=Europe/Berlin:20230530T160000
DTSTAMP:20260505T035640
CREATED:20250707T130709Z
LAST-MODIFIED:20250829T135211Z
UID:10000094-1685462400-1685462400@www.trr352.de
SUMMARY:Vacuum solutions in the theory of electroweak interactions
DESCRIPTION:In this talk I will describe the vacuum sector of the Weinberg-Salam (WS) model of electroweak forces. In the vacuum sector the WS model yields the U(2)-Yang-Mills-Higgs equations. We show that at large constant magnetic fields the translational symmetry of the equations is broken spontaneously. Namely\, there are solutions\, which in the plane orthogonal to the magnetic field have the symmetry of a lattice and which have lower energy locally than the homogeneous (gauge-translationally invariant) solutions. The stability of these solutions is an open problem.
URL:https://www.trr352.de/event/vacuum-solutions-in-the-theory-of-electroweak-interactions/
LOCATION:Room C3N16\, An der Morgenstelle 10\, Tübingen\, 72076\, Germany
CATEGORIES:Talks
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