Calendar of Physics Talks Vienna

O(D,D) and string alpha'-corrections
Speaker:Linus Wulff (Masaryk University)
Abstract:String theory on a d-dimensional torus features an O(d,d) duality symmetry. It has been suggested that the low-energy effective action can be formulated with a larger O(D,D) symmetry (D=10 or 26), even before putting the theory on a torus. This approach, which goes by the name of Double Field Theory (DFT), has proven very useful. I will address the problem of constructing higher derivative invariants in this formalism. In agreement with the literature we find that a quadratic Riemann invariant can be constructed, which can account for the first alpha'-correction to the bosonic and heterotic string. However, we find that no cubic or quartic Riemann invariants can be constructed. This suggests that the quartic Riemann terms arising at order alpha'^3 in string theory do not have a DFT embedding.
Date: Tue, 13.04.2021
Time: 14:00
Duration: 60 min
Contact:Céline Zwikel

Neutrinoless double beta decay in effective field theory
Speaker: Wouter Dekens (UC San Diego)
Abstract:Neutrinoless double beta decay (NLDBD) is the most sensitive probe of lepton-number violation. Its discovery would be a clear signal of physics beyond the Standard Model, confirm the Majorana nature of neutrinos, and provide insight into scenarios of baryogenesis through leptogenesis. Whenever lepton-number violation arises at a scale well above the electroweak scale, it can be described by effective interactions in an effective-field theory framework. In this talk, I will outline the necessary steps to assess the impact on NLDBD half lives, paying special attention to the matching of the effective interactions onto Chiral Effective Theory at low energies. Finally, I will illustrate how this framework can be extended to include the effects of light sterile neutrinos and discuss the resulting constraints on the lepton-number violating interactions.
Date: Tue, 13.04.2021
Time: 16:00
Duration: 60 min
Contact:A. Hoang, P. Stoffer

Stable cosmologies with collisionless charged matter
Speaker:Hamed Barzegar (Vienna)
Abstract:In this talk, I will discuss the recent work with David Fajman on stability of a subclass of the negatively curved FLRW models, the so-called Milne universe, in the set of the solutions to the Einstein-Vlasov-Maxwell system. The Milne universe is a vacuum non-accelerating expanding cosmological model for which some stability results are known. After reviewing the previous results on the stability of this model, I will describe the ideas of the proof and focus on the subtleties of the Einstein-Vlasov-Maxwell case that arise from the coupling of the two matter fields which again couple to the Einstein equations in the so-called CMCSH gauge. This work provides the first stability result for the Einstein-Vlasov-Maxwell system and it generalizes the results of Andersson-Moncrief, Andersson-Fajman, and Branding-Fajman-Kröncke in 3+1 dimensions.
Date: Thu, 15.04.2021
Time: 15:00
Duration: 60 min
Contact:Piotr Chrusciel, David Fajman

Rolling down to the end of the world
Speaker:Angel Uranga (IFT Madrid)
Abstract:We discuss string theory configurations sitting on the slope of scalar potentials (aka tadpoles) and discuss properties of their spacetime dependent solutions. We argue that these solutions can extend only a finite distance away in the spacetime dimensions, scaling as \Delta^{-n}\sim {\cal T} with the strength of the tadpole {\cal T}. We show that naive singularities arising at this distance scale are physically replaced by ends of spacetime, related to the cobordism defects of the swampland cobordism conjecture. We illustrate these phenomena in large classes of examples, including susy and non-susy 10 string theories and a 6d string model whose tadpole triggers spontaneous compactification to a semirealistic 3-family MSSM-like particle physics model.
Date: Thu, 15.04.2021
Time: 16:30
Duration: 60 min
Contact:Laura Donnay, Niccolo Cribiori

First results from the Muon g-2 experiment at Fermilab
Speaker:Martin Fertl (Johannes Gutenberg University Mainz)
Abstract:The long-persisting discrepancy between the Standard Model prediction of the anomalous magnetic moment of the muon (aµ) and its latest measurement provides an intriguing hint to new physics. Over the years, the SM prediction was significantly improved without providing a resolution to the problem. At Fermi National Accelerator Laboratory, USA, the Muon g-2 collaboration is performing a new measurement of aµ aiming at an ultimately fourfold smaller uncertainty than achieved with the predecessor experiment at Brookhaven National Laboratory, USA. To extract the value of aµ a clock comparison experiment is performed with spin-polarized muons confined in a superbly controlled electric and magnetic field environment. The deviation of the Larmor from the cyclotron frequency, the anomalous spin precession frequency, is determined while a high-precision measurement of the magnetic field environme
Date: Fri, 16.04.2021
Time: 10:00
Duration: 45 min
Contact:Hartmut Abele