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Events on Tuesday, September 14th, 2021

Theory Seminar (High Energy/Cosmology)
The Geometric SMEFT description of curved Higgs Field Space(s)
Time: 4:00 pm
Place: Chamberlin 5280
Speaker: Michael Trott, Niels Bohr Institute
Abstract: In recent years, the effective field theory approach to the Standard Model, the SMEFT, has been used to study LHC data with ever increasing theoretical precision and sophistication. However, the complexity of this theory lead to several barriers to substantial theoretical progress. In particular, the explosion in the number of parameters in the SMEFT as a function of operator mass dimension, and the technical challenge or reformulating SM predictions consistently into the SMEFT were very serious problems, that called into question the possible success and value of the SMEFT physics program over the long term. I will discuss how these challenges have been overcome. The key point leading to this advance is the understanding that the projection of curved scalar field spaces generated by the Higgs onto a naive flat field space understanding implicitly embedded into the usual SMEFT Lagrangian was the root cause of many problems and confusions. Many outstanding issues have been remarkably addressed and immediately overcome by reformulating the SMEFT noting its curved scalar field space - in the Geometric SMEFT. Some examples of the benefits of this approach will be presented, and explained. Note: This is a hybrid event. A zoom link will be distributed via the seminar mailing list. To join, email the organizer.
Host: Lars Aalsma
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Network in Neutrinos, Nuclear Astrophysics, and Symmetries (N3AS) Seminar
The Milky Way is not special: accreted stars also inhabit the Spite Plateau
Time: 5:00 pm
Speaker: Dr. Jeffrey Simpson, UNSW, Australia
Abstract: The ESA Gaia astrometric mission has enabled the remarkable discovery that a large fraction of the stars within a few kiloparsecs of the Sun appear to be debris from a single in-falling system, the so-called Gaia-Sausage-Enceladus. One exciting feature of this result is that it gives astronomers for the first time a large sample of easily observable, unevolved stars that formed in an extra-Galactic environment, which can be compared to stars that formed within our Milky Way. In this talk I will discuss using these stars to investigate the "Spite Plateau" – the near-constant lithium abundance observed in metal-poor dwarf stars across a wide range of metallicities (-3 < [Fe/H] < -1). In particular our aim was to test whether the stars that formed in Gaia-Sausage-Enceladus show a different Spite Plateau to Milky Way stars that inhabit the disk and halo. Individual galaxies could have different Spite Plateaus – e.g., the interstellar medium could be more depleted in lithium in a lower galactic mass system due to it having a smaller reservoir of gas. We find that the Gaia-Sausage-Enceladus stars show the same lithium abundance as other likely accreted stars and in situ Milky Way stars, strongly suggesting that the "lithium problem" is not a consequence of the formation environment. This result fits within the growing consensus that the Spite Plateau, and more generally the "cosmological lithium problem" – the observed discrepancy between the amount of lithium in warm, metal-poor dwarf stars in our Galaxy, and the amount of lithium predicted to have been produced by Big Bang Nucleosynthesis – is the result of lithium depletion processes within stars.
Host: Baha Balantekin
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