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This Week at Physics

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Events on Friday, April 5th, 2019

Theory Seminar (High Energy/Cosmology)
Large Field Ranges from Aligned and Misaligned Winding
Time: 2:00 pm
Place: 5280 Chamberlin Hall
Speaker: Andreas Schachner, Heidelberg University
Abstract: One of the most prominent aspects of the landscape-swampland program is the quest for large field ranges in string compactifications. One reason for this is the interest in large-field inflation. Another is the hope for a deeper understanding of general quantum gravity constraints and therefore of quantum gravity itself. In the present talk, I focus on large axionic field ranges summarizing work done in collaboration with A. Hebecker and D. Junghans (arXiv: 1812.05626). More specifically, I explain our attempt to construct effective axions with parametrically large decay constants in type IIB string models. I argue that such axions can be realised as long winding trajectories in complex-structure moduli space by an appropriate flux choice. The main findings are: The simplest models with aligned winding in a 2-axion field space fail due to a general no-go theorem. However, equally simple models with misaligned winding, where the effective axion is not close to any of the fundamental axions, appear to work to the best of the present understanding. These models have large decay constants but no large monotonic regions in the potential, making them unsuitable for large-field inflation. I also show that the no-go theorem can be avoided by aligning three or more axions. Contrary to misaligned models, such models can in principle have both large decay constants and large monotonic regions in the potential. These results may be used to argue against the refined Swampland Distance Conjecture and strong forms of the axionic Weak Gravity Conjecture. After stabilizing Kähler moduli, it becomes apparent, however, that realizing inflation is by far harder than just producing a light field with large periodicity.
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Physics Department Colloquium
Special Event: Stefan Westerhoff Memorial Colloquium
Exploring Nature's Extreme Accelerators
Time: 3:30 pm
Place: 2241 Chamberlin Hall
Speaker: Julie McEnery, NASA
Abstract: Cosmic rays, neutrinos and gamma rays provide three different ways to identify and explore locations of the most efficient astrophysical particle accelerators in the universe. In the past decade we have transformed our understanding of the extreme universe. Ground-breaking gamma-ray observations with Fermi, HAWC and IACTs have uncovered many new classes of sources and provided detailed information on these objects; IceCube has broken new ground by observing astrophysical neutrinos; and we have refined our understanding of the origin of cosmic rays. In this talk, I will discuss some of the recent breakthroughs in the study of cosmic accelerators.

A reception and a concert will follow the colloquium
Host: Sridhara Dasu
Video: https://vod.physics.wisc.edu/media/2019_04_05.m4v
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Stefan Westerhoff Memorial Concert
Chamber Music
Time: 5:00 pm
Place: 2241 Chamberlin Hall
Speaker: Solano Quartet, UW-Madison
Abstract: In remembrance of Stefan Westerhoff's great love of music, we will have chamber music following the colloquium.
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