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Fall 2017

Seminars take place Fridays 3-4pm in West Hall Room #335

Organizer: Ben Safdi, Finn Larsen

 

Date Speaker Title Abstract
 9/15/17  Raymond Co (U-M)  A New Solution to the Gravitino Problem:Suppressed Production by Sgoldstino Dynamics

In supersymmetric theories, the gravitino is copiously produced by the scattering of the thermal particles at the end of inflationary reheating. The gravitino is overproduced unless the reheat temperature is sufficiently low, which is incompatible with thermal leptogenesis. This is known as the gravitino problem. In models of low scale mediation, the field value of the sgoldstino determines the mediation scale. We point out that the sgoldstino field value can be different in the early Universe than the present one. In particular, a large initial field value since the era of the inflationary reheating suppresses the gravitino production significantly and removes the gravitino problem. We rigorously analyze the cosmological evolution of the sgoldstino and show that the reheat temperature may well exceed the conventional upper bound, restoring the compatibility with thermal leptogenesis.

 9/22/17 No talk this week    
 9/29/17 Walter Goldberger (Yale) Gravitational radiation from classical QCD  
 10/6/17  Tongyan Lin
 (UC Berkeley/UCSD)
 Exploring the low mass frontier in dark matter direct detection

 I will discuss ideas and prospects to search for sub-GeV dark matter, below the typical thresholds of current direct detection experiments. While WIMP dark matter with mass above a GeV is increasingly constrained, there is a wide landscape of interesting candidates that may require new kinds of direct detection targets. I will highlight examples covering the meV-GeV mass range, including prospects for absorption of bosonic dark matter with current semiconductor targets as well as proposals to detect scattering of sub-MeV dark matter.

 10/13/17  No Talk  27th Midwest Gravity Meeting  
 10/20/17  Malte Buschmann (U-M)  Heavy Resonance Hunting at the LHC

The need for new physics beyond the Standard Model is apparent given all the evidence collected in experiments throughout the last decades. Many new physics models, that try to explain the deviations from the Standard Model, predict heavy particles that are accessible at the LHC. Although there are different ways to discover new particles, resonance searches belong to one of the most powerful types of analyses. In this talk I will present two different approaches using explicit example. For a quark flavour violating two Higgs doublet model we develop a new superior analysis for a top plus two Higgs final state and compare the results to existing and projected limits. And we use a displaced and prompt lepton jet analysis to study how effects of a parton shower in the dark sector can yield information about the underlying physics. 

 10/27/17  Marcus Spradlin (Brown)  Landau Singularities and the Amplituhedron

Modern methods for computing scattering amplitudes in quantum field theory get enormous mileage out of knowledge (or assumed knowledge) of their singularity structure.  I will demonstrate how, in the very special case of supersymmetric Yang-Mills theory, all information about this singularity structure can (in principle) be derived via combinatorial geometry problems using the amplituhedron, providing thereby the basic input to the "amplitude bootstrap" program.

 11/3/17  Tomer Volansky (Tel Aviv)  New Directions in the Search for Dark Matter

 

The existence of dark matter has been well established with overwhelming evidence, but its particle identity is still unknown. For more than three decades, significant theoretical and experimental efforts have been directed towards the search for a Weakly Interacting Massive Particle (WIMP), often overlooking other possibilities. The lack of an unambiguous positive WIMP signal, at both indirect- and direct-detection experiments and at the LHC, stresses the need to expand dark matter research into additional theoretical scenarios and, more importantly, to develop new experimental capabilities that go beyond the limitations of WIMP detection. In this talk I will shortly review the current status of the field and discuss new theoretical ideas and experimental avenues for searching for light dark matter in the MeV to GeV mass range, focusing on direct detection experiments.

 

 11/10/17  No talk    
 11/17/17  Matt Reece (Harvard)  Cosmology of a Fine-Tuned SUSY Higgs

I will discuss some work in progress that explores whether a mildly fine-tuned Higgs boson, as in (mini-)split supersymmetry, can have interesting or observable cosmological consequences. As moduli fields oscillate, the Higgs can respond and temporarily acquire very large values along a D-flat direction. Possible consequences include a burst of gravitational wave production and an altered estimate of the number of e-folds of inflation.

 11/24/17  No Talk - Thanksgiving    
 12/1/17  Mukund Rangamani (UC Davis)  Thermal equivariance and its applications

I will describe how techniques from topological field theory and equivariant cohomology find a role in physical problems. I will define the notion of thermal equivariance which will involve gauging thermal diffeomorphisms, and argue that these constructions naturally lead to entropy being interpretable as a Noether current.  I will outline an application to constructing dissipative hydrodynamic effective actions, reproducing previously known facts about the admissible constitutive relations.

 12/8/17  Jure Zupan (Cincinnati)  Effective field theories for dark matter direct detection

I will discuss the nonperturbative matching of the effective field theory describing dark matter interactions with quarks and gluons to the effective theory of nonrelativistic dark matter interacting with nonrelativistic nucleons. In general, a single partonic operator already matches onto several nonrelativistic operators at leading order in chiral counting. Thus, keeping only one operator at the time in the nonrelativistic effective theory does not properly describe the scattering in direct detection. Moreover, the matching of the axial--axial partonic level operator, as well as the matching of the operators coupling DM to the QCD anomaly term, naively include momentum suppressed terms. However, these are still of leading chiral order due to pion poles and can be numerically important. I will illustrate the impact of these effects with several examples. Finally, I will comment about the importance of renormalization group running in direct dark matter detection.