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Past Events

Event Date Summary
Jagjit Singh Sidhu (CWRU) Tue. March 3rd, 2020
11:30 am-12:30 pm

Charge Constraints of Macroscopic Dark Matter

Macroscopic dark matter (macros) refers to a broad class of alternative candidates to particle dark matter with still unprobed regions of parameter space. Prior work on macros has considered elastic scattering to be the dominant energy transfer mechanism in deriving constraints on the abundance of macros for some range of masses and (geometric) cross-sections. However, macros with a significant amount of electric charge would, through Coulomb interactions, interact strongly enough to have produced observable signals on terrestrial, galactic and cosmological scales. We determine the expected phenomenological signals and constrain the corresponding regions of parameter space,

Continue reading… Jagjit Singh Sidhu (CWRU)

Shruti Paranjape (University of Michigan) Tue. February 25th, 2020
11:30 am-12:30 pm

Born-Infeld Theory Beyond the Leading Order

The modern approach to scattering amplitudes exploits the symmetries of effective field theories. In this talk, I will focus on Born-Infeld, a theory of non-linear electrodynamics that has a myriad of interesting properties: It can be obtained as the “double copy” of Yang-Mills and chiral perturbation theory and it is the supersymmetric truncation of low-energy brane dynamics. Born-Infeld theory also has a classical electromagnetic duality symmetry. I will discuss how one can use these nice properties to uniquely fix all tree-level amplitudes in the theory. At subleading order, I will address one-loop amplitudes and admissible higher derivative corrections to the Born-Infeld effective field theory.

Continue reading… Shruti Paranjape (University of Michigan)

Charlotte Sleight (IAS Princeton) Tue. February 11th, 2020
11:30 am-12:30 pm

A Mellin Space Approach to Scattering in de Sitter Space

Boundary correlators in (anti)-de Sitter space-times are notoriously difficult beasts to tame. In AdS, where such observables are equivalent to CFT correlation functions, recent years have seen significant progress in our understanding of their structure owing to the development of numerous systematic techniques, many of which have drawn inspiration from the successes and the strengths of the scattering amplitudes programme in flat space. In dS however, the problem is more complicated owing to the time-dependence of the background and it is unclear how consistent time evolution is encoded in spatial correlations on the boundary.

Continue reading… Charlotte Sleight (IAS Princeton)

Craig Hogan (University of Chicago) Tue. February 4th, 2020
11:30 am-12:30 pm

Holographic Inflation: Symmetries in the relic pattern of primordial perturbations from a coherent quantum inflationary horizon

A reconciliation of quantum mechanics with gravity might be achieved in a holographic theory of quantum gravity, based on coherent states of covariant causal structures. This talk will review the properties of quantum-gravitational perturbations generated during cosmic holographic inflation, in which the inflationary horizon is a coherent quantum object, like the horizon of a black hole. A new analysis of cosmic anisotropy will be described, which shows evidence for some of the new symmetries.

Continue reading… Craig Hogan (University of Chicago)

Matthew Digman (Ohio State University) Tue. January 28th, 2020
11:30 am-12:30 pm

Not as big as a barn: Upper bounds on dark matter-nucleus cross sections

Critical probes of dark matter come from tests of its elastic scattering with nuclei. The results are typically assumed to be model independent, meaning that the form of the potential need not be specified and that the cross sections on different nuclear targets can be simply related to the cross section on nucleons. For pointlike spin-independent scattering, the assumed scaling relation is σχA∝A2μ2AσχN∝A4σχN, where the A2 comes from coherence and the μ2A≃A2m2N from kinematics for mχ≫mA. Here we calculate where model independence ends,

Continue reading… Matthew Digman (Ohio State University)

Adi Nusser (Technion) Tue. January 14th, 2020
11:30 am-12:30 pm

New and old probes of the structure of the evolved Universe

The observed large scale distribution of galaxies and their peculiar motions (on top of the pure Hubble flow) are very well described in the framework of the standard Lambda Cold Dark Matter model. The model is founded on general relativity (GR) which in itself has recently gained substantial support by the detection of gravitational waves. Despite this success, observational data on large scales allow for deviations from the GR and the standard model. Any tiny deviation may have profound implications on fundamental physical theory of the Universe.

Continue reading… Adi Nusser (Technion)

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