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Monday, January 29th 2018

3:30 pm:

Following spectacular confirmation of the Standard Model at the LHC, the emphasis of particle physics shifts towards searches for physics beyond Standard Model. The clues for new physics may be hidden in cosmological data that suggest the dominance of dark matter and dark energy throughout the Universe. I will describe some recent aspects of widening the search for new physics focussing on light dark matter and in general on light weakly coupled states. I will introduce constraints on dark matter - electron scattering that result from a new phenomenon, the reflection of dark matter from the solar interior. I will also argue that besides conventional probes of light weakly coupled states, further insight can be gained by involving precision AMO tools, and describe some recent experimental activity in this direction.

Tuesday, January 30th 2018

1:00 pm:

Monday, February 12th 2018

3:30 pm:

“What is the Universe made of?” This question is the longest outstanding problem in all of modern physics, and it is one of the most important research topics in cosmology and particle physics today. The bulk of the mass in the Universe is thought to consist of a new kind of dark matter particle, and the hunt for its discovery in on. I'll start by discussing the evidence for the existence of dark matter in galaxies, and then show how it fits into a big picture of the Universe containing 5% atoms, 25% dark matter, and 70% dark energy. Neutrinos only constitute ½% of the content of the Universe, but much can be learned about neutrino properties from cosmological data. Leading candidates for the dark matter are Weakly Interacting Massive Particles (WIMPs), axions, and sterile neutrinos. WIMPs are a generic class of particles that are electrically neutral and do not participate in strong interactions, yet have weak-scale interactions with ordinary matter. There are multiple approaches to experimental searches for WIMPS: at the Large Hadron Collider at CERN in Geneva; in underground laboratory experiments; with astrophysical searches for dark matter annihilation products, and upcoming searches with the James Webb Space Telescope for Dark Stars, early stars powered by WIMP annihilation. Current results are puzzling and the hints of detection will be tested soon. At the end of the talk I'll briefly turn to dark energy and its effect on the fate of the Universe.

Tuesday, February 13th 2018

1:00 pm:

Monday, February 19th 2018

3:30 pm:

I will provide an introductory level overview of recent

applications of resurgent trans-series and Picard-Lefschetz theory to

quantum mechanics and quantum field theory.

Resurgence connects local perturbative data with global topological

structures. In quantum mechanical systems, this program provides a

constructive relation between different saddles. For example, in

certain cases it has been shown that all information around the

instanton saddle is encoded in perturbation theory around the

perturbative saddle. In quantum field theory, such as sigma-models

compactified on a circle, neutral bions provide a semi-classical

interpretation of the elusive IR-renormalon, and fractional kink

instantons lead to the non-perturbatively induced mass gap exactly of

order of the strong scale. I also describe the concept of hidden

topological angle, a phase associated with Lefschetz thimbles.

Hidden topological angle may provide destructive/constructive

interference effects between equally dominant saddles in the Lefschetz

thimble decomposition, providing resolution to some time standing

puzzles in non-perturbative analysis.

Tuesday, February 20th 2018

1:00 pm:

Monday, September 24th 2018

2:00 pm:

In a generic conformal field theory the spectrum of operators carrying a large U(1) charge can be analyzed semiclassically. The key is the operator state correspondence by which such operators are associated with a finite density superfluid phase for the theory quantized on the cylinder. The dynamics is dominated by the corresponding Goldstone hydrodynamic mode and the derivative expansion coincides with the inverse charge expansion. I will illustrate this situation by first considering simple quantum mechanical analogues and then will systematize the approach by employing the coset construction for non-linearly realized space-time symmetries. Focussing on a 3-dimensional theory I will illustrate that the three point function coefficients turn out to satisfy universal scaling laws and correlations as the charge and spin are varied. Lastly I’ll show how the approach can be generalized to the case of large spin by considering vortices in the superfluid.

Wednesday, October 3rd 2018

7:00 pm:

Recent announcements of the first ever detections of gravitational waves from colliding black holes and neutron stars have launched a new era of gravitational wave astrophysics. I will describe the science, technology, and human story behind these discoveries that provide a completely new window into some of the most violent and warped events in the Universe.

Monday, December 3rd 2018

12:30 pm:

By definition the choreography (dancing curve) is the trajectory

on which n classical bodies move chasing each other without collisions.

The first choreography (the remarkable Figure Eight) at zero angular

momentum was discovered unexpectedly by C Moore (Santa Fe) at 1993

for 3 equal mass bodies in R^3 Newtonian gravity numerically.

At the moment about 6,000 choreographies are known, all numerically

in Newtonian gravity. A number of 3-body choreographies is known

for Lenard-Jones potential again numerically.

Do exist (non)-Newtonian gravity for which dancing curve is known

analytically? - Yes, one example is known - it is algebraic lemniscate by

Jacob Bernoulli (1694) - and it will be the subject of the talk.

Astonishingly, Newtonian Figure Eight coincides with algebraic lemniscate

with accuracy 10^{ - 7}-
.

Monday, December 10th 2018

12:30 pm:

Ising model is a classical model for ferromagnetism in statistical mechanics. In a joint work with Pavel Galashin we completely describe by inequalities the set of boundary correlation matrices of planar Ising networks embedded in a disk. Specifically, we give a simple bijection between such correlation matrices and points in the totally nonnegative part of the orthogonal Grassmannian, which has been introduced recently in the study of the scattering amplitudes of ABJM theory. Under our correspondence, Kramers--Wannier's high/low temperature duality transforms into the cyclic symmetry of the Grassmannian. We also show that the edge parameters of the Ising model for reduced networks can be uniquely recovered from boundary correlations, solving the inverse problem.

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