Happening @ Michigan https://events.umich.edu/list/rss RSS Feed for Happening @ Michigan Events at the University of Michigan. HET Brown Bag Seminar | Detecting knot topology from Chern-Simons theory (February 15, 2023 1:00pm) https://events.umich.edu/event/104216 104216-21808659@events.umich.edu Event Begins: Wednesday, February 15, 2023 1:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

The topological knot invariants can be studied in the context of Chern-Simons theory both in the non-perturbative and the perturbative regimes. In the former case polynomial knot invariants can be obtained while in the latter case the so called Vassiliev knot invariants arise. Recent work in the non-perturbative regime has been done with the incorporation of entanglement entropy computations associated with knot states, while in the perturbative regime the Vassiliev invariants have been extended to include information of a vector field in the theory.

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Lecture / Discussion Mon, 30 Jan 2023 11:16:33 -0500 2023-02-15T13:00:00-05:00 2023-02-15T14:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminar | Veneziano Variations: How Unique are String Amplitudes? (March 8, 2023 1:00pm) https://events.umich.edu/event/103174 103174-21806230@events.umich.edu Event Begins: Wednesday, March 8, 2023 1:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

String theory offers an elegant and concrete realization of how to consistently couple states of arbitrarily high spin. But how unique is this construction? In this talk, I will derive a novel, multi-parameter family of four-point scattering amplitudes exhibiting i) polynomially bounded high-energy behavior and ii) exchange of an infinite tower of high-spin modes, albeit with a finite number of states at each resonance. These amplitudes take an infinite-product form and, depending on parameters, exhibit mass spectra that are either unbounded or bounded, thus corresponding to generalizations of the Veneziano and Coon amplitudes, respectively. For the bounded case, masses converge to an accumulation point, a peculiar feature seen in the Coon amplitude but more recently understood to arise naturally in string theory. Importantly, our amplitudes contain free parameters allowing for the customization of the slope and offset of the spin-dependence in the Regge trajectory. We compute all partial waves for this multi-parameter class of amplitudes and identify unitary regions of parameter space. For the unbounded case, we apply similar methods to derive new deformations of the Veneziano and Virasoro-Shapiro amplitudes.

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Lecture / Discussion Tue, 10 Jan 2023 12:36:34 -0500 2023-03-08T13:00:00-05:00 2023-03-08T14:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag | Non-isometric codes and the black hole interior (March 22, 2023 1:00pm) https://events.umich.edu/event/106237 106237-21813958@events.umich.edu Event Begins: Wednesday, March 22, 2023 1:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

At late times, any holographic map from the large semiclassical Hilbert space in the interior of a black hole to the smaller Hilbert space in the boundary must be non-isometric. This implies that a large set of states in the bulk description do not exist in the fundamental description of the system. Despite this, I will show using a simple model that bulk states and operators whose complexity is sub-exponential in the black hole entropy can be represented in the boundary. I will also discuss the validity of the quantum extremal surface formula and entanglement wedge reconstruction for this non-isometric map.

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Lecture / Discussion Wed, 15 Mar 2023 14:44:23 -0400 2023-03-22T13:00:00-04:00 2023-03-22T14:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Models of Higgsed CP and their Cosmology (March 29, 2023 1:00pm) https://events.umich.edu/event/106355 106355-21814121@events.umich.edu Event Begins: Wednesday, March 29, 2023 1:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Nelson-Barr models, which assume that CP is a spontaneously broken symmetry of nature, are a well-known solution to the strong CP problem with no new light degrees of freedom. Nevertheless, the spontaneous breaking of CP can have dramatic implications in cosmology. It was recently shown that domain walls which form from this spontaneous breaking are exactly stable, and therefore must be inflated away. Combined with the "Nelson-Barr quality problem", which sets an upper bound on the breaking scale to avoid the effects of dangerous irrelevant operators, this puts an upper bound on the scale of inflation and the subsequent reheating temperature. In this talk, I will briefly review the Nelson-Barr solution to the strong CP problem, its quality problem, and demonstrate that minimal Nelson-Barr models are in tension with simple models of inflation and thermal leptogenesis. I will also show one possibility for ameliorating this tension by introducing a new, chiral symmetry which forbids the most dangerous dimension-5 operators.

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Lecture / Discussion Fri, 17 Mar 2023 09:59:14 -0400 2023-03-29T13:00:00-04:00 2023-03-29T14:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminar | 3d gravity and Teichmuller TQFT (April 5, 2023 1:00pm) https://events.umich.edu/event/106490 106490-21815395@events.umich.edu Event Begins: Wednesday, April 5, 2023 1:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

I will describe a proposal that relates AdS_3 quantum gravity to a topological quantum field theory known as ``Teichmuller TQFT.’’ This proposal makes precise the idea that pure AdS_3 quantum gravity is related to two copies of SL(2,R) Chern-Simons theory and resolves some well-known issues with this lore. I will argue that moreover this proposal provides a systematic and practical tool for the computation of partition functions of 3d gravity, and will describe how it elucidates the recent ensemble interpretation of semiclassical 3d gravity. (Based on work in progress with Lorenz Eberhardt and Mengyang Zhang.)

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Lecture / Discussion Mon, 03 Apr 2023 10:10:08 -0400 2023-04-05T13:00:00-04:00 2023-04-05T14:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminar | Generalized entropy for general subregions in quantum gravity (September 6, 2023 11:00am) https://events.umich.edu/event/110530 110530-21825018@events.umich.edu Event Begins: Wednesday, September 6, 2023 11:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

I will describe a construction of algebras of observables associated with local subregions in quantum gravity in the small G_N limit. This algebra consists of operators dressed to a semiclassical observer degree of freedom which serves as an anchor defining the subregion. I will argue that properly implementing the gravitational constraints on this algebra results in a type II von Neumann algebra, which possesses a well-defined notion of entropy. Up to a state-independent constant, this entropy agrees with the UV-finite generalized entropy of the subregion, consisting of a Bekenstein-Hawking area term and a bulk entropy term. This gives an algebraic explanation for the finiteness of the generalized entropy, and provides a number of tools for investigating aspects of semiclassical gravitational entropy, including the generalized second law, the quantum focusing conjecture, and the quantum extremal surface prescription in holography.

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Lecture / Discussion Mon, 21 Aug 2023 11:14:46 -0400 2023-09-06T11:00:00-04:00 2023-09-06T12:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Brown Bag Seminar | Physical Signatures of Fermion-Coupled Axions (September 13, 2023 11:00am) https://events.umich.edu/event/111380 111380-21826916@events.umich.edu Event Begins: Wednesday, September 13, 2023 11:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

While there is an abundance of experiments searching for axion dark matter (DM) via its electromagnetic coupling, there are fewer utilizing its derivative coupling to electrons and nucleons. This direct coupling generates dynamical effects through the fermion spin, and therefore spin-polarized targets are a naturally useful target. We find that spin-polarized or magnetized analogs of layered dielectric haloscopes can be powerful probes at both radio frequencies, with sensitivity to currently unexplored parameter space, and optical frequencies, with sensitivity comparable to current astrophysical bounds.

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Lecture / Discussion Tue, 05 Sep 2023 13:25:24 -0400 2023-09-13T11:00:00-04:00 2023-09-13T12:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Brown Bag Seminar | Geometry of Conformal Manifolds and the Inversion Formula (September 20, 2023 11:00am) https://events.umich.edu/event/111377 111377-21826915@events.umich.edu Event Begins: Wednesday, September 20, 2023 11:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Families of conformal field theories are naturally endowed with a Riemannian geometry which is locally encoded by correlation functions of exactly marginal operators. We show that the curvature of such conformal manifolds can be computed using Euclidean and Lorentzian inversion formulae, which combine the operator content of the conformal field theory into an analytic function. Analogously, operators of fixed dimension define bundles over the conformal manifold whose curvatures can also be computed using inversion formulae. These results relate curvatures to integrated four-point correlation functions which are sensitive only to the behavior of the theory at separated points. We apply these inversion formulae to derive convergent sum rules expressing the curvature in terms of the spectrum of local operators and their three-point function coefficients. We further show that the curvature can smoothly diverge only if a conserved current appears in the spectrum, or if the theory develops a continuum. We verify our results explicitly in 2d examples.

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Lecture / Discussion Wed, 06 Sep 2023 10:27:20 -0400 2023-09-20T11:00:00-04:00 2023-09-20T12:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminar | Bootstrapping large-N confining gauge theories (September 27, 2023 11:00am) https://events.umich.edu/event/110719 110719-21825353@events.umich.edu Event Begins: Wednesday, September 27, 2023 11:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Obtaining the low-energy EFT of a given large-N confining gauge theory is in general a very difficult problem. Instead, one can proceed by carving out the space of allowed EFTs using the constraints on scattering amplitudes that follow e.g. from unitarity and crossing symmetry. In this talk I will review how to do this in the context of pion physics, with large-N QCD as our target. I will discuss what bounds this imposes on the chiral Lagrangian, and what theories saturate the bounds. I will end by discussing how a mixed system of pions and photons allows us to input symmetries and anomalies into the bootstrap, paving the way for bootstrapping large N QCD.

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Lecture / Discussion Wed, 23 Aug 2023 10:48:10 -0400 2023-09-27T11:00:00-04:00 2023-09-27T12:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Brown Bag **Special Seminar** | Heisenberg's Path to Quantum Mechanics (October 3, 2023 12:00pm) https://events.umich.edu/event/112846 112846-21829647@events.umich.edu Event Begins: Tuesday, October 3, 2023 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

**Special Seminar** Please note time and location
In the summer of 1925, Heisenberg wrote the paper Über quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen, which laid the foundations of quantum mechanics. For a long time, this paper was considered to be inscrutable. This talk will show how one can make sense both of Heisenberg's formal manipulations and of his philosophical rhetoric, in particular by studying the letters he wrote in months leading up to his breakthrough. A particular emphasis will be placed on how different the theory that Heisenberg originally aimed to construct was from modern quantum mechanics

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Lecture / Discussion Thu, 21 Sep 2023 09:01:13 -0400 2023-10-03T12:00:00-04:00 2023-10-03T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Brown Bag Seminar | Non-perturbative de Sitter quantum gravity in low dimensions (October 4, 2023 11:00am) https://events.umich.edu/event/111381 111381-21826918@events.umich.edu Event Begins: Wednesday, October 4, 2023 11:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Little is known about non-perturbative quantum gravity in de Sitter spacetimes. As a useful low-dimensional model, we consider de Sitter Jackiw-Teitelboim (dS JT) gravity and solve it non-perturbatively in the genus expansion. This amounts to the first non-perturbatively solvable model of de Sitter cosmology. We find that dS JT gravity has an effective string coupling which is pure imaginary, rendering the S-matrix genus expansion Borel resummable. We further establish that dS JT gravity is dual to a formal matrix integral with a negative number of degrees of freedom. More broadly, our analysis unveils new ingredients in the de Sitter holographic dictionary, which may be applicable in more general contexts.

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Lecture / Discussion Fri, 08 Sep 2023 11:45:19 -0400 2023-10-04T11:00:00-04:00 2023-10-04T12:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Brown Bag Seminar | What can be measured asymptotically? (October 25, 2023 11:00am) https://events.umich.edu/event/111382 111382-21826919@events.umich.edu Event Begins: Wednesday, October 25, 2023 11:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

We consider asymptotic observables in quantum field theories in which the S-matrix makes sense. We argue that in addition to scattering amplitudes, a whole compendium of inclusive observables exists where the time ordering is relaxed. These include expectation values of electromagnetic or gravitational radiation fields as well as out-of-time-order amplitudes. We explain how to calculate them in different ways: by relating them to amplitudes and products of amplitudes and by using a generalization of the LSZ reduction formula. Finally, we discuss how to relate them to one another through new versions of crossing symmetry. As an application, we discuss one-loop contributions to gravitational radiation in the post-Minkowski expansion, emphasizing the role of classical cut contributions and highlighting the infrared physics of in-in observables.

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Lecture / Discussion Thu, 12 Oct 2023 14:32:26 -0400 2023-10-25T11:00:00-04:00 2023-10-25T12:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag | Loop-corrected soft photon theorems and large gauge transformations (November 1, 2023 11:00am) https://events.umich.edu/event/114231 114231-21832529@events.umich.edu Event Begins: Wednesday, November 1, 2023 11:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

In the last few years, a remarkable link has been established between the soft theorems and asymptotic symmetries of quantum field theories: soft theorems are Ward identities of the asymptotic symmetry generators. In quantum electrodynamics, Weinberg's soft photon theorem is nothing but the Ward identity of a gauge transformation whose parameter is non-trivial at infinity. Likewise, Low's tree-level subleading soft photon theorem is the Ward identity of a gauge transformation whose parameter diverges linearly at infinity. More recently, it has been shown that Low's theorem receives loop corrections that are logarithmic in soft photon energy. Then, it is natural to ask whether such corrections are associated with some asymptotic symmetry of the S-matrix. There have been proposals for conserved charges whose Ward identities yield the loop-corrected soft theorems, but a clear symmetry interpretation remains elusive. We explore this question in the context of scalar QED, in hopes of shedding light on the connection between asymptotic symmetries and loop-corrected soft theorems.

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Lecture / Discussion Thu, 19 Oct 2023 14:22:03 -0400 2023-11-01T11:00:00-04:00 2023-11-01T12:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Brown Bag Seminar | Near-Extremal Black Hole Entropies from Replica Matrices (November 8, 2023 11:00am) https://events.umich.edu/event/111383 111383-21826920@events.umich.edu Event Begins: Wednesday, November 8, 2023 11:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

A generic pathology one encounters when computing the thermal entropy of a black hole is that it becomes negatively divergent as the temperature goes to zero, and only those whose extremal limit preserve some supersymmetry yield a sensible low-temperature entropy. The physics relevant to these phenomena are all captured by Jackiw-Teitelboim theories of gravity, which have been rather explicitly shown to be dual to various matrix ensembles. The issues and features mentioned above can all be precisely understood from this perspective: traditional gravitational calculations are computing annealed quantities, which give inherently wrong approximations near extremality.
We use the matrix integral formulation to show how quenched quantities do in fact behave sensibly and yield non-negative entropies at all temperatures. By using a suitable replica trick, this is done for a completely general matrix ensemble, thus settling the question for any black hole whose near-extremal spectrum is captured by such ensembles. Crucially, this result only requires working perturbatively to leading order in the size of the matrices, which hints at the possibility of an analogous semiclassical gravitational computation where one just needs to account for wormhole contributions appropriately (and not for doubly non-perturbative effects in 1/G).

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Lecture / Discussion Tue, 10 Oct 2023 13:28:34 -0400 2023-11-08T11:00:00-05:00 2023-11-08T12:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Brown Bag Seminar | Probing Quantum Black Hole Microstates (November 15, 2023 11:00am) https://events.umich.edu/event/111384 111384-21826921@events.umich.edu Event Begins: Wednesday, November 15, 2023 11:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

It is now widely believed that black holes should be described by ordinary (though complicated) quantum systems. This can be made precise for supersymmetric (BPS) black holes in Anti de-Sitter space, where the AdS/CFT correspondence may be used to reliably count black hole microstates. We will review this proposal for 4d superconformal field theories dual to AdS5 black holes and explain the challenges in characterizing these microstates directly in terms of gravitational variables. Surprisingly, a gravitational path integral calculation predicts certain universal features of the spectrum, including a large number of exactly degenerate states and a "mass gap" between the BPS and non-BPS states.

If BPS black holes are described by ordinary quantum systems, we should be able to act with operators which probe the microstates. We find one such probe is a certain generalization of the supersymmetric Wilson line in 4d N=4 SYM; holographically dual to a D-brane which wraps the horizon, and further demonstrate a matching of these descriptions when the spacetime description is valid. In addition to detecting the familiar deconfinement transition in conformal gauge theories, this provides an example of a system in which a black hole interacts with other degrees of freedom but has an exact microscopic description.

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Lecture / Discussion Mon, 06 Nov 2023 12:29:06 -0500 2023-11-15T11:00:00-05:00 2023-11-15T12:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Brown Bag Seminar | Exotic energy injection in the early Universe (November 29, 2023 11:00am) https://events.umich.edu/event/111385 111385-21826922@events.umich.edu Event Begins: Wednesday, November 29, 2023 11:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

The production of electromagnetically interacting particles in the early Universe is a generic prediction of many extensions of both the standard models of particle physics and cosmology. In this talk, I will give an overview of recent progress in understanding how injected particles deposit their energy into regular matter, and highlight some novel signatures of new physics that are well within current and near-future experimental reach.

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Lecture / Discussion Wed, 15 Nov 2023 09:16:05 -0500 2023-11-29T11:00:00-05:00 2023-11-29T12:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Brown Bag Seminar | Searching for High Frequency Gravitational Waves with Phonons (December 6, 2023 11:00am) https://events.umich.edu/event/111386 111386-21826923@events.umich.edu Event Begins: Wednesday, December 6, 2023 11:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

With the direct detection of gravitational waves (GWs) from LIGO in 2016, and recent evidence from the NANOGrav collaboration for a stochastic GW background, GW astronomy is becoming an important tool for understanding the universe. Recently it has been shown that axion dark matter (DM) experiments can extend the search for GWs to much higher frequencies, kHz < f < GHz. In this talk we'll discuss how light DM detectors utilizing single phonon excitations in crystal targets, previously shown to be sensitive to a wide variety of DM candidates, are also sensitive to GWs in the frequency range, THz < f < 100 THz, corresponding to the range of optical phonon energies, meV < \omega < 100 meV. We'll discuss the mechanism by which high frequency GWs can generate single phonons, and consider the detector sensitivity of different target materials. Lastly, we'll discuss how these high frequency GWs may be produced in processes such as black hole inspirals and superradiance.

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Lecture / Discussion Tue, 05 Dec 2023 09:11:09 -0500 2023-12-06T11:00:00-05:00 2023-12-06T12:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminar | Finding isomorphic superconformal field theories (January 24, 2024 1:00pm) https://events.umich.edu/event/116785 116785-21837993@events.umich.edu Event Begins: Wednesday, January 24, 2024 1:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

When do two different looking quantum field theories describe the same physics? This is essentially asking when the quantum field theories are isomorphic. In the case of topological quantum field theories, there are sometimes a way to determine them via topological invariants. For a superconformal field theory, what would be the minimal set of “invariants” to determine when they are isomorphic? I will discuss some approaches to this question in the context of superconformal field theories in four and six dimensions. Utilizing 4d class S theories that also admits 6d (1,0) SCFT origins, I will explain how a certain class of 4d N=2 SCFTs, which a priori look like distinct theories, can be shown to describe the same physics. I will further explain how the 6d (1,0) origin sheds light on the 3d duality.

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Lecture / Discussion Tue, 09 Jan 2024 13:56:57 -0500 2024-01-24T13:00:00-05:00 2024-01-24T14:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminar | Probing poles at infinity using on-shell diagrams (January 31, 2024 1:00pm) https://events.umich.edu/event/116869 116869-21838122@events.umich.edu Event Begins: Wednesday, January 31, 2024 1:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Locality and unitary forces scattering amplitudes to factorize when taking the momentum of one of the external particles to zero. This factorization has proven very useful for recursion relations for amplitudes at high multplicities. The recursion can break down, however, when the amplitude contains a pole at infinity. In this talk we are going to make modest step towards a prescription of “unitarity at infinity”. We do this by studying on-shell diagrams, which are on-shell gauge invariant objects that appear as cuts of loop integrands in the context of generalized unitarity and serve as building blocks for amplitudes in recursion relations. In the dual formulation, they are associated with cells of the positive Grassmannian. We will describe on-shell diagrams in N<4 supersymmetric Yang-Mills (SYM) theory and show that there exists a diagrammatic operation that corresponds to sending one of the momenta to infinity.

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Lecture / Discussion Wed, 24 Jan 2024 10:35:55 -0500 2024-01-31T13:00:00-05:00 2024-01-31T14:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory