Happening @ Michigan https://events.umich.edu/list/rss RSS Feed for Happening @ Michigan Events at the University of Michigan. HET Seminar | The Large Charge Expansion (February 4, 2022 3:00pm) https://events.umich.edu/event/91660 91660-21681473@events.umich.edu Event Begins: Friday, February 4, 2022 3:00pm
Location: Off Campus Location
Organized By: Leinweber Center for Theoretical Physics

Over the last few years, it has become clear that working in sectors of large global charge leads to significant simplifications when studying strongly coupled CFTs, theories which are otherwise often inaccessible to analytic methods. It allows us in particular to calculate the CFT data as an expansion in inverse powers of the large charge.
In this talk, I will introduce the large-charge expansion via the simple example of the O(2) model and will then apply it to a number of other systems which display a richer structure, such as those with non-Abelian global symmetry groups. Using large-N methods in conjunction with large charge gives us even more control over the dynamics and lets us study the system away from the conformal point.

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Lecture / Discussion Fri, 28 Jan 2022 12:25:01 -0500 2022-02-04T15:00:00-05:00 2022-02-04T16:00:00-05:00 Off Campus Location Leinweber Center for Theoretical Physics Lecture / Discussion
HET Seminar | Quantum Field Theory Tools for Gravitational Wave Science (February 11, 2022 3:00pm) https://events.umich.edu/event/91921 91921-21684137@events.umich.edu Event Begins: Friday, February 11, 2022 3:00pm
Location: Off Campus Location
Organized By: Leinweber Center for Theoretical Physics

Future gravitational wave detectors will map out and characterize every binary merger in the history of the universe. The possibilities for new and unexpected scientific discoveries from this wealth of data is staggering, but hinges crucially on complementary advances in our theoretical understanding of the nature of gravitational wave sources. However, the path from Einstein’s equation to precision binary dynamics is notoriously difficult, and conventional methods may not scale to the demands of future detectors. I will describe our recent efforts in solving the relativistic two-body problem using modern tools from quantum field theory.

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Lecture / Discussion Thu, 03 Feb 2022 09:03:06 -0500 2022-02-11T15:00:00-05:00 2022-02-11T16:00:00-05:00 Off Campus Location Leinweber Center for Theoretical Physics Lecture / Discussion
HET Seminar | Entanglement between matrix degrees of freedom and gauge theory counterpart of entanglement island (February 18, 2022 3:00pm) https://events.umich.edu/event/92107 92107-21686884@events.umich.edu Event Begins: Friday, February 18, 2022 3:00pm
Location: Off Campus Location
Organized By: Leinweber Center for Theoretical Physics

In gauge/gravity duality, matrix degrees of freedom on the gauge theory side play important roles for the emergent geometry. In this talk, we discuss how the entanglement on the gravity side can be described as the entanglement between matrix degrees of freedom. Our approach, which we call "matrix entanglement", is different from "target-space entanglement" proposed and discussed recently by several groups. The examples studied include a small black hole in AdS5*S5 that can evaporate without being attached to a heat bath, for which our approach suggests a gauge theory counterpart of the entanglement island behind the horizon. Specifically, we propose that the confined degrees of freedom in the partially-deconfined states correspond to the island. Intuitively, the confined sector consists of D-branes sitting behind the horizon and sourcing the exterior geometry.

This talk is based on work in progress with Vaibhav Gautam, Antal Jevicki and Cheng Peng.

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Lecture / Discussion Tue, 08 Feb 2022 10:05:51 -0500 2022-02-18T15:00:00-05:00 2022-02-18T16:00:00-05:00 Off Campus Location Leinweber Center for Theoretical Physics Lecture / Discussion
HET Seminar | Cosmology from vacuum physics (February 25, 2022 3:00pm) https://events.umich.edu/event/92453 92453-21691572@events.umich.edu Event Begins: Friday, February 25, 2022 3:00pm
Location: Off Campus Location
Organized By: Leinweber Center for Theoretical Physics

We discuss a holographic approach to describing cosmological physics.
The cosmological spacetime is encoded in a special state of a
four-dimensional quantum field theory that is not conventionally
holographic. The state is produced via a Euclidean path integral that
includes a three-dimensional holographic theory at a boundary in the
Euclidean past. The same Euclidean path integral can be used to define a
dual static spacetime, and the many of the observables in the cosmology are equivalent to vacuum observables in the static spacetime. This duality has interesting consequences, for example it gives a simple explanation for correlations between regions of the universe that apparently were never in causal contact. The model gives an effective field theory whose fundamental constant that is negative, but generically will have a phase of accelerated expansion via a rolling scalar.

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Lecture / Discussion Wed, 16 Feb 2022 14:53:21 -0500 2022-02-25T15:00:00-05:00 2022-02-25T16:00:00-05:00 Off Campus Location Leinweber Center for Theoretical Physics Lecture / Discussion
HET Seminar | Topological solitons in gravity (March 18, 2022 3:00pm) https://events.umich.edu/event/93298 93298-21702261@events.umich.edu Event Begins: Friday, March 18, 2022 3:00pm
Location: West Hall
Organized By: Leinweber Center for Theoretical Physics

In this talk I will discuss aspects of microscopic degrees of freedom of gravity as motivated by string theory. Although these are expected to be generically quantum mechanical, our goal is to understand a class of such states that are coherent enough to admit classical descriptions in Einstein gravity. The construction of such states corresponds to adding interesting topological structures in spacetime with the help of compact extra dimensions. The constructions manifestly behave like ultra compact objects, dubbed topological stars, which can also model black hole microstates. I will discuss physical aspects of such constructions.

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Lecture / Discussion Thu, 10 Mar 2022 21:07:38 -0500 2022-03-18T15:00:00-04:00 2022-03-18T16:00:00-04:00 West Hall Leinweber Center for Theoretical Physics Lecture / Discussion West Hall
HET Seminar | Black Hole Searches for Ultralight Bosons (March 25, 2022 3:00pm) https://events.umich.edu/event/93597 93597-21706199@events.umich.edu Event Begins: Friday, March 25, 2022 3:00pm
Location: West Hall
Organized By: Leinweber Center for Theoretical Physics

Theories that seek to explain the outstanding puzzles of the Standard Model of particle physics often predict new, light, feebly-interacting particles whose discovery requires novel search strategies. These include light spin-0 axions and spin-1 dark photons. I will discuss how rotating black holes source clouds of exponentially large numbers of gravitationally-bound particles and so create nature's laboratories for ultralight bosons. This process causes black holes to spin down and the bound bosons emit gravitational waves, allowing observatories such as LIGO and Virgo to search for new particles. For a new dark photon particle that couples to the Standard Model, the systems could undergo dramatic electromagnetic cascades and appear as novel pulsar-like objects in the sky.

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Lecture / Discussion Fri, 18 Mar 2022 11:12:16 -0400 2022-03-25T15:00:00-04:00 2022-03-25T16:00:00-04:00 West Hall Leinweber Center for Theoretical Physics Lecture / Discussion West Hall
HET Seminar | A Step in Understanding the Hubble Tension (April 1, 2022 3:00pm) https://events.umich.edu/event/93945 93945-21711377@events.umich.edu Event Begins: Friday, April 1, 2022 3:00pm
Location: Off Campus Location
Organized By: Leinweber Center for Theoretical Physics

Precision cosmology has now allowed us to study whether the simple LCDM model agrees with data. Interestingly, a tension has arisen between measurements of the Hubble Parameter - how fast the universe is expanding - from the recent universe compared with values extracted from the early universe. I will discuss this tension and some ideas of how to address it requiring physics beyond LCDM. In particular, I will discuss models with a light (~eV) mass threshold as a means to address the tension and the possibility of testing these ideas in the future.

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Lecture / Discussion Thu, 24 Mar 2022 15:55:01 -0400 2022-04-01T15:00:00-04:00 2022-04-01T16:00:00-04:00 Off Campus Location Leinweber Center for Theoretical Physics Lecture / Discussion
HET Seminar | Thermal Squeezeout for Strongly Interacting Dark Matter (April 8, 2022 3:00pm) https://events.umich.edu/event/94237 94237-21726185@events.umich.edu Event Begins: Friday, April 8, 2022 3:00pm
Location: West Hall
Organized By: Leinweber Center for Theoretical Physics

I will discuss the potential importance of a dark-sector phase transition in the early universe in setting the measured relic abundance, for a simple scenario with strongly interacting dark matter. Enhancement of the dark matter density within shrinking pockets of the high-temperature phase leads to a dramatic reduction in the late-time dark matter abundance, allowing for much heavier dark matter than in the standard thermal freezeout scenario. I will show new results on a class of specific models realizing this scenario, including experimental constraints and the effects of entropy injection from decay of metastable dark-sector particles.

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Lecture / Discussion Thu, 31 Mar 2022 13:55:53 -0400 2022-04-08T15:00:00-04:00 2022-04-08T16:00:00-04:00 West Hall Leinweber Center for Theoretical Physics Lecture / Discussion West Hall
HET Seminar | Color-Dual Effective Field Theory (April 15, 2022 3:00pm) https://events.umich.edu/event/94554 94554-21748831@events.umich.edu Event Begins: Friday, April 15, 2022 3:00pm
Location: Off Campus Location
Organized By: Leinweber Center for Theoretical Physics

The duality between color and kinematics, and associated double copy construction has allowed some of the sharpest perturbative calculations in both supergravity theories and classical invariant observables relevant to next generation gravitational wave physics. I will talk about ways related insights can be applied to understanding the behavior of EFT operators in gauge and gravity theories. Pairs of color-dual numerators can be composed to generate new color-dual numerators. This presents an opportunity to efficiently climb to amplitudes of arbitrarily high mass dimension --- without resorting to ever more expensive Ansätze --- thereby spanning the tower of double-copy consistent gauge and gravity operators with a small number of building blocks. I will apply this technology towards discovering some hints about the color-dual fate of N=4 supergravity.

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Lecture / Discussion Tue, 12 Apr 2022 05:34:17 -0400 2022-04-15T15:00:00-04:00 2022-04-15T16:00:00-04:00 Off Campus Location Leinweber Center for Theoretical Physics Lecture / Discussion
HET Seminar | Discrete Holography (September 23, 2022 3:00pm) https://events.umich.edu/event/98878 98878-21797293@events.umich.edu Event Begins: Friday, September 23, 2022 3:00pm
Location: West Hall
Organized By: Leinweber Center for Theoretical Physics

I will review recent progress towards establishing a holographic duality for discrete spaces involving a regular tiling of hyperbolic space. In particular, I will present a recent example where an aperiodic XXZ spin chain is obtained naturally by extrapolating the bulk tiling to its boundary. The properties of this model are studied using RG techniques, which provide a tensor network construction for its ground state. We calculate and compare the entanglement entropy both at the boundary and in the bulk. I will comment on the next steps towards obtaining a full dynamical duality of discrete systems. In particular, this may be useful for going beyond the large N limit on the gravity side

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Lecture / Discussion Fri, 16 Sep 2022 09:44:59 -0400 2022-09-23T15:00:00-04:00 2022-09-23T16:00:00-04:00 West Hall Leinweber Center for Theoretical Physics Lecture / Discussion West Hall
HET Seminar | Parity symmetry breaking scale and Standard Model parameters (September 30, 2022 3:00pm) https://events.umich.edu/event/98811 98811-21797215@events.umich.edu Event Begins: Friday, September 30, 2022 3:00pm
Location: West Hall
Organized By: Leinweber Center for Theoretical Physics

The strong CP problem can be solved by parity symmetry. We first review two classes of models: the ones with the minimal fermion content and the ones with the minimal Higgs content. We then focus on the latter class of models and show that the parity symmetry breaking scale is predicted to be the energy scale at which the standard model Higgs quartic coupling vanishes. Surprisingly, after fixing the parity symmetry breaking scale in this way, the gauge coupling constants unify at a high energy scale. We also discuss a model with a dark matter candidate and show that the dark matter direct detection rate is predicted as a function of the standard model parameters.

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Lecture / Discussion Mon, 26 Sep 2022 18:27:34 -0400 2022-09-30T15:00:00-04:00 2022-09-30T16:00:00-04:00 West Hall Leinweber Center for Theoretical Physics Lecture / Discussion West Hall
HET Seminar | The Memory Effect and Infrared Divergences in Quantum Field Theory and Quantum Gravity (October 6, 2022 12:00pm) https://events.umich.edu/event/99177 99177-21798724@events.umich.edu Event Begins: Thursday, October 6, 2022 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

*Please note Special day and time: Thursday at Noon*

Abstract: The "memory effect" refers to the fact that at order 1/r, a massless field generically will not return to the same value at asymptotically late retarded times as it had at asymptotically early retarded times. There is nothing singular about states with memory in quantum field theory, but they do not lie in the standard Fock space and infrared divergences will arise as artifacts of trying to represent states with memory in the standard Fock space. As a practical matter, if one is interested only in quantities directly relevant to collider physics, one can deal with infrared divergences by well defined procedures for obtaining "inclusive quantities," but this is clearly unsatisfactory from a fundamental viewpoint on scattering theory. For QED with massive charged particles, Faddeev and Kulish gave a construction of "in" and "out" Hilbert spaces that incorporates memory (via the "dressing" of the charged particles) and thereby provides a well defined scattering theory. However, we show that this construction fails in massless QED (because the required dressing is highly singular) and fails in (nonlinear) quantum gravity (because, in essence, the dressing would require its own further dressing and there is no self-consistent way of accomplishing this). We believe that if one wishes to treat scattering at a fundamental level in quantum gravity—as well as in massless QED and Yang-Mills theory—it is necessary to approach it from an algebraic viewpoint o

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Workshop / Seminar Tue, 04 Oct 2022 11:03:21 -0400 2022-10-06T12:00:00-04:00 2022-10-06T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Workshop / Seminar Randall Laboratory
HET Seminar | Covariant prescriptions for holographic entanglement (October 21, 2022 3:00pm) https://events.umich.edu/event/99935 99935-21799588@events.umich.edu Event Begins: Friday, October 21, 2022 3:00pm
Location: West Hall
Organized By: Leinweber Center for Theoretical Physics

In the holographic setting of gauge/gravity duality, there has been a growing expectation that the emergence of the bulk gravitational spacetime is rooted in the entanglement structure of the dual gauge theory. While the deep connection remains mysterious, an early hint came from the holographic entanglement entropy prescription, which expresses the boundary entanglement entropy in terms of simple geometric constructs in the bulk. This talk will review the recent reformulations of this prescription presented in [2208.10507] in terms of several new (and fully covariant) formulas, including minimax, max U-flow, and min V-flow (the latter covariantizing the bit thread formulation of holographic entanglement entropy by Freedman and Headrick).

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Lecture / Discussion Mon, 17 Oct 2022 03:02:49 -0400 2022-10-21T15:00:00-04:00 2022-10-21T16:00:00-04:00 West Hall Leinweber Center for Theoretical Physics Lecture / Discussion West Hall
HET Seminar | Gravitational waves and the propagation of fermions in gauge-field inflation (October 28, 2022 3:00pm) https://events.umich.edu/event/100231 100231-21799372@events.umich.edu Event Begins: Friday, October 28, 2022 3:00pm
Location: West Hall
Organized By: Leinweber Center for Theoretical Physics

Degree-scale B-mode polarization of the cosmic microwave background sourced by primordial gravitational waves is the so-called smoking-gun signature of inflation. The detection of these primordial CMB B-modes is often described as would-be evidence that inflation occurred at or near the scale of grand unification, that the inflaton rolled over a super-Planckian distance in field space, and that gravity is quantized. In this talk, I describe a class of inflationary models that serve as a counter-example to these claims. Models involving classical non-Abelian gauge fields can produce observable gravitational waves at energy scales far below the scale of grand unification without the quantization of gravity, or super-Planckian field excursions. I show how the gauge field background violates parity, leading to the helical polarization of the gravitational wave background; a signature of this class of models. I also discuss the propagation and backreaction of fermions on the background field configurations, and some subtleties associated with renormalization of fermions in axion backgrounds.

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Lecture / Discussion Fri, 14 Oct 2022 05:21:06 -0400 2022-10-28T15:00:00-04:00 2022-10-28T16:00:00-04:00 West Hall Leinweber Center for Theoretical Physics Lecture / Discussion West Hall
HET Seminar | Subalgebra-subregion duality: emergence of space and time in holography (November 11, 2022 3:00pm) https://events.umich.edu/event/101049 101049-21800728@events.umich.edu Event Begins: Friday, November 11, 2022 3:00pm
Location: West Hall
Organized By: Leinweber Center for Theoretical Physics

TBD

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Lecture / Discussion Thu, 03 Nov 2022 17:41:39 -0400 2022-11-11T15:00:00-05:00 2022-11-11T16:00:00-05:00 West Hall Leinweber Center for Theoretical Physics Lecture / Discussion West Hall
HET Seminar | An Antipodal Duality Between Amplitudes and Form Factors (November 18, 2022 3:00pm) https://events.umich.edu/event/101200 101200-21800930@events.umich.edu Event Begins: Friday, November 18, 2022 3:00pm
Location: West Hall
Organized By: Leinweber Center for Theoretical Physics

Scattering amplitudes are where quantum field theory directly meets collider experiments. An excellent model for scattering in QCD is provided by N=4 super-Yang-Mills theory, particularly in the planar limit of a large number of colors, where the theory becomes integrable. The first nontrivial amplitude in this theory is for 6 gluons. It can be computed to 7 loops using a bootstrap based on the rigidity of the function space of multiple polylogarithms, together with a few other conditions. One can also bootstrap a particular form factor, for the chiral stress-tensor operator to produce 3 gluons, through 8 loops. This form factor is the N=4 analog of the LHC process, gluon gluon --> Higgs + gluon. Remarkably, the two sets of results are related by a mysterious “antipodal” duality, which exchanges the role of branch cuts and derivatives. I will describe how bootstrapping works and what we know about this new duality.

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Lecture / Discussion Wed, 09 Nov 2022 09:46:39 -0500 2022-11-18T15:00:00-05:00 2022-11-18T16:00:00-05:00 West Hall Leinweber Center for Theoretical Physics Lecture / Discussion West Hall
HET Seminar | A top-down dictionary for double holography (December 2, 2022 3:00pm) https://events.umich.edu/event/101339 101339-21801237@events.umich.edu Event Begins: Friday, December 2, 2022 3:00pm
Location: West Hall
Organized By: Leinweber Center for Theoretical Physics

Holographic interpretations of Randall-Sundrum (RS) branes provide a laboratory to explore the way quantum information evolves in field theories coupled to gravity. Despite this importance, the holographic interpretation of RS branes in terms of a theory of gravity coupled to a CFT is rather ad-hoc. In this talk, we use top-down constructions of RS branes in order to work out a precise dictionary for this "intermediate" holographic prescription, resolving serious causality problems of the naive picture often used in the literature while preserving many of the successes of the RS construction

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Lecture / Discussion Mon, 14 Nov 2022 13:40:37 -0500 2022-12-02T15:00:00-05:00 2022-12-02T16:00:00-05:00 West Hall Leinweber Center for Theoretical Physics Lecture / Discussion West Hall