Happening @ Michigan https://events.umich.edu/list/rss RSS Feed for Happening @ Michigan Events at the University of Michigan. CWoLa Hunting: Extending the Bump Hunt with Machine Learning (January 16, 2019 12:00pm) https://events.umich.edu/event/59607 59607-14754561@events.umich.edu Event Begins: Wednesday, January 16, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

New physics at the LHC would typically manifest as an anomalous overdensity of events in some phase space region of the high-dimensional feature space of LHC data. The traditional way to search for new physics is to make some theory-motivated guess as to what it will look like, and then make a phase space selection which is optimized using simulated data and then look in that region for an excess in the real LHC data. Higher sensitivity is often achieved at the expense of introducing stronger assumptions about the underlying signal model, which are used to make more optimised multivariate cuts using more event features. I will discuss a case study of an alternate paradigm, in which sensitive multivariate selections can be be found while maintaining few signal-model assumptions and without the need for potentially unreliable signal simulations. The key ingredient is a machine learning algorithm which searches for event over-densities on an otherwise smooth background, as is often the case in bump hunts for particle resonances. In this 'CWoLa-hunting' (Classification Without Labels) strategy, the selection cuts are not determined in advance but are rather dictated by the distribution of the actual measured LHC data. I will also provide a summary of some of the other ideas for using machine learning for model-agnostic searches that have been proposed in 2018.

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Lecture / Discussion Tue, 25 Jun 2019 14:46:35 -0400 2019-01-16T12:00:00-05:00 2019-01-16T13:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag | CWoLa Hunting -- Machine Learning for Model-Agnostic Bump Hunts (January 16, 2019 12:00pm) https://events.umich.edu/event/59652 59652-14777839@events.umich.edu Event Begins: Wednesday, January 16, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

New physics at the LHC would typically manifest as an anomalous overdensity of events in some phase space region of the high-dimensional feature space of LHC data. The traditional way to search for new physics is to make some theory-motivated guess as to what it will look like, and then make a phase space selection which is optimized using simulated data and then look in that region for an excess in the real LHC data. Higher sensitivity is often achieved at the expense of introducing stronger assumptions about the underlying signal model, which are used to make more optimised multivariate cuts using more event features. I will discuss a case study of an alternate paradigm, in which sensitive multivariate selections can be be found while maintaining few signal-model assumptions and without the need for potentially unreliable signal simulations. The key ingredient is a machine learning algorithm which searches for event over-densities on an otherwise smooth background, as is often the case in bump hunts for particle resonances. In this 'CWoLa-hunting' (Classification Without Labels) strategy, the selection cuts are not determined in advance but are rather dictated by the distribution of the actual measured LHC data. I will also provide a summary of some of the other ideas for using machine learning for model-agnostic searches that have been proposed in 2018.

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Workshop / Seminar Mon, 14 Jan 2019 08:38:46 -0500 2019-01-16T12:00:00-05:00 2019-01-16T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag | Analytic Approach to EIgenstate Thermalization (ETH) in the SYK Model and Schwarzian Theory (January 23, 2019 12:00pm) https://events.umich.edu/event/60107 60107-14838290@events.umich.edu Event Begins: Wednesday, January 23, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

The SYK model provides an uncommon example of a theory where Eigenstate Thermalization Hypothesis (ETH) can be verified in analytically. In this talk I will discuss this model in the deep infrared limit where the theory has an emergent conformal (reparametrization) symmetry that is broken both spontaneously and explicitly. To study the validity of ETH, we compute the heavy- light correlation functions of operators in the conformal spectrum of the theory. We compute these correlation functions with and without the contribution of the low energy (Schwarzian) modes, which are known to be the origin of the chaotic behaviour in this theory. In considering the contributions of the Schwarzian modes we find a weaker form of ETH: while the heavy operator insertions increase the effective temperature perceived by the light insertions, this effective temperature is proportional to the background temperature and goes to zero with the background temperature. In the case where Schwarzian modes aren’t considered, we find ETH in limit in which the weight of the heavy operators approach infinity. I will also discuss implications of these results for the states in AdS2 gravity dual.

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Workshop / Seminar Mon, 21 Jan 2019 09:41:55 -0500 2019-01-23T12:00:00-05:00 2019-01-23T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Seminar | Dark Matter Production: Finite Temperature Effects in the Early Universe (January 25, 2019 3:00pm) https://events.umich.edu/event/60108 60108-14838294@events.umich.edu Event Begins: Friday, January 25, 2019 3:00pm
Location: Randall Laboratory
Organized By: HET Seminars

In the early universe, the Standard Model particles formed a hot thermal bath. We highlight the importance of finite temperature corrections in these conditions on various production mechanisms of dark matter, primarily through temperature dependent masses and scalar vevs. We first consider a variation on standard freeze-out, where kinematic thresholds determine the relic abundance. We then consider a freeze-in model where the production rate is dramatically increased when a kinematic threshold opens. Finally, we present a qualitatively new production mechanism for dark matter, where dark matter decay is allowed for a limited amount of time just before the electroweak phase transition.

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Workshop / Seminar Mon, 21 Jan 2019 09:48:48 -0500 2019-01-25T15:00:00-05:00 2019-01-25T16:00:00-05:00 Randall Laboratory HET Seminars Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | Testing Models of Dark Matter and Modifications to Gravity using Local Milky Way Observables (January 30, 2019 12:00pm) https://events.umich.edu/event/60479 60479-14899147@events.umich.edu Event Begins: Wednesday, January 30, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Galactic rotation curves are often considered the first robust evidence for the existence of dark matter. However, even in the presence of a dark matter halo, other galactic-scale observations, such as the Baryonic Tully-Fisher Relation and the Radial Acceleration Relation, remain challenging to explain. This has motivated various models of dark matter as well as long-distance, infrared (IR) modifications to gravity as an alternative to the dark matter hypothesis. We present a framework to test a general class of such models using local Milky Way observables, including the vertical acceleration field, the rotation curve, the baryonic surface density, and the stellar disk profile. In this talk I will focus on models that predict scalar amplifications of gravity, i.e., models that increase the magnitude but do not change the direction of the gravitational acceleration. MOdified Newtonian Dynamics (MOND) as well as superfluid dark matter are examples. We find that models of this type are in tension with observations of the Milky Way scale radius and bulge mass and that cold non-interacting dark matter provides a better fit to the data. We conclude that models that result in a MOND-like force struggle to simultaneously explain both the rotational velocity and vertical motion of nearby stars in the Milky Way. A future publication will extend this analysis to include other models such as Strongly Interacting Dark Matter (SIDM).

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Workshop / Seminar Mon, 28 Jan 2019 09:02:39 -0500 2019-01-30T12:00:00-05:00 2019-01-30T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag | Hamiltonian Truncation and the S^3 Partition Function (February 6, 2019 12:00pm) https://events.umich.edu/event/60738 60738-14961638@events.umich.edu Event Begins: Wednesday, February 6, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

In this talk I discuss Hamiltonian truncation, a toolkit to construct quantum field theories. Hamiltonian truncation is in many ways orthogonal to the more familiar lattice regularization, and it can be used to systematically compute QFT observables with little computational effort. In the first part of this talk I will review the basic ideas behind this method, as well as some examples from the literature in d=2 and d>2 dimensions. In the second part I will discuss recent work involving strongly-coupled scalar theories on the three-dimensional sphere. Based on hep-th/1811.00528.

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Workshop / Seminar Mon, 04 Feb 2019 09:21:07 -0500 2019-02-06T12:00:00-05:00 2019-02-06T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag | Learning New Physics from a Machine (February 13, 2019 12:00pm) https://events.umich.edu/event/61034 61034-15024920@events.umich.edu Event Begins: Wednesday, February 13, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

I will discuss how to use neural networks to detect data departures from a given reference model, with no prior bias on the nature of the new physics responsible for the discrepancy. The algorithm that I will describe returns a global p-value that quantifies the tension between the data and the reference model. It also allows to compare directly what the network has learned with the data, giving a fully transparent account of the nature of possible signals. The potential applications are broad, from LHC physics searches to cosmology and beyond.

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Workshop / Seminar Mon, 11 Feb 2019 08:28:05 -0500 2019-02-13T12:00:00-05:00 2019-02-13T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
Learning New Physics from a Machine (February 13, 2019 12:00pm) https://events.umich.edu/event/61022 61022-15018179@events.umich.edu Event Begins: Wednesday, February 13, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

I will discuss how to use neural networks to detect data departures from a given reference model, with no prior bias on the nature of the new physics responsible for the discrepancy. The algorithm that I will describe returns a global p-value that quantifies the tension between the data and the reference model. It also allows to compare directly what the network has learned with the data, giving a fully transparent account of the nature of possible signals. The potential applications are broad, from LHC physics searches to cosmology and beyond.

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Lecture / Discussion Sun, 10 Feb 2019 13:46:20 -0500 2019-02-13T12:00:00-05:00 2019-02-13T13:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
energy condition, modular flow, and AdS/CFT (February 20, 2019 12:00pm) https://events.umich.edu/event/62591 62591-15407992@events.umich.edu Event Begins: Wednesday, February 20, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

In recent years, substantial progresses has been made in understanding and proving a number of energy conditions in quantum field theories (QFTs), which played very important roles for constraining quantum corrections to black hole dynamics in general relativity. In this talk, I will discuss proof of the quantum null energy condition (QNEC), both in holographic CFTs based on AdS/CFT, and in generic CFTs using techniques related to the entanglement structure. Furthermore, I will discuss the connection between the two approaches, and in doing this, deep relations between boundary modular flow and bulk RT surface dynamics will be revealed.

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Lecture / Discussion Tue, 26 Mar 2019 14:50:56 -0400 2019-02-20T12:00:00-05:00 2019-02-20T13:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag | Energy Condition, Modular Flow, and AdS/CFT (February 20, 2019 12:00pm) https://events.umich.edu/event/61328 61328-15088049@events.umich.edu Event Begins: Wednesday, February 20, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

In recent years, substantial progresses has been made in understanding and proving a number of energy conditions in quantum field theories (QFTs), which played very important roles for constraining quantum corrections to black hole dynamics in general relativity. In this talk, I will discuss proof of the quantum null energy condition (QNEC), both in holographic CFTs based on AdS/CFT, and in generic CFTs using techniques related to the entanglement structure. Furthermore, I will discuss the connection between the two approaches, and in doing this, deep relations between boundary modular flow and bulk RT surface dynamics will be revealed.

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Workshop / Seminar Mon, 18 Feb 2019 08:39:43 -0500 2019-02-20T12:00:00-05:00 2019-02-20T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag | Searching for Flavour Symmetries: Old Data New Tricks (February 27, 2019 12:00pm) https://events.umich.edu/event/61584 61584-15150258@events.umich.edu Event Begins: Wednesday, February 27, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

The observed pattern of mixing in the neutrino sector may be explained by the presence of a non-Abelian, discrete flavour symmetry broken into residual subgroups at low energies. These flavour models require the presence of Standard Model singlet scalars, namely flavons, which decay to charged leptons in a flavour-conserving or violating manner. In this talk, I will present the constraints on the model parameters of an A4 leptonic flavour model using a synergy of g-2, charged lepton flavour conversion and collider data. The most powerful constraints derive from the MEG collaboration's result and the reinterpretation of an 8 TeV ATLAS search for anomalous productions of multi-leptonic final states.

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Workshop / Seminar Mon, 25 Feb 2019 08:40:12 -0500 2019-02-27T12:00:00-05:00 2019-02-27T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
Searching for flavour symmetries: old data new tricks (February 27, 2019 12:00pm) https://events.umich.edu/event/61025 61025-15018181@events.umich.edu Event Begins: Wednesday, February 27, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

The observed pattern of mixing in the neutrino sector may be explained by the presence of a non-Abelian, discrete flavour symmetry broken into residual subgroups at low energies. These flavour models require the presence of Standard Model singlet scalars, namely flavons, which decay to charged leptons in a flavour-conserving or violating manner. In this talk, I will present the constraints on the model parameters of an A4 leptonic flavour model using a synergy of g-2, charged lepton flavour conversion and collider data. The most powerful constraints derive from the MEG collaboration's result and the reinterpretation of an 8 TeV ATLAS search for anomalous productions of multi-leptonic final states.

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Lecture / Discussion Tue, 26 Mar 2019 14:31:29 -0400 2019-02-27T12:00:00-05:00 2019-02-27T13:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag | Inflation and Supersymmetry Breaking in an M-theory Framework (March 12, 2019 12:00pm) https://events.umich.edu/event/62006 62006-15273938@events.umich.edu Event Begins: Tuesday, March 12, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

**Please note this talk will be on Tuesday at noon in 3481 Randall**

Compactifying M-theory on a manifold of G2 holonomy gives a UV complete 4D theory. It is supersymmetric, with soft supersymmetry breaking via gaugino condensation that simultaneously stabilizes all moduli and generates a hierarchy between the Planck and the Fermi scale. It has gauge matter, chiral fermions, and several other important features of our world, including a De Sitter vacuum. Here we show that the theory also contains a successful inflaton, which is essentially the overall volume modulus of the compactified manifold. We will discuss the cosmological and experimental implications of this theory.

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Workshop / Seminar Mon, 11 Mar 2019 08:48:46 -0400 2019-03-12T12:00:00-04:00 2019-03-12T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
Asymptotic Symmetries and the Soft Photon Theorem in Arbitrary Dimensions (March 13, 2019 12:00pm) https://events.umich.edu/event/62033 62033-15276114@events.umich.edu Event Begins: Wednesday, March 13, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

We show that Weinberg's leading soft photon theorem in massless quantum electrodynamics (QED) implies the existence of an infinite-dimensional large gauge symmetry, which acts non-trivially on the null boundaries of (d+2)-dimensional Minkowski spacetime. These symmetries are parameterized by an arbitrary function of the d-dimensional celestial sphere living at null infinity. This extends the equivalence between Weinberg’s leading soft photon theorem and the large gauge symmetries of QED from even dimensions higher or equal to four to all dimensions.

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Lecture / Discussion Tue, 26 Mar 2019 14:17:11 -0400 2019-03-13T12:00:00-04:00 2019-03-13T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag | Asymptotic Symmetries and the Soft Photon Theorem in Arbitrary Dimensions (March 13, 2019 12:00pm) https://events.umich.edu/event/62007 62007-15273940@events.umich.edu Event Begins: Wednesday, March 13, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

We show that Weinberg's leading soft photon theorem in massless quantum electrodynamics (QED) implies the existence of an infinite-dimensional large gauge symmetry, which acts non-trivially on the null boundaries of (d+2)-dimensional Minkowski spacetime. These symmetries are parameterized by an arbitrary function of the d-dimensional celestial sphere living at null infinity. This extends the equivalence between Weinberg’s leading soft photon theorem and the large gauge symmetries of QED from even dimensions higher or equal to four to all dimensions.

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Workshop / Seminar Mon, 11 Mar 2019 08:53:25 -0400 2019-03-13T12:00:00-04:00 2019-03-13T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag | Pulsar Timing as a Probe of Primordial Black Holes and Subhalos (March 20, 2019 12:00pm) https://events.umich.edu/event/62229 62229-15335273@events.umich.edu Event Begins: Wednesday, March 20, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Pulsars act as accurate clocks, sensitive to gravitational redshift and acceleration induced by transiting clumps of matter. In this talk, I study the sensitivity of pulsar timing arrays (PTA) to transiting compact dark matter objects, focusing on primordial black holes and subhalos. Such dark matter clumps can result in different classes of signals observable in pulsar timing experiments depending on the mass of the object. I will classify the types of signals, where they are most important, and the different search strategies resulting in possible constraints over a huge mass range, 10^−12 to 100 solar masses. Crucially, PTAs offer the opportunity to probe much less dense objects than lensing experiments due to the large effective radius over which such objects can be observed with a single pulsar. We project the reach possible with current and future pulsar timing experiments, with sensitivity to a dark matter sub-component reaching the sub-percent level over significant parts of this range with future detectors.

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Workshop / Seminar Mon, 18 Mar 2019 08:58:44 -0400 2019-03-20T12:00:00-04:00 2019-03-20T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
Pulsar timing as a probe of primordial black holes and subhalos (March 20, 2019 12:00pm) https://events.umich.edu/event/62490 62490-15372957@events.umich.edu Event Begins: Wednesday, March 20, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Pulsars act as accurate clocks, sensitive to gravitational redshift and acceleration induced by transiting clumps of matter. In this talk, I study the sensitivity of pulsar timing arrays (PTA) to transiting compact dark matter objects, focusing on primordial black holes and subhalos. Such dark matter clumps can result in different classes of signals observable in pulsar timing experiments depending on the mass of the object. I will classify the types of signals, where they are most important, and the different search strategies resulting in possible constraints over a huge mass range, 10^−12 to 100 solar masses. Crucially, PTAs offer the opportunity to probe much less dense objects than lensing experiments due to the large effective radius over which such objects can be observed with a single pulsar. We project the reach possible with current and future pulsar timing experiments, with sensitivity to a dark matter sub-component reaching the sub-percent level over significant parts of this range with future detectors.

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Lecture / Discussion Tue, 26 Mar 2019 14:25:21 -0400 2019-03-20T12:00:00-04:00 2019-03-20T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Dissertation Defense: Debiased post selection inference (March 25, 2019 10:00am) https://events.umich.edu/event/62360 62360-15355259@events.umich.edu Event Begins: Monday, March 25, 2019 10:00am
Location: Randall Laboratory
Organized By: Department of Statistics

This dissertation concerns the post-selection bias issue in statistical inference on treatment effects when a large number of covariates are present in a linear or partially linear model. While the estimation bias in an under-fitted model is well understood, we address a lesser known bias that arises from an over-fitted model. We show that the over-fitting bias can be reduced or eliminated through data splitting, and more importantly, smoothing over random data splits or bootstrap-induced splits can be pursued to mitigate the efficiency loss. We also discuss some of the existing methods for debiased inference and provide insights into their intrinsic bias-variance trade-off, which leads to an improvement in bias controls. Based on these insights, we thoroughly study the connections between our current framework and average treatment effects estimation under the Neyman-Rubin causal model. A careful analysis shows that the post-selection bias issue can exist in a wider range of treatment effect estimation procedures. Under appropriate conditions, we show that our proposed estimators for the treatment effects are asymptotically normal and their variances can be well estimated. We discuss the pros and cons of various methods both theoretically and empirically, and show that the proposed methods are valuable options in post-selection inference.

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Other Tue, 16 Jul 2019 14:26:31 -0400 2019-03-25T10:00:00-04:00 2019-03-25T12:00:00-04:00 Randall Laboratory Department of Statistics Other flyer
HET Brown Bag | Sphere Packing and Quantum Gravity (March 27, 2019 12:00pm) https://events.umich.edu/event/62522 62522-15397099@events.umich.edu Event Begins: Wednesday, March 27, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

The sphere packing problem asks to find the densest possible packing of identical spheres in d dimensions. The problem was recently solved analytically in 8 and 24 dimensions by Viazovska et al., building on linear programming bounds of Cohn+Elkies. I will show that there is a close connection between these results on sphere packing and the modular bootstrap in two-dimensional conformal field theories. In particular, I will explain that Viazovska's solution was essentially rediscovered in the conformal bootstrap literature in the guise of "analytic extremal functionals". It corresponds to saturation of the modular bootstrap bounds by known 2D CFTs. Sphere packing in a large number of dimensions maps to the modular bootstrap at large central charge, which can be used to constrain quantum gravity in large AdS_3. I will use the new analytic techniques to improve significantly on the best asymptotic upper bound on the mass of the lightest state in such theories.

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Workshop / Seminar Mon, 25 Mar 2019 08:55:03 -0400 2019-03-27T12:00:00-04:00 2019-03-27T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
Sphere packing and quantum gravity (March 27, 2019 12:00pm) https://events.umich.edu/event/62491 62491-15372958@events.umich.edu Event Begins: Wednesday, March 27, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

The sphere packing problem asks to find the densest possible packing of identical spheres in d dimensions. The problem was recently solved analytically in 8 and 24 dimensions by Viazovska et al., building on linear programming bounds of Cohn+Elkies. I will show that there is a close connection between these results on sphere packing and the modular bootstrap in two-dimensional conformal field theories. In particular, I will explain that Viazovska's solution was essentially rediscovered in the conformal bootstrap literature in the guise of "analytic extremal functionals". It corresponds to saturation of the modular bootstrap bounds by known 2D CFTs. Sphere packing in a large number of dimensions maps to the modular bootstrap at large central charge, which can be used to constrain quantum gravity in large AdS_3. I will use the new analytic techniques to improve significantly on the best asymptotic upper bound on the mass of the lightest state in such theories.

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Lecture / Discussion Fri, 22 Mar 2019 14:18:48 -0400 2019-03-27T12:00:00-04:00 2019-03-27T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Seminars | Cosmic Censorship Violation and Black Hole Collisions in Higher Dimensions (April 5, 2019 12:00pm) https://events.umich.edu/event/62737 62737-15457904@events.umich.edu Event Begins: Friday, April 5, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Seminars

The cosmic censorship conjecture raises the question of whether classical gravitational dynamics can drive a low-energy configuration into an accessible regime of quantum gravity, with Planck-scale curvatures and energy densities visible by distant observers. I will present evidence that cosmic censorship is violated in the quintessential phenomenon of General Relativity: the collision and merger of two black holes. It only requires a sufficient total angular momentum in a collision in high enough number of dimensions.
Nevertheless, I will argue that even if cosmic censorship is violated in this and in some other know instances, its spirit remains unchallenged: classical relativity describes the physics seen by observers outside the black holes accurately, with only minimal quantum input that does not entail macroscopic disruptions.

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Workshop / Seminar Mon, 01 Apr 2019 09:01:59 -0400 2019-04-05T12:00:00-04:00 2019-04-05T13:00:00-04:00 Randall Laboratory HET Seminars Workshop / Seminar Randall Laboratory
Gravity amplitudes from the ultraviolet (April 10, 2019 12:00pm) https://events.umich.edu/event/62639 62639-15416698@events.umich.edu Event Begins: Wednesday, April 10, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Scattering amplitudes in planar N=4 super Yang-Mills can be described in terms a geometrical object, the Amplituhedron. Special properties of loop integrands seem to indicate that this picture persists beyond the planar limit. My talk will describe a first step, and several challenges, in finding similar structures in gravity amplitudes.
I will explain how their ultraviolet behaviour, usually considered problematic, might hold the key to this problem

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Lecture / Discussion Wed, 27 Mar 2019 13:06:53 -0400 2019-04-10T12:00:00-04:00 2019-04-10T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag | Gravity Amplitudes from the Ultraviolet (April 10, 2019 12:00pm) https://events.umich.edu/event/62928 62928-15517952@events.umich.edu Event Begins: Wednesday, April 10, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Scattering amplitudes in planar N=4 super Yang-Mills can be described in terms a geometrical object, the Amplituhedron. Special properties of loop integrands seem to indicate that this picture persists beyond the planar limit. My talk will describe a first step, and several challenges, in finding similar structures in gravity amplitudes.
I will explain how their ultraviolet behaviour, usually considered problematic, might hold the key to this problem.

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Workshop / Seminar Mon, 08 Apr 2019 09:36:01 -0400 2019-04-10T12:00:00-04:00 2019-04-10T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag | Relic Neutrino Decoupling in Standard and Non-Standard Scenarios (April 17, 2019 12:00pm) https://events.umich.edu/event/63101 63101-15576709@events.umich.edu Event Begins: Wednesday, April 17, 2019 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

When the Universe was from about 1 second to 1 minute old, many interesting processes took place. On the one hand, weak interactions became inefficient and relic neutrinos decoupled from the cosmic plasma. And, at the far end, Big Bang Nucleosynthesis kicked off and the first light nuclei were formed. In between, electrons and positrons annihilated into photons, effectively reheating them with respect to the already decoupled neutrinos. The outcome of all these processes can affect the evolution of the Universe from that time until what we know today. In this talk I will focus on the decoupling process of relic neutrinos, starting with the standard scenario in which we properly accounted for flavour oscillations. Then I will explain how the effective number of relativistic species, also known as effective number of neutrinos (Neff) is modified assuming some non-standard scenarios. In this way, comparing the standard value of Neff with present and future observations we can get some insight about physics beyond the Standard Model, from the presence of non-standard interactions in the neutrino sector to the possibility of having an extra (sterile) neutrino species.

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Workshop / Seminar Mon, 15 Apr 2019 08:51:00 -0400 2019-04-17T12:00:00-04:00 2019-04-17T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
Special HEP-Astro Seminar | Recent developments in neutrino cosmology (April 18, 2019 12:00pm) https://events.umich.edu/event/62978 62978-15528489@events.umich.edu Event Begins: Thursday, April 18, 2019 12:00pm
Location: Randall Laboratory
Organized By: Department of Physics

A robust detection of neutrino masses is avowedly among the key goals of several upcoming Cosmic Microwave Background (CMB) and Large-Scale Structure (LSS) surveys. In this talk, I will describe recent progress in neutrino cosmology on three fronts. Firstly, I will illustrate the wealth of information on the sum of the neutrino masses obtainable from current cosmological probes, focusing on LSS data. Current upper limits begin favoring the normal neutrino mass ordering, emphasizing the need to develop statistical tools for quantifying this preference. Next, I will discuss galaxy bias as a limitation towards fully capitalizing on neutrino information hidden in LSS data, proposing a method for calibrating the scale-dependent galaxy bias using CMB lensing-galaxy cross-correlations. Moreover, in massive neutrino cosmologies the bias as usually defined is scale-dependent even on large scales: neglecting this effect will lead to incorrectly inferred parameters. Finally, I will take on a different angle and discuss degeneracies between neutrinos and other cosmological parameters. I will show how in certain physically motivated dynamical dark energy models the neutrino mass upper limits tighten instead of broadening, discussing implications for future laboratory determinations of the mass ordering. I will also discuss how neutrino unknowns affect constraints on inflationary models.

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Workshop / Seminar Thu, 18 Apr 2019 18:15:39 -0400 2019-04-18T12:00:00-04:00 2019-04-18T13:00:00-04:00 Randall Laboratory Department of Physics Workshop / Seminar Randall Laboratory
HET Brown Bag | Finding String Theory from the Large N Bootstrap (April 24, 2019 12:00pm) https://events.umich.edu/event/76370 76370-19711135@events.umich.edu Event Begins: Wednesday, April 24, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

I will discuss some recent methods for computing nonplanar CFT correlators, dual to one-loop amplitudes in AdS. This will include two applications to string theory: first, the development of a novel approach to computing perturbative string amplitudes; and second, a rigorous way to count the number of "large'' extra dimensions in the gravity dual of a strongly coupled, large N CFT.

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Lecture / Discussion Mon, 31 Aug 2020 12:13:04 -0400 2019-04-24T12:00:00-04:00 2019-04-24T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Special HEP-Astro Seminar | The quest for the Axion (April 25, 2019 12:00pm) https://events.umich.edu/event/63185 63185-15587259@events.umich.edu Event Begins: Thursday, April 25, 2019 12:00pm
Location: Randall Laboratory
Organized By: Department of Physics

Axions and axion-like particles are excellent dark matter candidates, spanning a vast range of mass scales from the milli- and micro-eV for the QCD axion, to 1E-22 eV for ultralight axions in string theory. In some scenarios, inhomogeneities in the axion density lead to the formation of compact structures known as axion “miniclusters” and axion stars. I will first discuss astrophysical and cosmological constraints on axions at either end of this spectrum, using data from the cosmic microwave background anisotropies and the effects of miniclusters on the gravitational microlensing and on direct detection. I will then assess the formation and the evolution of axion stars in various astrophysical regimes.

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Workshop / Seminar Thu, 25 Apr 2019 18:15:24 -0400 2019-04-25T12:00:00-04:00 2019-04-25T13:00:00-04:00 Randall Laboratory Department of Physics Workshop / Seminar Randall Laboratory
HET Brown Bag Seminar | Finding String Theory from the Large N Bootstrap (May 1, 2019 12:00pm) https://events.umich.edu/event/63423 63423-15692041@events.umich.edu Event Begins: Wednesday, May 1, 2019 12:00pm
Location: Randall Laboratory
Organized By: Department of Physics

Professor Perlmutter will discuss some recent methods for computing nonplanar CFT correlators, dual to one-loop amplitudes in AdS. This will include two applications to string theory: first, the development of a novel approach to computing perturbative string amplitudes; and second, a rigorous way to count the number of "large'' extra dimensions in the gravity dual of a strongly coupled, large N CFT.

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Workshop / Seminar Mon, 29 Apr 2019 10:38:34 -0400 2019-05-01T12:00:00-04:00 2019-05-01T13:00:00-04:00 Randall Laboratory Department of Physics Workshop / Seminar Randall Laboratory
Special CM Theory Seminar | Study of the Dirac material candidates in high magnetic fields (May 9, 2019 4:00pm) https://events.umich.edu/event/63456 63456-15710550@events.umich.edu Event Begins: Thursday, May 9, 2019 4:00pm
Location: Randall Laboratory
Organized By: Department of Physics

In this talk, I will focus on two series of Dirac candidates, (V,Nb,Ta)Al3 and CeSb(Se,Te). VAl_3 families are predicted as the type II Dirac semimetals where the Dirac bands are strongly tilted; therefore violate Lorentz-symmetry and have no analogue in high energy physics. CeSbTe were reported with multi Dirac/Weyl bands which can be tuned by magnetic fields.

By measuring de Hass-van Alphen effect using torque magnetomery in VAl_3 families. It revealed the existence of tilted Dirac cones with Dirac type-II nodes located at 100, 230 and 250 meV away from the Fermi level of VAl_3, NbAl_3, and TaAl_3, respectively. These results are consistent with earlier band structure calculations, which also predict a non-trivial electronic topology. However, for all three compounds we find that the cyclotron orbits on the Fermi surfaces, including an orbit nearly enclosing the Dirac type-II node, yield trivial Berry phases. We will show that in order to determine the Berry phases, the overall understanding of the topology of the Fermi surfaces and the g-factors are required.

CeSbSe shows magnetization plateaus between the antiferromagnetic states (M = 0) and the magnetization saturated states M_{sat}. The fractional plateau values of M/M_{sat} are equal to 1/6, 1/3, 5/12, 1/2, and 3/4. I will discuss a possible explanation between the magnetization plateaus and the magnetic structures of CeSbSe from the single crystal neutron diffraction data.

References:

[1] K.-W. Chen (1,2), X. Lian (1,2), Y. Lai (1,2), N. Aryal (1,2), Y.-C. Chiu (1,2), W. Lan (1,2), D. Graf (1), E. Manousakis (1,2), R. E. Baumbach (1,2), and L. Balicas (1,2), Phys. Rev. Lett. 120, 206401(2018).

[2] K.-W. Chen (1,2), Y. Lai (1,2), Y.-C. Chiu (1,2), S. Steven (3), T. Besara (1), D. Graf (1), T. Siegrist (1,4), T. E. Albrecht-Schmitt (3), L. Balicas (1,2), and R. E. Baumbach (1,2), Phys. Rev. B 96, 014421 (2017).


1 National High Magnetic Field Laboratory, Florida State University, Florida, USA
2 Department of Physics, Florida State University, Florida, USA
3 Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA
4 Department of Chemical and Biomedical Engineering, FAMU-FSU College of Engineering, Tallahassee, Florida 32310, USA


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Workshop / Seminar Thu, 09 May 2019 18:15:18 -0400 2019-05-09T16:00:00-04:00 2019-05-09T17:00:00-04:00 Randall Laboratory Department of Physics Workshop / Seminar Randall Laboratory
Special HET Seminar | UV Cancellations in Gravity Loop Integrands (May 13, 2019 3:00pm) https://events.umich.edu/event/63571 63571-15784206@events.umich.edu Event Begins: Monday, May 13, 2019 3:00pm
Location: Randall Laboratory
Organized By: HET Seminars

TBD

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Workshop / Seminar Fri, 10 May 2019 16:01:54 -0400 2019-05-13T15:00:00-04:00 2019-05-13T16:00:00-04:00 Randall Laboratory HET Seminars Workshop / Seminar Randall Laboratory
Special Cosmology Seminar | Galaxy Cluster Scaling Relations with the Magneticum Simulation (August 19, 2019 3:00pm) https://events.umich.edu/event/65271 65271-16563482@events.umich.edu Event Begins: Monday, August 19, 2019 3:00pm
Location: Randall Laboratory
Organized By: HEP - Astro Seminars

Galaxy clusters are one of the most powerful cosmological tool. Their abundance as a function of cluster mass is sensitive to both the expansion history and the history of structure formation in the Universe. Various cluster observables such as X-ray luminosity, temperature and Sunyaev- Zel’dovich (SZ) effect have been shown to scale with cluster mass, therefore, can be used as a proxy of total cluster mass.

We use Magneticum simulation setup to explore the cosmology dependence of galaxy cluster scaling relations which otherwise cannot be tested by observations. We run the same simulation set-up in fifteen different cosmological environments. Our simple, cosmology dependent mass-observable scaling relation parametrisation can be used to forecast the degeneracies between the amplitude of the scaling relation and the cosmological parameters as well as to explore the combination of potential probes to break these degeneracies.

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Workshop / Seminar Thu, 15 Aug 2019 14:03:00 -0400 2019-08-19T15:00:00-04:00 2019-08-19T16:00:00-04:00 Randall Laboratory HEP - Astro Seminars Workshop / Seminar Randall Laboratory
HET Brown Bag | Light thermal relic Dark Matter (September 11, 2019 12:00pm) https://events.umich.edu/event/66174 66174-16717506@events.umich.edu Event Begins: Wednesday, September 11, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

The leading candidate for dark matter that is thermally produced in the early Universe is the Weakly Interacting Massive Particle (WIMP). However, increasingly stringent bounds on WIMPs are now motivating the exploration of viable alternatives. One interesting possibility are DM candidates with sub-GeV masses. In this talk, I will present two such examples. First, I will focus on models where the dark matter abundance is set by mutual annihilations among multiple species. I will show how sizable mass splittings between the dark matter states naturally point to masses exponentially lighter than the weak scale. Light dark matter from coannihilation evades stringent bounds from the cosmic microwave background, but will be tested by future direct detection, fixed target, and long-lived particle experiments. Second, I will illustrate another viable thermal dark matter candidate with sub-GeV masses which has been overlooked in the literature: a cosmologically stable dark Higgs.

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Lecture / Discussion Wed, 18 Sep 2019 11:26:47 -0400 2019-09-11T12:00:00-04:00 2019-09-11T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminars | Wilson line dressings as carriers of asymptotic symmetry charges (September 18, 2019 12:00pm) https://events.umich.edu/event/67044 67044-16796475@events.umich.edu Event Begins: Wednesday, September 18, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

It is known that for a gauge-invariant formulation of QED and gravity, one should dress particles with Wilson lines stretching out to infinity. When considering asymptotic particles of scattering processes, such dressed particle states reduce to the infrared-finite states of Faddeev and Kulish. In quantum field theories in flat spacetime, the dressings of asymptotic states are known to carry a definite leading soft charge of the asymptotic symmetry, which can be interpreted as soft hair at infinity. Some recent attempts to extend this to subleading order will be briefly mentioned. We explore how this analysis can be extended to curved spacetimes with boundary, in particular, the Rindler and Schwarzschild spacetimes. More specifically, we will show that infalling dressed matter on the future Rindler and Schwarzschild horizons implant soft horizon hair.

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Lecture / Discussion Thu, 12 Sep 2019 15:28:20 -0400 2019-09-18T12:00:00-04:00 2019-09-18T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminars | Improving Numerical Integration and Event Generation with Normalizing Flows (September 25, 2019 12:00pm) https://events.umich.edu/event/67322 67322-16837722@events.umich.edu Event Begins: Wednesday, September 25, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

With the upcoming HL-LHC, the budget for computing will be insufficient to generate a sufficient amount of Monte-Carlo events for both signal and background predictions. The driving force behind these costs is the inefficiency of the Monte-Carlo phase space generators and the unweighting efficiencies.
After a short review of traditional algorithms, I will introduce a new Machine Learning algorithm that uses Normalizing Flows for efficient numerical integration and random sampling. This approach is especially efficient in high-dimensional integration spaces. I will show some preliminary results obtained with the matrix element generator of Sherpa and discuss different choices of hyperparameters and their influence on the result.

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Lecture / Discussion Wed, 25 Sep 2019 14:36:53 -0400 2019-09-25T12:00:00-04:00 2019-09-25T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminars | Massive Gravitons in Curved Spacetimes (October 2, 2019 12:00pm) https://events.umich.edu/event/67618 67618-16907162@events.umich.edu Event Begins: Wednesday, October 2, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

This talk will cover various interesting topics that occur in massive spin-2 on various spacetimes including de Sitter, anti-de Sitter, and flat space. In de Sitter, we examine what happens to massive gravity as its mass approaches the partially massless value. In this limit, if the interactions are chosen to be precisely those of the 'candidate' non-linear partially massless theory, the strong coupling scale is raised, giving the theory a wider range of applicability. In anti-de Sitter and flat spacetime, we show how shift symmetries acting on the vector modes emerge from massive spin-2 theories fixing the non-linear structure and discuss whether these theories have amplitudes that can be constructed via soft substracted recursion.

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Lecture / Discussion Thu, 03 Oct 2019 10:57:15 -0400 2019-10-02T12:00:00-04:00 2019-10-02T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminars | Dark matter - phonon scattering (October 9, 2019 12:00pm) https://events.umich.edu/event/67843 67843-16960472@events.umich.edu Event Begins: Wednesday, October 9, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Upcoming sensor technology allows for dark matter direct detection all the way down to the warm dark matter limit of ~ 10 keV. At such low masses, the usual nuclear recoil picture breaks down, as the dark matter recoils against individual athermal phonon modes instead. I will show how the rate for these processes can be calculated and why superfluid helium and polar materials are good targets for this type of dark matter. In the latter case the crystal axis can provide a daily modulation of the scattering rate.

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Lecture / Discussion Thu, 10 Oct 2019 09:39:21 -0400 2019-10-09T12:00:00-04:00 2019-10-09T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Euclidean Black Saddles and AdS4 Black Holes (October 16, 2019 12:00pm) https://events.umich.edu/event/68134 68134-17011973@events.umich.edu Event Begins: Wednesday, October 16, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

The entropy of a class of asymptotically-AdS4 black holes can be reproduced by the partition function of the dual ABJM theory via localization. However, establishing this match requires a particular extremization over field theory parameters. This begs the question: what are the bulk dual geometries when we do not extremize in the field theory? In this talk, I will show that these bulk duals are smooth Euclidean geometries with finitely-capped throats. These geometries generically have no clear interpretation in Lorentzian signature, but when their throat becomes infinitely long they become black holes with an AdS2 near-horizon geometry. For any set of field theory parameters whose extremization is compatible with a black hole, we find a large family of Euclidean geometries whose on-shell action reproduces the ABJM partition function exactly, without the need to extremize,thus establishing a more complete understanding of AdS4/CFT3 holography.

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Lecture / Discussion Mon, 07 Oct 2019 14:32:27 -0400 2019-10-16T12:00:00-04:00 2019-10-16T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminars | Fine probes of quantum chaos (October 23, 2019 12:00pm) https://events.umich.edu/event/68274 68274-17037498@events.umich.edu Event Begins: Wednesday, October 23, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Quantum chaotic dynamics manifests itself in transport, thermalization, and the butterfly effect. Hydrodynamics is the universal effective description of transport in the long distance, late time regime. We can gain insight into the process of thermalization from the time evolution of entanglement entropy, for which I introduce an effective theory valid in the hydrodynamic regime. I derive this theory in the special case of holographic gauge theories, and present strong evidence for its validity in any chaotic system. I discuss the interplay between this effective theory and chaotic operator growth that is responsible for the butterfly effect, and present new general results on the Lyapunov exponent characterizing this phenomenon. I conclude with some exciting implications for quantum gravity through gauge/gravity duality.

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Lecture / Discussion Wed, 23 Oct 2019 14:57:03 -0400 2019-10-23T12:00:00-04:00 2019-10-23T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminars | Looking for Axion Dark Matter: from Dwarf Galaxies to Pulsars (October 30, 2019 12:00pm) https://events.umich.edu/event/67394 67394-16846510@events.umich.edu Event Begins: Wednesday, October 30, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Axion and Axion-like particles are fascinating dark matter candidates and a great effort has been devoted to their study, both theoretically and experimentally. In this talk I will discuss two different astrophysical searches. One consists in looking with radio telescopes for the spontaneous decay of axion dark matter using different targets as Dwarf Galaxies, Clusters or the Galactic Center. The second one uses the parity violating axion interactions to exploit the extreme precision of pulsar timing measurements and look for oscillations in the polarization angle of the pulsar signal.

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Lecture / Discussion Wed, 18 Sep 2019 11:51:02 -0400 2019-10-30T12:00:00-04:00 2019-10-30T13:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminars | Extremal Black Holes and EFTs (November 6, 2019 12:00pm) https://events.umich.edu/event/68797 68797-17153400@events.umich.edu Event Begins: Wednesday, November 6, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Higher-dimension operators in the action modify the extremality condition for black holes. In this talk, I will explore implications for these extremality corrections as a consequence of bounds on Wilson coefficients coming from scattering amplitudes. I will discuss connections to the Weak Gravity Conjecture and generalizations to dyonic, spinning, and BTZ black holes, as well as bounds on Wilson coefficients coming from consistency of black hole entropy.

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Lecture / Discussion Thu, 07 Nov 2019 15:41:48 -0500 2019-11-06T12:00:00-05:00 2019-11-06T13:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag Seminars | "Fundamental Physics with Supernovae and Superconductors" (November 13, 2019 12:00pm) https://events.umich.edu/event/68809 68809-17155478@events.umich.edu Event Begins: Wednesday, November 13, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

In the first part of this talk I will describe how type 1a supernovae (SN) can be used to constrain the interactions of heavy dark matter (DM), which may heat a white dwarf (WD) sufficient to trigger runaway fusion and ignite a SN. Based on the existence of long-lived WDs and the observed supernovae rate, we constrain ultra-heavy DM candidates that produce high energy SM particles in a WD. This rules out supersymmetric Q-ball DM in parameter space complementary to terrestrial bounds. We also constrain DM which is captured by WDs and forms a self-gravitating DM core. Such a core may form a black hole that ignites a SN via Hawking radiation, or which causes ignition via a burst of annihilation during gravitational collapse. It is intriguing that these DM-induced ignition scenarios provide an alternative mechanism of triggering SN from sub-Chandrasekhar mass progenitors. In the second part of the talk, I will present a new technique which utilizes superconducting RF cavities to significantly improve the sensitivity of "light shinning through walls" searches for axion-like particles (ALPs). Our design uses a gapped toroid to confine the static magnetic field responsible for axion-photon conversion, and thereby prevent quenching of the superconducting cavities . Such a search has the potential to probe axion-photon couplings to g ~ 2 x 10^-11 GeV^-1, comparable to future optical and solar searches.

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Lecture / Discussion Thu, 14 Nov 2019 15:45:58 -0500 2019-11-13T12:00:00-05:00 2019-11-13T13:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Special Cosmology Seminar | Preheating on Curved Field-Space Manifolds (November 14, 2019 12:00pm) https://events.umich.edu/event/69271 69271-17277410@events.umich.edu Event Begins: Thursday, November 14, 2019 12:00pm
Location: Randall Laboratory
Organized By: Department Colloquia

I will discuss preheating in multi-field models of inflation with a curved field-space manifold. In the case of two-field generalizations of $\alpha$-attractor models with is a highly curved hyperbolic field-space manifold, analytical progress can be made for preheating using the WKB approximation and Floquet analysis. I will show the emergence of a simple scaling behavior of the Floquet exponents for large values of the field-space curvature, that enables a quick estimation of the reheating efficiency for any large value of the field-space curvature. In this regime one can observe and explain universal preheating features that arise for different values of the potential steepness. In general preheating is faster for larger negative values of the field-space curvature and steeper potentials. For very highly curved field-space manifolds preheating is essentially instantaneous.
In case of multi-field models with non-minimal couplings, where the field-space in the Einstein frame is highly curved near the origin, I will describe recent lattice simulations that have been used to capture significant nonlinear effects like backreaction and rescattering. I will show how we can we extract the effective equation of state and typical time-scales for the onset of thermalization, quantities that could affect the usual mapping between predictions for primordial perturbation spectra and measurements of anisotropies in the cosmic microwave background radiation. For large values of the nonminimal coupling constants, efficient particle production gives rise to nearly instantaneous preheating. Moreover, the strong single-field attractor behavior that was identified for these models in linearized analyses remains robust in the full theory, and in all cases considered the attractor persists until the end of preheating. Finally, I will discuss the implications for Higgs inflation.

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Workshop / Seminar Fri, 08 Nov 2019 15:43:27 -0500 2019-11-14T12:00:00-05:00 2019-11-14T13:00:00-05:00 Randall Laboratory Department Colloquia Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | A Mellin Space Approach to Scattering in de Sitter Space (November 20, 2019 12:00pm) https://events.umich.edu/event/69298 69298-17299783@events.umich.edu Event Begins: Wednesday, November 20, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

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. This makes application of our hard-earned wisdom from flat and AdS spaces far from straightforward. In this talk we explain how boundary correlators in AdS and dS can be placed on an equal footing by adopting a Mellin-Barnes representation in momentum space, providing a framework in which techniques and results available in AdS can be generalised to de Sitter. This connection allows us to systematically derive expressions for exchange diagrams in de Sitter involving fields with and without spin. Throughout we shall keep in mind applications to the classification of possible non-Gaussianities in cosmological correlation functions, of both scalar and tensor fluctuations.

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Lecture / Discussion Thu, 21 Nov 2019 10:10:00 -0500 2019-11-20T12:00:00-05:00 2019-11-20T13:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
Special Cosmology Seminar | The Robustness of Slow Contraction to Initial Conditions, and Other Perks of Bouncing (November 21, 2019 12:00pm) https://events.umich.edu/event/69531 69531-17357969@events.umich.edu Event Begins: Thursday, November 21, 2019 12:00pm
Location: Randall Laboratory
Organized By: Department Colloquia

In this talk, I will discuss how a slowly-contracting primordial epoch generically smooths and flattens the universe, using the full power of numerical general relativity. In addition, I will review recent progress on studying the generation of primordial perturbations as well as constructing smooth cosmological bounces.

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Workshop / Seminar Mon, 18 Nov 2019 08:32:10 -0500 2019-11-21T12:00:00-05:00 2019-11-21T13:00:00-05:00 Randall Laboratory Department Colloquia Workshop / Seminar Randall Laboratory
HET Brown Bag | The Inconsistency of Superfluid Dark Matter with Milky Way Dynamics (December 11, 2019 12:00pm) https://events.umich.edu/event/69885 69885-17482923@events.umich.edu Event Begins: Wednesday, December 11, 2019 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

There are many well-known correlations between dark matter and baryons that exist on galactic scales. These correlations can essentially be encompassed by a simple scaling relation between observed and baryonic accelerations, historically known as the Mass Discrepancy Acceleration Relation (MDAR). The existence of such a relation has prompted many theories that attempt to explain the correlations by invoking additional fundamental forces on baryons. The standard lore has been that a theory that reduces to the MDAR on galaxy scales but behaves like cold dark matter (CDM) on larger scales provides an excellent fit to data, since CDM is desirable on scales of clusters and above. However, this statement should be revised in light of recent results showing that a fundamental force that reproduces the MDAR is challenged by Milky Way dynamics. In this study, we test this claim on the example of Superfluid Dark Matter. We find that a standard CDM model is strongly preferred over a static superfluid profile. This is due to the fact that the superfluid model over-predicts vertical accelerations, even while reproducing galactic rotation curves. Our results establish an important criterion that any dark matter model must satisfy within the Milky Way.

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Lecture / Discussion Thu, 12 Dec 2019 09:56:29 -0500 2019-12-11T12:00:00-05:00 2019-12-11T13:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory
HET Brown Bag | Effective field theory near and far from equilibrium (January 15, 2020 12:00pm) https://events.umich.edu/event/71081 71081-17774965@events.umich.edu Event Begins: Wednesday, January 15, 2020 12:00pm
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

I will discuss effective field theories for two classes of non-equilibrium systems, one far and one near equilibrium. In the first part I will present an effective response theory for topological driven (Floquet) systems, which are inherently far from equilibrium. As an example, I will discuss a topological chiral Floquet drive coupled to a background $U(1)$ field, which gives rise to a theta term in the effective action. In the second part, I will discuss an ongoing project using effective field theories for hydrodynamics. I will show that chiral diffusion for interacting systems in 1+1 dimensions, which may be relevant to edge transport in quantum Hall systems, has an infrared instability. I will then discuss the fate of this instability.

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Lecture / Discussion Tue, 21 Jan 2020 15:25:14 -0500 2020-01-15T12:00:00-05:00 2020-01-15T13:00:00-05:00 Randall Laboratory Leinweber Center for Theoretical Physics Lecture / Discussion Randall Laboratory