Happening @ Michigan https://events.umich.edu/list/rss RSS Feed for Happening @ Michigan Events at the University of Michigan. HET Brown Bag Seminars | Statistical Mechanics of a Two-Dimensional Black Hole (September 12, 2018 12:00pm) https://events.umich.edu/event/54936 54936-13654180@events.umich.edu Event Begins: Wednesday, September 12, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

The dynamics of a nearly-AdS2 spacetime with boundaries can be reduced to that of two particles in the anti-de Sitter space. We determine the class of physically meaningful wavefunctions, and prescribe the statistical mechanics of a black hole. We demonstrate how wavefunctions for a two-sided black hole and a regularized notion of trace can be used to construct thermal partition functions, and more generally, arbitrary density matrices. We also obtain correlation functions of external operators. The talk is based on work with A. Kitaev in the preprint arXiv:1808.07032.

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Workshop / Seminar Thu, 06 Sep 2018 15:22:53 -0400 2018-09-12T12:00:00-04:00 2018-09-12T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminar | Cosmological Signatures of Sub-MeV Dark Matter Freeze-In (September 19, 2018 12:00pm) https://events.umich.edu/event/53968 53968-13504400@events.umich.edu Event Begins: Wednesday, September 19, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Dark matter could be a thermal relic of freeze-in, where the dark matter is produced by extremely feeble interactions with Standard Model particles dominantly at low temperatures. The simplest sub-MeV dark matter models with freeze-in include models with a kinetically-mixed dark photon mediator, or equivalently models where dark matter is millicharged under the Standard Model U(1). In this talk I will discuss how such models can impact and be constrained by cosmological observables, including the CMB, the Lyman-alpha forest, and the EDGES observation of the cosmological 21 cm global signal.

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Workshop / Seminar Mon, 17 Sep 2018 11:07:21 -0400 2018-09-19T12:00:00-04:00 2018-09-19T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminar | Soft Gravitons and Hawking Radiation (September 26, 2018 12:00pm) https://events.umich.edu/event/55886 55886-13802781@events.umich.edu Event Begins: Wednesday, September 26, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

We study the effect of the factorization of infrared dynamics on the process of particle creation near a black hole horizon. We show that the emission of soft particles factors out of the S-matrix in the fixed-background approximation and to leading order in the soft limit. The factorization is implemented by dressing the incoming and outgoing asymptotic states with clouds of soft photons and soft gravitons. We find that while the soft photon cloud has no effect, the soft graviton cloud induces a phase shift in the Bogolyubov coefficients relating the incoming and outgoing modes. However, the flux of outgoing particles, given by the absolute value of the Bogolyubov coefficient, is insensitive to this phase.

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Workshop / Seminar Mon, 24 Sep 2018 08:44:29 -0400 2018-09-26T12:00:00-04:00 2018-09-26T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
Special HEP-Astro Seminar | Cosmological Results from the Final Data Release of the Planck Satellite (September 27, 2018 12:00pm) https://events.umich.edu/event/55389 55389-13725242@events.umich.edu Event Begins: Thursday, September 27, 2018 12:00pm
Location: Randall Laboratory
Organized By: Department of Physics

Planck is an ESA satellite aimed at the observation of the Cosmic Microwave Background. This year, the Planck collaboration has released the final data and results from the mission. In this talk, I will describe the main results on cosmology from the mission, highlighting the changes with respect to previous releases, the agreement with other cosmological probes and the unsolved questions opened for the future.

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Workshop / Seminar Thu, 27 Sep 2018 18:17:29 -0400 2018-09-27T12:00:00-04:00 2018-09-27T13:00:00-04:00 Randall Laboratory Department of Physics Workshop / Seminar Randall Laboratory
HET Brown Bag Seminar | Detecting Dark Matter from Supernovae (October 3, 2018 12:00pm) https://events.umich.edu/event/56206 56206-13867054@events.umich.edu Event Begins: Wednesday, October 3, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

The central region of Supernovae are one of the hottest and densest regions in the Universe. Due to the high temperatures, particles with sub-GeV masses can be copiously produced if they have non-negligible couplings to the Standard Model. If dark matter has sub-GeV mass it will be produced in the hot Supernovae core and it will have sufficiently large momenta to be detectable in direct detection experiments. In this talk I discuss the sensitivity of current and future Xenon based direct detection experiments to a simplified model of dark matter which interacts with the Standard Model via the dark photon portal.

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Workshop / Seminar Mon, 01 Oct 2018 08:47:35 -0400 2018-10-03T12:00:00-04:00 2018-10-03T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminar | Lessons from the Landscape (October 10, 2018 12:00am) https://events.umich.edu/event/56486 56486-13930952@events.umich.edu Event Begins: Wednesday, October 10, 2018 12:00am
Location: Randall Laboratory
Organized By: HET Brown Bag Series

I will discuss how the string landscape might inform how we think about low energy effective field theories coupled to gravity. By studying the largest-to-date ensembles of geometries for string compactifications, we find several striking generic features: large hidden gauge sectors, regions of strong coupling, and large numbers of light axions. Understanding these ensembles, and the landscape as whole, requires a new set of tools, both formal and computational, including new mathematics and tools from data science, the development of which I will discuss.

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Workshop / Seminar Mon, 08 Oct 2018 08:39:12 -0400 2018-10-10T00:00:00-04:00 2018-10-10T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
Modeling Dark Energy Observations in the Nonlinear Regime (October 15, 2018 9:00am) https://events.umich.edu/event/64729 64729-16436924@events.umich.edu Event Begins: Monday, October 15, 2018 9:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Dragan Huterer (LCTP), Yuanyuan Zhang (Fermilab)

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Conference / Symposium Tue, 30 Jul 2019 14:31:56 -0400 2018-10-15T09:00:00-04:00 2018-10-15T17:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Conference / Symposium Randall Laboratory
Modeling Dark Energy Observations in the Nonlinear Regime (October 16, 2018 9:00am) https://events.umich.edu/event/64729 64729-16436930@events.umich.edu Event Begins: Tuesday, October 16, 2018 9:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Dragan Huterer (LCTP), Yuanyuan Zhang (Fermilab)

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Conference / Symposium Tue, 30 Jul 2019 14:31:56 -0400 2018-10-16T09:00:00-04:00 2018-10-16T17:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Conference / Symposium Randall Laboratory
Modeling Dark Energy Observations in the Nonlinear Regime (October 17, 2018 9:00am) https://events.umich.edu/event/64729 64729-16436931@events.umich.edu Event Begins: Wednesday, October 17, 2018 9:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Dragan Huterer (LCTP), Yuanyuan Zhang (Fermilab)

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Conference / Symposium Tue, 30 Jul 2019 14:31:56 -0400 2018-10-17T09:00:00-04:00 2018-10-17T17:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Conference / Symposium Randall Laboratory
Modeling Dark Energy Observations in the Nonlinear Regime (October 18, 2018 9:00am) https://events.umich.edu/event/64729 64729-16436932@events.umich.edu Event Begins: Thursday, October 18, 2018 9:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Dragan Huterer (LCTP), Yuanyuan Zhang (Fermilab)

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Conference / Symposium Tue, 30 Jul 2019 14:31:56 -0400 2018-10-18T09:00:00-04:00 2018-10-18T17:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Conference / Symposium Randall Laboratory
Modeling Dark Energy Observations in the Nonlinear Regime (October 19, 2018 9:00am) https://events.umich.edu/event/64729 64729-16436933@events.umich.edu Event Begins: Friday, October 19, 2018 9:00am
Location: Randall Laboratory
Organized By: Leinweber Center for Theoretical Physics

Dragan Huterer (LCTP), Yuanyuan Zhang (Fermilab)

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Conference / Symposium Tue, 30 Jul 2019 14:31:56 -0400 2018-10-19T09:00:00-04:00 2018-10-19T17:00:00-04:00 Randall Laboratory Leinweber Center for Theoretical Physics Conference / Symposium Randall Laboratory
HET Brown Bag Seminars | Neutrino-dark matter interactions (October 24, 2018 12:00pm) https://events.umich.edu/event/54071 54071-13521837@events.umich.edu Event Begins: Wednesday, October 24, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

I will describe scenarios where the dark matter couples to neutrinos. This possibility has important implications for structure formation. I will describe novel probes of this possibility at the LHC and intensity frontier facilities. Additionally, the possibility of detecting neutrinos from dark matter decays at future experiments looking for the cosmic neutrino background such as PTOLEMY will be discussed.

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Lecture / Discussion Mon, 22 Oct 2018 08:34:29 -0400 2018-10-24T12:00:00-04:00 2018-10-24T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Lecture / Discussion Randall Laboratory
HET Brown Bag Seminars | Dark Matter and Fusion: Signals and Constraints from the Dark and the Light (October 31, 2018 12:00pm) https://events.umich.edu/event/54073 54073-13521839@events.umich.edu Event Begins: Wednesday, October 31, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Over the past several years, non-WIMP dark matter candidates have attracted a surge of interest in the particle physics community. In this two-part talk, I will summarize the underlying physics motivation for (and observable consequences of) two such candidates, which share the feature that they are bound states of more familiar constituents. The first part of the talk will examine the astrophysical implications of a dark fermion that can form two-body bound states. The second part of the talk will examine new constraints on the "dibaryon", a hypothetical QCD bound state of six light quarks. The common thread of the talk will be the unique signals of fusion within or into a dark matter sector.

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Workshop / Seminar Mon, 29 Oct 2018 08:36:02 -0400 2018-10-31T12:00:00-04:00 2018-10-31T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | Holographic Entanglement and BMS blocks in three dimensional flat space (November 7, 2018 12:00pm) https://events.umich.edu/event/57371 57371-14182266@events.umich.edu Event Begins: Wednesday, November 7, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

I will discuss the holographic construction of entanglement entropy and blocks in three-dimensional flat space-times. I will present a prescription based on world-line methods in the probe limit, inspired by recent analog calculations in AdS/CFT. Building on this construction, a full extrapolate dictionary will be proposed, and used to compute holographic correlators and blocks away from the probe limit. Blocks involving heavy operators will be shown to involve probe particles propagating in flat space cosmologies.

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Workshop / Seminar Mon, 05 Nov 2018 08:31:32 -0500 2018-11-07T12:00:00-05:00 2018-11-07T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag | Higgs Parity, Strong CP Problem and Unification (November 14, 2018 12:00pm) https://events.umich.edu/event/57623 57623-14243985@events.umich.edu Event Begins: Wednesday, November 14, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

The quartic coupling of the Standard Model Higgs nearly vanishes at a high energy scale. We show that this is explained by the parity symmetry and its spontaneous break down by the condensation of the parity partner of the Higgs. The parity can solve the strong CP problem. The theory is embedded into SO(10) unification and the precise gauge coupling unification is achieved.

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Workshop / Seminar Mon, 12 Nov 2018 08:30:20 -0500 2018-11-14T12:00:00-05:00 2018-11-14T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag | M-theory and String Theory S-matrix From CFT (November 21, 2018 12:00pm) https://events.umich.edu/event/57765 57765-14303997@events.umich.edu Event Begins: Wednesday, November 21, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

SPECIAL SEMINAR

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Workshop / Seminar Mon, 19 Nov 2018 08:29:27 -0500 2018-11-21T12:00:00-05:00 2018-11-21T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag | Path Integrals, Finite Temperature, and Lattices (November 28, 2018 12:00pm) https://events.umich.edu/event/57851 57851-14363800@events.umich.edu Event Begins: Wednesday, November 28, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Surprisingly, partition functions for some model systems in statistical mechanics are invariant under formally reflecting the sign of temperature, T: +T -> -T. We call this T-reflection invariance. Clearly, partition functions for generic statistical systems cannot be invariant under T-reflection. However, in this talk we focus on finite-temperature path integrals and give a general picture for why finite-temperature path integrals in quantum field theory *should* behave well under T-reflection. We probe this general picture in the context of the harmonic oscillators (in one-dimension) and in conformal field theories on the two-torus (in two-dimensions) and in the mathematics of modular forms. We find that the relevant path integrals are often invariant only up to overall T-independent phases, which could be naturally interpreted as new anomalies under large coordinate transforms.

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Workshop / Seminar Mon, 26 Nov 2018 08:37:33 -0500 2018-11-28T12:00:00-05:00 2018-11-28T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag | Cosmology with Sub-MeV Thermal Relics (December 5, 2018 12:00pm) https://events.umich.edu/event/58101 58101-14424582@events.umich.edu Event Begins: Wednesday, December 5, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

The nature of dark matter (DM) is unknown, with a vast array of possibilities able to account for the missing mass of the universe. A predictive subset of DM models has DM in thermal equilibrium with Standard Model particles in the early universe. A well-known example of this is the Weakly-Interacting Massive Particle (WIMP) with an electroweak-scale mass. However, as direct searches for WIMP-nucleus interactions set stronger and stronger limits, attention has turned to less well-explored DM candidates. Sub-MeV thermal relics, in particular, have received little attention, in part due to the apparently stringent bounds from astrophysics and cosmology. For example, such particles contribute to the energy density of the universe at the time of nucleosynthesis and recombination. The resulting constraints on extra degrees of freedom typically exclude even the simplest of such dark sectors. I will describe the physics that leads to these bounds and show that if a sub-MeV dark sector entered equilibrium with the Standard Model after neutrino-photon decoupling, these constraints are alleviated. This scenario naturally arises in theories of neutrino mass generation through the spontaneous breaking of lepton number. Dark matter relic abundance in these models independently motivates the MeV scale. This scenario will be decisively tested by future measurements of the cosmic microwave background and large scale structure of the universe.

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Workshop / Seminar Mon, 03 Dec 2018 08:38:19 -0500 2018-12-05T12:00:00-05:00 2018-12-05T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
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