Happening @ Michigan https://events.umich.edu/list/rss RSS Feed for Happening @ Michigan Events at the University of Michigan. HET Brown Bag | Worldsheet CFTs for Microstate Geometries (September 20, 2017 12:00pm) https://events.umich.edu/event/44540 44540-9923133@events.umich.edu Event Begins: Wednesday, September 20, 2017 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

In string theory, black hole microstates at finite coupling give rise to horizon-scale structures that might solve the information paradox. Explicit constructions of these solutions are based on configurations of branes puffed up by the supertube effect. In an appropriate duality frame, we can construct the simplest supertube by adding momentum to a symmetric distribution of NS5 branes on their Coulomb branch. This suggests an exact worldsheet description of the supertube as a null gauged Wess-Zumino-Witten model. Such exact treatment in worldsheet string theory also describes BPS and non-BPS three-charge microstate geometries. This construction reveals stringy structures that are invisibile in the supergravity approximation, and that play a crucial role in understanding the constituents that carry most of the entropy.

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Workshop / Seminar Thu, 14 Sep 2017 16:17:11 -0400 2017-09-20T12:00:00-04:00 2017-09-20T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET BROWN BAG | Topics in Axion Cosmology (September 27, 2017 12:00pm) https://events.umich.edu/event/44957 44957-10015370@events.umich.edu Event Begins: Wednesday, September 27, 2017 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

(Which topics? The interesting ones!) Light pseudo-Goldstone bosons arise in many compelling models of particle physics and string theory. These particles can modify cosmology in interesting, surprising, and testable ways. In this talk I will discuss three topics. First I’ll argue that the dynamics of an axion field during inflation can give rise to the matter / antimatter asymmetry of the universe via the production of helical magnetic fields (which persist today and might be detectable!). Second, I’ll discuss what goes wrong when you try to implement the same idea with chiral gravitational waves instead of magnetic fields. Finally, I’ll talk about new phenomena that arise in multi-axion models, such as the recent proposed `clockwork’ axion, that have a large hierarchy between the scale of PQ-breaking and the axion decay constant.

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Workshop / Seminar Fri, 22 Sep 2017 16:32:29 -0400 2017-09-27T12:00:00-04:00 2017-09-27T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
Special Cosmology Seminar | Integrated Approach to Cosmology (September 29, 2017 12:00pm) https://events.umich.edu/event/44880 44880-10000731@events.umich.edu Event Begins: Friday, September 29, 2017 12:00pm
Location: Randall Laboratory
Organized By: Department of Physics

Recent progress in observational cosmology and the establishment of ΛCDM have relied on the combination of different cosmological probes. These probes are not independent, since they all measure the same physical fields. The resulting cross-correlations allow for a robust test of the cosmological model through the consistency of different physical tracers and for the identification of systematics. Integrated analyses taking into account both the auto- as well as the cross-correlations between cosmological probes therefore present a promising analysis method for both current as well as future data.

In this talk, I will present an integrated analysis of CMB temperature anisotropies, CMB lensing, galaxy clustering and weak lensing as well as background probes. I will describe the cosmological probe combination framework, the obtained results and illustrate how this analysis has provided a confirmation of ΛCDM through the consistency of different probes. Furthermore, I will discuss possible tensions between the derived constraints on cosmological parameters and existing ones.

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Workshop / Seminar Thu, 21 Sep 2017 11:01:52 -0400 2017-09-29T12:00:00-04:00 2017-09-29T13:00:00-04:00 Randall Laboratory Department of Physics Workshop / Seminar Randall Laboratory
Special Cosmology Seminar | SPIDER: Searching for Primordial Gravitational Waves From a Long Duration Balloon (October 3, 2017 3:00pm) https://events.umich.edu/event/45275 45275-10150117@events.umich.edu Event Begins: Tuesday, October 3, 2017 3:00pm
Location: Randall Laboratory
Organized By: Department of Physics

SPIDER is a CMB polarimeter that completed its first long duration ballooning flight from Antarctica in January 2015. From its vantage point at 36 km above the ground, it observed 12% of the sky over 16 days at 94 and 150 GHz. I will discuss the design of SPIDER, including our reasons for choosing the ballooning platform. I will also describe some of the subsystems and how they performed during flight. Then I will show preliminary results from the ongoing data analysis. Finally, I will give an update on SPIDER 2, which will add focal planes at 280 GHz to improve our sensitivity to Galactic dust, and is expected to fly in December of 2018.

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Workshop / Seminar Mon, 02 Oct 2017 08:20:44 -0400 2017-10-03T15:00:00-04:00 2017-10-03T16:00:00-04:00 Randall Laboratory Department of Physics Workshop / Seminar Randall Laboratory
HET Brown Bag | Operator Dynamics in Quantum Chaos: Part I - Internal Degrees of Freedom (October 4, 2017 12:00pm) https://events.umich.edu/event/45281 45281-10150121@events.umich.edu Event Begins: Wednesday, October 4, 2017 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

We study operator growth in quantum chaos by considering the SYK model, a toy model of holography containing only internal degrees of freedom which evolve via q-local interactions. First, we note that the product length of an operator is directly related to its sensitivity to small perturbations. This reveals that in the SYK model, the commutator-squared/out-of-time-ordered correlator - a new diagnostic of quantum chaos - is literally measuring the effective length of the operator. It is known that this quantity grows exponentially in time with a "Lyapunov exponent", and thus we conclude that lengths of operators grows exponentially in time (amongst the internal degrees of freedom). Motivated by this, we group the operators into families defined by their lengths, thereby explicitly solving for the coarse-grained dynamics of an operator in the large N, large q limit. We also note that one can understand the time evolution of operators by relating it to the quantum mechanics of a particle on a graph with a nontrivial topology. Lastly, we may make some comments on the bulk interpretation of operator growth in SYK.

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Workshop / Seminar Mon, 02 Oct 2017 10:13:11 -0400 2017-10-04T12:00:00-04:00 2017-10-04T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminar | Soft Photons, Soft Gravitons and Decoherence (October 11, 2017 12:00pm) https://events.umich.edu/event/45552 45552-10228908@events.umich.edu Event Begins: Wednesday, October 11, 2017 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Central to the solution of the infrared catastrophe of quantum electrodynamics and perturbative quantum gravity is the idea that detection apparatus inevitably have limited resolution and, in any scattering process, an infinite number of arbitrarily soft photons and gravitons are produced and escape detection. Photons and gravitons have polarizations and momenta and one might suspect that those which escape can carry away a significant amount of information. In this talk, I will examine the question as to the quantity of this information loss, its consequences.

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Workshop / Seminar Mon, 09 Oct 2017 11:16:47 -0400 2017-10-11T12:00:00-04:00 2017-10-11T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag | Extended Steinmann Relations and Cosmic Galois Theory in Planar N = 4 (October 25, 2017 12:00pm) https://events.umich.edu/event/46076 46076-10387184@events.umich.edu Event Begins: Wednesday, October 25, 2017 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

While traditional methods for calculating scattering amplitudes prove too computationally intensive to be useful at higher loop orders, a great deal is now known about the analytic and kinematic properties of amplitudes to all orders in planar N=4. This information can be leveraged to construct these amplitudes directly, by putting together an ansatz of the relevant class of functions and requiring that it share the distinctive properties of a given amplitude. In this talk, I will describe how this bootstrap-type approach can be used to uniquely determine all six-particle amplitudes in this theory through (at least) five loops, focusing on how these methods make transparent the Steinmann relations and bear out the predictions of cosmic Galois theory. I will also discuss how these methods can be generalized to quantities of direct relevance to particle physics experiments.

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Workshop / Seminar Mon, 23 Oct 2017 08:56:36 -0400 2017-10-25T12:00:00-04:00 2017-10-25T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | Searching for Dark Matter in Distant Galaxies (November 1, 2017 12:00pm) https://events.umich.edu/event/46335 46335-10464010@events.umich.edu Event Begins: Wednesday, November 1, 2017 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Galaxies beyond our own represent some of the brightest potential sources of dark matter flux on the sky. As such they represent excellent candidates for indirect detection and in this talk I will demonstrate how to exploit this information to search for dark matter using the Fermi telescope. In particular I will outline how to map from an observed baryonic galaxy to its underlying dark matter distribution and a demonstration that our methods work in a simulated N-body environment.

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Workshop / Seminar Mon, 30 Oct 2017 08:42:34 -0400 2017-11-01T12:00:00-04:00 2017-11-01T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | Searching for weakly-coupled particles: from stars to colliders (November 8, 2017 12:00pm) https://events.umich.edu/event/46529 46529-10543995@events.umich.edu Event Begins: Wednesday, November 8, 2017 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Many theories of beyond Standard Model physics include new light, weakly-coupled particles, which can be challenging to search for experimentally. I will talk about two observational probes of such particles. The first is based on “stellar cooling”: if new particles are produced in the hot cores of stars, they can escape from the star and carry away energy, affecting its structure and evolution. I’ll describe how the plasma environment in stellar cores can parametrically alter the rates for these process, and how this can significantly change the constraints and discovery potential for some new particle candidates.

I will also discuss searches for light vectors at colliders. Unless these couple to a fully conserved SM current, the production rate for longitudinal modes is enhanced by (energy / vector mass)^2. This is true even if the current is only broken at loop level, as for anomalous vectors, and can result in significantly improved constraints on many models of phenomenological interest.

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Workshop / Seminar Mon, 06 Nov 2017 10:55:41 -0500 2017-11-08T12:00:00-05:00 2017-11-08T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
Special Cosmology Seminar | Quantum Theory and Cosmology away from the Planck Regime (November 21, 2017 3:10pm) https://events.umich.edu/event/46897 46897-10670076@events.umich.edu Event Begins: Tuesday, November 21, 2017 3:10pm
Location: Randall Laboratory
Organized By: Department of Physics

We will review the so called “measurement problem” in quantum theory and argue that it becomes exacerbated in the cosmological context, and see how this connects with some problematic aspects of the standard accounts for the inflationary origin of cosmic structure.
We will argue that new physics, possibly tied to novel aspects of quantum gravity, should be invoked if we want to fully justify the phenomenological success of the basic inflationary scheme. The general view is one that has been strongly advocated by R. Penrose and we will discuss
how that can possibly be accommodated within our current understanding of the interface of quantum theory and gravitation.
We will then see, in particular that, such view leads to a modified outlook to that presented by the standard treatments, regarding the famous and yet undetected primordial tensor modes.
We will end with a proposal, motivated by the preceding discussion, of a novel approach to dealing with the so called “dark energy” puzzle.

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Workshop / Seminar Fri, 17 Nov 2017 13:20:53 -0500 2017-11-21T15:10:00-05:00 2017-11-21T16:00:00-05:00 Randall Laboratory Department of Physics Workshop / Seminar Randall Laboratory
HET Brown Bag | Dark Fires in the Sky: Model-Independent Dark Matter Detection via Kinetic Heating of Neutron Stars (November 29, 2017 12:00pm) https://events.umich.edu/event/47036 47036-10776986@events.umich.edu Event Begins: Wednesday, November 29, 2017 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

I present a largely model-independent probe of dark matter-nucleon interactions. Accelerated by gravity to relativistic speeds, local dark matter scattering against old neutron stars deposits kinetic energy at a rate that heats them to infrared blackbody temperatures. The resulting radiation is detectable by next generation telescopes such as James Webb and the Thirty Meter Telescope. While underground direct detection searches are not (or poorly) sensitive to dark matter with sub-GeV masses, higher-than-weak-scale masses, scattering with strong cross-sections, scattering below neutrino floors, spin-dependent per-nucleon scattering below per-nuclear cross-sections, velocity-dependent scattering, and inelastic scattering for inter-state transitions exceeding O(100 keV), the (non-)observation of dark kinetic heating of neutron stars should advance these frontiers by orders of magnitude. Popular dark matter candidates previously suspected elusive, such as the thermal Higgsino, may be discovered.

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Workshop / Seminar Mon, 27 Nov 2017 08:14:02 -0500 2017-11-29T12:00:00-05:00 2017-11-29T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminar | From higher spins to generalized SYK models (December 6, 2017 12:00pm) https://events.umich.edu/event/46737 46737-10592252@events.umich.edu Event Begins: Wednesday, December 6, 2017 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

The spectrum of the Sachdev-Ye-Kitaev (SYK) model consists of an infinite tower of operators, which resembles the spectra of various vector models that are holographically dual to higher spin gravity theories. In this talk, I will discuss a direct connection between SYK-like tensor models and the Gross-Neveu vector model. This is achieved by studying a toy model where a tensor field is coupled with some vector fields. By integrating out the tensor field, the toy model reduces to the Gross-Neveu model in 1 dimension. At a different corner of the moduli space of this toy model, a perturbation can be turned on and the toy model flows to an SYK-like model at low energy. In addition, a chaotic-nonchaotic phase transition is observed as the sign of the perturbation is altered. If time permitted, I will briefly discuss some aspects of supersymmetric SYK-like models.

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Workshop / Seminar Mon, 04 Dec 2017 08:35:51 -0500 2017-12-06T12:00:00-05:00 2017-12-06T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | Simplified Limits on Resonances at the LHC (January 10, 2018 12:00pm) https://events.umich.edu/event/48219 48219-11191402@events.umich.edu Event Begins: Wednesday, January 10, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

When an excess appears in LHC data, we should compare the results with broad classes of models, to get an immediate sense of which kinds of BSM theories could conceivably be relevant. Often, the new physics is likely to be an s-channel resonance. In this case, a simplified model of the resonance can translate an estimated signal cross section into bounds on the product of the dominant production and decay branching ratios. This quickly reveals whether a given class of models could possibly produce a signal of the required size at the LHC. This talk will outline a general framework and show how it operates for resonances of varying widths and with different numbers of production and decay modes. It will also discuss applications to cases of experimental interest, including resonances decaying to di-bosons, di-leptons, or di-jets. If the LHC experiments start reporting searches for BSM resonances in terms of the simplified limits variable ζ defined here, the community will home in more quickly on the models most likely to explain any observed excess.

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Workshop / Seminar Fri, 05 Jan 2018 12:22:25 -0500 2018-01-10T12:00:00-05:00 2018-01-10T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | The strong CP problem and UV instantons (January 17, 2018 12:00pm) https://events.umich.edu/event/48221 48221-11191405@events.umich.edu Event Begins: Wednesday, January 17, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

The absence of sizeable CP violation in the strong sector is a long standing puzzle. A class of solutions to this problem rely on a global U(1) symmetry that is anomalous with QCD. These solutions lead to robust low-energy predictions, for example a massless up quark or a light axion. I will present simple extensions to such solutions which can dramatically change these low-energy predictions. In our models, contributions from small instantons play a significant role in affecting the low-energy physics while preserving the solution to the strong CP problem.

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Workshop / Seminar Fri, 05 Jan 2018 12:24:20 -0500 2018-01-17T12:00:00-05:00 2018-01-17T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | Astrophysical Signatures of Dark Matter Accumulation in Neutron Stars (January 31, 2018 12:00pm) https://events.umich.edu/event/49364 49364-11450939@events.umich.edu Event Begins: Wednesday, January 31, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Over the past few decades, terrestrial experiments have placed increasingly strong limits on the dark matter-nucleon scattering cross-section. However, a significant portion of the standard dark matter parameter space remains beyond our reach. Due to their extreme density and huge gravitational fields, neutron stars stand as optimal targets to probe dark matter-neutron interactions. As an example, over the last few years, the existence of Gyr-age neutron stars has placed strong limits on models of asymmetric dark matter. In this talk, I will discuss novel methods which utilize neutron stars to potentially detect dark matter interactions by studying the galactic morphology of neutron stars, as well as electromagnetic signals which may be produced via neutron star collapse. Intriguingly, these observations can probe extremely generic dark matter models spanning from MeV - PeV energies, and including troublesome portions of parameter space such as pure-Higgsino dark matter.

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Workshop / Seminar Mon, 29 Jan 2018 08:29:24 -0500 2018-01-31T12:00:00-05:00 2018-01-31T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | Loops from Nodes: Two-Loop Supergravity Amplitudes From the Ambitwistor String (February 7, 2018 12:00pm) https://events.umich.edu/event/49369 49369-11450943@events.umich.edu Event Begins: Wednesday, February 7, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

The last years have seen remarkable progress in understanding the scattering amplitudes of massless particles in arbitrary dimensions.Underlying the simple formulae are chiral worldsheet models, known as Ambitwistor Strings. While correlators of these models admit a conventional genus expansion of the worldsheet, the amplitudes actually localize on the maximal non-separating degeneration. We explore this simplification at two loops for type II supergravity, concluding in several observations for generic massless field theories.

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Workshop / Seminar Mon, 29 Jan 2018 08:55:36 -0500 2018-02-07T12:00:00-05:00 2018-02-07T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Series | The Quest for New Physics: From Atomic Physics to the LHC (February 14, 2018 12:00pm) https://events.umich.edu/event/49947 49947-11608279@events.umich.edu Event Begins: Wednesday, February 14, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

The Standard Model of particle physics well describes a vast number of observables up to the TeV scale. However, it cannot be a complete description of Nature as it cannot explain various experimental observations. For example, it lacks a viable dark matter candidate and can neither explain the observed matter/antimatter asymmetry of our Universe nor neutrino oscillations. Thus, physics beyond the Standard Model is well motivated. In this seminar, we explore different methods to probe new physics at multiple energy scales, from high energy colliders, such as the LHC, to precision low energy experiments. In particular, we focus on searches for new force carriers at the LHCb experiment and in precision atomic spectroscopy. We show that the inclusive search for dark photons at the LHCb experiment already probes new parameter space and can be easily interpreted for a large variety of new physics models. On the precision frontier, we explore the potential of isotope shift spectroscopy to probe new long range force carriers.

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Workshop / Seminar Mon, 12 Feb 2018 08:19:16 -0500 2018-02-14T12:00:00-05:00 2018-02-14T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | Quantum Curves and Q-deformed Painlevé Equations (February 21, 2018 12:00pm) https://events.umich.edu/event/49953 49953-11608291@events.umich.edu Event Begins: Wednesday, February 21, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

In this talk I will first review some aspects of Painlevé equations and their connection to four dimensional gauge theory; then I will generalise this construction to q-difference Painlevé equations and topological string theory. I will show that their tau-functions are Fredholm determinant of operators associated to quantum mirror curves on a corresponding geometry. As a consequence, the zeroes of these tau-functions compute the exact spectrum of the associated quantum integrable systems. I will focus on the particular example of q-Painlevé III_3 which is related to topological string on local P1xP1 and to relativistic Toda system.

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Workshop / Seminar Mon, 12 Feb 2018 09:40:56 -0500 2018-02-21T12:00:00-05:00 2018-02-21T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | Holographic Mellin Amplitudes (March 7, 2018 12:00pm) https://events.umich.edu/event/49954 49954-11608292@events.umich.edu Event Begins: Wednesday, March 7, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Holographic four-point functions are known for their notorious computational difficulties. In the past two decades, only a handful of them have been explicitly calculated using the standard algorithm. In this talk I will introduce modern methods to compute holographic correlators efficiently, which are inspired by the bootstrap philosophy and the on-shell methods of scattering amplitudes in flat space. I will show that by translating the problem into Mellin space many difficulties encountered when applying the traditional method are avoided. I will argue that imposing symmetry constraints and general consistency conditions -- avoiding all details of the complicated effective Lagrangian -- leads to many novel results for holographic four-point functions in AdS5×S5, AdS7×S4 and AdS4×S7. I will conclude by outlining some interesting future directions of this program.

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Workshop / Seminar Mon, 12 Feb 2018 09:42:47 -0500 2018-03-07T12:00:00-05:00 2018-03-07T13:00:00-05:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Series | Empirical Determination of the Dark Matter Velocity Distribution (March 14, 2018 12:00pm) https://events.umich.edu/event/50189 50189-11656314@events.umich.edu Event Begins: Wednesday, March 14, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

Using the hydrodynamic simulation Eris, as well as various realizations of the Milky Way from the FIRE simulation, we found that the kinematics of dark matter follows closely the kinematics of old metal poor stars. We use this correspondence to obtain the first empirical measurement of the local velocity distribution of dark matter, by first analyzing the Gaia data release coupled with RAVE as well as the ninth release from the Sloan Digital Sky Survey and computing the velocity distribution of metal poor stars. We find that this velocity distribution is peaked at lower velocities than the generally assumed Maxwell Boltzmann distribution, leading to a weakening of direct detection limits at dark matter masses less than 10 GeV by a factor of a few. We also found a few kinematic outliers in the stellar data that might be hints of dark matter substructure.

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Workshop / Seminar Fri, 16 Feb 2018 15:05:30 -0500 2018-03-14T12:00:00-04:00 2018-03-14T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Series | Conformal truncation: A new method for studying strong-coupled QFTs (March 21, 2018 12:00pm) https://events.umich.edu/event/51154 51154-12007285@events.umich.edu Event Begins: Wednesday, March 21, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

I will present a new numerical method for studying strongly-coupled QFTs. The method is formulated for continuum spacetime of any dimension, in real time and infinite volume, and is thus complementary to other numerical methods, such as the lattice. The method harnesses conformal symmetry, but in a manner applicable to general, non-conformal QFTs. Specifically, the input is information about the UV CFT from which the QFT originates. The output is the physical IR QFT spectrum, along with real-time, infinite-volume correlation functions. I will discuss applications to 2D phi^4 theory, where we have performed novel computations of correlation functions at any coupling, such as the Zamolodchikov c-function along the full RG-flow. The 2D Ising model provides a highly-nontrivial cross-check of our numerics.

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Workshop / Seminar Mon, 19 Mar 2018 08:22:22 -0400 2018-03-21T12:00:00-04:00 2018-03-21T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Series | A Natural Generalization of the Standard Randall-Sundrum Framework and its Phenomenological Implications (March 28, 2018 12:00pm) https://events.umich.edu/event/51355 51355-12086777@events.umich.edu Event Begins: Wednesday, March 28, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

In the first part of the talk, I will introduce a very natural extension of well-motivated extra-dimensional framework of Randall-Sundrum type. Such a generalization is motivated by (null) results from both high energy (LHC) and low energy (flavor, CP, and electroweak precision) experiments. In particular, null results from the LHC led us to consider the possibility that little hierarchy may exist. In addition to the consistency with low energy bounds, our generalization can address the question of the form of TeV scale new physics we can expect. I will argue that such new physics appearing at the TeV scale is in the form of vector-like confinement with new states interacting with SM through mostly flavor universal couplings. In the second part of the talk, I will discuss several exciting signals probable at the LHC and in future colliders.

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Workshop / Seminar Mon, 26 Mar 2018 08:22:19 -0400 2018-03-28T12:00:00-04:00 2018-03-28T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Series | Supertranslations and Superrotations at the Black Hole Horizon (April 4, 2018 12:00pm) https://events.umich.edu/event/51560 51560-12167536@events.umich.edu Event Begins: Wednesday, April 4, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

In this talk, we study the asymptotic symmetries in the near-horizon region of extremal and non-extremal black holes. By prescribing a physically sensible set of boundary conditions at the horizon, we derive the algebra of asymptotic Killing vectors, which is shown to be infinite-dimensional; it includes two sets of supertranslations and two mutually commuting copies of the Virasoro algebra. We define the surface charges associated to these large diffeomorphisms and evaluate them for different stationary black hole solutions. We finally discuss the relationship between these horizon charges and the Bondi-Metzner-Sachs (BMS) ones by computing the memory effect produced at the black hole horizon by a gravitational shock wave sent from null infinity.

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Workshop / Seminar Mon, 02 Apr 2018 08:20:37 -0400 2018-04-04T12:00:00-04:00 2018-04-04T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
HET Brown Bag Seminars | GeV-Mass Thermal WIMPs: Not Even Slightly Dead (April 11, 2018 12:00pm) https://events.umich.edu/event/51779 51779-12248758@events.umich.edu Event Begins: Wednesday, April 11, 2018 12:00pm
Location: Randall Laboratory
Organized By: HET Brown Bag Series

A leading dark matter candidate is a Weakly Interacting Massive Particle (WIMP). The observed dark matter abundance can be naturally obtained through freezeout of the thermal annihilation rate. The defining feature of a thermal WIMP is that its total annihilation cross section is specified through the rate ~ 3 x 10^-26 cm^3/s, inversely proportional to the dark matter density. Searches for dark matter annihilation products have set strong limits in certain cases, requiring that the dark matter mass be greater than around 100 GeV if annihilation proceed solely to b quarks (Fermi), τ leptons (Fermi), or electrons (AMS). We construct the first limits on the total annihilation cross section, showing that allowed combinations of the annihilation-channel branching ratios considerably weaken these limits. We will show that GeV-mass thermal WIMPs have not yet been adequately tested, and outline ways forward.

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Workshop / Seminar Mon, 09 Apr 2018 08:28:47 -0400 2018-04-11T12:00:00-04:00 2018-04-11T13:00:00-04:00 Randall Laboratory HET Brown Bag Series Workshop / Seminar Randall Laboratory
Department of Physics | Cluster Polylogarithms with Applications to Scattering Amplitudes (May 14, 2018 2:00pm) https://events.umich.edu/event/52259 52259-12579623@events.umich.edu Event Begins: Monday, May 14, 2018 2:00pm
Location: Randall Laboratory
Organized By: Department of Physics

I will present several new results in the intersection of cluster algebras and polylogarithm functions motivated by the study of scattering amplitudes. For example, I will show how the iterated integral structure of polylogarithms can be intimately tied to the structure of cluster algebras through a property called cluster adjacency. As an example I will give a polylogarithm function of weight 4 related to the A_2 cluster algebra. I will then discuss systematic ways in which larger cluster algebras can be associated with more complicated polylogarithm functions, such as scattering amplitudes, through various subalgebra decompositions.

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Workshop / Seminar Wed, 09 May 2018 12:02:32 -0400 2018-05-14T14:00:00-04:00 2018-05-14T15:00:00-04:00 Randall Laboratory Department of Physics Workshop / Seminar Randall Laboratory
Special Cosmology Seminar | Photo-z’s and Cosmology From Weak Lensing Cross-Correlations in DES (June 5, 2018 3:30pm) https://events.umich.edu/event/52497 52497-12840321@events.umich.edu Event Begins: Tuesday, June 5, 2018 3:30pm
Location: Randall Laboratory
Organized By: Department of Physics

In this talk I will explain how we can use weak lensing cross-correlations, in particular galaxy-galaxy lensing, to constrain the redshift distributions of the source galaxies. I will present the results obtained using this technique on DES Y1 data. Also, I will describe how using a similar method but now including CMB lensing cross-correlations we can constrain cosmological parameters, using SPT and Planck data.

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Workshop / Seminar Mon, 04 Jun 2018 09:41:30 -0400 2018-06-05T15:30:00-04:00 2018-06-05T16:30:00-04:00 Randall Laboratory Department of Physics Workshop / Seminar Randall Laboratory
SPECIAL SEMINAR | The Future of Fundamental Particle Physics – Should China Build the Great Collider? (June 8, 2018 4:00pm) https://events.umich.edu/event/52469 52469-12793961@events.umich.edu Event Begins: Friday, June 8, 2018 4:00pm
Location: Randall Laboratory
Organized By: Department of Physics

The Standard Models of particle physics and cosmology are wonderful theories that fully describe our world. But there are some hidden aspects of nature we don’t understand yet, such as dark matter, a quantum theory of gravity, and more. There are some counterintuitive things we know – for example the earth orbits the sun, although it does not seem to. There may be more counterintuitive aspects of nature such as extra space dimensions that arise in string theory. The talk, based on discussions with Stephen Hawking, will describe the Standard Models, the puzzling issues beyond the Standard Models, and how the well-motivated Great Collider will contribute to solving them. The Great Collider will also provide major economic and cultural development.

The talk will begin at 4:00 p.m. sharp!

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Workshop / Seminar Tue, 05 Jun 2018 14:46:09 -0400 2018-06-08T16:00:00-04:00 2018-06-08T17:00:00-04:00 Randall Laboratory Department of Physics Workshop / Seminar Randall Laboratory
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