The University of Florida Theoretical Astrophysics Seminar is held on Wednesdays at 1:45pm in Room 2165 of the New Physics Building.

Spring 2018 Schedule

January 17:

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January 24:

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January 31:

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February 7:

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February 14:

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February 21:

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February 28:

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March 7: No Seminar [Spring Break]

March 14:

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March 21:

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March 28:

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April 4: Kohta Murase (Penn State)

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April 11: Smadar Naoz (UCLA)

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April 18:

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April 25: Tamara Bogdanovic (Georgia Tech)

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Fall 2017 Schedule

September 6: Shun-Pei Miao (NCKU)

Title: Electrodynamic Effects of Inflationary Gravitons

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I begin by describing the origin of big IR effects during primordial inflation. I then review a series of works on EM + GR from flat space to de Sitter, commenting in particular on the issue of gauge dependence. Finally, I make a conjecture for resolving the issue, and present the latest work which has been done to test this conjecture.

September 27: Special Event [NPB Rm. 2205]

Title: Academic Jobs Panel

October 4: Richard Woodard (UF Physics)

Title: MOND Cosmology

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MOND is a phenomenological model which modifies the extreme weak field regime of Newtonian gravity so as to explain galactic rotation curves without dark matter. If correct, it must be the non-relativistic, static limit of some relativistic modified gravity theory. I show how the only possible metric-based modification of gravity is nonlocal, and I construct the action using the Tully-Fisher relation and weak lensing. Then I explore the consequences of this model for cosmology. This talk is based on three arXiv papers: 1106.4984, 1405.0393 and 1608.07858.

October 11: Adrian Hamers (IAS)

Title: Dynamics around supermassive black holes: from mpc to kpc

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We consider orbital dynamics at various scales around supermassive black holes (MBHs) with masses comparable to the MBH in the Milky Way Galactic Center (GC). First, we address the relativistic regime within a few mpc from the MBH. In this regime, orbital diffusion is affected by relativistic precession which has implications for the evolution of stars like the S-stars, and for the rates of inspirals of compact objects onto the MBH (i.e., EMRIs). Second, we consider the X-ray and near-IR flares that are observed from the MBH in the GC on an approximately daily basis. A proposed origin for these flares is the tidal disruption of large (> 10 km radius) planetesimals, and we study the dynamics of such planetesimals in the GC at the parsec scale, giving clues into their origin. Lastly, we venture to larger scales of up to a kpc from the MBH and consider relaxation of objects, in particular binary stars, due to transient nuclear spiral arms. We show how this relaxation process can enhance the disruption rates of stellar binaries, with implications for the orientation of hypervelocity stars originating from the GC.

October 17: Special Event [12:45pm, Bryant Space Center Rm. 217]

Title: Discussion of LIGO results

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Steve Eikenberry will lead a discussion about the discovery of a binary neutron star merger by LIGO. (*Note the unusual time and location.*)

October 25: Cole Miller (Univ. of Maryland)

Title: When Neutron Stars Collide

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On August 17, gravitational waves and gamma rays from a merger of two neutron stars reached the Earth. Over the next several weeks, astronomers studied this event across the electromagnetic spectrum, leading to remarkable confirmation of predictions and also some fascinating new puzzles to consider. I will share some perspectives about the importance of the observations in many subjects: from tests of theories of strong gravity to the structure of neutron stars to the nature of short gamma-ray bursts and the production of heavy elements. I will also speculate about the return we can expect from gravitational wave observing runs in the coming years.

November 1: Leo Stein (Caltech)

Title: Probing strong-field gravity: Black holes and mergers in general relativity and beyond

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General relativity-Einstein's theory of gravitation-has been studied for more than 100 years. Over the past century, we have learned that the theory agrees with all available experimental and observational tests. At the same time we know that the theory is incomplete, as it leads to inconsistencies when coupled with quantum mechanics. The strong-field regime is our best hope to study GR, both observationally and theoretically, and thus understand how to correct its shortcoming. In this talk, I will discuss investigations in the strong-field, including black holes and neutron stars, in GR and theories beyond GR. The main focus will be predicting gravitational waves from merging black holes beyond GR. These predictions will allow for the most rigorous testing of general relativity, using LIGO, in the dynamical strong-field regime.

November 8: Steffen Aksteiner (Princeton)

Title: Black Hole Perturbations. A complete set of local gauge invariants

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Pertubation theory on black hole spacetimes is commonly treated by wave-like equations for certain decoupled, gauge invariant curvature components known as Teukolsky equations. In this talk we present additional (locally independent) gauge invariants, discuss some of their properties and discuss in which sense they form a complete set. This is joint work with contributions by Lars Andersson, Thomas Backdahl, Igor Khavkine, Abhay Shah and Bernard Whiting.

November 15: Desika Narayanan (UF Astronomy)

Title: Tracing the (Baryonic) Dark Sector of Galaxies

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Stars form in giant clouds comprised of molecular (H2) gas in galaxies. Tracing this gas, however, is a complicated mess. The radiation field from nearby stars, cosmic rays from supernovae, and collisions with energetic dust can all dictate the thermal, radiative, and chemical properties of this gas. In this talk, I go through pedagogical exercises aimed at non-experts in the physics of the star-forming interstellar medium, and provide evidence that up to half the gas in galaxies may be hitherto undetected.

November 29: Jack Hewitt (Univ. of North Florida)

Title: Galactic Accelerators: Understanding the Sources and Propagation of Cosmic Rays

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Observations with the Fermi Large Area Telescope have raised new questions about particle accelerators within the Galaxy, including supernova remnants, pulsar wind nebulae, and star forming regions. Recent surveys with Fermi have detected more than 50 spatially extended sources, which is the most certain means of identifying these source classes. Joint studies with TeV observatories - HAWC, HESS, MAGIC and VERITAS - allow us to measure cosmic ray propagation and acceleration (or re-acceleration) in these sources. Continued studies promise to resolve whether we have identified the long-sought PeVatrons that produce Galactic cosmic rays.

December 6: Anna Heffernan (UF Physics)

Title: The self-force: Who? What? How? Why? When? Gravity? Florida?

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The University of Florida historically boasts one of the biggest, most productive AND most famous self-force / gravity groups in the world - it's why I came here. After almost 2 years of chats, I've realised not everybody here is fully aware of the major contributions that were born here at Florida, nor the exact concept of the self-force and how it fits in the grander scheme of general relativity, gravitational wave detection and the very exciting future space based gravitational wave detector, LISA. This talk will serve to explain the basic concepts of the self-force, how it has progressed since it's birth, and the major current themes of research. I will depict how the Florida gravity group fits into all of the above, including highlights of my own research. Spoiler: I'll be talking about black hole binaries and their role in the LISA mission.

Other Events

Students may receive credit for attending the Astrophysics Seminar by registering for PHY 6391.