# Strong Gravity

This series consists of talks in areas where gravity is the main driver behind interesting or peculiar phenomena, from astrophysics to gravity in higher dimensions.

## Seminar Series Events/Videos

Mar 13 2014 - 1:00pm
Room #: 400
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Mar 20 2014 - 1:00pm
Room #: 400
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Mar 27 2014 - 1:00pm
Room #: 400
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Apr 17 2014 - 1:00pm
Room #: 400
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May 8 2014 - 1:00pm
Room #: 400
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## Sequestering Lorentz violation in the Lifshitz sector

Thursday Mar 06, 2014
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Horava's proposal to use Lifshitz propagators for gravitons above certain energy scales may provide a viable theory of quantum gravity without further need of UV completion. In my talk, I will address the question of whether the complete lack of Lorentz invariance above a certain energy scale is a big problem for any realistic construction. I will argue that it is not, provided that the onset of Lifshitz scaling for gravitons occurs at momentum scale much lower than the Planck mass.

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## On null singularities in general relativity

Thursday Feb 13, 2014
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This talk will discuss the formation, structure and interaction of null singularities for
the Einstein equations, as well as what this all means for the singular boundary
of generic space times within black hole regions.

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## The Radius of Neutron Stars and the Dense Matter Equation of State

Thursday Feb 06, 2014
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The equation of state of matter at and above nuclear densities remains a major theoretically uncertain prediction of QCD. Observations of the mass-radius relationship of neutron stars constrain, and can directly measure, the dense matter equation of state. I will discuss how measurements of neutron star radii have already constrained the dEOS, and how future work will directly measure the dEOS, providing an important constraint on models of the strong force.

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## Charged particle motion in magnetized black holes

Thursday Nov 21, 2013
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There exist evidences that magnetic field in
the vicinity of astrophysical black holes plays an important role. In
particular it is required for explanation of such phenomenon as jet formation.
Study of such problems in all their complexity requires 3D numerical
simulations of the magnetohydrodynamics in a strong gravitational field. Quite
often when dealing with such a complicated problem it is instructive to
consider first its simplifications, which can be treated either analytically,

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## Self-force and Green function in Schwarzschild spacetime via quasinormal modes and branch cut

Thursday Nov 14, 2013
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The modelling of gravitational wave sources is of timely interest given the exciting prospect of a first detection of gravitational waves by the new generation of detectors.  The motion of a small compact object around a massive black hole deviates from a geodesic due to the action of its own field, giving rise to a self-force and the emission of gravitational waves. The self-force program has recently achieved important results using well-established methods.

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## New lessons about hydrodynamics from gravity

Thursday Oct 31, 2013
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within the last 10 years, a lot of attention. The reason for it, on one hand,
is the quest for theoretical understanding of the quark-gluon plasma created in
heavy ion collisions and, on the other, advances in holographic duality and
black hole physics in anti-de Sitter spacetimes. I will describe recent
progress in answering foundational issues in hydrodynamics of strongly coupled
systems, i.e. questions about its applicability and the character of

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## Quasinormal modes of rapidly rotating black holes/ Stability of tidally perturbed neutron stars

Thursday Oct 17, 2013
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I
will review recent work in two very different topics. First, I will discuss the
quasinormal mode spectrum of nearly extremal Kerr black holes, where a
bifurcation of the frequency spectrum is observed. In addition, collective
oscillations of many modes is possible, resulting in a power-law rather than
exponentially decaying ringdown. Next, I will discuss a recent proposal for how
tidally induced, multimode coupling of normal modes in neutron stars can
destabilize the stars. Such an instability could hamper gravitational wave

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## Plasma without Plasma: Exploring Force-Free Magnetospheres

Thursday Oct 10, 2013
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Pulsars have enormous magnetic fields whose energy density
dwarfs the rest mass density of their plasma magnetosphere.  In this
regime of a plasma, the particles drop out of the description, leaving a set of
equations for the electromagnetic field alone.  This non-linear,
deterministic system is known as force-free electrodynamics, and turns out to
have some beautiful and bizarre features.  I will give a pedagogical
introduction to these equations and their role in astrophysics and then discuss

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## Neutron Stars and the Dense Matter Equation of State

Thursday Aug 08, 2013
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Implications of
recently well-measured neutron star masses, particularly near and above 2 solar masses, for the equation of state (EOS) of neutron star matter will be highlighted.  Model independent upper

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## Dynamic and Thermodynamic Stability of Black Holes and Black Branes

Thursday Jun 13, 2013
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I describe recent work with with Stefan Hollands that establishes a new criterion for the dynamical stability of black holes in $D \geq 4$ spacetime dimensions in general relativity with respect to axisymmetric perturbations: Dynamic stability is equivalent to the positivity of the canonical energy, $\mathcal E$, on a subspace of linearized solutions that have vanishing linearized ADM mass, momentum, and angular momentum at infinity and satisfy certain gauge conditions at the horizon.  We further show that $\mathcal E$ is related to the second order variations of mass, angular momentum, an

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## RECENT PUBLIC LECTURE

### The National Ingnition Facility: Pathway to Energy Security and Physics of the Cosmos

Speaker: Edward Moses