# Seminars

PHY 393S:*Seminar in Relativity*, FALL 2009

*Tuesday, Thursday 3:30-4:45 PM, RLM 6.124*

(regular group meetings are held on Thursdays at 3:30 PM in RLM 9.202)

### Past Seminars:

- Tuesday, February 17, 2009:

**Asif Hassan**

"Ashtekar variables and spinors"

- Tuesday, March 3, 2009:

**Asif Hassan**

"Ashtekar variables and spinors, part deux"

- Thursday, April 16, 2009:

**Stephen G. Low**

"Relativity groups consistent with Heisenberg commutation relations"

*Abstract:*Special relativistic quantum mechanics may be understood in terms of the projective representations of the inhomogeneous Lorentz group. Projective representations are required as quantum states are rays in a Hilbert space and these representations are equivalent to unitary (or anti-unitary) representations of the central extension of the group. The central extension of the inhomogeneous Lorentz group is its cover, the Poincaré group, and the unitary representations of this semidirect product group may be determined using the Mackey method.

The Heisenberg uncertainty commutation relations are the Hermitian representation of the algebra corresponding to the unitary representations of the Weyl-Heisenberg group. The Weyl-Heisenberg group is a one parameter central extension of an even dimensional abelian group, that in this case are translations on phase space, that results in it being the semidirect product of two abelian groups. Therefore the unitary representations of the Weyl-Heisenberg are a particular projective representation of this abelian translation group that may also be determined using the Mackey method.

The Heisenberg commutation relations must be valid in any state related by a relativity group. This requires the relativity group to be a subgroup of the automorphism group of the Weyl-Heisenberg group. This automorphism group is essentially the symplectic group semidirect the Weyl-Heisenberg group. The inhomogeneous Lorentz group that relates inertial states in special relativity is a subgroup of this automorphism group that leaves invariant a degenerate orthogonal Minkowski line element. Considering a nondegenerate orthogonal line element results in a group that relates noninertial states. Thisresults in the relativity of the inertial frame analogous to the relativity of the rest frame in special relativity. The basic consequences of the reciprocal relativity group, its projective representations and its contraction limits is outlined.

- Tuesday, November 18, 2008:

**Deirdre Shoemaker**

*Georgia Tech*

"Simplicity of Binary Black Hole Coalescence and its Implications for Detection" [pdf of talk]

*Abstract:*A black hole in isolation is a very simple object, described by its mass, spin, and charge. Two black holes in the process of coalescing are not simple, requiring a large set of individual and orbital parameters to describe their motion. Now that the binary black hole problem has been solved, we explore the dynamics of black hole binaries as they merge and ringdown to a single black hole. We look at one small segment of the parameter space and study the role of eccentricity throughout the history of a binary black hole merger and the role eccentricity plays in detection by gravitational wave detectors.

- March 27, 2008:

**Jon Allen**

*University of Texas at Austin*

"Gauge Fixing for Numerical Relativity (Part 1)"

- March 25, 2008:

**Andrea Nerozzi**

*University of Jena, Germany*

"Optimizing Wave Extraction in Numerical Relativity"

*Abstract:*With the recent breakthroughs in numerical relativity, the problem of extracting waveforms from a numerically evolved space-time has become of primary importance. The Newman-Penrose formalism and in particular the Weyl scalar Psi4 is used for this purpose, however in order for this to be done correctly, the null tetrad used to calculate it must be chosen carefully. We present the latest results concerning the study of the optimal tetrad for wave extraction.

- March 18, 2008:

**Ulrich Sperhake**

*University of Jena, Germany*

"Numerical simulations of high energy collisions of black holes" [ppt of talk]

*Abstract:*We present numerical simulations of collisions of black holes with varying boost parameter. This study covers the range from vanishing initial boost to the regime where the total mass is dominated by the kinetic energy. The resulting horizon properties and gravitational wave emission are studied and compared with analytic predictions.

- March 20, 2008:

**Sarp Akcay**

*University of Texas at Austin*

"Area Invariance of Horizons under Spin-Boost Transformations" [ppt of talk]

- December 6, 2007:

**Erin Bonning**

*University of Texas at Austin*

"Recoiling Black Holes in Quasars"

- May 1, 2007:

**Stephen Low**

*Technology Director, HP*

"Reciprocal Relativity of noninertial frames: quantum mechanics" [pdf of talk] [pdf of paper]

- Relativity Seminar Archive