High Energy
Wednesday, January 16, 2019
3:30 PM
Physics Building, Room 204

Reserved  Please see the Colloquia Schedule
[Host: Diana Vaman]


High Energy
Wednesday, January 23, 2019
3:30 PM
Physics Building, Room 204

Reserved  Please see the Colloquia Schedule
[Host: Diana Vaman]


High Energy
Wednesday, January 30, 2019
3:30 PM
Physics Building, Room 204

Reserved  Please see the Colloquia Schedule
[Host: Diana Vaman]


High Energy
Wednesday, February 6, 2019
3:30 PM
Physics Building, Room 204

Reserved  Please see the Colloquia Schedule
[Host: Diana Vaman]


High Energy
Wednesday, February 13, 2019
3:30 PM
Physics Building, Room 204

Reserved  Please see the Colloquia Schedule
[Host: Diana Vaman]


High Energy
Wednesday, February 20, 2019
3:30 PM
Physics Building, Room 204

Reserved  Please see the Colloquia Schedule
[Host: Diana Vaman]


High Energy
Wednesday, February 27, 2019
3:30 PM
Physics Building, Room 204

Available


Special Joint Nuclear and High Energy Seminar
Thursday, February 28, 2019
3:30 PM
Physics Building, Room 204
Note special date.

Oleg Denisov
[Host: Dustin Keller]
COMPASS experiment
"TBA"


High Energy
Wednesday, March 6, 2019
3:30 PM
Physics Building, Room 204

"Available"


High Energy
Wednesday, March 20, 2019
3:30 PM
Physics Building, Room 204

"Available"


High Energy
Wednesday, March 27, 2019
3:30 PM
Physics Building, Room 204

"Available"


High Energy
Wednesday, April 3, 2019
3:30 PM
Physics Building, Room 204

RESERVED


High Energy
Wednesday, April 10, 2019
3:30 PM
Physics Building, Room 204

Bertrand Echenard
[Host: Craig Group]
Caltech
"Light dark matter searches at BABAR and LDMX"


High Energy
Wednesday, April 17, 2019
3:30 PM
Physics Building, Room 204

"Available"


High Energy
Wednesday, April 24, 2019
3:30 PM
Physics Building, Room 204

Pedro Cunha
[Host: Kent Yagi]
University of Lisbon
"Light ring stability in ultracompact objects"

ABSTRACT:
The following theorem is proven: axisymmetric, stationary solutions of the Einstein field equations formed from classical gravitational collapse of matter obeying the null energy condition, that are everywhere smooth and ultracompact (i.e., they have a light ring, a.k.a. circular photon orbit) must have at least two light rings, and one of them is stable. It has been argued that stable light rings generally lead to nonlinear spacetime instabilities. Thus this result implies that smooth, physically and dynamically reasonable ultracompact objects are not viable as observational alternatives to black holes whenever these instabilities occur on astrophysically short time scales. The proof of the theorem has two parts: (i) We show that light rings always come in pairs, one being a saddle point and the other a local extremum of an effective potential. This result follows from a topological argument based on the Brouwer degree of a continuous map, with no assumptions on the spacetime dynamics, and hence it is applicable to any metric gravity theory where photons follow null geodesics. (ii) Assuming Einstein’s equations, we show that the extremum is a local minimum of the potential (i.e., a stable light ring) if the energymomentum tensor satisfies the null energy condition.


High Energy
Wednesday, May 1, 2019
3:30 PM
Physics Building, Room 204

RESERVED

