GRAVITY THEORY SEMINARS, Spring
"Analog models of GR from Bose-Einstein Condensates"
We shall discuss the prospects for the use of Bose-Einstein condensates as systems able to mimic the kinematical aspects of general relativity. Taking a long-term view, we ask what the ultimate limits of such a system mightbe.To this end, we consider a very general version of the Gross-Pitavæskii equation that can be used in discussing Bose-Einsteincondensates in heterogeneous and highly nonlinear systems. Wedemonstrate that at low momenta linearized excitations of the phase of thecondensate wavefunction obey a (3+1)-dimensional d'Alembertian equationcoupling to a (3+1)-dimensional Lorentzian-signature "effective metric"that is generic, and depends algebraically on the background field.
"Quantum phases: the basic structire of quantum theory?"
We explain how quantum phases are operationally determined in measurement of systems at more than one moment of time. They do not correspond to any self-adjoint operator. We study how they can be quantified and then explain an axiomatic framework that takes the notion of phases as primitive. In fact, such a description needs not make reference at all to a Hilbert space, which provides a stepping stone for novel interpretational schemes for quantum theory.
"Black holes, Hawking radiation, entropy, and information loss in a thinfilm of 3He-A"
The Hawking process---quantum decay of a black hole via emission ofthermal radiation---is theoretically compelling, yet it raises deep puzzles aboutquantum gravity and is observationally remote. Condensed matter analogs ofblack holes have already yielded insights into one ofthe puzzles, and mayone day allow us to experimentally study Hawking radiation analogs in thelaboratory. This talk will focus on a black hole analog employing a domainwall texture in a thin film of super fluid helium-3 in the A-phase. The causalstructure of the effective black holewill be discussed, and a model of blackhole formation and subsequent evaporation will be presented which exhibitsthe transfer of information to a disconnected "sister universe".
"Critical behavior in gravitational collapse."
Critical behavior analogous to the one in condensed
matter physics occurs in gravitational collapse of many systems.
It is characterized by (1) scaling and (2) universality. Namely, for generic one-parameter family of initial data parametrized
by $p$, where those with $p> p^*$ evolve into a black hole and
those with $p<p^*$ do not, solutions near $p=p^*$ satisfy the following:
(1) the mass $M$ of black hole formed obeys the scaling relation
(2) the critical exponent $\beta$ does not depend on the one-parameter
This is an introductory talk about the subject focused on what it
"BF gravity and the Immirzi parameter"
It is proposed a novel BF-type formulation of real four-dimensional gravity, which generalizes previous models. In particular, it allows for an arbitrary Immirzi parameter. In addition, it is constructed the analogue of the Urbantke metric for this model. Finally, it is performed the canonical analyzis of the BF action leading to Ashtekar-Barbero phase variables.
Apr. 6, Fri., 2:00pm, Room 4208
Dieter Brill, University of Maryland
"2+1 dimensional black holes: the inside story"
"On effective Maxwell and Dirac equations in loop quantum gravity"
Simple arguments indicate cosmological GRB's might
probe quantum gravity scales. Candidate theories have been studied accordingly.
In this talk a coarse grained approximation in loop quantum gravity with
matter fields is described yielding Planckian modifications to Maxwell
and Dirac equations in flat spacetime. The corresponding Planckian dispersion
relations are hence derived.
"Inflationary Cosmology: Progress and Problems"
Inflationary cosmology has become a cornerstone
of moderncosmology. In spite of the success in terms of explaining
many observations, current realizations of inflation suffer from several conceptual problems. In this lecture I will
mention a couple of areas of inflationary cosmology in which there has been substantial progress in our understanding,
such as the theory of reheating (with applications to Anderson localization) and the theory of cosmological perturbations.
I will then focus on several important conceptual problems (e.g. the trans-planckian problem) and mention some possible new
Apr. 27, Fri., 2:00pm, Room 4208
Peter Fritschel, MIT
"Pursuing gravitational wave astrophysics with LIGO"
"Future directions in gravitational wave astronomy"
Space based gravitational wave observatories, such as the Laser Interferometer Space Antenna (LISA), will open an exciting new window on the universe. I will discuss the LISA mission and some potential LISA follow-on missions in terms of their science potential. One exciting possibility is a mission to measure the cosmic gravitational wave background that is produced during the formation of the universe.
"Search for a string-theory predicted violation of gravitational inverse-square law"
I will discuss the design of a cryogenic null
test for the 1/r2 law with expected resolution of 10-3 at 50 mm.
Achieving the desired sensitivity requires not only extremely low intrinsic
noise but careful attention to metrology errors and extremely low coupling
to seismic, gravitational, and magnetic disturbances. A null source
is employed to minimize Newtonian errors. A circular disk of large
diameter with a correction ring produces two second-order null points near
its center; where test masses are located. The test masses are thin
sapphire disks with superconducting coils deposited. Magnetic flux
trapped in these coils allows levitation and self-alignment of the test
masses with respect to the magnetic shield and the source mass. Superconducting
sensing coils, located near the levitated test masses, are connected together
to a SQUID to form a sensitive differential accelerometer. Due to
reflection symmetry in the source-detector configuration, the 1/r2 violation signal appears at the second harmonic of the source motion. This frequency discrimination, combined with the differential measurement, gives the required isolation for source-induced vibration. Most metrology and density errors average out due to the cylindrical symmetry in the design. Superconducting magnetic levitation allows soft, low-loss suspension of the test masses. The low intrinsic noise of the detector, combined with reduced metrology errors, leads to high resolution of the experiment.
"Generation and detection of gravitational waves in the presence of large compact extra dimensions"
The concepts underlying the physics of generation
and detection of gravitational waves are substantially changed when one
consider the existence of large compact extra dimensions. However, in normal
situations these new concepts give place to the same measurable results.
In this talk, I will explain what do we mean by normal situations and in
which form the existence of large compact extra dimensions could
shows up when leaving these normal regimes.
"Energy localization in general relativity and gravitational waves"
"Hawking radiation as a probe of Quantum Gravity"
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