Cosmology and gravity seminars 2016-2017

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Past seminars

  Thursday September 28, 2pm, room 110

Sergey Sibiryakov (CERN) : Beta-functions and asymptotic freedom in (2+1)-dimensional Horava gravity

  Thursday June 15, 2pm, room 110

Chiara Caprini (APC Paris) : Cosmology with gravitational wave detection, Part 2

The space based interferometer LISA has a great potential in probing cosmology. This talk presents two observables through which LISA could provide us with new information on the characteristics of the universe, complementary to what can be gathered from electromagnetic observations : the detection of a stochastic background of gravitational waves coming from the very early universe, and the use of massive black hole binaries as standard sirens to test the expansion of the universe.

  Thursday May 18, 2pm, room 110

Antoine Klein (IAP Paris) : Fourier domain gravitational waveforms for eccentric precessing systems

With the advent of gravitational wave astronomy, it is important to develop reliable and efficient waveforms to extract the maximum information out of binary coalescence signals. Spin-induced precession has been known to encapsulate useful information, by modulating the signal in such a way as to break some parameter degeneracies and improve parameter estimation. Some binary formation models predict a significant residual eccentricity for observable systems, and information about eccentricity and spins will be useful for discriminating between different such models. I will present here an efficient Fourier-domain gravitational waveform that encapsulate both those effects, that will be useful to measure eccentricity, spin magnitude and spin alignment together in gravitational wave experiments.

  Thursday April 6, 2pm, room 110

Sebastian Garcia-Saenz (IAP) : Galileon p-form theories

  Thursday March 16, 2pm, room 110

Matteo Bonetti (Universita degli Studi dell’Insubria) : Post-Newtonian Dynamics of Massive Black Hole Triplets

Massive black-hole binaries (MBHBs) are thought to be the main source of gravitational waves (GWs) in the low-frequency domain surveyed by ongoing and forthcoming Pulsar Timing Array campaigns and future space-borne missions, such as LISA. However, many low-redshift MBHBs in realistic astrophysical environments may not reach separations small enough to allow significant GW emission. We investigate about the possibility that this "last-parsec problem" can be eased by the appearance of a third massive black hole (MBH) as a consequence of a second galaxy merger. The perturbation induced by this third MBH can generate a very complex dynamics and can force, under certain conditions, the former MBHB on a very eccentric orbit, hence allowing intense GW emission eventually leading to coalescence. A detailed assessment of the process requires a general relativistic treatment, but also the inclusion of the environmental effects due to the stellar background. In order to tackle this problem, we have developed a three-body Post-Newtonian (PN) code framed in a realistic galactic potential, including both general relativistic corrections up to 2.5PN order and dissipative environmental effects. In this talk, I will depict how the various phenomena that characterize such a three-body interaction can affect its dynamics and I will provide some representative examples.

  Wednesday March 1, 2pm, room 110

Blaise Gouteraux (Nordita) : Bad Metals, Density Waves and Black Holes

So-called ’bad metals’ present a long-standing conundrum to theory. In particular, their electric resistivity is too high to be accounted for by weakly coupled quasiparticles as in conventional metals. In this talk, I will argue that ac and dc transport in the bad metallic regime can be explained by a long wavelength description of fluctuating charge density waves. Both ac and dc transport are governed by Planckian dynamics, which suggests that quantum fluctuations play an important role. I’ll conclude by mentioning how gauge/gravity duality can be used to efficiently perform calculate conductivities in the quantum critical regime.

  Thursday February 23, 2pm, room 110

Chiara Caprini (APC Paris) : Cosmology with gravitational wave detection

The space based interferometer LISA has a great potential in probing cosmology. This talk presents two observables through which LISA could provide us with new information on the characteristics of the universe, complementary to what can be gathered from electromagnetic observations : the detection of a stochastic background of gravitational waves coming from the very early universe, and the use of massive black hole binaries as standard sirens to test the expansion of the universe.

  Thursday November 17, 2pm, room 110

Clement Berthiere (LMPT Tours) : Boundary effects in entanglement entropy

Entanglement entropy is a useful tool which plays an important role in modern physics. The geometrical nature of entanglement entropy explains why it finds so many applications in various fields of physics, from black holes and holography to integrable models and quantum computers. For conformal field theories, the entanglement entropy plays a special and important role since the logarithmic terms in the entropy are related to the conformal anomalies. Recently there has been some progress in understanding the conformal anomalies in the case where the spacetime is not infinite but has some boundaries. It is interesting that in the presence of boundaries the integrated anomaly is non-vanishing in odd spacetime dimensions, the relevant contribution being produced by the boundary terms only. The boundary phenomenon in entanglement entropy is more general and is not restricted only to conformal field theories. Yet, the explicit calculations for arbitrary boundaries and surfaces are technically complicated, if even possible. Therefore, it is instructive to first analyze the problem in some simple cases, wher e the spacetime is flat and the boundary is composed by a collection of planes.

  Thursday October 27, 2pm, room 110

Marios Petropoululos (CPHT, Ecole Polytechnique) : Holography, duality and integrability

  Thursday October 13, 2pm, room 110

Victor Berezin (INR Moscow) : Particle creation phenomenology, Dirac sea and the induced Weyl and Einstein-dilaton gravity

  Thursday October 6, 2am, room 110

Alessandro Fabbri (Enrico Fermi Ctr., Rome & Orsay, LPT) : Quantum backreaction in rotating BTZ black holes

  Thursday September 29, 11am, room 114

Yann Mambrini (LPT Orsay) : Dark matter : an historical perspective

I will review in this seminar this historical evolution of the concept of"Dark Matter", from the first observations of "anomalies" in the 30’s until the development of the hypothesis of the existence of a dark halo. The presentation will be entirely based on the original historical authors, reconstructing (by their ideas but also their mistakes) the appearance of a dark side of the Universe. The talk will include discussions of original articles by Poincaré, Zwicky, Oort, Jansky, Gamow, Peebles, Zeldovich, Bond and many others, opening on the prospect for the near future.