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Cosmology & Gravitation

This series consists of talks in the areas of Cosmology, Gravitation and Particle Physics.

Seminar Series Events/Videos

Currently there are no upcoming talks in this series.

 

Mardi nov 17, 2015
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The next hope to constrain cosmological parameters observationally is in surveys of the large scale structure (LSS) of the universe. LSS has the potential to rival the CMB in cosmological constraints because the number of modes scales like the volume, but the nonlinear clustering due to gravity makes it more difficult to extract primordial parameters. In order to take full advantage of the constraining power of LSS, we must understand it in the quasi-nonlinear regime.

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Mardi nov 10, 2015
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Cosmic neutrinos carry a wealth of information about both cosmology and particle physics, but they are notoriously difficult to observe. Rapid advancement in measurements of the cosmic microwave background, however, have allowed us to indirectly constrain some properties of the cosmic neutrino background. I will discuss the current status and future prospects for improving constraints on cosmic neutrinos, focusing in part of the phase shift of acoustic peaks in the cosmic microwave background which results from neutrino fluctuations.

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Jeudi nov 05, 2015
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Magnetars are exceptional neutron stars with the highest magnetic

fields ( 10^15 gauss) in the universe, an unusual quasi steady X

radiation (10^35 ergs/sec) and also produce flares which are some of

the brightest events (10^46 ergs in one fifth of a second) to be

recorded. There is no satisfactory model of magnetars.

The talk will cover neutron stars and a new model for the origin of

the magnetic fields in which magnetars arise from a high baryon

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Mardi nov 03, 2015

Is the graviton a truly massless spin-2 particle, or can the graviton have a small mass? If the mass of the graviton is of order the Hubble scale today, it can potentially help to explain the observed cosmic acceleration. Previous attempts to study massive gravity have been spoiled by the fact that a generic potential for the graviton leads to an instability called the Boulware-Deser ghost. Recently, a special potential has been constructed which avoids this problem while maintaining Lorentz invariance.

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Mardi oct 27, 2015

Despite being ubiquitous throughout the Universe, the fundamental physics governing dark matter remains a mystery. While this physics plays little role in the current evolution of large-scale cosmic structures, it did have a major impact in the early epochs of the Universe on the evolution of cosmological density fluctuations on small causal length scales. Studying the astrophysical structures that resulted from the gravitational collapse of fluctuations on these small scales can thus yield important clues about the physics of dark matter.

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Jeudi oct 22, 2015
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Mardi oct 20, 2015
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I will talk about a novel theory of dark matter superfluidity that matches the success of LCDM model on cosmological scales while simultaneously reproducing the MOND phenomenology on galactic scales.

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Mardi oct 13, 2015
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I will first briefly report the current status on the stability problem of global AdS space under gravitational self-interaction. I will then present evidence that the possibility of a blackhole-forming instability is strongly connected to phase-locked cascade, which is different from the usual energy cascade in turbulent flow.

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Mardi sep 29, 2015
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In order for quantum fluctuations during inflation to be converted to classical stochastic perturbations, they must couple to an environment which produces decoherence. Gravity introduces inevitable nonlinearities or mode couplings. We study their contribution to quantum-to-classical behavior during inflation. Working in the Schrodinger picture, we evolve the wavefunctional for scalar fluctuations, accounting for minimal gravitational nonlinearities. The reduced density matrix for a given mode is then found by integrating out shorter-scale modes.

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Mardi sep 22, 2015
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I describe an inflation model that can generate a cosmological magnetic seed field of nG strength on Mpc length scales today that could explain observed few microG large-scale galactic magnetic fields. I also summarize some of the extensions of this model that have been developed over the last two decades, as well as open questions about such models.

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