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.

 

Tuesday Jan 12, 2016

Fast radio bursts (FRBs) are bright, broadband, non-repeating, millisecond flashes of unknown astronomical origin.

Collection/Series: 
Scientific Areas: 

 

Tuesday Dec 15, 2015
Speaker(s): 

In this talk I derive the evolution equations for two scalar fields with non-canonical field space metric up to third order in perturbation theory, employing the covariant formalism. These equations can be used to calculate the local bi- and trispectra of the non-minimal ekpyrotic model. Remarkably, the nearly scale-invariant entropy perturbations have vanishing bi- and trispectra during the ekpyrotic phase.

Collection/Series: 
Scientific Areas: 

 

Tuesday Dec 08, 2015

In light of the upcoming Generation 2 (G2) direct-detection experiments attempting to record dark matter scattering with nuclei in underground detectors, it is timely to inquire about their ability to single out the correct theory of dark-matter-baryon interactions, in case a signal is observed. I will present a recent study in which we perform statistical analysis of a large set of direct-detection simulations, covering a wide variety of operators that describe scattering of fermionic dark matter with nuclei.

Collection/Series: 
Scientific Areas: 

 

Tuesday Dec 01, 2015
Speaker(s): 

With the completion of the Planck satellite, in order to continue collecting cosmological information it is

important to gain a precise understanding of the formation of Large Scale Structures (LSS) of the universe.

The Effective Field Theory of LSS (EFTofLSS) offers a consistent theoretical framework that aims to develop

an analytic understanding of LSS at long distances, where inhomogeneities are small. We present the recent

Collection/Series: 
Scientific Areas: 

 

Thursday Nov 19, 2015
Speaker(s): 

We argue that theories with multiple axions generically contain a large
number of vacua that can account for the smallness of the cosmological
constant. In a theory with N axions, the dominant instantons with charges Q
determine the discrete symmetry of vacua. Subleading instantons break the
leading periodicity and lift the vacuum degeneracy. For generic integer charges
the number of distinct vacua is given by |det(Q)|~exp(N). Our construction
motivates the existence of a landscape with a vast number of vacua in

Collection/Series: 
Scientific Areas: 

 

Tuesday Nov 17, 2015
Speaker(s): 

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.

Collection/Series: 
Scientific Areas: 

 

Tuesday Nov 10, 2015
Speaker(s): 

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.

Collection/Series: 
Scientific Areas: 

 

Thursday Nov 05, 2015
Speaker(s): 

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

Collection/Series: 
Scientific Areas: 

 

Tuesday 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.

Collection/Series: 
Scientific Areas: 

 

Tuesday 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.

Collection/Series: 
Scientific Areas: 

Pages