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Past Events

Event Date Summary
Sarah Shandera (Penn State) Tue. May 9th, 2017
11:00 am-12:00 pm

Cosmological open quantum systems

Our current understanding of the universe relies on an inherently quantum origin for the rich, inhomogeneous structure we see today. Inflation (or any of the alternative proposals for the primordial era) easily generates a universe exponentially larger than what we can observe. In other words, the modes that are observationally accessible make up an open quantum system. I will discuss what we might learn by thinking about the universe in this way, even though the quantum structure is probably not observable.

Ema Dimastrogiovanni (CWRU) Tue. April 25th, 2017
11:00 am-12:00 pm

Primordial gravitational waves: Imprints and search

Discussed will be some interesting scenarios for the generation of gravitational waves from inflation and the characteristic imprints we can search with upcoming cosmological observations.

Matthew Johnson (Perimeter Institute) Tue. April 18th, 2017
11:00 am-12:00 pm

Mapping Ultra Large Scale Structure

Anomalies in the CMB on large angular scales could find an explanation in terms of pre-inflationary physics or intrinsic statistical anisotropies. However, due to cosmic variance it is difficult to conclusively test many of these ideas using the primary cosmic microwave background (CMB) alone. In this talk, I will outline a program to place stringent observational constraints on theories that predict ultra-large scale structure or statistical anisotropies using the secondary CMB (the Sunyaev Zel’dovich effect, polarization form the post-reionization era, lensing, etc.) and tracers of large-scale structure. These methods will become accessible with next-generation CMB experiments and planned galaxy surveys.

David Chuss (Villanova) Tue. April 11th, 2017
11:00 am-12:00 pm

The Cosmology Large Angular Scale Surveyor (CLASS)

Precise observations of the cosmic microwave background have played a leading role in the development of the LCDM model of cosmology, which has been successful in describing the universe’s energy content and evolution using a mere six parameters. With this progress have come hints that the universe underwent an inflationary epoch during its infancy.  Cosmic inflation is predicted to produce a background of gravitational waves that would imprint a distinct polarized pattern on the cosmic microwave background (CMB). Measurement of this polarized signal would provide the first direct evidence for inflation and would provide a means to study physics at energy scales around the predicted GUT scale. 

Donghui Jeong (Penn State) Tue. April 4th, 2017
11:00 am-12:00 pm

Non-linearities in large-scale structure: Induced gravitational waves, non-linear galaxy bias

I will present my recent work on non-linearities in large-scale structures of the Universe. For the first part, I will discuss the gauge dependence of the scalar-induced tensor perturbations and its implication on searching the primordial gravitational wave signature from the large-scale structure. For the second part of the talk, I will give a brief overview of the recent review on large-scale galaxy bias (Desjacques, Jeong & Schmidt, 1611.09787) that contains a complete expression for the perturbative bias expansion that must hold on large scales.

Ben Monreal (CWRU) Tue. March 28th, 2017
11:00 am-12:00 pm

Nuclei, neutrinos, and microwaves: searching for the neutrino mass in tritium decay

When Enrico Fermi published his theory of beta decay in 1934—what we now call the weak interaction—he suggested how experiments could measure the neutrino mass: by looking at the shape of the energy distribution of beta decay electrons.  We’re still doing exactly that!  I will talk about the state of the art of tritium beta decay electron measurements: the KATRIN experiment, which starts science runs soon with a molecular tritium source towards sub-0.3 eV sensitivity; and the Project 8 experiment, which aims to develop a future atomic tritium experiment sensitive to neutrino masses below 0.05 eV.  

Mauricio Bustamante (CCAPP, OSU) Tue. March 21st, 2017
11:00 am-12:00 pm

Prospecting for new physics with high-energy astrophysical neutrinos

High-energy astrophysical neutrinos, recently discovered by IceCube, are fertile ground to look for new physics.  Due to the high neutrino energies — tens of TeV to a few PeV — we can look for new physics at unexplored energies.  Due to their cosmological-scale baselines — Mpc to Gpc — tiny new-physics effects, otherwise unobservable, could accumulate and become detectable.  Possibilities include neutrino decay, violation of fundamental symmetries, and novel neutrino-neutrino interactions.  I will show that the spectral features, angular distribution, and flavor composition of neutrinos could reveal the presence of new physics and,
Robert Caldwell (Dartmouth) Tue. March 7th, 2017
11:00 am-12:00 pm

Cosmology with Flavor-Space Locked Fields

We present new models of cosmic acceleration built from a cosmological SU(2) field in a flavor-space locked configuration. We show that such fields are gravitationally birefringent, and absorb and re-emit gravitational waves through the phenomenon of gravitational wave — gauge field oscillations. As a result, a cosmological SU(2) field leaves a unique imprint on both long-wavelength gravitational waves of primordial origin as well as high frequency waves produced by astrophysical sources. We show that these effects may be detected in the future using the cosmic microwave background and gravitational wave observatories.

Matthew Baumgart (Perimeter Institute) Tue. February 14th, 2017
11:00 am-12:00 pm

De Sitter Wavefunctionals and the Resummation of Time

The holographic RG of Anti-De Sitter gives a powerful clue about the underlying AdS/CFT correspondence. The question is whether similar hints can be found for the heretofore elusive holographic dual of De Sitter. The framework of stochastic inflation uses nonperturbative insight to tame bad behavior in the perturbation series of a massless scalar in DS at late times. Remarkably, this fully quantum system loses phase information and exhibits semiclassical dynamics in the leading approximation. Recasting this as a “resummation of time,” we wish understand whether the distributions that result can be thought of as an attractive UV fixed point of a theory living on a spacelike slice of DS.

Andrew Zentner (Pittsburgh) Tue. February 7th, 2017
11:00 am-12:00 pm

The Power-Law Galaxy Correlation Function

For nearly 40 years, the galaxy-galaxy correlation function has been used to characterize the distribution of galaxies on the sky. In addition, the galaxy correlation function has been recognized as very nearly power-law like despite the fact that it is measured over a wide range of scales. In particular, the galaxy correlation function has been measured on very large scales (~30 Mpc), on which density fluctuations are mild and perturbative approaches are appropriate, as well as very small scales (~0.1 Mpc), on which the evolution of the density field of the universe is quite nonlinear.

Kurt Hinterbichler (CWRU) Tue. January 31st, 2017
11:00 am-12:00 pm

Partially Massless Higher-Spin Gauge Theory

The higher spin theories of Vasiliev are gauge theories that contain towers of massless particles of all spins, and are thought to be UV complete quantum theories that include gravity, describing physics at energies much higher than the Planck scale. We discuss Vasiliev-like theories that include towers of massless and partially massless fields. These massive towers can be thought of as partially Higgs-ed versions of Vasiliev theory. The theory is a fully non-linear theory which contains partially massless modes, is expected to be UV complete, includes gravity, and can live on dS as well as AdS.

Lucile Savary (MIT) — Michelson Postdoctoral Prize Lecturer Tue. January 24th, 2017
11:00 am-12:00 pm

Quantum Spin Ice

Recent work has highlighted remarkable effects of classical thermal fluctuations in the dipolar spin ice compounds, such as “artificial magnetostatics.” In this talk, I will address the effects of terms which induce quantum dynamics in a range of models close to the classical spin ice point. Specifically, I will focus on Coulombic quantum spin liquid states, in which a highly entangled massive superposition of spin ice states is formed, allowing for dramatic quantum effects: emergent quantum electrodynamics and its associated emergent electric and magnetic monopoles. I will also discuss how random disorder alone may give rise to both a quantum spin liquid and a Griffiths Coulombic liquid–a Bose glass-like phase.

Lucile Savary (MIT) — Michelson Postdoctoral Prize Lecturer Mon. January 23rd, 2017
4:15 pm-5:15 pm

A New Type of Quantum Criticality in the Pyrochlore Iridates

The search for truly quantum phases of matter is one of the center pieces of modern research in condensed matter physics. Quantum spin liquids are exemplars of such phases. They may be considered “quantum disordered” ground states of spin systems, in which zero point fluctuations are so strong that they prevent conventional magnetic long range order. More interestingly, quantum spin liquids are prototypical examples of ground states with massive many-body entanglement, of a degree sufficient to render these states distinct phases of matter. Their highly entangled nature imbues quantum spin liquids with unique physical aspects,

Claire Zukowski (Columbia U.) Tue. January 17th, 2017
11:00 am-12:00 pm

Emergent de Sitter Spaces from Entanglement Entropy

A theory of gravity can be holographically “emergent” from a field theory in one lower dimension. In most known cases, the gravitational theory lives in an asymptotically anti- de Sitter spacetime with very different properties from our own de Sitter universe. I will introduce a second emergent “auxiliary” spacetime constructed from the entanglement entropy of subregions in the field theory. In 2d, this auxiliary space is either a de Sitter spacetime or its various identifications. The modular Hamiltonian, which encodes information about the entanglement properties of a state in the field theory,

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