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Friday Seminar

The Cosmology Lunch Seminar are scheduled on Fridays from 12:00pm-1:00pm.

Barry Goldwater Building, 5th floor, Conference Room 505

FALL 2019

DateSpeakerInstitution Title Abstract
9/6/2019
9/13/2019
9/20/2019
9/27/2019
10/4/2019Mustafa AminRice
10/11/2019
10/18/2019
10/25/2019
11/1/2019
11/08/2019
11/15/2019
11/22/2019Levon PogosianSimon Fraser
11/29/2019
12/6/2019
12/13/2019

Spring 2019

Date SpeakerInstitutionTitle Abstract
2/1/2019Joseph LesnefskyASUGeodesic completenessUnderstanding the geometric constraints required for geodesic completeness
2/8/2019Victoria MartinASU Connecting quasinormal modes and heat kernels We connect two different approaches for calculating functional determinants on quotients of hyperbolic spacetime: the heat kernel method and the quasinormal mode method. For the example of a rotating BTZ background, we show how the image sum in the heat kernel method builds up the logarithms in the quasinormal mode method, while the thermal sum in the quasinormal mode method builds up the integrand of the heat kernel. More formally, we demonstrate how the heat kernel and quasinormal mode methods are linked via the Selberg zeta function. We show that a 1-loop partition function computed using the heat kernel method may be cast as a Selberg zeta function whose zeros encode quasinormal modes. We discuss how our work may be used to predict quasinormal modes on more complicated spacetimes
2/15/2019Southwest Strings MeetingASU Website: https://southweststringsme.wixsite.com/2019
2/22/2019Andy SveskoASUHamiltonian Analysis of Vacuum Energy SequesteringI carry out the Hamiltonian analysis of the local vacuum energy sequestering model -- a manifestly local and diffeomorphism invariant extension of general relativity which has been shown to remove the radiatively unstable contribution to the vacuum energy generated by matter loops. I will show that the degravitation of this UV sensitive quantity is enforced via global relations that are a consequence of the model’s peculiar constraint structure.
3/1/2019Ayush SaurabhASUDecay of Cosmic String Loops Due to Particle Radiation.Constraints on the tension and the abundance of cosmic strings depend crucially on rate at which they decay into particles and gravitational radiation. I will talk about our study of the decay of cosmic string loops in the Abelian-Higgs model. We have found that the half-life of a loop is proportional to L^2, where L is the length of the loop. Since the half-life due to gravitational wave emission scales in proportion to L, we conclude that particle emission is the primary energy loss mechanism for smaller loops, while gravitational emission dominates for loops larger than a certain transition length that is inversely proportional to the string tension. Implications of these results for observational bounds on cosmic strings will be discussed.
3/8/2019Latham BoylePerimeter InstituteCPT-Symmetric UniverseI will introduce our recent proposal that the state of the universe does *not* spontaneously violate CPT. Instead, the universe after the big bang is the CPT image of the universe before it, both classically and quantum mechanically. The pre- and post-bang epochs comprise a universe/anti-universe pair, emerging from nothing directly into a hot, radiation-dominated era. CPT symmetry selects a unique QFT vacuum state on such a spacetime, providing a new interpretation of the cosmological baryon asymmetry, as well as a remarkably economical explanation for the cosmological dark matter. Requiring only the standard three-generation model of particle physics (with right-handed neutrinos), a Z_2 symmetry suffices to render one of the right-handed neutrinos stable. We calculate its abundance from first principles: matching the observed dark matter density requires its mass to be 4.8 x 10^{8} GeV. Several other testable predictions follow: (i) the three light neutrinos are Majorana and allow neutrinoless double beta decay; (ii) the lightest neutrino is massless; and (iii) there are no primordial long-wavelength gravitational waves. The proposal also has interesting things to say about the strong CP problem and the observed electrodynamic arrow of time.
3/16/2019Logan ThomasASUCosmological Correlation Functions and Conformal Field TheoryIn this talk, we will review the in-in formalism for calculating correlation functions in cosmology. Then, within the context of conformal field theory, we will discuss the analytic continuation of correlators from Euclidean to Lorentzian time.
3/22/2019Jonathan LunineCornellThe search for life in the Ocean Worlds of the solar system. Please Note this talk will be @ ISTB4 ROOM 240The ocean worlds of the solar system include the Earth, and outer solar system bodies known or suspected to have liquid water in their interiors. Those for which the evidence is very strong are Jupiter’s moon Europa, and Saturn’s moons Enceladus and Titan. Our knowledge of each differs, and it is Enceladus for which we have remarkably detailed evidence about the interior ocean thanks to a plume of gas, ice and dust that emanates from the interior. The search for evidence of life can begin there, while for Europa additional information is needed from the upcoming Europa Clipper mission. And for Titan, the enigmatic methane seas provide a chance to look for biology based on a different chemical toolkit than that for water-based life.
4/5/2019Zidu LinASUDetectability of neutrinos from binary compact-object mergersIn this work, we propose a long-term strategy for detecting neutrinos from the remnant of binary compact-object mergers with a future M-ton water-Cherenkov detector such as Hyper-Kamiokande. Neutrino luminosity and average energy from the merger remnant are extracted from several state-of-the-art binary merger simulations and are applied to our estimation of signal events on a M-ton water detector on the Earth. By using the timing information from gravitational-wave detector, we only focus on Δt≈1s after each merger. The neutrino backgrounds from other sources will then be greatly reduced and the probability to detect statistically significant neutrino signals from mergers increases. The central remnant of a binary merger is not well-determined given initial binary parameters. It can immediately collapse to a black hole, or evolve to a hyper massive neutron star, or even evolve to a stable massive neutron star. We consider all these 3 possibilities and calculate the corresponding neutrino signal events on a Cherenkov detector. The main goal of this project is to study under which scenario the binary mergers will give us unambiguous neutrino signals on a M-ton scale water detector. If the neutrino signals from mergers can be observed, we will have a better chance to understand the mechanism of binary mergers, the production of short gamma ray burst, as well as heavy element nucleosynthesis.
4/19/2019Tucker MantonASUGradient instabilities of cosmological time crystals and their cure from effective field theory.The effective field theory (EFT) of Dark Energy provides a novel environment in which to study stability aspects of scalar fields in an expanding Friedmann universe. Focusing on four dimensions, the EFT is carried out on three dimensional hypersurfaces defined by constant scalar field. This explicitly breaks time diffeomorphism invariance and has the effective of moving the scalar degree of freedom out of the matter field and into the metric. Crucially, this process leaves the background equations unaffected, allowing for a systematic study of the metric perturbations. The EFT operators have a significant effect on the propagation speed (or sound speed) of the scalar perturbations. We apply these operators to scalar fields that exhibit oscillatory dynamics in their lowest energy states. Such fields are cosmological realizations of time crystals, and generally suffer from instabilities stemming from cycles where the sound speed becomes imaginary. This is referred to as a gradient instability, and we show how the EFT operators serve to correct the instability, providing the first example of stable cosmological time crystals in the literature.
4/26/2019Eric PerlmutterCal TechRegge Trajectories in Conformal Field Theory and Bound States in 3D Quantum GravityI will describe some aspects of the structure of operator spectra and correlations in conformal field theories, and their holographic interpretation in quantum gravity. This will include a formula for the gravitational binding energy of multi-particle states in 3D AdS quantum gravity at finite Newton's constant, which has a precise interpretation in two-dimensional conformal field theories. Our results employ modern methods of the conformal bootstrap.
5/3/2019Yasha ShnirTrinity College DublinSpinning black holes with Skyrme hairHere the scalar hairs represent topologically trivial clouds surrounding rotating black hole, they are counterparts of the "cloudy" black holes in the Einstein-Klein-Gordon theory, that trivialise both in the absence of a black hole and in the at flat space limit. We found that the spinning axially symmetric cloudy solutions of the O(3) sigma model also exist in the regular asymptotically flat space-time without the event horizon. These congurations are similar to the usual rotating boson stars, which, in the at flat space limit are linked to the axially symmetric Q-balls, in both cases the solutions exist for some restricted range of values of the angular frequency and possess a quantized angular momentum. However, unlike boson stars in the model with sextic potential, the O(3) scalar clouds do not posses a at space limit. We show that, depending on the values of the parameters of the model and the Hawking temperature, the branch structure of the cloudy solutions varies from the usual inspirraling pattern, which is typical for the boson stars, to the two branch structure, similar to that of the black holes with Skyrme hairs