Cosmology Seminar - Wednesday

The Cosmology Seminars are scheduled on Wednesdays from 2:00pm-3:00pm.

Barry Goldwater Building, 5th floor, Conference Room 505


Date	Speaker	Institution	Title	Host	Abstract

1/30/2019	George Zahariade	ASU	Classical-Quantum Correspondence and Backreaction	Dr. Vachaspati	We map the quantum problem of a free bosonic field in a space-time dependent background into a classical problem. N degrees of freedom of a real field in the quantum theory are mapped into 2*N^2 classical simple harmonic oscillators with specific initial conditions. We discuss how this classical-quantum correspondence (CQC) may be used to evaluate quantum radiation and also to analyze the backreaction of quantum fields on classical backgrounds. We also analyze the agreement between results obtained with the CQC and with a full quantum analysis
2/6/2019	Raisa Trubko	Harvard	Precision Tune-out Wavelength Measurement with Atom Interferometry	Dr. Lunardini	Precision measurements of atomic properties are important because they serve as a benchmark test of atomic structure calculations of line strengths, oscillator strengths, and dipole matrix elements. In this talk, I will describe how I used a three nanograting Mach-Zehnder atom beam interferometer to make precision measurements of atomic properties, such as polarizabilities and tune-out wavelengths (where the polarizability is zero). I will present my measurement of the longest tune-out wavelength in potassium, 768.9701(4) nm. This result is 7.5 times more precise than state-of-the-art calculations. I will also explain how tune-out wavelength measurements can be remarkably sensitive to rotation rates and will demonstrate a new type of atom interferometer gyroscope that uses tune-out wavelengths. Lastly, I will describe my current research, where I use nitrogen-vacancy centers in diamond to measure magnetic fields with high spatial resolution.

2/20/2019	Christoph Keller	University of Arizona	Holographic Conformal Field Theories in Two Dimensions	Dr. Keeler	Conformal Field Theories (CFTs) in two dimensions can be described mathematically by the theory of Vertex Operator Algebras. This allows a more rigorous study of their properties, and allows the construction of large classes of examples. I'll explain the differences between 2d CFTs and higher dimensional CFTs. I'll then present work on holographic 2d CFTs, that is CFTs which can describe quantum gravity on anti-de Sitter space through the AdS/CFT correspondence. I'll discuss new examples constructed from orbifolds, and the relation between the growth of the number of states and black hole entropy.
2/27/2019	Maulik Parikh	ASU	Forever Never Lasts: The Unruh-de Sitter State and the End of Eternal Inflation	Dr. Wilczek	Motivated by black hole physics, I will define the Unruh state for de Sitter space. Like the Bunch-Davies state, the Unruh-de Sitter state appears thermal to a static observer. However, the Unruh-de Sitter state breaks some of the de Sitter symmetries. Nevertheless, it may be a natural vacuum state for patches of de Sitter space. I will then show by explicit calculation in two dimensions that the Unruh-de Sitter state carries a negative vacuum energy density that, when extrapolated to the s-wave sector in four dimensions, backreacts on the de Sitter geometry semi-classically. This causes de Sitter space to be destabilized on a timescale set by the gravitational entropy. Analogous to black hole evaporation, the endpoint of this instability is a singular geometry outside the regime of effective field theory. If these calculations are correct, "eternal" inflation will come to an end, possibly preventing the population of the landscape of string vacua.
3/13/2019	Yanou Cui	UC Riverside	Probing the early Universe with gravitational waves from cosmic strings	Dr. Vachaspati	Many motivated extensions of the Standard Model of particle physics predict the existence of cosmic strings. Gravitational waves originating from the dynamics of the resulting cosmic string network have the ability to probe many otherwise inaccessible properties of the early universe. In this study we show how the spectrum of gravitational waves from a cosmic string network can be used to test the equation of state of the early universe prior to Big Bang Nucleosynthesis (BBN). We also demonstrate that current and planned gravitational wave detectors such as LIGO, LISA, DECIGO/BBO, and ET/CE have the potential to detect signals of a non-standard pre-BBN equation of state and evolution of the early universe (e.g., early non-standard matter domination or kination domination) or new degrees of freedom active in the early universe beyond the sensitivity of terrestrial collider experiments and cosmic microwave background measurements.
3/20/2019	Andrew Long	University of Michigan	Ultra-light dark photons from a network of cosmic strings	Dr. Vachaspati	A variety of experimental efforts are currently underway to detect ultra-light dark photon dark matter — a spin-1 particle dark matter candidate with mass below 1 eV. However, dark photon dark matter has a notorious production problem: it is challenging to write down a model that yields the correct relic abundance of non-relativistic dark photons. In this talk I will discuss how dark photon dark matter is created from a network of near-global, Abelian-Higgs cosmic strings. These strings are expected to survive in the universe today, and their motions create a stochastic gravitational wave noise.
3/27/2019	Yuber Perez	Fermi Lab	Neutrinos in Dark Matter detection experiments: Standard Model and Beyond.	Dr. Lunardini	Negative results of direct detection searches so far have driven proposals for the next generation experiments with higher exposures. Nevertheless, such future facilities will face an irreducible background coming from the coherent elastic scattering of solar and atmospheric neutrinos with the nuclei in the detector. Such background is usually parametrized through the introduction of a neutrino discovery limit, a neutrino floor. Interestingly, if beyond the Standard Model interactions are present in the scattering, the neutrino floor can be significantly modified; thus, direct detection experiments can constrain such new interactions. We will present flavor dependent and independent scenarios of non-standard neutrino interactions, and we will show their impact in future searches.

4/10/2019	Andres Luna	UCLA	Black holes and the double copy.	Dr. Keeler	The double copy relates scattering amplitudes in gauge and gravity theories,and it was shown later that similar relations occur between classical solutions, including black holes.
4/17/2019	Lucien Heurtier	UofA	EeV scale dark-matter: production mechanism through the inflaton portal and experimental signatures using the ANITA collaboration	Dr. Baumgart	In this talk I will present two models involving a very heavy dark matter candidate of mass as large as the EeV scale. In a first part I will present an original paradigm for producing such a dark-matter candidate in which the only contact between the Standard Model and dark-matter particles is the inflationary sector. I will show that such framework is strongly constrained by the study of inflationary observables and the presence of an early domination era. Given that such a dark-matter candidate can be produced in the early universe in one way or another, I will then expose the possibility that a heavy dark-matter particle couples to right-handed neutrinos and has some signature in the neutrino sector, interpreting the ANITA anomalous events and IceCube PeV events reported recently as coming from a decay of dark-matter in the galaxy.
4/24/2019	Eleni Kontou	University of York		Dr. Vachaspati
5/1/2019	Timothy Tait	UC Irvine		Dr. Baumgart
5/8/2019	Daniele Alves	LANL		Dr. Baumgart

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