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Cosmology Seminar - Wednesday

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

Due to the COVID PRECAUTIONS - All Seminars will be ONLINE via ZOOM info -

FALL 2020


Date	Speaker	Institution	Host	Title	Abstract		Zoom Link(s)
9/9/2020	Geoffrey Penington	Stanford University	Cynthia Keeler	Replica Wormholes and Quantum External Surfaces	Hawking famously argued, based on semiclassical calculations, that the radiation from evaporating black holes is always perfectly thermal and contains no information about the matter that fell in. Such a result is inconsistent with the unitarity of quantum mechanics. In this talk, I will argue that a more careful replica trick calculation shows that the gravitational path integral becomes dominated at late times by saddles containing spacetime wormholes. These wormholes cause the entropy to decrease after the Page time, consistent with unitarity, and allow information to escape from the interior of the black hole. In very simple toy models, we can evaluate the path integral exactly, and see the information emerge. In more realistic black holes, the full wormhole solutions cannot be found explicitly. However, their existence, and their most important consequences, can be derived by studying the location and properties of a non-trivial ‘quantum extremal surface’ in the original Hawking solution		Zoom link: https://asu.zoom.us/j/96750706842 Meeting ID: 967 5070 6842

9/23/2020	Tom Kephart	Vanderbilt Univ		Antichirp: Gravitational Waves from a Black Hole Orbiting in a Wormhole Geometry	After a brief review of black hole--black hole mergers, and some background on wormholes and their construction, we discuss the case of a black hole orbiting a wormhole and the gravitational waves emitted. Results are based on recent work in collaboration with James Dent, Bill Gabella and Kelly Holly-Bockelmann (arXiv:2007.09135).		Zoom Link: https://asu.zoom.us/j/93004494556 Meeting ID: 930 0449 4556
9/30/2020	Ke Fang	Kavli Stanford	Dr. Lunardini	Multi-messenger Astrophysics: Probing Compact Objects with Cosmic Particles	The study of compact objects such as black holes and neutron stars is an important component of modern astrophysics. Recent detections of astrophysical neutrinos, gamma-rays, ultrahigh energy cosmic rays, and gravitational waves open up opportunities to study compact objects with multi-messengers. In this talk, we first review the latest progress in Astroparticle Physics, including some surprising puzzles revealed by new observations. We demonstrate that the key to Multi-messenger Astrophysics is to understand and establish the link between the messengers. We then illustrate how to reach this goal from both theoretical and observational perspectives. From the theoretical side, we show that high-energy particle propagation in the vicinity of compact objects may play an important role in connecting multi-wavelength observation and source physics. From the observational side, we investigate analysis frameworks aiming to exploit data across multiple wavelengths and messengers.		Zoom Link: https://asu.zoom.us/j/93004494556 Meeting ID: 930 0449 4556

10/14/2020	Xavier Siemens	University of Wisconsin	Dr. Vachaspati	The NANOGrav search for nanohertz gravitational waves	Supermassive black hole binaries (SMBHBs), and possibly other sources, generate gravitational waves in the nanohertz part of the spectrum. For over a decade and a half the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) has been using the Green Bank Telescope, the Arecibo Observatory, and, more recently, the Very Large Array to observe millisecond pulsars. Our goal is to directly detect nanohertz gravitational waves, which cause small correlated perturbations to the times of arrival of radio pulses from millisecond pulsars. We currently monitor almost 80 millesecond pulsars with sub-microsecond precision and weekly to monthly cadences. I will present an overview of NANOGrav Physics Frontiers Center activities and summarize the results of our most recent search for a stochastic background of gravitational-waves on the 12.5-yr dataset.		Zoom Link: https://asu.zoom.us/j/93004494556 Meeting ID: 930 0449 4556

10/28/2020	Cecilia Lunardini	Arizona State University		Has IceCube observed neutrinos from the tidal disruption of stars? A concordance scenario.	When a star falls within a critical distance from a supermassive black hole, it is disrupted, and its debris are in part accreted by the black hole. The accretion in these Tidal Disruption Event (TDE) results in a flare, and, in extreme cases, it can generate a relativistic hadronic jet, where high energy neutrinos could be produced. Recently, IceCube has detected a neutrino in spatial- and time-coincidence with tidal disruption event AT2019dsg. I present a phenomenological concordance scenario for this TDE, that includes a relativistic jet with efficient neutrino production. The model is based on the observed radiation spectra from AT2019dsg, and is consistent with numerical simulations of TDEs. This scenario offers an interpretation of the IceCube observation, and suggests that X-ray bright TDEs might be promising neutrino sources		Zoom Link: https://asu.zoom.us/j/93004494556 Meeting ID: 930 0449 4556
11/4/2020 @ 5PM AZ MST	Sergey Ketov	Tokyo Metropolitan University and Kavli IPMU, Japan	Carlos Cardona	Starobinsky inflation, primordial black holes and induced gravitational waves from modified supergravity	Basic (Starobinsky) inflationary model is reviewed as the theoretical probe of a more fundamental theory of gravity. Modified supergravity is introduced as an example of such theory towards a deeper understanding of cosmological inflation and (possible) formation of primordial black holes in the early Universe. A specific model of both phenomena in modified supergravity is proposed and investigated in detail. Their observational predictions (including black hole masses, dark matter and induced gravitational waves) are derived and compared to the current and future astrophysical and cosmological observations. The seminar is designed for those who are interested in theoretical cosmology and astrophysics, theoretical high energy physics, gravitational theory and string theory.		Zoom Link: https://asu.zoom.us/j/93004494556 Meeting ID: 930 0449 4556
11/11/2020
12/2/2020

Spring 2020


Date	Speaker	Institution	Host	Title		Abstract

01/22/2020	Daniele Steer	APC (Paris)	Dr. Vachaspati	Cosmology and tests of General Relativity with gravitational waves		In the this talk I will discuss how current, and also future, GW observations can help probe the standard cosmological model and what lies beyond it. In the first part I will focus on the determination of the Hubble Constant with LIGO-Virgo, providing the latest results, and I will also explain how the errors on the Hubble constant depend on the position of the source in the sky, Namely I will try to answer the question "What would the error on $H_0$ have been had the BNS event GW170817 been in a different position in the sky"? Then we will consider what GWs can say about modified gravity, and discuss new constraints.
01/29/2020	Thomas Bachlechner	UCSD	Dr. Vachaspati	Testing the electric Aharonov-Bohm effect: electromagnetic memory vs. boundary gauge invariance		The relative phase shift of two electrons that transit distinct regions of vanishing fields, but differing electric potentials is frozen and represents an electromagnetic memory. This is the archetypal electric Aharonov-Bohm (AB). Faddeev and Jackiw proposed an alternative to Dirac quantization that removes the electric potential from the quantum theory. This in turn eliminates the electric AB effect and instead ensures boundary gauge invariance. Perhaps surprisingly, the electric AB effect was never experimentally verified, but a null observation has been reported. This motivates a new experiment that would yield a conclusive test of QED and would inform our understanding of quantum gravity.
02/05/2020	Peter Geltenbort	Institut Laue Langevin	Dr. Alarcon	Probing Early Universe Particle Physics with Neutrons		Due to their outstanding property to be storable and hence observable for long periods of time (several hundreds of seconds) in suitable material or magnetic traps, ultra-cold neutrons (UCN) with energies around 100 neV are an unique tool to study fundamental properties of the free neutron, like its beta-decay lifetime, its electric dipole moment and its wave properties. The search for the electric dipole moment (EDM) of the neutron plays a prominent role in particle physics because of its direct bearing on CP and T violation: a non-zero value of the neutron EDM would be evidence of CP and T violation. Precision measurements of the neutron lifetime provide stringent tests of the standard electroweak model as well as crucial inputs for tests of Big-Bang nucleosynthesis. Neutron lifetime can be related to CKM Matrix unitarity. Neutron lifetime also dominates the uncertainty in theoretical calculation of primordial 4He. After the observation of quantum states of UCN in the gravitational potential of the Earth, a new powerful resonance spectroscopy technique has been established. It allows precision experiments as tests of the equivalence principle and Newton’s gravity law at the micrometre scale. In this talk, current experiments linked to these fundamental questions are presented and outlook is given. A brief introduction to the Institute Laue-Langevin (ILL) in Grenoble, France, which is a world leader in academic research with neutrons will be given.
02/13/2020 (Thursday @ 12PM)	Kathryn Zurek	CalTech	Dr.Keeler	Spacetime fluctuations in AdS/CFT		Technical Talk on recent work
02/19/2020	Tanmay Vachaspati	ASU	COSMO	Dynamical quantum collapse and an experimental test		The quantum measurement problem may have a resolution in semiclassical de Broglie-Bohm theory in which measurements lead to dynamical wavefunction collapse. We study the collapse in a simple setup and find that there may be slight differences between probabilities derived from standard quantum mechanics versus those from semiclassical de Broglie-Bohm theory in certain situations, possibly paving the way for an experimental test.
02/26/2020	Benjamin Basso	ENS (Paris)	Dr. Belitsky	Six-gluon scattering amplitude at the origin in planar N=4 SYM
04/15/2020	Dr. Xiao Fang	University of Arizona	Cecilia Lunardini	ONLINE ONLY	Join from PC, Mac, Linux, iOS or Android:	Zoom Info link:	https://asu.zoom.us/j/325364671
04/22/2020	Prof. Lam Hui	Columbia University		ONLINE ONLY	Join from PC, Mac, Linux, iOS or Android:	Zoom Info link:	https://asu.zoom.us/j/91489619064
04/29/2020
05/13/2020	Seminar cancelled

FALL 2019


Date	Speaker	Institution	Title	Host	Abstract
9/11/2019	FALL 2019 Welcome Reception	ASU		Tanmay Vachaspati
9/18/2019	Henry Lamm	University of Maryland	Quantum Computers for Quantum Field Theory	Rich Lebed	The advent of quantum computing for scientific research presents the possibility of calculating time-dependent observables in quantum field theories like viscosity and parton distributions. In order to utilize this new tool, a number of theoretical and practical issues must be addressed related to efficiently digitize, initialize, propagate, and evaluate quantum field theory. In this talk, I will discuss a number of projects being undertaken by the NuQS collaboration to realize calculations on NISQ era and beyond quantum computers.
9/25/2019	Ryan Westernacher-Schneider	University of Arizona	Multimessenger Seismology of Core-Collapse Supernovae	Dr. Lunardini	Asteroseismology of the inner core of a core-collapse supernova is possible in principle with gravitational waves and neutrinos. The excitation of a linear mode of the core can imprint itself on the neutrino luminosity, provided the mode amplitude is large enough in the vicinity of the neutrinosphere. This can occur with sufficient rotation. Thus, neutrinos carry information about the mode excitation at the neutrinosphere radii, whereas gravitational waves probe deeper.
10/1/2019	Ubirajara van Kolck	Institut de Physique Nucleaire d'Orsay and University of Arizona	A New Leading Mechanism for Neutrinoless Double-Beta Decay	Matthew Baumgart	A new leading mechanism for neutrinoless double-beta decay or how to attract the ire of the community. The neutrinoless double-beta decay of nuclei is essentially the only way to test lepton-number violation coming from the possible Majorana character of neutrinos. Tremendous effort is dedicated to its measurement and to reducing the theoretical uncertainty in the calculation of the nuclear matrix elements needed for its interpretation. We increase the uncertainty.
10/9/2019	Yue Zhao	University of Utah	Searching for Dark Photon Dark Matter with Gravitational Wave Detectors	Matthew Baumgart	If dark matter stems from the background of a very light gauge boson, this gauge boson could exert forces on test masses in gravitational wave detectors, resulting in displacements with a characteristic frequency set by the gauge boson mass. We outline a novel search strategy for such dark matter, assuming the dark photon is the gauge boson of U(1)_B or U(1)_{B-L}. We show that both ground-based and future space-based gravitational wave detectors have the capability to make a 5-sigma discovery in unexplored parameter regimes.
10/16/2019	Thiago Fleury	Federal University of Rio Grande do Norte	Correlation Functions in N=4 SYM and Integrability	Andrei Belitsky	In this set of three lectures, I will explain a method for computing correlation functions in N=4 Super-Yang-Mills using integrability. The method consist in decomposing the correlators into integrable form-factors and it is nonperturbative. The first lecture will contain a brief review of N=4 SYM and the hexagon form-factor will be introduced. The process of gluing hexagons together will also be described. If time permits, the fishnets theories which are deformations of N=4 SYM wiil also be described. In the second lecture, I will compute some examples of correlations functions and discuss the multi-particle process. The third lecture will contain nonplanar corrections and a list of open problems and recent results
10/23/2019	Heling Deng	Arizona State University	Primordial black holes from primordial bubbles	Tanmay Vachaspati	I will show a new mechanism of primordial black holes, where the black holes are formed from bubbles that possibly nucleate during inflation. These black holes may have a wide distribution of masses and some interesting astronomical effects subject to observational constraints.
10/30/2019	Sergej Moroz	Technical University of Munich	Confined phases of fermions coupled to Z2 gauge fields	Andrei Belitsky	After briefly summarizing my long-term interest in quantum physics of low-dimensional spinless fermions that attract each other, I will present our recent study of a quantum many-body lattice system of one-dimensional fermions interacting with a dynamical Z2 gauge field. The gauge field mediates long-range attraction between fermions resulting in their confinement into bosonic dimers. At strong coupling we developed an exactly solvable effective theory of such dimers with emergent constraints. I will show that even at a generic coupling and fermion density, the model can be rewritten as a local spin 1/2 chain and forms a Luttinger liquid. In a finite chain we observed the doubling of the period of Friedel oscillations which paves the way towards experimental detection of confinement in this system. Finally, I will also discuss the possibility of a Mott phase at the commensurate filling 2/3, connection to quantum scars and our plans to extend this study to two spatial dimensions in pursuit of exotic p-wave superfluidity.
11/6/2019	Atsushi Naruko	Yukawa Institute for Theoretical Physics	Possible resolution of a spacetime singularity with field transformations	George Zahariade	In this talk, we show that there is a class of spacetime curvature singularities which can be resolved with metric and matter field transformations. As an example, we consider an anisotropic power-law inflation model with gauge and scalar fields in which a space-like curvature singularity exists at the beginning of time. First, we provide a transformation of the metric to the flat geometry. The transformation is regular in the whole region of spacetime except for the singularity. Thus the geometry becomes extendible beyond the singularity. In general, matter fields are still singular after such a metric transformation. However, we explicitly show that there is a case in which the singular behavior of the matter fields can be completely removed by a field re-definition. Since the action is invariant under any metric and matter field transformations, the regularity of the action at the original singularity is a necessary condition for the complete removal of a singularity.
11/13/2019	Ira Z. Rothstein	Carnegie Mellon University	Effective field theory for quantum mechanical black holes	Matthew Baumgart	I will present an effective theory of Schwarzschild black holes which captures the physics of Hawking radiation. The formalism can be used to calculate quantum gravity effects due to the horizon in processes involving scattering of and off of holes.
11/20/2019	Jaime Besprosvany	UNAM	Heavy quarks within the electroweak multiplet	Tanmay Vachaspati	Standard-model fields and their associated electroweak Lagrangian are equivalently expressed in a shared spin basis. The scalar-vector terms are written with scalar-operator components acting on quark-doublet elements, and shown to be parametrization-invariant. Such terms, and the t- and b-quark Yukawa terms are linked by the identification of the common mass-generating Higgs operating upon the other fields, after acquiring a vacuum expectation value v. Thus, the customary vector masses are related to the fermions', fixing the t-quark mass mt with the relation mt^2 +mb^2 =v^2/2 either for maximal hierarchy, or given the b-quark mass mb, implying mt≃173.9 GeV, for v=246 GeV. A sum rule is derived for all quark masses that generalizes this restriction. An interpretation follows that electroweak bosons and heavy quarks belong in a multiplet.
HOLIDAY - THANKSGIVING
12/4/2019	Jun Nian	Leinweber Center for Theoretical Physics, University of Michigan	Microstate Counting of Asymptotically AdS (Near-)BPS Black Holes and Hawking Radiation	Cynthia Keeler	The problems of counting the microstates of asymptotically flat and AdS_3 BPS black holes were solved in 90s. Despite the great success of the AdS/CFT correspondence, the same problem for asymptotically AdS_5 BPS black holes had remained open for many years. Recently, several different groups resolved this problem by deriving the entropy function of 1/16-BPS AdS_5 black holes from N=4 SYM using supersymmetric localization or superconformal index. Inspired by this work, we can also count the microstates for both BPS and near-BPS asymptotically AdS black holes in various dimensions. More interestingly, we obtain a microscopic derivation of the Hawking radiation for near-extremal asymptotically AdS_5 black holes, generalizing the well-known work by Callan and Maldacena. In this talk I will briefly review the historical developments, and discuss some aspects of these new approaches on black hole microstate counting. This talk is based on the papers 1907.02505, 1909.07943 and some work in progress.

Spring 2019


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	Quantum strong energy inequality and the Hawking singularity theorem	Dr. Vachaspati	Hawking's singularity theorem concerns matter obeying the strong energy condition (SEC), which means that all observers experience a nonnegative effective energy density (EED), thereby guaranteeing the timelike convergence property. However, some classical and all quantum fields, violate the SEC. Therefore there is a need to develop theorems with weaker restrictions, namely energy conditions averaged over an entire geodesic and quantum energy inequalities (QEIs), weighted local averages of energy densities.
5/1/2019	Timothy Tait	UC Irvine	An Early Phase of QCD Confinement and the Baryon Asymmetry of the Universe	Dr. Baumgart	I’ll explore the possibility that physics beyond the Standard Model influences the phase transition in which the strong nuclear force moves from being described by a plasma of quarks and gluons to an ensemble of confined hadrons in the early Universe. The Standard Model predicts that this transition happens at temperatures around 1 GeV, and I will discuss the possibility that it happens much earlier — around temperatures of 1 TeV.

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