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Friday Seminar

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

 All Seminars will be hosted In-Person | Goldwater Building 5th floor | Conference room 505


DateSpeakerInstitutionFaculty HostTitleAbstract
1/27/2023Raphaela WutteTU WienCindy KeelerHyperbolic Mass and Gluings of Initial DataThe question of boundedness of mass from below in general relativity for negative cosmological constant is wide open. For time-symmetric initial data sets, this is the question of whether the mass of asymptotically locally hyperbolic spaces is bounded from below. After giving a short review of the currently known bounds, I describe the construction of asymptotically locally hyperbolic spaces with constant negative scalar curvature, conformal infinity of arbitrary high genus, and negative total mass. (based on joint work with Piotr Chruściel and Erwann Delay)
2/2/2023 - THURSDAY @ 11 AMKevin HarringtonUMASSSeth CohenPASSAGES into the ISM conditions of high-z starburstsThe peak epoch of cosmic star formation also broadly coincides with the peak in the cosmic co-moving molecular gas mass density, at z ~ 2, but we do not have a full understanding of the array of processes that turn gas into stars at high redshift. Even with sensitive interferometers, only strongly lensed galaxies offer the feasibility to efficiently and systematically detect multiple emission lines tracing the multi-phase interstellar medium (ISM) for high-z galaxies. In the past few years, our team has developed the Planck All-Sky Survey to Analyze Gravitationally-lensed Extreme Starbursts (PASSAGES) in order to conduct such systematic studies to better understand the most active star-forming galaxies in the early Universe. In this talk I will focus on results from state-of-the-art radiative transfer modelling using the largest assembly of ~200 CO/[CI] lines for any high-z sample to-date, explicitly deriving the infamous alpha conversion factors without assuming any excitation corrections or typically applied values. I will discuss the implications based on such spatially unresolved measurements, and further describe an overview of the diversity of follow-up studies to further probe the multi-phase ISM in these PASSAGES.
2/3/2023Fumio UchidaUniversity of TokyoTanmay VachaspatiToward the description of the evolution of the primordial magnetic fieldMagnetic fields are observed everywhere in the present universe. Among them, the intergalactic magnetic field in voids is likely separated from astrophysics and therefore implies its cosmological origin. Many mechanisms for generating the primordial magnetic field in the early universe have been proposed, which may be tested by the observation of the intergalactic magnetic field in voids. However, the description of the evolution of the primordial magnetic field after its generation was not complete, due to the difficulty of analyzing nonlinear magneto-hydrodynamics. In the talk, I will introduce a simple analysis based on the recently proposed conserved quantity, Hosking integral. If time allows, I will also briefly advertise my previous work constraining the scenarios of magnetogenesis.
2/24/2023Don PageUniversity of AlbertaPaul DaviesPossibilities for ProbabilitiesIn ordinary situations involving a small part of the universe, Born's rule seems to work well for calculating probabilities of observations in quantum theory. However, there are a number of reasons for believing that it is not adequate for many cosmological purposes. Here a number of possible generalizations of Born's rule are discussed, explaining why they are consistent with the present statistical support for Born's rule in ordinary situations but can help solve various cosmological problems.
3/3/2023Nemanja KaloperUC DavisLars AalsmaA Quantum-Mechanical Mechanism for Reducing the Cosmological ConstantWe discuss a mechanism which dynamically adjusts cosmological constant toward 0+. The adjustment is quantum-mechanical, discharging cosmological constant in random discrete steps. It renders de Sitter space unstable, and triggers its decay toward Minkowski. Since the instability dynamically stops at vanishing cosmological constant, the evolution favors the terminal Minkowski space without a need for anthropics. The mechanism works for any QFT coupled to gravity.
4/14/2023 Scott WatsonSyracuseDamien Easson
4/21/2023Levon PogosianSimon Fraser UniversityTanmay Vachaspati

FALL 2022

DateSpeakerInstitutionTitleAbstractFaculty Host
8/19/2022Dr. Jeremy LimUniversity of Hong KongReading the Historical Record of Cluster Evolutionary Growth from the Thermodynamics of the Intracluster MediumGalaxy clusters are immersed in hot-Xray emitting gas constituting their intracluster medium (ICM). This gas, accreted from the surroundings, is heated by converting its potential to thermal energy on infalling into a galaxy cluster - and therefore preserves a historical record of the cluster growth. Galaxy clusters are known to display a variety of ICM thermodynamic profiles, indicating that they are in different physical states. Furthermore, some clusters host, at their centres, giant elliptical galaxies that are engaged in star formation, suspected to be fuelled by cooling of the ICM. Here, we show how to read the historical record of cluster growth from the ICM thermodynamics, thus providing an improved understanding of how galaxy clusters reached their observed physical states. We also explain the connection between star formation in cluster central elliptical galaxies and the ICM properties of their host clusters.Rogier Windhorst
09/16/2022Claire ZukowskiArizona State UniversityEntanglement Berry PhasesHolography encompasses the duality between a “boundary” conformal field theory in a particular state and a “bulk” asymptotically anti- de Sitter geometry. In the holographic context, I will describe a boundary parallel transport process related to entanglement properties of the state. Although defined on the boundary, it can be used to derive information about the geometry of the dual bulk spacetime. One tool for this is an auxiliary symplectic geometry that underlies the parallel transport. I will end with a brief advertisement about recent extensions of this framework to a notion called circuit complexity.Cindy Keeler
09/23/2022Daniel Jimenez AguilarBilbaoThe dynamics of domain wall strings: In many field theories, solitonic solutions admit localized excitations with unnaturally long lifetimes in their spectrum of perturbations. These bound states may play a significant role in the dynamics of solitons, and in particular, they could shed light on some aspects concerning the evolution of cosmic string networks. In this talk I will discuss the influence of this type of excitations on the dynamics of string-like domain walls in 2+1 dimensions, focusing mostly on interesting resonance phenomena arising from the interaction of different modes at a non-linear level. The processes by which the excited string can emit radiation will also be analyzed, and the motion of the soliton in lattice field theory simulations will be contrasted with the one predicted by the Nambu-Goto action. Tanmay Vachaspati
9/30/2022Alex MaloneyMcGill UniversityThe Uses and Abuses of WormholesA wormhole is a geometry which connects two widely separated regions of space-time. Wormholes appear ubiquitous in the traditional approach to quantum gravity as a path integral over a space of geometries. I will study a simple theory of gravity – three dimensional general relativity with a negative cosmological constant – where the effects of wormholes can be made completely precise. In the context of AdS/CFT, this has a remarkable implication: Einstein gravity is dual to an ensemble average of two dimensional conformal field theories, much like a spin glass or other system with quenched disorder. I will describe this average explicitly. This provides a realization of an old idea due to Coleman: in a theory of gravity with wormholes, the coupling constants of nature are random variables. Cindy Keeler
10/07/2022Stephen MartinezArizona State University The Next Chapter for the Dynamical Diquark Model of Heavy Quark ExoticsAlmost twenty years of direct study pointed towards the experimentally evidenced heavy-quark exotic hadrons has produced a multitude of appealing theoretical paradigms. Still, no single picture has emerged as the undeniable forerunner. Enter the Dynamical Diquark Model. This model has since produced a number of exciting results, and continues to survive the seemingly endless onslaught of new experimental data being produced in this field. However, it was not until recently that an attempt was made to incorporate so-called 'threshold effects' into the model. It seems that it must be no coincidence that so many exotic states lie just below (or even just above) the energy threshold of di-hadron configurations. In this presentation, we will review the core components of the dynamical diquark picture and model, and describe how the incorporation of the diabatic formalism (an extension of the adiabatic approximation) may allow for these threshold effects to manifest.Cindy Keeler
10/28/2022Kate ScholbergDuke UniversityWhat Stubs and Sparkles In Vast Vats of Liquid Will Tell Us About Exploding StarsWhen a massive star collapses at the end of its life, nearly all of the gravitational binding energy of the resulting compact remnant is released in the form of a brilliant burst of neutrinos. I will discuss the nature of the core-collapse neutrino burst and what we can learn about particle physics and about astrophysics from the detection of these neutrinos. I will cover supernova neutrino detection techniques in general, current supernova neutrino detectors, and prospects for specific future experiments.Cecilia Lunardini
11/04/2022Tucker MantonBrown UniversityGravity, fermions, and non-compact gauge theoryThe gravitational spin connection is an essential player when coupling fermions to General Relativity. The spin connection can be understood as the non-Abelian gauge potential associated with the Lorentz group SO(3,1), which is non-compact. In this talk, we will explore a Yang-Mills type theory for the spin connection coupled to Dirac fermions. After describing the emergence of the spin connection and its role in General Relativity, we will motivate the pure gauge theory and discuss the subtleties surrounding the quantum fields of non-compact gauge groups. We then show that fermion scattering via a spin connection exchange induces a 4-Fermi interaction involving both the axial and vector currents, which differs from the analogous calculation in pure General Relativity.Damien Easson
11/11/2022No Talk ScheduledUniversity Holiday
11/18/2022Samarth Chawla Arizona State UniversityThe Square Root of Black Holes in Higher DimensionsColor-kinematics duality, also known as the double copy, is an enigmatic map between gravity and gauge amplitudes, describing a scattering amplitude of a gravitational theory as the "square" of a corresponding one in a gauge theory. This duality has a classical cousin which relates classical solutions in gravity to solutions in gauge theory. After making the squaring relations described above explicit, we will discuss recent work that shows how a class of highly symmetric spacetimes in general dimension can be described as the square of similarly special Maxwell fields.William Munizzi
12/02/2022Victoria MartinUniversity of IcelandLessons from the geometric structure of black holesThe Selberg zeta function and trace formula are powerful tools used to calculate kinetic operator spectra (which govern quantum corrections) and quasinormal modes on hyperbolic quotient spacetimes. In this talk, we extend this formalism to non-hyperbolic quotients by constructing a Selberg zeta function for warped AdS3 black holes. We also consider the so-called self-dual solutions, which are of interest in connection to near-horizon extremal Kerr. We establish a map between the zeta function zeroes and the quasinormal modes on warped AdS3 black hole backgrounds. In the process, we use a method involving conformal coordinates and the symmetry structure of the scalar Laplacian to construct a warped version of the hyperbolic half-space metric, which to our knowledge is new and may have interesting applications of its own, which we describe. We end by discussing several future directions.Cynthia Keeler
12/09/2022Alvaro Pozo Larrocha UPV/EHU, LeioaObservational Tests of Wave and Particle Dark Matter PredictionsRecent discoveries of large halos of stars and dark matter around some of the lowest mass galaxies defy expectations that dwarf galaxies should be small and dense. Furthermore, these halos are seen to surround a dense core within each dwarf, with a clear density transition visible between the core and the halo at a radius of ' 1.0kpc. This common core-halo structure is hard to understand for standard heavy particle dark matter where featureless, con- centrated profiles are predicted, whereas dark matter as a Bose-Einstein condensate, ψDM, naturally accounts for the observed profiles, predicting a dense soliton core in every galaxy surrounded by a tenuous halo of interfering waves. We show that the stellar profiles of the well studied “dwarf Spheroidal" (dSph) class, and also the equally numerous “ultra faint dwarfs" (UFD) are accurately fitted by the core-halo structure of ψDM, suggesting two boson species which are reinforced by parallel relations seen between the central density and radius of UDF and dSph dwarfs respectively, which both match the steep prediction, ρc ∝ R−^4c , for soliton cores in the ground state.Rogier Windhorst


DateSpeakerInstitutionHostTitleAbstractZoom Info
2/25/2022Manizheh BotshekananfardUniversity of KashanInduced energy-momentum tensor of Dirac field in 2-dimensional de Sitter quantum electrodynamicsZoom link: https://asu.zoom.us/j/84582482821?pwd=K1g4UWtVK2EyWVJaZlk4WU0xWEJpQT09 Password: 000000 Meeting ID: 845 8248 2821
5/6/2022Sudipta SarkarIndian Institute of Technology GandhinagarTowards Relativity: Einstein and His CompassThe advent of special relativity resulted from intense scientific thinking spanning several decades. The history of relativity begins with the strive to understand motion, inertia, and light, which finally led to the Einsteinian revolution in 1905. In this seminar, I attempt to summarize the rich history of the theory of relativity; the emphasis would be to discuss the contributions of several physicists and mathematicians and the uniqueness of the approach taken by Einstein.Zoom link: https://asu.zoom.us/j/87832893642?pwd=K1J4L0lrd2hiZy9QSUhMeWs2bS9rUT09 Password: 000000 Meeting ID: 878 3289 3642

FALL 2021

DateSpeakerInstitutionHostTitleAbstractZoom Info
10/1/2021Alankrita PriyaASUCynthia Keeler Towards Large-D/CFT via a relation between hidden conformal symmetries and killing tensorsWe generalize the notion of hidden conformal symmetry in Kerr-CFT to general dimensions, finding sets of SL(2,R) generators via the explicit relationship between hidden symmetries and generators.Join via: ZOOM | Join from PC, Mac, Linux, iOS or Android: https://asu.zoom.us/j/81874415520?pwd=NDBMcmxvTEdraVRVTWtscEFyUVd5UT09 Password: 000000
11/12/2021Don PageUniversity of AlbertaPaul DaviesObservational Probabilities Instead of Preferred Basis StatesEverett showed that one need not have wavefunction collapse in quantum theory. Instead, one can have a single quantum state (in the Heisenberg picture) that never changes. However, if one decomposes the state into basis states, there will generically be nonzero amplitudes for many different basis states, sometimes called `Everett many worlds.' Many have sought to answer the challenge of finding a preferred set of basis states in order to give a preferred set of `Everett worlds.' I argue that this search for preferred basis states is misguided, and what we need instead is a set of preferred positive operators. These would be the operators whose expectation values I propose would give the relative measures for observations.Join via: ZOOM | Join from PC, Mac, Linux, iOS or Android: https://asu.zoom.us/j/87438532880?pwd=V3VURkc2ZzlQRkgyTkp6UTRPUG1TQT09 Password: 000000

Spring 2021

DateSpeakerInstitutionHostTitleAbstractZoom Info
4/30/2021Brandon ThorntonASUSpeaker : 1Global Cosmic Strings: Toward Observing the Goldstone BosonCosmic strings are speculated to have emerged as a result of phase transitions in the early universe and can be simply modeled by a classical complex scalar field with a quadratically-shifted quartic potential. This scalar-field model has a global U(1) symmetry broken by its ground-state. In this talk, I’ll introduce said model of the global cosmic string and its Goldstone boson, which is speculated to be a dark-matter candidate.Join via: ZOOM | Join from PC, Mac, Linux, iOS or Android: https://asu.zoom.us/j/86481557848?pwd=MDR2OEZCeFVBaE5kTjJEY0xKbHRJdz09 Meeting ID: 864 8155 7848 Passcode: 762345
Heling DengASUSpeaker : 2A Possible Mass Distribution of Primordial Black Holes Implied by LIGO-VirgoThe LIGO-Virgo Collaboration has so far detected around 90 black holes, whose mass distribution appears to have a peak at ∼ 30M☉ and two tails on the ends. By assuming that they all have a primordial origin, we analyze the GWTC-1 (O1&O2) and GWTC-2 (O3a) datasets by performing maximum likelihood estimation on a broken power-law mass function, which appears to behave better than the popular log-normal mass function. Surprisingly, such a simple distribution can be realized in our previously proposed mechanism of PBH formation, where the black holes are formed by vacuum bubbles that nucleate during inflation via quantum tunneling.

FALL 2020

DateSpeakerInstitutionHostTitleAbstractZOOM Link
11/13/2020Logan ThomasASUCFTs in the CMBA generic prediction of inflationary theory is the presence of tensor perturbations, which may be measured in the polarization of the Cosmic Microwave Background (CMB). In this talk, we will discuss how the spectrum of tensor perturbations can be significantly influenced by a hidden matter sector. In particular, we will consider a Conformal Field Theory (CFT) of arbitrary central charge which couples only to the tensor perturbations. The resulting modified power spectrum of primordial gravitational waves can then be used to give a bound on how large the hidden sector may be.https://asu.zoom.us/j/86220047912
12/4/2020Lena FunckePerimeter InstituteRethinking the origin of neutrino masses: the role of gravityThe most popular directions of model building beyond the Standard Model focus on new phenomena at the high energy scales of the early Universe. As an alternative direction, we have developed a novel class of low-energy solutions to the neutrino mass and strong CP problems at a new infrared gravitational scale, which is numerically coincident with the scale of dark energy. In my talk, I will focus on the neutrino mass model and present some of its phenomenological implications. In particular, I will discuss the weakening of the cosmological neutrino mass bounds, the emergence of soft topological defects, and the distinction between Majorana and Dirac neutrinos through astrophysical neutrino decays. This talk is based on 1602.03191, 1608.08969, 1811.01991, 1905.01264, and ongoing work. https://asu.zoom.us/j/86220047912
12/11/2020Alankrita Priya ASUSymmetries of the Kerr black hole and its extension to large dimensionsIn this talk I'll review different approaches on building symmetries of the Kerr black hole, namely the Kerr/CFT correspondence, the monodromy method, building killing tensor and building symmetries of the scalar wave equation. I'll also discuss our current/ongoing work on connecting these approaches and extending it to large dimensionshttps://asu.zoom.us/j/86220047912


DateSpeakerInstitutionHostTitle Time Abstract
01/24/2020 Timothy CarletonUniversity of MissouriDr. WindhorstThe Origin of Ultra-Diffuse GalaxiesEver since the identification of a large population of Ultra-Diffuse Galaxies (UDGs) in the Coma Cluster, there has been renewed interest in the properties of low-surface brightness galaxies. Evidence from the abundance and morphologies of UDGs suggest that cluster environments play an important role in the evolution of these unique systems. Motivated by this evidence, I will present a model for the formation of UDGs through tidal heating of dwarf-elliptical galaxies in clusters. This model is able to reproduce many aspects of the observed UDG population, including the size distribution and the dependence of UDG abundance with cluster mass, assuming that UDGs fall into the cluster living in cored dark matter halos. However, this picture becomes more complicated when considering low-surface brightness galaxies in the field and high-surface brightness galaxies in clusters. I will discuss how observations of dynamics, stellar populations, and globular cluster systems of Ultra-Diffuse and non-Ultra Diffuse galaxies in clusters and the field can inform a more holistic understanding of dwarf galaxy structural evolution.
02/14/2020Mainak Mukhopadhyay ASURolling with Quantum FieldsIn cosmic inflation the quantum fluctuations of the inflaton are thought to break translational symmetry. Here we study the simpler problem of a classical rolling homogeneous field bi-quadratically coupled to a quantum field. We explicitly solve the problem using the newly developed classical-quantum correspondence, in which the dynamics of a quantum variable is seen to be equivalent to that of a complexified classical variable. We find that homogeneous initial conditions evolve homogeneously such that the quantum dynamics does not break translational invariance, contrary to the common lore of cosmic inflation.
02/21/2020Ayush SaurabhASUThe decay of global cosmic string loops. "I will be talking about our latest work on the decay of global cosmic string loops due to radiation of Goldstone bosons and massive scalar (χ) particles. This is relevant to models in which axions are proposed as a means to solve the strong CP problem."
02/28/2020Tucker MantonASU Horizons of Kerr and non-singular black holes: the view from the double copyThe double copy program has provided a robust way to understand and calculate graviton scattering amplitudes in terms of simpler gauge theory amplitudes, both at tree and loop level. The classical double copy, on the other hand, is a duality between exact solutions in gauge theories and exact solutions in general relativity, although exactly why the duality holds non-perturbatively remains somewhat elusive. In this work, we study the radial electric fields obtained through the double copy mapping in both static and stationary black hole spacetimes. We show that for spacetimes with two or more horizons, the radial electric field undergoes a sign change on a hypersphere located between horizons. We discuss possible interpretations of this phenomena in addition to a few other intriguing aspects of the classical double copy for static black holes.
03/06/2020Andrew SveskoASUExtended Thermodynamics and Entanglement of Hairy Black HolesAfter a broad review of black hole thermodynamics and holographic entanglement, I will discuss how we can analytically study phase transitions of Renyi entropy and its generalization. Specifically, I will show that the phase transition of a hyperbolic AdS black hole to a neutral charged dilatonic black hole is dual, in the holographic sense, to the phase transition of the Renyi entropy of a vacuum state of a conformal field theory reduced to a ball in Minkowski space. Motivated by extended thermodynamics of black holes, I will also present the holographic phase transitions of a generalized Renyi entropy and discuss its gravitational interpretation.
03/27/2020 Seminar cancelled
04/03/2020 Seminar cancelled
06/12/2020George ZahariadeASUQuantum Mechanics of Gravitational Waves1:00 PMIn this informal talk I will discuss recent work done with Maulik Parikh and Frank Wilczek, where we study the effect of a quantized gravitational wave on a model gravitational wave detector, more precisely one arm of a gravitational wave interferometer. We find that the arm-length is subject to a stochastic tidal force whose properties depend on the exact quantum state of the gravitational field. This should appear in the signal as an additional noise source. Link to presentation: https://documentcloud.adobe.com/link/review?uri=urn:aaid:scds:US:1bb21034-a3da-4044-8957-972287afab5b

FALL 2019

DateSpeakerInstitution Title Abstract
9/13/2019Akash MishraIITSome Aspects of Higher Curvature GravityAlthough General Relativity(GR) is a tremendously successful theory at macroscopic length scale, it suffers non-renormalizable UV divergence when one attempts to quantize it, suggesting that GR is not complete. Hence, such a theory can only make sense as an effective field theory of a more general theory which must contain higher derivative correction over the Einstein Hilbert action. This motivates one to study these effective higher curvature corrections to GR, and in this talk, I'll illustrate some implications of these terms. In particular, I'll discuss how one can put constraints on these corrections from the Gravitational Wave observations. Also, I'll discuss the problem of Strong Cosmic Censorship in the context of higher curvature gravity.
9/20/2019Carlos CardonaASUOPE inversion, light cone bootstrap and large spin perturbation theoryI would like to discuss some recent developments on the conformal bootstrap program for extracting OPE conformal field theory data by means of S-matrix techniques. I will discuss the OPE inversion formula and its applications to large spin perturbation theory within the light-cone bootstrap approach.
10/4/2019Mustafa AminRiceNon-perturbative Dynamics of Cosmological FieldsIn this informal talk, I will touch briefly upon three topics: 1. The production of gravitational waves from ultra-compact soliton collisions 2. The stochastic production of particles during and after inflation (and a novel connection to Anderson localization) 3. A connection between fine tuning of the Higgs potential and production of gravitational waves in the early universe Time permitting (or if there is interest), I can also talk about our recent efforts to resolve the “Hubble Tension”.
10/11/2019Thiago FleuryFederal University of Rio Grande do NorteCorrelation Functions in N=4 SYM and IntegrabilityIn 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.
10/18/2019Thiago FleuryFederal University of Rio Grande do NorteCorrelation Functions in N=4 SYM and IntegrabilityThe third lecture will contain nonplanar corrections and a list of open problems and recent results.
10/25/2019 Nikhil Monga ASUFrom Navier Stokes to Maxwell: A look at the fluid-gravity duality under the lens of the double copy.Work done by Bredberg et. al. 2011 showed that for certain algebraically special metrics it was possible to obtain the incompressible Navier Stokes equations. They show that satisfying Einstein's equations for these metrics is equivalent to obtaining the incompressible Navier Stokes equations. Monteiro et. al. 2014 showed that for metrics which can be written in the Kerr-Schild form. We extend the fluid-gravity picture by combining these ideas, in particular by using the Weyl double copy (Luna et. al. 2018). We observe for algebraically special type D spacetimes, the Maxwell field strength tensor is proportional to the vorticity of the fluid. In the limit that we produce only magnetic fields. Further we show that E.B is proportional to the enstrophy density. These parallels are strongly suggestive of a fluid-gauge duality for such metrics.
11/1/2019Cecilia LunardiniASUneutrinos from primordial black holes In this very informal talk, I will discuss how the evaporation of primordial black holes depends on the neutrinos being massive particles. The effect of the neutrino mass on the black hole lifetime, and new constraints on the abundance of primordial black holes will be presented. The futuristic possibility to directly detect neutrinos from primordial black holes will be highlighted briefly.
11/08/2019Alex van EngelenASUTwo topics for upcoming CMB experiments: one opportunity and one concernI will highlight two topics relevant for upcoming surveys of the cosmic microwave background ( CMB ) . First, I will give some good news: I will explain a cosmological signal that was recently found to be detectable, the thermal-kinetic Sunyaev-Zel'dovich (SZ) effect. Although this signal is much weaker than the better-known thermal and kinetic SZ effects, it has some advantages over these two effects. I will then switch gears and give some less-than-good news: I'll discuss a concern for the measurements of the gravitational lensing of the CMB to measure the mass of neutrinos. I will discuss how these measurements were recently found to be significantly affected by astrophysical uncertainties relating to baryonic feedback from active galactic nuclei and supernovae.
11/22/2019Levon PogosianSimon FraserCosmological Tests of GravityI will discuss two aspects of testing models of dark energy and modified gravity using cosmological datasets. The first is the choice of priors when trying to constrain general functions of redshift. The second is the physical interpretation of such tests and their implications for particular types of theories.
12/6/2019Brandon ThorntonASUToward Gluon Scattering Amplitudes through Wilson Loops: A CalculationI describe a calculation of polygonal Wilson Loop expectation values which contain information about next-to-maximal-helicity-violating gluon scattering amplitudes in N = 4 Super Yang-Mills at tree level, through a (Wilson loop)-(scattering amplitude) duality. Such calculations are part of a larger effort to obtain nonperturbative gluon amplitudes (i.e., amplitudes at all orders in their coupling) in N = 4 Super Yang-Mills.

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