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Cosmology Seminar - Wednesday

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

Due to the COVID campus closure - All Seminars will be Online via ZOOM info - Barry Goldwater Building, 5th floor, Conference Room 505

Spring 2020

01/22/2020Daniele SteerAPC (Paris)Dr. VachaspatiCosmology and tests of General Relativity with gravitational wavesIn 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.
01/29/2020Thomas BachlechnerUCSDDr. VachaspatiTesting the electric Aharonov-Bohm effect: electromagnetic memory vs. boundary gauge invarianceThe 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.
02/05/2020Peter GeltenbortInstitut Laue LangevinDr. AlarconProbing Early Universe Particle Physics with NeutronsDue 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 ZurekCalTechDr.KeelerSpacetime fluctuations in AdS/CFTTechnical Talk on recent work
02/19/2020Tanmay VachaspatiASUCOSMODynamical quantum collapse and an experimental testThe 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.
02/26/2020Benjamin BassoENS (Paris)Dr. Belitsky Six-gluon scattering amplitude at the origin in planar N=4 SYM
04/15/2020Dr. Xiao Fang University of Arizona Cecilia LunardiniONLINE ONLYJoin from PC, Mac, Linux, iOS or Android: Zoom Info link: https://asu.zoom.us/j/325364671
04/22/2020Prof. Lam Hui Columbia UniversityONLINE ONLYJoin from PC, Mac, Linux, iOS or Android: Zoom Info link: https://asu.zoom.us/j/91489619064
05/13/2020 Seminar cancelled

FALL 2019

9/11/2019FALL 2019 Welcome Reception ASU Tanmay Vachaspati
9/18/2019Henry LammUniversity of MarylandQuantum Computers for Quantum Field TheoryRich LebedThe 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.
9/25/2019Ryan Westernacher-SchneiderUniversity of ArizonaMultimessenger Seismology of Core-Collapse SupernovaeDr. LunardiniAsteroseismology 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.
10/1/2019Ubirajara van KolckInstitut de Physique Nucleaire d'Orsay and University of ArizonaA New Leading Mechanism for Neutrinoless Double-Beta DecayMatthew BaumgartA 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.
10/9/2019Yue ZhaoUniversity of UtahSearching for Dark Photon Dark Matter with Gravitational Wave DetectorsMatthew 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.
10/16/2019Thiago FleuryFederal University of Rio Grande do NorteCorrelation Functions in N=4 SYM and IntegrabilityAndrei BelitskyIn 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 DengArizona State UniversityPrimordial black holes from primordial bubblesTanmay 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.
10/30/2019Sergej MorozTechnical University of MunichConfined phases of fermions coupled to Z2 gauge fieldsAndrei BelitskyAfter 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.
11/6/2019Atsushi NarukoYukawa Institute for Theoretical PhysicsPossible resolution of a spacetime singularity with field transformationsGeorge ZahariadeIn 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.
11/13/2019Ira Z. RothsteinCarnegie Mellon UniversityEffective field theory for quantum mechanical black holesMatthew 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.
11/20/2019Jaime Besprosvany UNAMHeavy quarks within the electroweak multiplet Tanmay VachaspatiStandard-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.
12/4/2019Jun NianLeinweber Center for Theoretical Physics, University of MichiganMicrostate Counting of Asymptotically AdS (Near-)BPS Black Holes and Hawking RadiationCynthia KeelerThe 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

1/30/2019George ZahariadeASUClassical-Quantum Correspondence and BackreactionDr. VachaspatiWe 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
2/6/2019Raisa TrubkoHarvardPrecision Tune-out Wavelength Measurement with Atom InterferometryDr. LunardiniPrecision 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.
2/20/2019Christoph KellerUniversity of ArizonaHolographic Conformal Field Theories in Two DimensionsDr. KeelerConformal 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.
2/27/2019Maulik ParikhASU Forever Never Lasts: The Unruh-de Sitter State and the End of Eternal InflationDr. WilczekMotivated 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.
3/13/2019Yanou CuiUC Riverside Probing the early Universe with gravitational waves from cosmic stringsDr. VachaspatiMany 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.
3/20/2019Andrew LongUniversity of MichiganUltra-light dark photons from a network of cosmic stringsDr. VachaspatiA 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.
3/27/2019Yuber PerezFermi LabNeutrinos in Dark Matter detection experiments: Standard Model and Beyond.Dr. LunardiniNegative 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.
4/10/2019Andres LunaUCLABlack holes and the double copy.Dr. KeelerThe 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 HeurtierUofAEeV scale dark-matter: production mechanism through the inflaton portal and experimental signatures using the ANITA collaborationDr. BaumgartIn 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.
4/24/2019Eleni KontouUniversity of YorkQuantum strong energy inequality and the Hawking singularity theoremDr. VachaspatiHawking'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.
5/1/2019Timothy TaitUC IrvineAn Early Phase of QCD Confinement and the Baryon Asymmetry of the UniverseDr. BaumgartI’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.