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Cosmology Seminar - Wednesday

The Cosmology Seminars are scheduled on Wednesdays from 2:00pm-3:00pm. (Unless Noted for time change )

 Seminars will be ONLINE via ZOOM info or may be attended in person in GWC505 - Masks are REQUIRED.

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Meeting ID: 831 0177 0815


01/19/2022Natalia Pinzani-FokeevaMITEnstrophy and black hole supertranslations Enstrophy is an approximately conserved quantity in 2+1 dimensional nonrelativistic fluids that implies an inverse energy cascade in turbulent flows. In this talk, I will present an algorithm on how to construct an enstrophy current for generic fluid flows (relativistic and non). In addition, I will show how a subset of certain horizon symmetries of 3+1 dimensional AdS black holes also lead to enstrophy conservation in the dual holographic fluid theory.
02/02/2022David DunskyUC Berkeley Gravitational Wave GastronomyThe symmetry breaking of grand unified gauge groups in the early universe often leaves behind relic topological defects such as cosmic strings, domain walls, or monopoles. For some symmetry breaking chains, hybrid defects can form where cosmic strings attach to domain walls or monopoles attach to strings. In general, such hybrid defects are unstable and can leave behind unique gravitational wave fingerprints. In this talk, I will discuss the gravitational wave spectrum from 1) the destruction of a cosmic string network by the nucleation of monopoles which cut up and `eat’ the strings, 2) the collapse and decay of a monopole-string network by strings that ‘eat’ the monopoles, 3) the destruction of a domain wall network by the nucleation of string-bounded holes on the wall that expand and `eat’ the wall, and 4) the collapse and decay of a string-bounded wall network by walls that `eat’ the strings. We call the gravitational wave signals produced from the `eating’ of one topological defect by another “gravitational wave gastronomy”. We find that the gravitational wave gastronomy signals considered yield unique spectra that can be used to narrow down the SO(10) symmetry breaking chain to the Standard Model and the scales of symmetry breaking associated with the consumed topological defects.
02/16/2022Jacob LittererTufts University Bound on Squeezed State Gravitational Wave Fluctuations from LIGOGravitational wave observations at LIGO are in good agreement with classical predictions, with a residual that does not exhibit any unexplained correlations. In the context of general relativity as an effective quantum theory, gravitational waves have been thought to be in the most classical coherent state, in which quantum fluctuations are far too small to see at LIGO. However, it is plausible to suppose that gravitational waves may be produced in a more interesting squeezed state, in which quantum fluctuations can be exponentially enhanced by the squeezing parameter as pointed out in recent work. Computing space and time correlations of a class of squeezed states and taking into account the detector response, a simple comparison to LIGO data puts a bound on the squeezing parameter
03/02/2022David CyncynatesStanford UniversityFriendship in the AxiverseThe Axiverse is a scenario in which axion-like particles are distributed over many orders of magnitude in mass and interact with one another through a joint potential. In this talk, I will show how non-linearities in this potential lead to a new type of resonant energy transfer between "friendly" axions with nearby masses. This resonance generically transfers energy from axions with larger decay constants to those with smaller decay constants, leading to a multitude of signatures. These include enhanced direct detection prospects for a resonant pair comprising even a small subcomponent of dark matter, and boosted small-scale structure if the pair is the majority of DM. Near-future iterations of experiments such as ADMX and DM Radio will be sensitive to this scenario, as will astrophysical probes of DM substructure.
3/16/2022 - @ 4PMYuta MichimuraUniversity of TokyoDANCE: Dark matter Axion search with riNg Cavity ExperimentAxion and axion-like particles are leading candidates for ultralight dark matter, and there have been enormous efforts to search for their signatures through a variety of experiments and astrophysical observations. Axion may cause a polarization rotation of light through the parity-violating interaction with photons. Recently, we have proposed to search for axion dark matter by enhancing the polarization rotation effect using a bow-tie optical ring cavity [PRL 121, 161301 (2018)]. We have shown that this Dark matter Axion search with riNg Cavity Experiment (DANCE) can improve the sensitivity to axion-photon coupling for axion mass m_a<10^{-10} eV by up to several orders of magnitude, compared with the current best limits. Currently, a prototype experiment DANCE Act-1 is underway at Tokyo to demonstrate the feasibility of the method. In this talk, I will present the principle of DANCE and the status of DANCE Act-1, including some of the preliminary results from the first 12-day run in May 2021.
3/30/2022Glennys FarrarNew York UniversitySexaquarks can be the Dark Matter: abundance, direct detection constraints, laboratory searches and neutron starsIt is possible that a neutral dibaryon composed of uuddss is sufficiently deeply bound that its mass is less than ~ 2.05 GeV, in which case it is effectively stable. Such a particle is designated S or sexaquark, to avoid confusion with hexaquarks which are generically short-lived. As will be explained, such a particle would not have been detected in experiments to date. Constraints on its mass and cross sections will be quickly reviewed and it will be shown that it is an excellent Dark Matter candidate. Undetected S Sbar production can also naturally explain the discrepancy between the measured cross section for e+e- -> hadrons, and lattice QCD and g-2 experimental determinations.
4/06/2022Bryce CyrMcGill UniversityDirect collapse black holes from superconducting cosmic stringsThe observation of supermassive black holes in high redshift quasars presents a tantalizing mystery in astrophysics and cosmology, as they are difficult to explain within the standard LCDM paradigm. I will briefly review these challenges, and introduce a possible resolution through the monolithic collapse of a primordial gas cloud. I will present the astrophysical conditions necessary to achieve such a collapse, and show how a gas cloud surrounding a superconducting cosmic string is an ideal environment to satisfy these conditions. Finally, I will discuss the nuances of combining other constraints on superconducting strings with this idea, as well as introduce ongoing work to predict the number density of these string-seeded black holes.
4/13/2022Tucker MantonArizona State UniversitySelected studies in the double copy: non-singular black holes, fluid/gravity duality, and external sourcesThe double copy is a procedure that relates gravity to simpler gauge and scalar field theories. Double copy structure was first discovered in the context of scattering amplitudes, and has since been realized at the level of classical fields and curvatures. In this defense, I focus on mappings between fields (the Kerr-Schild double copy) and curvatures (the Weyl double copy). First, I build the connection between non-singular black holes and non-singular gauge theories. Here, we find a subtlety between gravitational horizons and the gauge field strength. I will then study a perturbative double copy in the context of the fluid/gravity duality, where the associated gauge quantities have elegant interpretations in terms of certain classes of Navier-Stokes solutions. Finally, I will present a new formula that provides a consistent treatment of external sources in the Weyl double copy. After illustrating its consistency with the Kerr-Schild double copy, I apply the sourced Weyl double copy to the most general Petrov type D electro-vac spacetime before discussing various limits of the general solution.
4/27/2022David HoskingUniversity of OxfordDecay of primordial magnetic fields via reconnection can explain cosmic-void observationsIt has been suggested [see 1, 2, and references therein] that the weak magnetic field hosted by the intergalactic medium (IGM) in voids might be a relic from the early Universe. If so, the strength and coherence length of void fields could be “predicted” from reasonable assumptions about the properties that the primordial field had at its genesis, provided the evolution of the field in the intervening time were understood. Previously held theories [1, 2] based on magnetogenesis at the electroweak phase transition (EWPT) indicated that parity-invariant primordial fields would have decayed too quickly to be consistent with the observational constraints on void fields. Thus, the “relic-field” hypothesis appeared unlikely [3]. However, recent numerical developments have shown that these decay theories are flawed: they do not predict the “inverse transfer” of magnetic energy to larger scales that has been observed in simulations [4, 5]. In my talk, I present a theory of the decay based on the conservation of the “fluctuation level” of magnetic helicity [6], with dynamics controlled by the reconnection of magnetic-field lines [6, 7, 8]. I show that this theory explains the “inverse-transfer” phenomenon, and predicts a slower decay of primordial fields, thus restoring consistency between the relic-field hypothesis and the observational constraints.

FALL 2021

DateSpeakerInstitutionHostTitle Abstract
9/22/2021Andy SveskoUniversity College LondonSemi-classical thermodynamics of quantum extremal surfaces in 2D gravity Quantum extremal surfaces (QESs) play an important role in the study of the black hole information problem, and, in a sense, are semi-classical generalizations of black hole horizons. Their thermodynamics, however, have largely been unexplored because a proper interpretation requires a detailed understanding of the backreaction of quantum fields outside of a black hole. In this talk I will consider a massless quantum field theory outside of an eternal anti-de Sitter (AdS) black hole in two-dimensional (2D) dilaton gravity, where back reaction may be studied exactly
10/6/2021Michael ZantedeschiLudwig-Maximilians-UniversitätPrimordial Black Holes from Confinement In this talk I will present a novel mechanism for the formation of primordial black holes. Here, heavy quarks of a confining gauge theory produced by de Sitter fluctuations are pushed apart by inflation and get confined after horizon re-entry
10/13/2021Suvrat RajuTata Institute of Fundamental ResearchHolography of Information and Massive IslandsWe will review recent results that suggest that, in any standard theory of quantum gravity, information available on the bulk of a Cauchy slice must also be available near the boundary of the slice. These ideas indicate how holography should be extended to four dimensional asymptotically flat spacetimes but they also shed light on the origins of AdS/CFT. We contrast this picture with the paradigm of islands and argue that islands are consistent only in theories of massive gravity. References: 1) "Holography from the Wheeler-DeWitt equation" https://arxiv.org/abs/2107.14802 2) "Inconsistency of Islands in Theories with Long-Range Gravity" https://arxiv.org/abs/2107.03390 3) "Lessons from the Information Paradox" (review) https://arxiv.org/abs/2012.05770
10/20/2021Anson HookUniversity of MarylandBlack Hole Production of Monopoles in the Early UniverseIn the early universe, evaporating black holes heat up the surrounding plasma and create a temperature profile around the black hole that can be more important than the black hole itself. As an example, we demonstrate how the hot plasma surrounding evaporating black holes can efficiently produce monopoles via the Kibble-Zurek mechanism. In the case where black holes reheat the universe, reheat temperatures above ∼ 700 GeV can already lead to monopoles overclosing the universe.
11/10/2021William TerranoArizona State University Learning about Cosmology from Nuclear SpinsThe most sensitive measurements of the energy splitting between quantum states are made on highly-coherent nuclear spin states. I will discuss how studying these energy splittings can inform our knowledge of cosmology and particle physics, in particular of baryogenesis (through EDM measurements) and of dark matter properties. I will describe how these measurements work, what makes them so powerful and the prospects for significant improvements here in the Goldwater basement.
12/1/2021 Jose Juan Blanco-Pillado Ikerbasque and UPV/EHUDynamics of Excited SolitonsMany solitonic configurations in field theory have localized bound states in their spectrum of linear perturbations. This opens up the possibility of having long lived excitations of these solitons that could affect their dynamics. In this talk we will describe in detail how these states appear in some field theory models of low dimensionality like kinks in 1+1 dimensions and vortices in 2+1 dimensions and study their dynamical properties through a series of numerical experiments.

Spring 2021

1/27/2021 @ 3PM MSTKohei KamadaThe University of Tokyo, TokyoDr. Tanmay VachaspatiConstraints on the primordial hypermagnetic fields from the baryon isocurvature perturbationsGamma-ray observations of blazars suggest the existence of the intergalactic magnetic fields and their origin is interest for both astro physicsts and cosmologists. Among several proposals, magnetogenesis in the early Universe is an interesting option since it might also be a probe for the physics beyond the Standard Model of particle physics. Recently, it has also been proven that the baryon asymmetry of the Universe can be also generated if the magnetic fields are produced before the electroweak symmetry breaking with helicity without imposing any new physics. However, baryon isocurvature perturbations are also generated at the scale of the magnetic field coherence length in the mean time, which is constrained by the inhomogeneous Big Bang Nucleosynthesis. Note that this is an inevitable consequence of the Standard Model of particle physics. In this talk, I give generic constraints of the hypermagnetic field properties generated before the electroweak symmetry breaking. Noting that the baryon isocurvature perturbations are generated even from non-helical magnetic fields, I show that with reasonable parameter sets for the Standard Model of particle physics and magnetic field evolution laws, the intergalactic magnetic fields suggested by the blazar observations are hardly explained solely by the hypermagnetic fields generated before the electroweak symmetry breaking. Helical hypermagnetic fields can still be the origin of the present baryon asymmetry of the Universe, but we need an additional magnetogenesis or an unknown magnetic field amplification mechanism.
2/3/2021Michael DineUniversity of California at Santa CruzDr. VachaspatiAxion Cosmic Strings: Players in the Early Universe?Axion cosmic strings have long been considered as a potential source of enhancement of axion dark matter production, and have been the subject of extensive simulations in recent years. But axion strings are rather peculiar entities. We explore some aspects of these objects, and suggest that they may not play a distinguished role in early universe cosmology
2/24/2021Gordon BaymUniversity of Illinois Urbana-ChampaignDr. Igor Shovkovy / Dr. VachaspatiThe evolution of primordial neutrino helicities under gravitational and magnetic fields and implications for their detectionPrimordial neutrinos decoupled in the early universe in helicity eigenstates. As I will discuss, two effects -- dependent on neutrinos having a non-zero mass -- can modify their helicities as they propagate through the cosmos. First, finite mass neutrinos have a magnetic moment and thus their spins, but not their momenta, precess in cosmic and galactic magnetic fields. The second is the propagation of neutrinos past cosmic matter density fluctuations, which bend their momenta, and bend their spins by a smaller amount. (The latter is a general relativistic effect.) Both effects turn a fraction of left-handed neutrinos into right-handed neutrinos, and right-handed antineutrinos into left-handed. If neutrino magnetic moments approach that suggested by the XENON1T experiment as a possible explanation of their excess of low energy electron events -- a value well beyond the moment predicted by the standard model -- helicities of relic Dirac (but not Majorana) neutrinos could be considerably randomized. I finally will discuss the implications of neutrino helicity rotation, as well as their Dirac vs. Majorana nature, on their detection rates via the Inverse Tritium Beta Decay reaction.
3/31/2021Cecilia LunardiniArizona State UniversityDr. Carlos CardonaHas 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
4/14/2021Mudit JainRice UniversityDr. Tanmay Vachaspati CMB birefringence from ultralight axion string networks Ultralight axions (ULA), whose masses can lie in a wide range of values and can be even smaller than 10^{-28} eV, are generically predicted in UV theories such as string theory. In the cosmological context, the early Universe may have gotten filled with a network of ultralight axion (ULA) cosmic strings which, depending upon the mass of the axion, can survive till very late times. If the ULA also couples to electromagnetism, and the network survives post recombination, then the interaction between the strings and the CMB photons induces a rotation of the polarization axis of the CMB photons (otherwise known as the birefringence effect). This effect is independent of the string tension, and only depends on the coupling between the ULA and the photon (which in turn is sensitive to UV physics). In this talk I will present an analytical formalism to calculate this birefringence effect on the CMB photons, due to such ULA string networks. I will then consider three different models for the string networks and highlight some of the key features in the associated angular power spectrum, also comparing the results against some future CMB experiments.
4/21/2021Tina Kahniashvili & Emma ClarkeCarnegie Mellon University Gravitational Waves from Early-Universe Turbulence: LISA Prospects and nanoGrav Signal EvidenceWe will discuss gravitational wave signals sourced by hydrodynamic and hydromagnetic turbulent sources that might have been present in the early universe at epochs such as the electroweak and quantum chromodynamic (QCD) phase transitions. We consider various models of primordial turbulence: purely hydrodynamical turbulence induced by fluid motions, magnetohydrodynamic (MHD) turbulence dominated either by kinetic or magnetic energy both with and without helicity. We will also address the generation of circularly polarized gravitational waves by parity violating turbulent sources. We will present our results of numerical modeling of the early-universe turbulence and resulting gravitational waves and we will review the signal detection prospects through space based laser interferometers such as Laser Interferometer Space Antenna (LISA) and Pulsar Timing Arrays (PTAs). In particular, we will discuss the potential of explaining the recent observational evidence by NANOGrav collaboration for a stochastic gravitational wave background in the nanohertz frequency range through hydro and hydromagnetic turbulence at the QCD energy scale.
4/28/2021Manibrata SenUC Berkeley and Northwestern UniversityDr.Cecilia LunardiniWhat can we learn from the future observation of the diffuse supernova neutrino background?The Universe is awash with tens-of-MeV neutrinos of all species coming from all past core-collapse supernovae, also known as the diffuse supernova neutrino background (DSNB). Detecting the DSNB would open up new avenues in multi-messenger astronomy. In particular, it offers the unique opportunity to probe properties of the cosmos using neutrinos, as opposed to photons. The Super-Kamiokande experiment, loaded with gadolinium, is expected to collect dozens of events from the DSNB in the next decade. Future detectors such as Hyper-Kamiokande and Theia will perform even better, collecting hundreds of events after a decade of data-taking. In this talk, I will discuss how a future detection of the DSNB can be used to inform various research topics in cosmology, astrophysics and particle physics, focusing on a few examples from each field. In particular, I will expand on how the DSNB can be used to infer measurements of the Hubble constant, as well as constrain various parameters of the cosmological star formation rate. On the particle physics side, the DSNB can be used to probe the neutrino lifetime and the possibility that neutrinos are pseudo-Dirac fermions.

FALL 2020

DateSpeakerInstitutionHostTitle Abstract
9/9/2020Geoffrey PeningtonStanford UniversityCynthia KeelerReplica Wormholes and Quantum External SurfacesHawking 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
9/23/2020Tom KephartVanderbilt UnivAntichirp: Gravitational Waves from a Black Hole Orbiting in a Wormhole GeometryAfter 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).
9/30/2020Ke FangKavli StanfordDr. LunardiniMulti-messenger Astrophysics: Probing Compact Objects with Cosmic ParticlesThe 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.
10/14/2020Xavier SiemensUniversity of WisconsinDr. VachaspatiThe NANOGrav search for nanohertz gravitational wavesSupermassive 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.
10/28/2020Cecilia LunardiniArizona 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
11/4/2020 @ 5PM AZ MSTSergey Ketov Tokyo Metropolitan University and Kavli IPMU, JapanCarlos CardonaStarobinsky inflation, primordial black holes and induced gravitational waves from modified supergravityBasic (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.

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.