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Cosmology Seminar - Wednesday

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

 Seminars may be attended in person | Goldwater Building 5th Floor | Conference room 505


DateSpeakerInstitutionFaculty HostTitleAbstract
1/18/2023Aditya DhumuntaraoUMN/BrandeisCindy KeelerMaximal Entangling Rates from HolographyWe prove novel speed limits on the growth of entanglement, equal time correlators, and spacelike Wilson loops in spatially uniform time-evolving states in strongly coupled CFTs with holographic duals. These bounds can also be viewed as quantum weak energy conditions. Several of the speed limits are valid for regions of arbitrary size and with multiple connected components, and our findings imply new bounds on the effective entanglement velocity of small subregions. In 2d CFT, our results prove a conjecture by Liu and Suh for a large class of states. Key to our findings is a momentum-entanglement correspondence, showing that entanglement growth is computed by the momentum crossing the HRT surface. In our setup, we prove a number of general features of boundary-anchored extremal surfaces, such as a sharp bound on the smallest radius that a surface can probe, and that the tips of extremal surfaces cannot lie in trapped regions. Our methods rely on novel global GR techniques, including a delicate interplay between Lorentzian and Riemannian Hawking masses. While our proofs assume the dominant energy condition in the bulk, we provide numerical evidence that our bounds are true under less restrictive assumptions.
1/25/2023 Simon Foreman ASUTanmay VachaspatiMapping the Universe in HDThe period of cosmic history known as the "Dark Ages", between hydrogen recombination and the formation of the first stars, holds a huge amount of cosmological information but presents serious challenges to access observationally. After introducing the physics of the Dark Ages and the qualities that make this epoch an appealing science target, I will discuss an idea for observing the Dark Ages via radiation from rotational transitions in hydrogen deuteride. I will then discuss what hydrogen deuteride may be able to tell us about the universe at later times, and evaluate the corresponding observational prospects.
2/15/2023Masha BaryakhtarUWMatt BaumgartMultimessenger signals from dark photons around black holes.Theories that seek to explain the outstanding puzzles of the Standard Model of particle physics often predict new, light, feebly-interacting particles whose discovery requires novel search strategies. I will discuss how rotating black holes source exponentially large numbers of gravitationally-bound ultralight particles, creating nature's laboratories for new physics. These systems emit gravitational waves, allowing observatories such as LIGO to search for axions and dark photons. If the dark photons interact with the Standard Model, black holes could turn into a new type of bright pulsar in the sky. I will focus on the electrodynamics of a kinetically mixed dark photon cloud that forms through superradiance around a spinning black hole. I will describe the resulting multimessenger signals of these systems which, if they exist, could result in some of the brightest X-ray sources in the universe.
2/22/2023Anna SuligaUW-Madison / UC-BerkeleyCecilia LunardiniCore-collapse supernovae as probes of not only non-standard neutrino physics: Core-collapse supernovae are among the most spectacular and efficient neutrino factories known so far. Detection of these neutrinos allows us to probe physics in extreme conditions not accessible on Earth. But so far, even with the detection of about twenty electron antineutrinos from SN 1987 A, we are yet to test even the most basic prediction about the neutrino emission, i.e., different neutrino flavors produced during the collapse share a comparable amount of the released energy. Existing detectors can register significantly more neutrinos of all flavors from the closeby core-collapse supernova and test this assumption. In this talk, I will discuss the implications of a phase transition from hadronic to quark matter on the neutrino emission from core-collapse supernovae and how the detection of such a signal on Earth can be used to point to the location of the supernova and set stringent limits on the absolute active neutrino mass. Unfortunately, core-collapse supernovae extreme phenomenon rarely occurs in our galaxy and its vicinity, only a few times per century. Because of that, it is essential to observe neutrinos from multiple supernova events – the diffuse supernova neutrino background (DSNB). While the limit on the electron antineutrino component of the DSNB is only a factor of 2-3 above most of the theoretical predictions, the situation is worse for other flavors. In this talk, I will present how the large-scale direct dark matter detectors can help significantly tighten the upper limits on the non-electron component of DSNB.
3/1/2023Stephon Alexander Colloquium
3/15/2023Andy SveskoUniversity College LondonLars AlasmaThe minus sign in the first law of de Sitter horizonsWhile formally analogous, the thermodynamics of the de Sitter cosmological horizon is more subtle than its black hole counterpart. For example, the first law of de Sitter horizons has a minus sign indicating the entropy of a cosmological horizon is reduced by the addition of matter Killing energy. Even more, there is no asymptotic boundary in de Sitter space where thermodynamic data may be fixed to sensibly define a thermal ensemble. In this talk, I will discuss how both of these issues can be clarified by introducing a finite timelike boundary inside the de Sitter static patch. In particular, I will argue the confusion about the minus sign in the first law is due to a mistaken interpretation of the added Killing energy as the total internal energy. Rather, the total energy of the canonical ensemble is given by the quasi-local Brown-York energy. In the limit the boundary shrinks to zero size, the standard Gibbons-Hawking result is recovered. If the Killing matter is in global equilibrium at the de Sitter temperature, the first law becomes the statement that the generalized entropy is stationary. With time permitting, I will discuss how de Sitter thermodynamics with timelike boundaries relates to various proposals of de Sitter holography.
4/5/2023Joaquin TuriaciUWLars Alasma
4/12/2023Gopolang MohlabengUCIMatt Baumgart
4/19/2023 Douglas ScottUBCSimon Foreman
4/26/2023Tongyan LinUCSDMatt Baumgart

FALL 2022

DateSpeakerInstitutionFaculty HostTitleAbstract
9/7/2022George ZahariadeInst HEP (IFAE)Tanmay VachaspatiQuantum formation of topological defectsIn this blackboard talk I will describe recent work (in collaboration with M. Mukhopadhyay, O. Pujolas and T. Vachaspati) about the quantum formation of kinks and antikinks during a quantum phase transition in 1+1 dimensions. I will evaluate the number density of kinks as a function of time and show that it scales as t^{-1/2} in the late time limit (and independently of the details of the phase transition). This decay can be interpreted in terms of ballistic annihilation of kink-antikink pairs. Finally I will discuss the extension of the model to the case of asymmetric initial conditions.
9/21/2022Lars AalsmaArizona State UniversityCynthia KeelerEntropic Aspects of De Sitter Quantum Gravity in Two DimensionsIn recent years, the (non-)existence of metastable de Sitter vacua in quantum gravity has been a subject of intense debate. Nonetheless, there is one aspect of de Sitter quantum gravity that has been widely accepted: the cosmological horizon carries an entropy proportional to its area. In an explicit two-dimensional setting, I will explain how this can lead to an information paradox, its resolution, and the consequences for the validity of semi-classical EFT.
9/28/2022Dan StolarskiCarleton via UCSD Matt BaumgartA chiral SU(5) theory with three generationsI will present a study of an interesting strongly coupled chiral quantum field theory. This theory has the same particle content as the simplest grand unified theory of the Standard Model. I will employ tools such as 't Hooft anomaly matching and softly broken supersymmetry to analyze the non-perturbative dynamics of the theory. I will also speculate on the more general lessons of my analysis.
10/12/2022Pouya AsadiOregon UniversityMatt BaumgartThermal Squeezeout of Dark MatterThere has been substantial effort on searching for thermal Dark Matter (DM) in the conventional mass window of GeV to tens of TeV without any positive results. This null result has motivated efforts to develop new dynamics in the dark sector that allow us go beyond the usual thermal DM mass window. In this talk, I introduce one such simple dynamic in a broad class of confining dark sectors. I will point out a potentially dramatic effect on the DM abundance during its deconfinement phase transition. I will also discuss the effect of long-living glueballs in such a sector. Potential signals of such a sector will be briefly presented too.
10/26/2022Peter KoroteevBerkeleyAndrei BelitskiFrom Instantons to Vortices via a Double-Scaling Limit.I will review the connection between soluble many-body systems and supersymmetric gauge theories. I will then study the so-called Inosemtsev limit which involves certain double-scaling, and which will enable us to transition from the moduli space of instantons to the moduli space of vortices.
11/2/2022Kanu SinhaArizona State UniversityTanmay VachaspatiQuantum fluctuation phenomena in nanoscale quantum systemsQuantum fluctuation phenomena are a fascinating and fundamental feature of quantum electrodynamics (QED), with implications spanning spontaneous emission of atoms, stability of colloidal suspensions such as milk, adhesive properties of gecko feet and, potentially, the density perturbations in the cosmic microwave background. When considering particle-surface interactions at nanoscales, such fluctuation-induced interactions become an imperative element of consideration in understanding and designing nanoscale quantum systems. In this talk, I will introduce an open quantum systems approach to engineer fluctuation phenomena at nanoscales -- Casimir-Polder forces, dissipation and decoherence -- particularly focusing on fluctuation-induced decoherence of levitated nanoparticles. Our results illustra
11/9/2022Kurt HinterbichlerCase WesternClaire ZukowskiSymmetries and anomalies at the IR fixed point of gravityI will discuss symmetries that arise at the infrared fixed point of the RG flow of Einstein gravity, including conformal vs. scale invariance in various dimensions, as well as 1-form generalized global symmetries and new anomalies that arise among them.
11/30/2022Francis -Cyr-RacineNew Mexico UniversityMatt BaumgartScaling Invariance and the Origins of Cosmological ConstraintsSince they naturally live in angular and redshift space, astronomical observations have a built-in invariance under rescaling all length scales in the problem. Breaking this invariance requires the use of anchors, such as known distances or energy scales, that can set the absolute scale of the problem. These anchors are fundamental to our knowledge of cosmological distances throughout the Universe, and provide the backbone on which much of our knowledge of cosmology rests. These pillars have recently come under renewed scrutiny due to apparently discrepant measurements of the Hubble constant, a very important cosmological quantity which sets the size and age of the observable Universe. Here, we carefully examine the key anchors underpinning observations of the cosmic microwave background and baryon acoustic oscillations, finding ways to detach these measurements from their traditional anchors and fully restore their intrinsic scaling invariance. Not only can this help to understand the possible cause of the Hubble constant discrepancy, but it also sheds new light on the origins of cosmological constraints on new physics beyond the Standard Model. This in turn provides us with a general toolbox to design novel cosmological models that are automatically compatible with observations.
12/07/2022Xiurui ZhaoHarvard UniversityRolf JansenActive Galactic Nuclei in NuSTAR Era Active galactic nuclei (AGN), which represent the rapidly growing phase of the supermassive black holes, radiate across the whole electromagnetic spectrum from radio to Gamma-rays. X-rays, which are seen in most AGN, are an important tool to study AGN. Thanks to the launch of NuSTAR in 2012, we are able to probe detailed AGN properties in the hard X-ray regime for the first time. In this presentation, I will introduce our group’s recent progress on different aspects of AGN using deep NuSTAR observations, including AGN demographics and the properties of the dusty tori and X-ray emitting corona.


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

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 waves
01/29/2020Thomas BachlechnerUCSDDr. VachaspatiTesting the electric Aharonov-Bohm effect: electromagnetic memory vs. boundary gauge invariance
02/05/2020Peter GeltenbortInstitut Laue LangevinDr. AlarconProbing Early Universe Particle Physics with Neutrons
02/13/2020 (Thursday @ 12PM) Kathryn ZurekCalTechDr.KeelerSpacetime fluctuations in AdS/CFT
02/19/2020Tanmay VachaspatiASUCOSMODynamical quantum collapse and 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 ONLY
04/22/2020Prof. Lam Hui Columbia UniversityONLINE ONLY

FALL 2019

9/11/2019FALL 2019 Welcome Reception ASU Tanmay Vachaspati
9/18/2019Henry LammUniversity of MarylandQuantum Computers for Quantum Field TheoryRich Lebed
9/25/2019Ryan Westernacher-SchneiderUniversity of ArizonaMultimessenger Seismology of Core-Collapse SupernovaeDr. Lunardini
10/1/2019Ubirajara van KolckInstitut de Physique Nucleaire d'Orsay and University of ArizonaA New Leading Mechanism for Neutrinoless Double-Beta DecayMatthew Baumgart
10/9/2019Yue ZhaoUniversity of UtahSearching for Dark Photon Dark Matter with Gravitational Wave DetectorsMatthew Baumgart
10/16/2019Thiago FleuryFederal University of Rio Grande do NorteCorrelation Functions in N=4 SYM and IntegrabilityAndrei Belitsky
10/23/2019 Heling DengArizona State UniversityPrimordial black holes from primordial bubblesTanmay Vachaspati
10/30/2019Sergej MorozTechnical University of MunichConfined phases of fermions coupled to Z2 gauge fieldsAndrei Belitsky
11/6/2019Atsushi NarukoYukawa Institute for Theoretical PhysicsPossible resolution of a spacetime singularity with field transformationsGeorge Zahariade
11/13/2019Ira Z. RothsteinCarnegie Mellon UniversityEffective field theory for quantum mechanical black holesMatthew Baumgart
11/20/2019Jaime Besprosvany UNAMHeavy quarks within the electroweak multiplet Tanmay Vachaspati
12/4/2019Jun NianLeinweber Center for Theoretical Physics, University of MichiganMicrostate Counting of Asymptotically AdS (Near-)BPS Black Holes and Hawking RadiationCynthia Keeler

Spring 2019

1/30/2019George ZahariadeASUClassical-Quantum Correspondence and BackreactionDr. Vachaspati
2/6/2019Raisa TrubkoHarvardPrecision Tune-out Wavelength Measurement with Atom InterferometryDr. Lunardini
2/20/2019Christoph KellerUniversity of ArizonaHolographic Conformal Field Theories in Two DimensionsDr. Keeler
2/27/2019Maulik ParikhASU Forever Never Lasts: The Unruh-de Sitter State and the End of Eternal InflationDr. Wilczek
3/13/2019Yanou CuiUC Riverside Probing the early Universe with gravitational waves from cosmic stringsDr. Vachaspati
3/20/2019Andrew LongUniversity of MichiganUltra-light dark photons from a network of cosmic stringsDr. Vachaspati
3/27/2019Yuber PerezFermi LabNeutrinos in Dark Matter detection experiments: Standard Model and Beyond.Dr. Lunardini
4/10/2019Andres LunaUCLABlack holes and the double copy.Dr. Keeler
4/17/2019 Lucien HeurtierUofAEeV scale dark-matter: production mechanism through the inflaton portal and experimental signatures using the ANITA collaborationDr. Baumgart
4/24/2019Eleni KontouUniversity of YorkQuantum strong energy inequality and the Hawking singularity theoremDr. Vachaspati
5/1/2019Timothy TaitUC IrvineAn Early Phase of QCD Confinement and the Baryon Asymmetry of the UniverseDr. Baumgart