Scientific Series

Holography with branes and/or cutoff surfaces presents a promising approach to studying quantum gravity beyond asymptotically anti-de Sitter spacetimes. However, this generalized holography is known to face several inconsistencies, including potential violations of causality and fundamental entropic inequalities. In this talk, we address these challenges by investigating the bulk scattering process and its holographic realization. Specifically, we propose that causality of a radially propagating excitation should be an induced one originating from a fictitious boundary behind the brane/cutoff surface. We present its consistency by checking the connected wedge theorem supported from quantum cryptography and (strong) subadditivity of holographic entanglement entropies. While the induced light cone seemingly permits superluminal signaling, we argue that this causality violation can be an artifact of state preparation in our picture. This talk is based on 2308.00739 [10.1007/JHEP10(2023)104] with Beni Yoshida.

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Zoom link https://pitp.zoom.us/j/98252951858?pwd=RVNZUjNVM2JkZXRlSXJVbEZ6cUpsUT09

The recent data releases by multiple pulsar timing array (PTA) experiments show evidence for Hellings-Downs angular correlations indicating that the observed stochastic common spectrum can be interpreted as a stochastic gravitational wave background. We study whether the signal may originate from gravitational waves induced by high-amplitude primordial curvature perturbations. Such large perturbations may be accompanied by the generation of a sizable primordial black hole (PBH) abundance. We discuss in which scenarios the inclusion of non-Gaussianities in the computation of the abundance can lead to a signal compatible with the PTA experiments without overproducing PBHs.

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Zoom link https://pitp.zoom.us/j/95261778825?pwd=QndRd0xQVFpNVzk0VXpRUkNqR1JXZz09

Quantum vortices are two-dimensional solitons which carry a topological charge - the first Chern number n. They play a crucial role in many physical concepts from cosmic strings to mirror symmetry and dualities of supersymmetric models. When n grows the vortices become giant. The giant vortices are observed experimentally in a variety of quantum systems. Thus, it is quite appealing to identify their characteristic features and universal properties, which is quite a challenging mathematical problem. Though the nonlinear vortex equations may look deceptively simple, their analytic solution is not available. In this talk I demonstrate how by borrowing the asymptotic methods of fluid dynamics such a solution can be found in the large-n limit. I then construct a systematic expansion in inverse powers of the topological charge about this asymptotic solution which works amazingly well all the way down to the elementary vortex with n=1. I use this result to study the Majorana zero modes bound to giant vortices. The resulting local density of states has a number of features which give remarkable signatures for an experimental observation of the "Majorana fermions" in two dimensions.

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Zoom link https://pitp.zoom.us/j/98994856372?pwd=ZFBOemRZQS9WbHAzMTN6R2lKZEdXQT09

Learn more about the benefits of creating an accessible environment and how you play a part. Dr. Mahadeo Sukhai and Ainsley Latour are scientists, researchers, educators and IDEA professionals, who are passionate about and committed to inclusion in the scientific research and training enterprise. 

• Learning Objective 1 – provide an understanding of the “leaky funnel” in STEM training for persons with disabilities
• Learning Objective 2 – provide an overview of the principles underpinning a culture of accessibility and inclusion in the sciences
• Learning Objective 3 – provide an appreciation for the importance of accessibility in scientific conferences and publications

Dr. Mahadeo A. Sukhai (He/Him), Ph.D. is the world’s first congenitally blind geneticist. Dr. Sukhai is Vice-President Research & International Affairs and Chief Accessibility Officer for the CNIB (Canadian National Institute for the Blind), having previously served as a researcher in cancer genomics at the University Health Network in Toronto. Dr. Sukhai also holds an adjunct faculty appointment in the Department of Ophthalmology, School of Medicine, Queens University (Kingston, ON, Canada), as well as additional Adjunct roles in the Faculty of Business and Information Technology at Ontario Tech University and in the Inclusive Design Program at OCAD University. In his role at CNIB, Dr. Sukhai is responsible for organizational employee culture-building strategy related to inclusion, accessibility and employee wellness. Dr. Sukhai is the Principal Investigator for "Creating a Culture of Accessibility in the Sciences," a book based on his ground-breaking work on access to science within higher education, and serves as the principal investigator for national projects to examine accessibility and inclusion within science education and healthcare. Dr. Sukhai co-founded IDEA-STEM, and INOVA, the international Network of researchers with Visual impairments and their Allies, a new professional society with the mission to improve accessibility and inclusion in the biomedical sciences for researchers with vision loss. Dr. Sukhai is the External Co-Chair for the Canadian Institutes of Health Research External Advisory Committee on Accessibility and Systemic Ableism and the Chair of the Employment Technical Committee for Accessibility Standards Canada.

Ms. Ainsley R. Latour (She/Her), B.Ed., MLT, M.Sc. is the president and co-founder of IDEA-STEM, an organization created to enhance the participation and inclusion for people with disabilities in STEM.  She identifies as hard of hearing and neurodiverse.  She also serves on the Government of Ontario’s AODA Post-Secondary Education Standards Development Committee. Ainsley's work on the experience of students with disabilities in Canada has been presented at national and international conferences on science and disability, including SciAccess 2019 and 2020, the ISLAND 2020 conference, and the American Association for the Advancement of Science (2018, 2019 and 2021).  She also maintains a practice as a licensed cytogenetic and molecular genetic technologist (MLT).  She holds two undergraduate degrees, two graduate diplomas and will graduate soon with a masters in marine environmental genetics from the Memorial University of Newfoundland.

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Zoom link:  https://pitp.zoom.us/j/99867497693?pwd=ZDRkdE44dVBWRDdtS3J3ZzFOMFlHZz09

Axions and axion-like particles are well motivated candidates for dark matter (DM) and have a signature two photon vertex. The most sensitive axion DM search is at the gigahertz (GHz) regime. It relies on microwave cavities with high quality factors resonantly converting axion DM to cavity photons in the background of a static magnetic field. However, axion DM mass could span a vast range above or below GHz. We describe a new proposal using integrated/on-chip photonic systems to search for axion DM at the optical frequency. This enables the use of waveguides to collect signal photons, which improves the detection efficiency, as well as the use of single photon, micron-sized detector, such as a skipper charge-coupled device, which has a dark count rate as low as 1e-9 per second per pixel. Furthermore, by coupling a series of resonators of different frequencies to a single receiver bus, the detection can be broadband in terms of the axion masses and has sensitivities to the axion-photon couplings expected for the QCD axion at the axion masses of around 0.2 eV.

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Zoom link https://pitp.zoom.us/j/94515300239?pwd=VVBkaGM5K24yN2F4SFV0MGZ5Vk9LZz09

We use a result of Hawking and Gilkey to define a Euclidean path integral of gravity and matter which has the special property of being independent of the choice of basis in the space of fields. This property allows the path integral to describe also physical regimes that do not admit position bases. These physical regimes are pre-geometric in the sense that they do not admit a mathematical representation of the physical degrees of freedom in terms of fields that live on a spacetime. In regimes in which a spacetime representation does emerge, the geometric properties of the emergent spacetime, such as its dimension and volume, depend on the balance of fermionic pressure and bosonic and gravitational pull. That balance depends, at any given energy scale, on the number of bosonic and fermionic species that contribute, which in turn depends on their masses. This yields an explicit mechanism by which the effective spacetime dimension can depend on the energy scale.

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Zoom link https://pitp.zoom.us/j/91471624951?pwd=RDBYTXc2MGs5bkFKUytYR0huOHYwdz09

If axion Dark Matter exists, then they can collapse to form self-gravitating exotic compact objects known as axion stars. As mergers of such compact objects can potentially yield detectable gravititational waves which are correlated with a burst of electromagnetic radiation, much effort have been expended to compute these signals. I will discuss both the technical and theoretical challenges of this endeavour, and demonstrate such decays. I will show that axion stars may not be stable to electromagnetic decay, raising the question on whether we should expect to see these objects in the first place.

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Zoom link https://pitp.zoom.us/j/98298572209?pwd=WVFZUFJqQzZQdU8vcjhQRVpzVHZDdz09

We will begin by reviewing the work of Kazhdan and Lusztig, who established an equivalence between certain affine Lie algebra representations and quantum group representations. It can be thought of as a logarithmic version of the CS-WZW correspondence. In a joint work with Lin Chen, we used factorization algebras to establish an extended version of this equivalence. We will explain the main structure of the proof, and draw some connections with Kazhdan and Lusztig's original proof. The key idea is that of Kac-Moody localization, a parametrized version of factorization homology. Time permitting, we will also explain how this idea plays a role in the recently announced proof (by Gaitsgory et al.) of the de Rham geometric Langlands conjecture.

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Zoom link https://pitp.zoom.us/j/98932564942?pwd=WWdMLzI5WktkZnMrQmplU0J3Mk43dz09

Obtaining a description of cosmology is a central open problem in holography. Studying simple models can help us gain insight on the generic properties of holographic cosmologies. In this talk I will describe the construction of entangled microstates of a pair of holographic CFTs whose dual semiclassical description includes big bang-big crunch AdS cosmologies in spaces without boundaries. The cosmology is supported by inhomogeneous heavy matter and it partially purifies the bulk entanglement of two auxiliary AdS spacetimes. In generic settings, the cosmology is an entanglement island contained in the entanglement wedge of one of the two CFTs. I will then describe the properties of the non-isometric bulk-to-boundary encoding map and comment on an explicit, state-dependent boundary representation of operators acting on the cosmology. Finally, if time allows, I will argue for a non-isometric to approximately-isometric transition of the encoding of "simple" cosmological states as a function of the bulk entanglement, with tensor network toy models of the setup as a guide.

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Zoom link https://pitp.zoom.us/j/93483219872?pwd=TGpJVVlaNDVGWTN5ZHpkTHp6a2hTZz09

If dark energy evolves in time its dynamical component could be dominated by a bath of dark radiation. Since dark energy was subdominant in the early universe, the dark energy radiation evades the usual stringent constraints on extra relativistic species from the cosmic microwave background, allowing for an O(1) fraction of the energy density today to be dark radiation. In this talk, I will discuss how dark energy radiation can emerge from a fundamental theory, its predictions for cosmological observables, as well as discovery potential and constraints with existing and future precision cosmological datasets including measurements of the cosmic microwave background, baryon acoustic oscillations, and supernova data. I’ll conclude with the prospects of measuring the particle content of the dark energy radiation in direct-detection experiments in the presence of interactions between the Standard Model and the dark radiation sector, focusing on neutrinos, axions and dark photons.

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Zoom link https://pitp.zoom.us/j/97180285756?pwd=aEtlYmFSRzFSZVBvY3lnMmtPYWc3Zz09

I will present work on probing the large scale structure of the universe using CMB lensing from the upcoming Data Release 6 of the Atacama Cosmology Telescope (ACT) and cross-correlations with galaxies from the unWISE galaxy catalog. My talk will focus on how our highly competitive constraints from CMB lensing and CMB lensing cross-correlations can provide insight into the widely discussed “S8/sigma8 tension”. For this purpose I will briefly introduce the high fidelity CMB lensing reconstruction obtained by the ACT Collaboration and results from the analysis of the lensing auto-correlation. I will discuss new results from the cross-correlation between ACT CMB lensing and unWISE galaxies, highlighting improvements to the analysis pipeline compared to previous work on the cross-correlation between Planck CMB lensing and unWISE by some of my collaborators (Krolewski et al. 2021). I will also show a reanalysis of Planck CMB lensing x unWISE and a joined analysis of the ACT and Planck CMB lensing cross-correlations with unWISE.

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Zoom link https://pitp.zoom.us/j/99192611116?pwd=TU9iMjhrejVESjNRdi92M0ZXN2ZEQT09

In this talk, we identify anomalies of 1+1d lattice Hamiltonian systems as ’t Hooft anomalies. We consider anomalies in internal symmetries as well as Lieb-Schultz-Mattis (LSM) type anomalies involving lattice translations. Using topological defects, we derive a simple formula for the ‘anomaly cocycle’ and show it is the obstruction to gauging even on the lattice. We reach this by introducing a systematic procedure to gauge arbitrary internal symmetries on the lattice that may not act on-site. As a by-product of our gauging procedure, we construct non-invertible lattice translation symmetries from LSM anomalies.

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Zoom link https://pitp.zoom.us/j/98084408560?pwd=cllSVnpWcEhPK21aVDZubU4yYWNyQT09