Jeremy Hahn

I am an assistant professor at MIT.
I study Algebraic Topology, with a particular emphasis on structured ring spectra.
Here is my CV.

Contact Information:
Email: jhahn01 at mit dot edu


Current Seminars Current Teaching Preprints and Publications Past Seminars Past Teaching


Seminars

Teaching

Published and accepted papers

  1. Wilson Spaces, Snaith Constructions, and Elliptic Orientations with Hood Chatham and Allen Yuan. Inventiones Mathematicae. To appear.
      We construct a canonical family of even periodic E∞-ring spectra, with exactly one member of the family for every prime p and chromatic height n. At height 1 our construction is due to Snaith, who built complex K-theory from CP∞. At height 2 we replace CP∞ with a p-local retract of BU<6>, producing a new theory that orients elliptic, but not generic, height 2 Morava E-theories. In general our construction exhibits a kind of redshift, whereby BP<n-1> is used to produce a height n theory. A familiar sequence of Bocksteins, studied by Tamanoi, Ravenel, Wilson, and Yagita, relates the K(n)-localization of our height n ring to work of Peterson and Westerland building (En)hSG from K(Z,n+1).


  2. Odd primary analogs of Real orientations with Andrew Senger and Dylan Wilson. Geometry and Topology. Volume 27, 2023, pages 87-129.
      We define, in Cp-equivariant homotopy theory for p>2, a notion of p-orientation analogous to a C2-equivariant Real orientation. The definition hinges on a Cp-space CP p, which we prove to be homologically even in a sense generalizing recent C2-equivariant work on conjugation spaces. We prove that the height p-1 Morava E-theory is p-oriented and that tmf(2) is 3-oriented. We explain how a single equivariant map S2ρ → Σ∞CP p completely generates the homotopy of Ep-1 and tmf(2), expressing a height-shifting phenomenon pervasive in equivariant chromatic homotopy theory.


  3. On the boundaries of highly connected, almost closed manifolds with Robert Burklund and Andrew Senger. Acta Mathematica. Volume 231(2), 2023, pages 205-344.
      Building on work of Stolz, we prove for integers 0 ≤ d ≤ 3 and k > 232 that the boundaries of (k-1)-connected, almost closed (2k+d)-manifolds also bound parallelizable manifolds. Away from finitely many dimensions, this settles longstanding questions of C.T.C. Wall, determines all Stein fillable homotopy spheres, and proves a conjecture of Galatius and Randal-Williams. Implications are drawn for both the classification of highly connected manifolds and, via work of Krannich and Kreck, the calculation of their mapping class groups.

      Our technique is to recast the Galatius and Randal-Williams conjecture in terms of the vanishing of a certain Toda bracket, and then to analyze this Toda bracket by bounding its HFp-Adams filtrations for all primes p. We additionally prove new vanishing lines in the HFp-Adams spectral sequences of spheres and Moore spectra, which are likely to be of independent interest. Several of these vanishing lines rely on an Appendix by Robert Burklund, which answers a question of Mathew about vanishing curves in BP<n>-based Adams spectral sequences.



  4. Redshift and multiplication for truncated Brown-Peterson spectra with Dylan Wilson. Annals of Mathematics. Volume 196(3), 2022, pages 1277-1351.
      We equip BP<n> with an E3-BP-algebra structure, for each prime p and height n. The algebraic K-theory of this E3-ring is of chromatic height exactly n+1, and the map from K(BP<n>)(p) to LfnK(BP<n>)(p) has bounded above fiber.


  5. Real topological Hochschild homology and the Segal conjecture with Dylan Wilson. Advances in Mathematics. Volume 387, 2021, 107839.
      We give a new proof, independent of Lin's theorem, of the Segal conjecture for the cyclic group of order two. The key input is a calculation, as a Hopf algebroid, of the Real topological Hochschild homology of F2. This determines the E2-page of the descent spectral sequence for the map NF2 → F2, where NF2 is the C2-equivariant Hill-Hopkins-Ravenel norm of F2. The E2-page represents a new upper bound on the RO(C2)-graded homotopy of NF2, from which the Segal conjecture is an immediate corollary.


  6. Exotic Multiplications on Periodic Complex Bordism with Allen Yuan. Journal of Topology. Volume 13, 2020, pages 1839-1852.
      Victor Snaith gave a construction of periodic complex bordism by inverting the Bott element in the suspension spectrum of BU. This presents an E∞ structure on periodic complex bordism by different means than the usual Thom spectrum definition of the E∞-ring MUP. Here, we prove that these two E∞-rings are in fact different, though the underlying E2-rings are equivalent. Nonetheless, we prove that both rings E∞-orient 2-completed KU and other forms of K-theory.


  7. Eilenberg-MacLane spectra as equivariant Thom spectra with Dylan Wilson. Geometry and Topology. Volume 24, issue 6 (2020), pages 2709-2748.
      We prove that the G-equivariant mod p Eilenberg-MacLane spectrum arises as an equivariant Thom spectrum for any finite, p-power cyclic group G, generalizing a result of Behrens and the second author in the case of the group C2. We also establish a construction of HZ(p), and prove intermediate results that may be of independent interest. Highlights include constraints on the Hurewicz images of equivariant spectra that admit norms, and an analysis of the extent to which the non-equivariant HFp arises as the Thom spectrum of a more than double loop map. Accepted by Geometry and Topology.


  8. Real Orientations of Lubin-Tate Theories with Xiaolin Danny Shi. Inventiones Mathematicae. Volume 221, 2020, pages 731-776.
      We show that Morava E-theories at the prime 2 are Real oriented and Real Landweber exact. The proof is an application of the Goerss-Hopkins-Miller theorem to algebras with involution. For each height n, we compute the entire homotopy fixed point spectral sequence for En with its C2-action by the formal inverse. We study, as the height varies, the Hurewicz images of the stable homotopy groups of spheres in the homotopy of these C2-fixed points.


  9. Multiplicative Structure in the Stable Splitting of ΩSLn(C) with Allen Yuan. Advances in Mathematics. Volume 348, 2019, pages 412-455.
      The space of based loops in SLn(C), also known as the affine Grassmannian of SLn(C), admits an E2 or fusion product. Work of Mitchell and Richter proves that this based loop space stably splits as an infinite wedge sum. We prove that the Mitchell--Richter splitting is coherently multiplicative, but not E2. Nonetheless, we show that the splitting becomes E2 after base-change to complex cobordism. Our proof of the A∞ splitting involves on the one hand an analysis of the multiplicative properties of Weiss calculus, and on the other a use of Beilinson--Drinfeld Grassmannians to verify a conjecture of Mahowald and Richter. Other results are obtained by explicit, obstruction-theoretic computations.


  10. Appendix to: Brown Peterson cohomology from Morava E-theory by Tobias Barthel and Nathaniel Stapleton. Compositio Mathematica. Volume 153, 2017, pages 780-819.
      We provide the proof of a technical lemma about torsion in the Morava E theory of finite abelian groups modulo transfers. The theorems of Barthel and Stapleton then allow conclusions about BP cohomology modulo transfers.

ArXiv Preprints



  1. K-theoretic counterexamples to Ravenel's telescope conjecture with Robert Burklund, Ishan Levy, and Tomer Schlank.
      At each prime p and height n+1 ≥ 2, we prove that the telescopic and chromatic localizations of spectra differ. Specifically, for Z acting by Adams operations on BP<n>, we prove that the T(n+1)-localized algebraic K-theory of BP<n>hZ is not K(n+1)-local. We also show that Galois hyperdescent, A1-invariance, and nil-invariance fail for the K(n+1)-localized algebraic K-theory of K(n)-local rings.


  2. Examples of disk algebras with Sanath Devalapurkar, Tyler Lawson, Andrew Senger, and Dylan Wilson.
      We produce refinements of the known multiplicative structures on the Brown--Peterson spectrum BP, its truncated variants BP<n>, Ravenel's spectra X(n), and evenly graded polynomial rings over the sphere spectrum. Consequently, topological Hochschild homology relative to these rings inherits a circle action.


  3. A motivic filtration on the topological cyclic homology of commutative ring spectra with Arpon Raksit and Dylan Wilson.
      For a prime number p and a p-quasisyntomic commutative ring R, Bhatt--Morrow--Scholze defined motivic filtrations on the p-completions of THH(R),TC-(R),TP(R), and TC(R), with the associated graded objects for TP(R) and TC(R) recovering the prismatic and syntomic cohomology of R, respectively. We give an alternate construction of these filtrations that applies also when R is a well-behaved commutative ring spectrum; for example, we can take R to be S, MU, ku, ko, or tmf. We compute the mod (p,v1) syntomic cohomology of the Adams summand and observe that, when p=3, that the corresponding motivic spectral sequence collapses at the E2-page.


  4. Inertia groups in the metastable range with Robert Burklund and Andrew Senger.
      We prove that the inertia groups of all sufficiently-connected, high-dimensional (2n)-manifolds are trivial. Specifically, for m≫0 and k>5/12, suppose M is a (km)-connected, smooth, closed, oriented m-manifold and Σ is an exotic m-sphere. We prove that, if M#Σ is diffeomorphic to M, then Σ bounds a parallelizable manifold. Our proof is an application of higher algebra in Pstragowski's category of synthetic spectra, and builds on previous work of the authors.


  5. Galois reconstruction of Artin-Tate R-motivic spectra with Robert Burklund and Andrew Senger.
      We explain how to reconstruct the category of Artin-Tate R-motivic spectra as a deformation of the purely topological C2-equivariant stable category. The special fiber of this deformation is algebraic, and equivalent to an appropriate category of C2-equivariant sheaves on the moduli stack of formal groups. As such, our results directly generalize the cofiber of τ philosophy that has revolutionized classical stable homotopy theory. A key observation is that the Artin-Tate subcategory of R-motivic spectra is easier to understand than the previously studied cellular subcategory. In particular, the Artin-Tate category contains a variant of the τ map, which is a feature conspicuously absent from the cellular category.


  6. The Lubin-Tate Theory of Configuration Spaces: I with Lukas Brantner and Ben Knudsen.
      We construct a spectral sequence converging to the Morava E-theory of unordered configuration spaces and identify its E2-page as the homology of a Chevalley-Eilenberg-like complex for Hecke Lie algebras. Based on this, we compute the E-theory of the weight p summands of iterated loop spaces of spheres (parametrising the weight p operations on En-algebras), as well as the E-theory of the configuration spaces of p points on a punctured surface. We read off the corresponding Morava K-theory groups, which appear in a conjecture by Ravenel. Finally, we compute the Fp-homology of the space of unordered configurations of p particles on a punctured surface.


  7. Nilpotence in normed MGL-modules with Tom Bachmann.
      We establish a motivic version of the May Nilpotence Conjecture: if E is a normed motivic spectrum that satisfies E^HZ=0, then also E^MGL=0. In words, motivic homology detects vanishing of normed modules over the algebraic cobordism spectrum.


  8. Nilpotence in En algebras.
      Nilpotence in the homotopy of E∞-ring spectra is detected by the classical HZ-Hurewicz homomorphism. Inspired by questions of Mathew, Noel, and Naumann, we investigate the extent to which this criterion holds in the homotopy of En-ring spectra. For all odd primes p and all chromatic heights h, we use the Cohen-Moore-Neisendorfer theorem to construct examples of K(h)-local, E2n-1-algebras with non-nilpotent pn-torsion. We exploit the interaction of the Bousfield-Kuhn functor on odd spheres and Rezk's logarithm to show that our bound is sharp at height 1, and remark on the situation at height 2.


  9. On the Bousfield classes of H∞-ring spectra
      We prove that any K(n)-acyclic, Dp-ring spectrum is K(n+1)-acyclic, affirming an old conjecture of Mark Hovey.


  10. Appendix to: Equivariant nonabelian Poincar duality and equivariant factorization homology of Thom spectra by Asaf Horev, Inbar Klang, and Foling Zou.
      In an appendix joint with Dylan Wilson, we explain how to use the main theorem of the paper to assemble an integral calculation of the Real THH of Z.


  11. Quotients of even rings with Dylan Wilson.
      A short note about quotients of even rings remaining highly structured. It was the genesis of our later construction of multiplicative structures on truncated Brown--Peterson spectra.


    Present work supported by the Sloan foundation and Rockwell international career development assistant professorship. Work from 2013-2018 was supported by an NSF GRFP under Grant DGE-1144152. Work from Fall 2018-2021 was supported by the NSF under Grant DMS-1803273.

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Past seminars