Disciplines / Research questions
Mathematics
247 research topics · 1651 questions
Transcendence of the Riemann function at odd positive integers10 questions
Determining the -dimension of the span of : linear independence of odd zeta values
Open for about 48 yearsIs Apéry's constant transcendental, and are and algebraically independent?
Open for about 47 yearsIrrationality of odd zeta values: is ζ(5) irrational, and how many of ζ(3), ζ(5), …, ζ(s) are irrational?
Open for about 47 yearsThe Sondow–Zlobin conjecture on triangle integrals: prove that is never a rational multiple of for any integer
Open for about 19 yearsIrrationality of
Open for about 47 yearsIrrationality of the Riemann zeta values at odd integers: is ζ(s) irrational for any fixed odd s ≥ 5?
Open for about 48 yearsArithmetic nature of the odd Riemann zeta values: irrationality of for
Open for about 47 yearsClosed forms for odd zeta values: whether is a rational multiple of
Open for about 47 yearsImproving the lower bound for the number of irrational odd zeta values
Open for about 24 yearsIrrationality of individual odd zeta values: is ζ(5) irrational?
Open for about 48 years
Riemann Conjecture6 questions
Open analytical questions for Voros's discretized Keiper–Li sequence: transseries asymptotics, all- positivity, and remainder bounds
Open for about 9 yearsThe zeta spiral on the critical line: denseness of the values of in and the unconditional curvature sign
Open for about 16 yearsThe Alternative Hypothesis for zeta-zero pairs: determinacy of the limiting densities p_{k/2} under AH-Pairs alone
Open for about 30 yearsThe missing direction of the Soundararajan and Radziwiłł equivalence between small gaps of zeros of the Riemann zeta-function and the horizontal distribution of zeros of ζ′(s), and the conjectured small-v asymptotics of m(v) and m′(v)
Open for about 28 yearsDenseness of the values of on the critical line: the remaining case of the Bohr–Courant value-distribution problem
Open for about 112 yearsUnconditional discrete second moments of the Riemann zeta-function along polynomial shifts: closing the abscissa gap to the line
Open for about 6 years
Lie algebras and their classification of nilpotent elements in dual spaces7 questions
The normal-form map versus the Kazhdan–Lusztig map, and the even-depth analogue of the minimal reducing subalgebra theorem for nilpotent elements
Open for about 5 yearsCanonical forms for coadjoint orbits of maximal unipotent subgroups: Surkov's Conjecture 3.8 for root systems beyond G_2 and F_4
Open for about 1 yearGeneral classification of nilpotent orbits in real graded semisimple Lie algebras: completing the real carrier-algebra programme
Open for about 12 yearsClassification of coadjoint orbits of maximal dimension for Borel nilradicals in types , and
Open for about 64 yearsNilpotent orbit finiteness, separability, and Howe's conjecture for non-split reductive groups over local fields of positive characteristic
Open for about 10 yearsSpaltenstein's conjecture: every stabiliser sheet of a reductive Lie algebra contains a unique nilpotent orbit, in arbitrary characteristic
Open for about 44 yearsCoincidence of the two Springer correspondences for the dual of a classical Lie algebra in characteristic 2 (Xue's Remark 5.19 expectation)
Open for about 16 years
Branching laws for representations of Lie groups5 questions
Packet-level multiplicity-one for the branching of to beyond regular parameters, small-rank signatures, and a Gross–Prasad-type law for non-tempered packets
Open for about 7 yearsClassification of the triples with admissible restriction of a discrete series representation to an embedded
Open for about 8 yearsFinite multiplicity of the continuous spectrum in discrete series branching laws: a per-representation criterion and the finite-infinite boundary for symmetric pairs beyond the real-spherical class
Open for about 13 yearsKobayashi's conjecture on admissible restrictions: does -admissibility imply -admissibility?
Open for about 26 yearsBlattner-type multiplicity formula for discretely decomposable restrictions of Zuckerman modules to symmetric subgroups (Ørsted–Speh conjecture)
Open for about 18 years
Classification of unitary representations of Lie groups8 questions
Positive energy versus semiboundedness for irreducible unitary representations of full hermitian Lie groups
Open for about 15 yearsThe unitary duals of the complex exceptional simple Lie groups , , , and
Open for about 37 yearsGeneral super imprimitivity theorem: Mackey induction and systems of imprimitivity for super homogeneous spaces with odd directions
Open for about 21 yearsUnitary dual of Drinfeld doubles of q-deformations of compact semisimple Lie groups beyond the almost-real regime
Open for about 10 yearsThe Salamanca-Riba–Vogan unitarily-small infinitesimal-character conjecture for real reductive groups beyond
Open for about 27 yearsStructural theory of the FS-scattered part of the Dirac series for real exceptional Lie groups: u-small K-types, unipotent representations, and cancellation in the Dirac index
Open for about 6 yearsMaking the FPP description of the unitary dual of real reductive groups algorithmically effective
Open for about 3 yearsAlgebraic constructions of first-reduction-point and exceptional unitary highest weight modules
Open for about 3 years
Decoding Problems of Reed-Solomon Code7 questions
Hardware realization of quasi-linear FFT-based Reed–Solomon decoders (the modular-approach MA/FDMA/FMA family)
Open for about 4 yearsLow-complexity algebraic soft-decision decoding of Reed–Solomon codes: closing the performance–complexity gap of Koetter–Vardy decoding
Open for about 22 yearsCombinatorial List-Size Classification of Linearized Reed–Solomon Codes Across All Sum-Rank Parameter Regimes
Open for about 5 yearsEfficient decoding, list-decodability, and dual insdel distance of Reed–Solomon codes under insertion–deletion errors
Open for about 6 yearsEfficient list-decoding of Reed-Solomon codes at the generalized Singleton radius, and efficient certification of optimal list-decodability
Open for about 6 yearsExplicit Reed–Solomon codes achieving capacity-level list-decodability over small fields
Open for about 5 yearsProximity gaps for Reed–Solomon codes above the Johnson radius: list- and line-decodability over prime fields up to the Elias radius
Open for about 6 years
Determining the cardinality of the continuum5 questions
Consistency strength of the higher Solovay configuration at singular cardinals of countable cofinality: measurability of in and the -perfect set property
Woodin's Ω Conjecture: completeness of Ω-logic under a proper class of Woodin cardinals
Optimal large-cardinal strength for blowing up the power of a singular cardinal of uncountable cofinality that is singular in the core model
Optimal hypotheses for Easton's theorem at measurable and strong cardinals
The Revision Hypothesis: must every limit cardinal be a revision cardinal?
Quantum Layer Conjecture7 questions
Bound states of the Dirichlet Laplacian in the Fichera layer and generalized Fichera layers: exact counts
Open for about 8 yearsGeometric characterization of the discrete spectrum of quantum layers and their nonsmooth analogues: bound states, thickness uniformity, and the converse problem
Open for about 25 yearsDiscrete spectrum of curved quantum layers: the Lu–Rowlett open problems on uniform thin-layer existence, the positive-total-Gauss-curvature domination inequality, and the thick-layer dichotomy
Open for about 14 yearsEmpty discrete spectrum of generalized quantum tubes: the converse problem beyond thin layers and surfaces
Open for about 20 yearsWidth-uniform existence of bound states in hard-wall quantum layers over finite-total-curvature surfaces
Open for about 19 yearsCurvature-induced bound states in quantum layers over non-parabolic hypersurfaces in dimensions four and higher
Open for about 14 yearsThe quantum layer conjecture: bound states in hard-wall layers over nonplanar asymptotically flat surfaces with finite total curvature
Open for about 25 years
The quantum minimal model conjecture7 questions
Invariance and decomposition of quantum cohomology under flips and birational maps between minimal models
Open for about 27 yearsReduction conjecture for arbitrary smooth GIT quotients and quantum D-module decomposition for arbitrary standard flips
Open for about 3 yearsEffective computation of quantum cohomology across conifold transitions: a blow-up formula along Weil divisors
Open for about 11 yearsDoes blowing up a Fano manifold along a smooth Fano center strictly increase the spectral radius of quantum multiplication by the first Chern class (Conjecture 1.1 of Hu–Ke–Li–Song)?
Open for about 2 yearsGlobalizing the quantum-flips F-embedding: big quantum cohomology under general global simple (r,r′) flips
Open for about 6 yearsEstablish the -equivariant noncommutative minimal model program: quasi-convergent paths of equivariant stability conditions from the equivariant quantum differential equation
Open for about 3 yearsBlow-up compatibility of reflection vectors in quantum cohomology: convergence of the quantum cohomology of Bl(X) and the reflection-vector property for pullbacks of exceptional objects
Open for about 3 years
Quantum Yang-Mills Millennium Problem4 questions
Extending the provable area-law regime for lattice Yang-Mills: the linear-in-N ('t Hooft) regime with uniform string tension, and fixed small N at large coupling
Open for about 52 yearsDeconfinement for trivial-center lattice Yang–Mills in the strong-coupling regime and mass-gap criteria beyond the Bakry–Émery approach
Open for about 47 yearsDeconfinement of trivial-center lattice Yang-Mills theories: uniform perimeter law for all strong-coupling beta, extensions to SO(2N+1) and general representations, the weak-coupling regime, and the large-N reconciliation
Open for about 47 yearsYang–Mills existence and mass gap: a fully quantized, background-independent four-dimensional theory with a gauge-invariant positive mass gap
Open for about 26 years
List Coloring Conjecture9 questions
The List Equitable Total Coloring Conjecture
Open for about 8 yearsEnumerative chromatic-choosability of joins with complete graphs (the enumerative Ohba conjecture of Allred and Mudrock)
Open for about 1 yearThe Proportional Choice Number of Complete Bipartite and Complete Multipartite Graphs: Exact Value, Classification, and Asymptotics
Open for about 6 yearsIs every line graph -choosable?
Open for about 50 yearsGeneralized Ohba conjecture for r-uniform hypergraphs: chromatic-choosability at high chromatic number
Open for about 8 yearsThe List Coloring Conjecture: is the list chromatic index of every multigraph equal to its chromatic index?
Open for about 51 yearsList and correspondence colouring reconfiguration conjectures: optimal diameters and
Open for about 4 yearsPaintability of balanced complete multipartite graphs with parts of size three: is for every , and what is ?
Open for about 14 yearsOpen problems on the λ-choosability of planar graph families from Zhu's refinement of choosability
Open for about 7 years
Existence of a complex structure on the six-dimensional sphere6 questions
Integrability of the Clifford-induced almost complex structure on level hypersurfaces of OT-FKM isoparametric families
Open for about 4 yearsThe Hopf problem in generalized geometry: existence of an integrable generalized complex structure on the six-sphere
Open for about 2 yearsHopf's problem: does the six-sphere admit a complex structure?
Open for about 79 yearsVanishing and Chern-class constraints for compact complex threefolds with and holomorphic algebraic reduction in full generality
Open for about 28 yearsComplex-structure rigidity without the Kähler hypothesis for the two exceptional flag manifolds and
Open for about 6 yearsA necessary-and-sufficient curvature characterization of integrability of almost complex structures
Open for about 11 years
Does the travelling salesman problem admit an approximation ratio below 1.5?7 questions
Is the integrality gap of the subtour-elimination LP for the metric s-t path TSP exactly 3/2?
Open for about 10 yearsA 3/2-Approximation for Prize-Collecting TSP and a Black-Box Reduction from TSP to PCTSP
Open for about 3 yearsThe exact integrality ratio of the Held-Karp relaxation for the metric s-t path TSP
Open for about 14 yearsThe 4/3 conjecture for the integrality gap of the subtour elimination relaxation of the metric traveling salesman problem
Open for about 46 yearsThe 4/3-Conjecture for the Integrality Gap of the Subtour (Held–Karp) Relaxation of the Metric Traveling Salesman Problem
Open for about 36 yearsSchalekamp–Williamson–van Zuylen conjecture: is the integrality gap of the subtour LP attained on half-integral vertices?
The integrality ratio of the standard LP relaxation for the metric s-t-path TSP
Open for about 14 years
The travelling salesman problem7 questions
The exact integrality ratio of the Held-Karp (subtour) LP relaxation for the metric s-t path TSP
Open for about 35 yearsComputational Complexity of the Symmetric Circulant Traveling Salesman Problem
Open for about 41 yearsThe four-thirds conjecture for the subtour elimination relaxation of the metric traveling salesman problem and the existence of a 4/3-approximation algorithm
Open for about 36 yearsDetermining the Beardwood–Halton–Hammersley constant for the random Euclidean traveling salesman problem: improving the rigorous lower bound 0.6277 and closing the gap to the upper bound 0.90367
Open for about 66 yearsIs the integrality gap of the subtour LP for metric TSP attained on half-integral vertices? (Schalekamp–Williamson–van Zuylen conjecture)
Open for about 13 yearsConstant-Factor Approximability of the Traveling Salesman Problem with Line Neighborhoods in
Open for about 13 yearsComplexity of the Euclidean TSP with neighborhoods: optimal tours for rays in the plane and approximation for lines in 3-dimensional space
Open for about 14 years
The Rohlin problem8 questions
Rokhlin's multiple mixing problem: does mixing imply mixing of all orders for measure-preserving automorphisms?
Open for about 77 yearsDoes exponential mixing imply multiple exponential mixing for smooth measure-preserving systems? (Problem 5.2 of Dolgopyat–Dong–Kanigowski–Nándori)
Open for about 6 yearsRohlin's multiple mixing problem for -actions: does mixing imply mixing of all orders?
Open for about 77 yearsIs the weak Ratner property an isomorphism invariant for measure-preserving flows?
Open for about 16 yearsOpen problems in the rigidity theory of actions with extreme deviation from multiple mixing
Open for about 8 yearsThe Rohlin problem: does mixing imply mixing of all orders for measure-preserving -actions?
Open for about 77 yearsNon-trivial pairwise-independent 3-fold self-joinings of zero-entropy mixing stationary processes
Open for about 39 yearsRohlin's problem: does strong mixing imply mixing of all orders for measure-preserving -actions?
Open for about 77 years
Several problems in Rota-Baxter algebra5 questions
Realizing subgroups as images of Rota–Baxter operators on groups: the free-group instance (Kourovka Notebook Problem 20.124) and Rota–Baxter operators on free non-abelian groups
Open for about 5 yearsA polarized classical Yang–Baxter equation for matching Rota–Baxter Lie algebras of weight zero
Open for about 6 yearsExtended double shuffle completeness and Zagier's dimension conjecture for multiple zeta values
Open for about 32 yearsRota-Baxter indices of upper-triangular and semisimple matrix algebras and the derived-algebra nilpotency bound for
Open for about 8 yearsRestricted post-Lie structures induced by tridendriform algebras in prime characteristic
Open for less than 1 year
Is the Fitting subgroup of a solvable group satisfying the minimal condition on normal subgroups nilpotent?3 questions
Minimal condition on normal subgroups of infinite rank for locally soluble groups
Open for about 12 yearsNilpotence of the Fitting subgroup of a soluble group with the minimal condition on normal subgroups
Open for about 7 yearsMinimal condition on normal subgroups of infinite rank for locally soluble groups
Existence of infinitely many solutions of nonlinear elliptic equations without symmetry7 questions
Geometric uniformity of minimizing tiled deformations for non-symmetric elliptic equations: extending the Bahri–Lions multiplicity theorem to arbitrary bounded smooth domains
Open for about 37 yearsInfinitely many solutions of the Dirichlet -Laplacian with nonzero boundary data throughout the subcritical range
Open for about 28 yearsPersistence of infinitely many solutions for the perturbed elliptic system , in the full subcritical range (Salvatore's open problems)
Open for about 16 yearsBroken-symmetry multiplicity for superlinear elliptic Dirichlet problems: the Bahri–Lions conjecture on general domains
Open for about 37 yearsSharp thresholds for infinitely many solutions of quasilinear equations perturbed from symmetry
Open for about 12 yearsExtending the network-gluing construction of finite-energy solutions with trivial symmetry group to non-even nonlinearities and higher dimensions
Open for about 12 yearsInfinitely many solutions for the superlinear Dirichlet problem with fixed inhomogeneous data in G-invariant domains: the full subcritical range
Open for about 37 years
Semiprimeness of smash products of module algebras10 questions
Semiprimeness transfer to smash products of weak Hopf algebra actions: beyond the involutive, PI, finite-action case
Open for about 40 yearsDoes H-semiprimeness imply semiprimeness for PI-algebras acted on by finite-dimensional semisimple Hopf algebras in positive characteristic?
Open for about 19 yearsThe Cohen–Fishman question: is the smash product of a semisimple Hopf algebra with a semiprime module algebra always semiprime?
Open for about 40 yearsPrime and semiprime smash products for finite-dimensional pointed Hopf algebras beyond quantum linear spaces
Open for about 6 yearsSemiprimitivity and semiprimality of partial smash products: the general partial-action analogue of the Cohen–Fishman–Linchenko–Montgomery question
Open for about 10 yearsUnconditional semiprimality and semiprimitivity transfer for partial smash products of semisimple Hopf algebra actions
Open for about 10 yearsPrime and semiprime smash products for finite-dimensional pointed Hopf algebra actions beyond quantum linear spaces
Open for about 7 yearsClassifying finite-dimensional Hopf algebras whose actions force a nilpotent Jacobson radical on invariant rings
Open for about 8 yearsIntrinsic criteria for equality of the graded and ordinary Jacobson radical of finite groupoid graded algebras beyond trace invertibility
Open for about 7 yearsThe Cohen–Fischman semiprime smash product question and Jacobson-radical stability for Hopf actions on PI-algebras
Open for about 40 years
Kac-Weisfeiler Conjecture in Modular Lie Algebra Representation Theory8 questions
The super Kac-Weisfeiler divisibility property for the strange classical Lie superalgebras and
Open for about 18 yearsSuper Kac–Weisfeiler divisibility for arbitrary restricted Lie superalgebras: irreducible module dimensions, the maximal-locus statement, and support-variety refinements
Open for about 18 yearsThe first Kac–Weisfeiler conjecture for restricted Lie algebras and the index of algebras with isomorphic enveloping algebras
Open for about 55 yearsTikaradze's Kac–Weisfeiler-type conjecture for filtered algebras in positive characteristic:
Open for about 16 yearsThe second Kac-Weisfeiler divisibility conjecture for truncated current Lie algebras
Open for about 55 yearsEffective thresholds for the first Kac–Weisfeiler conjecture in large characteristics and the Frobenius-characterisation conjecture for arbitrary restricted Lie algebras
Open for about 55 yearsSuper first Kac–Weisfeiler conjecture for finite-dimensional restricted Lie superalgebras
Open for about 55 yearsMinimal-dimensional representations of finite -superalgebras and attainability of the super Kac–Weisfeiler bounds (Zeng–Shu Conjecture 0.3)
Open for about 11 years
Singularities induced by characteristic vectors in quasilinear hyperbolic systems6 questions
No shock formation for totally linearly degenerate quasilinear hyperbolic systems: the conjecture beyond block-structured classes
Open for about 42 yearsMajda's no-shock conjecture for one-dimensional linearly degenerate quasilinear hyperbolic systems: ODE-type amplitude blowup versus shock formation
Open for about 42 yearsMajda's conjecture: ODE-type singularity for linearly degenerate quasilinear hyperbolic systems
Open for about 42 yearsMajda's conjecture: ODE-type singularity formation for one-dimensional quasilinear hyperbolic systems with linearly degenerate characteristic fields
Open for about 42 yearsGlobal regularity versus finite-time singularity formation in linearly degenerate dissipative relativistic fluid models
Open for about 2 yearsSpectral-data regularity and normalized coordinates for quasilinear hyperbolic systems with non-constant characteristic multiplicity
Open for about 19 years
Computation and additivity of knot crossing numbers7 questions
Additivity of the crossing number of knots under connected sum (Tait's problem; Kirby Problem 1.65)
Open for about 149 yearsThe satellite crossing number conjecture
Open for about 30 yearsAdditivity of the triple-crossing number under connected sum and sharpness of the genus lower bound
Open for about 6 yearsConstancy of the quadratic Jones-slope coefficient functions in the colored Jones degree quasipolynomials of a knot
Open for about 5 yearsMonotonicity of the crossing spectrum of knots and the additivity threshold for multi-crossing numbers
Open for about 12 yearsAdditivity of the crossing number under connected sum of knots
Open for about 31 yearsCompleting the restricted-Reidemeister-move route to crossing-number additivity: robust diagram invariants and a topological interpretation of the restricted move set (Weinstein 2025, Questions 1-2)
Open for less than 1 year
Computation and additivity of unknotting numbers6 questions
The band-unknotting number of the double twist knots
Open for less than 1 yearThe unknotting number of the knot : deciding between and
Open for less than 1 yearDoes the unknotting number of a connected sum of knots grow with the number of summands?
Open for about 49 yearsExact unknotting numbers of the connected sums of two-strand torus knots with their mirrors, and exact Reidemeister move counts for unlinking
Open for about 15 yearsQuasi-additivity of the Delta-unknotting number, a strand-independent braid-knot constant, and primality of knots with Delta-unknotting number one
Open for less than 1 yearHow badly unknotting number fails to be additive under connected sum: the max bound, universally additive knots, and the exact value of
Open for about 1 year
Transcendence of Euler's constant10 questions
Apéry-type rational approximations to Euler's constant: a second-order homogeneous recurrence construction, or integer linear forms in 1 and γ of better-than-sub-exponential quality
Open for about 47 yearsIs Euler's constant a value of an arithmetic Gevrey series? Membership of in the rings , and
Open for about 3 yearsThe arithmetic nature of the Euler–Gompertz constant: irrationality and transcendence of
Open for about 58 yearsIrrationality and arithmetic nature of the Euler–Mascheroni constant
Open for about 126 yearsArithmetic nature of the linear combinations of the Euler–Mascheroni and Euler–Gompertz constants for
Open for about 292 yearsArithmetic nature of the non-trivial zeros of the Riemann zeta function and of their power sums at algebraic arguments
Open for about 8 yearsUnconditional algebraic independence of the logarithmic parts of generalized Euler–Briggs constants (removing the Weak Schanuel hypothesis in Gun–Murty–Saha)
Open for about 10 yearsOccurrence of the exceptional algebraic generalized Euler–Briggs constant in the families of Gun–Saha–Sinha
Open for about 16 yearsErdős's conjecture on the non-vanishing of for -valued periodic functions (Erdősian functions)
Open for about 61 yearsDetermine the arithmetic nature of generalized Euler–Kronecker constants of number fields (algebraic or transcendental)
Open for about 295 years
Well-posedness of global weak solutions of the Euler equations8 questions
Beyond the Yudovich class for the 2D Euler equations: propagating localized instability to full non-uniqueness of unforced weak solutions, Gevrey-type well-posedness, and the self-similar structure of the algebraic singularity
Open for about 39 yearsExistence of global energy-admissible weak solutions of the incompressible Euler equations for arbitrary initial data in the energy space
Open for about 15 yearsUniqueness versus non-uniqueness for the 2D incompressible Euler equations with vorticity in , (the Yudovich gap)
Open for about 39 yearsWell-posedness of the 2D Euler equations with bounded, non-decaying planar vorticity: uniqueness of Yudovich-type limits beyond symmetry and far-field prescriptions
Open for about 9 yearsExistence of energy-admissible global weak solutions to the incompressible Euler equations for arbitrary initial data
Open for about 15 yearsExistence of invariant measures for the 2D stochastic Euler equations driven by linear multiplicative noise on a bounded domain
Open for about 3 yearsWell-posedness of the two-dimensional Euler equations with merely bounded vorticity in wide planar sectors and general unbounded domains (the Caprino–Marchioro one-point Green-function conjecture)
Open for about 17 yearsUniqueness for the two-dimensional incompressible Euler equations with unbounded vorticity
Open for about 63 years
Schoen's conjecture on harmonic maps of the Poincaré disk4 questions
Finite non-transversality of positive maps into flag varieties for general Guichard–Wienhard positive structures
Open for less than 1 yearHarmonic diffeomorphisms between Euclidean and hyperbolic model spaces: the open non-symmetric and higher-dimensional cases of Schoen's problem
Open for about 33 yearsNonvanishing of the Jacobian for harmonic quasiconformal mappings in dimensions (Problem 7.3 of Todorčević, 2019)
Open for about 11 yearsNonexistence of harmonic diffeomorphisms from the disk onto a complete parabolic plane (Mazet–Rodríguez–Rosenberg conjecture)
Open for about 10 years
Penrose's Conjecture6 questions
The Penrose inequality for general (non-time-symmetric) asymptotically flat initial data sets
Open for about 52 yearsThe sharp Penrose inequality for asymptotically (locally) hyperbolic initial data
Open for about 27 yearsPenrose inequality and positive mass theorem under averaged dominant energy conditions beyond spherical symmetry
Open for about 1 yearExtremal Reissner–Nordström–Tangherlini rigidity at equality in the charged positive mass inequality for higher-dimensional black-hole initial data
Open for about 12 yearsThe Penrose inequality for general asymptotically flat initial data sets beyond the 2-convexity condition
Open for about 53 yearsLower bounds for black hole area in terms of mass, charge, and angular momentum: minimal enclosing area, multiple black holes, and rigidity
Open for about 13 years
Poincaré's problem on degrees of invariant curves of planar vector fields5 questions
Divergent separatrices of holomorphic foliations on the complex projective plane with a unique singular point: an explicit saddle-node example and rigorous divergence for the Alcántara–Mozo-Fernández nilpotent family
Open for about 3 yearsCharacterizing when the index–Diophantine strategy bounds the degrees of algebraic solutions of non-degenerate polynomial differential equations
Open for about 8 yearsRealizability of the pure algebraic multiplicity and topological invariance of the algebraic multiplicity for dicritical foliation germs (Genzmer–Mol's open questions)
Open for about 10 yearsThe algebraic-critical case of the Poincaré problem: which local algebraic solutions extend to global invariant algebraic curves
Open for about 21 yearsGenus-one rational first integrals and intrinsic dicritical bounds in the effective Poincaré problem for foliations of the projective plane
Open for about 14 years
Homogeneous Einstein manifolds8 questions
Splitting of complete negative Einstein manifolds with cocompact connected Lie group symmetry: Conjecture 1.1 of Böhm–Lafuente without unimodularity
Open for about 3 yearsThe Böhm–Lafuente splitting conjecture for negative Einstein manifolds with cocompact isometric symmetry
Open for about 3 yearsWhich compact homogeneous spaces admit an invariant Einstein metric: completing the topological existence criteria of Wang–Ziller, Böhm, and Graev
Open for about 40 yearsGlobke–Nikolayevsky conjecture: every compact pseudo-Riemannian Einstein solvmanifold is a nilmanifold
Open for about 9 yearsThe dynamical Alekseevskii conjecture in dimensions six and above
Open for about 9 yearsWhich nilpotent Lie algebras are Einstein nilradicals? (Lauret–Will Problem 3 and the positive-graph question)
Open for about 20 yearsThe Böhm–Wang–Ziller Finiteness Conjecture: finiteness of invariant Einstein metrics on compact homogeneous spaces
Open for about 22 yearsFiniteness of the moduli space of invariant Einstein metrics on a compact homogeneous space
Open for about 22 years
Resolution of singularities7 questions
Extension of the idealistic filtration resolution algorithm to ambient dimension 4 and above in positive characteristic (Kawanoue–Matsuki)
Open for about 14 yearsResolution of the monomial case of the Idealistic Filtration Program in positive characteristic in dimension four and higher
Open for about 11 yearsGluing local resolutions into a global resolution over perfect fields, and geometric resolution of singular moduli spaces (open problems from Hu's 'Grassmannians and Singularities')
Open for about 62 yearsCanonical resolution of singularities in positive and mixed characteristic via cobordant blow-ups at weighted centers
Open for about 4 yearsEmbedded resolution of singularities in positive characteristic: stability of the residual order under permissible blowups and the existence of a terminating resolution invariant
Open for about 62 yearsForced point centers and the residual-order cycle obstruction to resolution of singularities in positive characteristic
Open for about 8 yearsCanonical functorial resolution of singularities in positive characteristic: extending McQuillan's characteristic-zero invariant beyond equicharacteristic zero
Open for about 61 years
Problem of singular cardinals4 questions
Consistency strength of Ord-long strictly increasing iterates of Shelah's pcf operator
Class-many strong limit singular cardinals with in ZFC (Garti's Conjecture 3.4 on weak diamond and pcf theory)
Stationary reflection with the failure of SCH at a singular cardinal of uncountable cofinality without supercompactness
The residual program for Shelah's approachability ideal at successors of singular cardinals: uniform non-approachability, global failure of SCH and approachability, Woodin's AP-versus-SCH question, and the Tree Property at every successor of a singular (Jakob-Poveda, Questions 5.1-5.4)
Embedding conjecture9 questions
An explicit counterexample to Connes' embedding conjecture: a concretely presented type II factor not embedding into an ultrapower of the hyperfinite factor
Open for about 6 yearsThe GNRS conjecture for minor-excluding graph families: the planar embedding and -sum conjectures
Open for about 27 yearsStrong embeddings of 3-connected cubic planar graphs on surfaces of negative Euler characteristic
Open for about 2 yearsThe Dèbes–Deschamps conjecture: regular Galois solvability of finite split embedding problems over for an arbitrary field
Open for about 29 yearsAbhyankar–Sathaye embedding conjecture for hypersurfaces in affine space
Open for about 52 yearsThe planar embedding conjecture: constant-distortion embeddings of planar graph metrics into
Open for about 26 yearsRegularity of the left-Garside category LD+ and the Embedding Conjecture for free left-self-distributive systems
Open for about 17 yearsThe convex greedy embedding conjecture for 3-connected planar graphs and the Tutte spring-weight question
Open for about 22 yearsExistence of the enforceable II factor
Open for about 9 years
Artificial boundary method for solving nonlinear partial differential equations in unbounded domains7 questions
Explicit time-step bounds and Padé artificial-boundary-condition modeling error for the nonlinear time-fractional Burgers equation on unbounded domains
Open for about 5 yearsHigher-order, multi-dimensional fast discretizations with exact fractional artificial boundary conditions for the time-fractional Schrödinger equation on unbounded domains
Open for about 9 yearsPressure-type artificial boundary conditions for steady Navier-Stokes flows in pipe systems beyond the small-data regime
Open for about 19 yearsHigher-order diagonal Padé nonlinear absorbing boundary conditions for nonlinear time-fractional parabolic problems on unbounded domains
Open for about 10 yearsEfficient and provably stable numerical realization of exact artificial boundary conditions for heat equations with nonlinear boundary conditions on unbounded domains
Open for about 19 yearsStability, error, and convergence analysis of the artificial boundary method for the two-dimensional Burgers equation on unbounded domains
Open for about 18 yearsDiscrete error estimates and higher-order-in-time boundary discretizations for the artificial-boundary finite difference scheme for nonlinear Schrödinger equations on unbounded domains
Open for about 8 years
Optimal methods for solving linear algebraic systems6 questions
Convergence of AdaRBFGS: adaptive randomized BFGS matrix inversion with iterate-dependent sketching
Open for about 10 yearsTruly linear working space and the bit-time frontier for rational linear-system solvers with entrywise multiplicative guarantees
Open for about 1 yearCertified construction of Lagrange-principle optimal recovery methods for finite-dimensional linear systems: the general mixed-constraint case
Open for about 19 yearsThe Time Complexity of Solving Dense Linear Systems with k Large Singular Values: Logarithmic Factors, Matrix-Multiplication Dependence, and Derandomization
Open for about 2 yearsParameter selection for the HSS preconditioner: transfer of condition-number-balancing estimates from the HSS iteration and matrix-free parameter estimation
Open for about 10 yearsStochastic preconditioning: designing the reformulation parameters (B, D) to minimize the condition number zeta(A, B, D) in stochastic reformulations of linear systems
Open for about 9 years
Rigidity of spheres and algebraic domains6 questions
Sharp degree bounds for rational proper holomorphic maps between balls: the D'Angelo conjecture and the classification of valid quadruples (n, r, d, k)
Open for about 37 yearsSharp degree bounds for rational proper maps between balls of maximal geometric rank: sharpness at minimal target dimension and the above-minimal regime (Problem (D))
Open for about 33 yearsRigidity of proper holomorphic maps between unit balls with non-compact symmetry at low Hölder boundary regularity
Open for about 25 yearsD'Angelo's degree conjecture for rational proper holomorphic maps between complex unit balls: unresolved regimes beyond the third gap interval
Open for about 33 yearsGroup data versus map data for rational proper maps of balls: detection of map invariants from the associated symmetry groups
Open for about 9 yearsClassifying local orthogonal pairs and generalized Huang equations between hyperquadrics at the borderline dimension
Open for about 2 years
Raising Pieri-type formulas for zonal functions7 questions
Affine Pieri rule for periodic Macdonald spherical functions of the excluded twisted type , and identification of the deformed fusion ring with deformed Verlinde algebras
Open for about 4 yearsSchur positivity of the -Macdonald polynomials and the positive -character expansion of the Macdonald series
Open for about 3 yearsMixed-type twisted Pieri formulas for Jack polynomials
Open for about 5 yearsExplicit Pieri formulas for Macdonald spherical functions and polynomials beyond small dominant weights
Open for about 23 yearsTwisted Pieri formulas beyond type : extensions to -type root systems, -Macdonald polynomials, and elliptic analogues
Open for about 6 yearsFactorized product forms for the Pieri-type coefficients of nonsymmetric Macdonald polynomials and the effective choice of the reduction index
Open for about 16 yearsA Pieri-type multiplication rule for spherical functions: Bravi–Gandini Conjecture 1.1 for spherical pairs of type A (including F4/Spin(9)) and the Hermitian symmetric cases of types B, C, BC
Open for about 5 years