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Search Results: 1 - 10 of 403804 matches for " Nathan M. Dunfield "
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A knot without a nonorientable essential spanning surface
Nathan M. Dunfield
Mathematics , 2015,
Abstract: This note gives the first example of a hyperbolic knot in the 3-sphere that lacks a nonorientable essential spanning surface; this disproves the Strong Neuwirth Conjecture formulated by Ozawa and Rubinstein. Moreover, this knot has no even strict boundary slopes, disproving the Even Boundary Slope Conjecture of the same authors. The proof is a rigorous calculation using Thurston's spun-normal surfaces in the spirit of Haken's original normal surface algorithms.
A table of boundary slopes of Montesinos knots
Nathan M. Dunfield
Mathematics , 1999,
Abstract: This note corrects errors in Hatcher and Oertel's table of boundary slopes of Montesinos knots which have projections with 10 or fewer crossings.
Examples of non-trivial roots of unity at ideal points of hyperbolic 3-manifolds
Nathan M. Dunfield
Mathematics , 1998,
Abstract: This paper gives examples of hyperbolic 3-manifolds whose SL(2,C) character varieties have ideal points whose associated roots of unity are not 1 or -1. This answers a question of Cooper, Culler, Gillet, Long, and Shalen as to whether roots of unity other than 1 and -1 occur.
Alexander and Thurston norms of fibered 3-manifolds
Nathan M. Dunfield
Mathematics , 1999,
Abstract: For a 3-manifold M, McMullen derived from the Alexander polynomial of M a norm on H^1(M, R) called the Alexander norm. He showed that the Thurston norm on H^1(M, R), which measures the complexity of a dual surface, is an upper bound for the Alexander norm. He asked if these two norms were equal on all of H^1(M,R) when M fibers over the circle. Here, I give examples which show that the answer to this question is emphatically no. This question is related to the faithfulness of the Gassner representations of the braid groups. The key tool used to understand this question is the Bieri-Neumann-Strebel invariant from combinatorial group theory. Theorem 1.7, which is of independant interest, connects the Alexander polynomial with a certain Bieri-Neumann-Strebel invariant.
Cyclic surgery, degrees of maps of character curves, and volume rigidity for hyperbolic manifolds
Nathan M. Dunfield
Mathematics , 1998, DOI: 10.1007/s002220050321
Abstract: This paper proves a theorem about Dehn surgery using a new theorem about PSL(2, C) character varieties. Confirming a conjecture of Boyer and Zhang, this paper shows that a small hyperbolic knot in a homotopy sphere having a non-trivial cyclic slope r has an incompressible surface with non-integer boundary slope strictly between r-1 and r+1. A corollary is that any small knot which has only integer boundary slopes has Property P. The proof uses connections between the topology of the complement of the knot, M, and the PSL(2, C) character variety of M that were discovered by Culler and Shalen. The key lemma, which should be of independent interest, is that for certain components of the character variety of M, the map on character varieties induced by the inclusion of boundary M into M is a birational isomorphism onto its image. This in turn depends on a fancy version of Mostow rigidity due to Gromov, Thurston, and Goldman.
Increasing the number of fibered faces of arithmetic hyperbolic 3-manifolds
Nathan M. Dunfield,Dinakar Ramakrishnan
Mathematics , 2007, DOI: 10.1353/ajm.0.0098
Abstract: We exhibit a closed hyperbolic 3-manifold which satisfies a very strong form of Thurston's Virtual Fibration Conjecture. In particular, this manifold has finite covers which fiber over the circle in arbitrarily many ways. More precisely, it has a tower of finite covers where the number of fibered faces of the Thurston norm ball goes to infinity, in fact faster than any power of the logarithm of the degree of the cover, and we give a more precise quantitative lower bound. The example manifold M is arithmetic, and the proof uses detailed number-theoretic information, at the level of the Hecke eigenvalues, to drive a geometric argument based on Fried's dynamical characterization of the fibered faces. The origin of the basic fibration of M over the circle is the modular elliptic curve E=X_0(49), which admits multiplication by the ring of integers of Q[sqrt(-7)]. We first base change the holomorphic differential on E to a cusp form on GL(2) over K=Q[sqrt(-3)], and then transfer over to a quaternion algebra D/K ramified only at the primes above 7; the fundamental group of M is a quotient of the principal congruence subgroup of level 7 of the multiplicative group of a maximal order of D. To analyze the topological properties of M, we use a new practical method for computing the Thurston norm, which is of independent interest. We also give a non-compact finite-volume hyperbolic 3-manifold with the same properties by using a direct topological argument.
Quantum invariants of random 3-manifolds
Nathan M. Dunfield,Helen Wong
Mathematics , 2010, DOI: 10.2140/agt.2011.11.2191
Abstract: We consider the SO(3) Witten-Reshetikhin-Turaev quantum invariants of random 3-manifolds. When the level r is prime, we show that the asymptotic distribution of the absolute value of these invariants is given by the standard Rayleigh distribution and independent of the choice of level. Hence the probability that the quantum invariant certifies the Heegaard genus of a random 3-manifold of a fixed Heegaard genus g is positive but very small, less than 10^-7 except when g < 4. We also examine random surface bundles over the circle and find the same distribution for quantum invariants there.
Commensurability of 1-cusped hyperbolic 3-manifolds
Danny Calegari,Nathan M. Dunfield
Mathematics , 2001,
Abstract: We give examples of non-fibered hyperbolic knot complements in homology spheres that are not commensurable to fibered knot complements in homology spheres. In fact, we give many examples of knot complements in homology spheres with the property that every commensurable knot complement in a homology sphere has non-monic Alexander polynomial.
Automorphic forms and rational homology 3--spheres
Frank Calegari,Nathan M Dunfield
Mathematics , 2005, DOI: 10.2140/gt.2006.10.295
Abstract: We investigate a question of Cooper adjacent to the Virtual Haken Conjecture. Assuming certain conjectures in number theory, we show that there exist hyperbolic rational homology 3-spheres with arbitrarily large injectivity radius. These examples come from a tower of abelian covers of an explicit arithmetic 3-manifold. The conjectures we must assume are the Generalized Riemann Hypothesis and a mild strengthening of results of Taylor et al on part of the Langlands Program for GL_2 of an imaginary quadratic field. The proof of this theorem involves ruling out the existence of an irreducible two dimensional Galois representation (rho) of Gal(Qbar/Q(sqrt(-2))) satisfying certain prescribed conditions. In contrast to similar questions of this form, (rho) is allowed to have arbitrary ramification at some prime of Z[sqrt(-2)]. Finally, we investigate the congruence covers of twist-knot orbifolds. Our experimental evidence suggests that these topologically similar orbifolds have rather different behavior depending on whether or not they are arithmetic. In particular, the congruence covers of the nonarithmetic orbifolds have a paucity of homology.
Certifying the Thurston norm via SL(2, C)-twisted homology
Ian Agol,Nathan M. Dunfield
Mathematics , 2015,
Abstract: We study when the Thurston norm is detected by twisted Alexander polynomials associated to representations of the 3-manifold group to SL(2, C). Specifically, we show that the hyperbolic torsion polynomial determines the genus for a large class of hyperbolic knots in the 3-sphere which includes all special arborescent knots and many knots whose ordinary Alexander polynomial is trivial. This theorem follows from results showing that the tautness of certain sutured manifolds can be certified by checking that they are a product from the point of view of homology with coefficients twisted by an SL(2, C)-representation.
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