45 research outputs found
Subspaces of tensors with high analytic rank
It is shown that for any subspace V⊆Fn×⋯×np of d-tensors, if dim(V)≥tnd−1, then there is subspace W⊆V of dimension at least t/(dr)−1 whose nonzero elements all have analytic rank Ωd,p(r). As an application, we generalize a result of Altman on Szemerédi's theorem with random differences
Subspaces of tensors with high analytic rank
It is shown that if V ⊆
F
p
n
×⋯×np is a subspace of d-tensors with dimension at least tnd-1, then there is a subspace W ⊆ V of dimension at least t/(dr)−1
p is a subspace of d-tensors with dimension whose nonzero elements all have analytic rank Ωd,p(r). As an application, we generalize a result of Altman on Szemerédi's theorem with random differences
Gaussian width bounds with applications to arithmetic progressions in random settings
Motivated by two problems on arithmetic progressions (APs)—concerning large
deviations for AP counts in random sets and random differences in Szemer´edi’s theorem—
we prove upper bounds on the Gaussian width of the image of the n-dimensional Boolean
hypercube under a mapping ψ : Rn → Rk, where each coordinate is a constant-degree
multilinear polynomial with 0/1 coefficients. We show the following applications of our
bounds. Let [Z/NZ]p be the random subset of Z/NZ containing each element independently
with probability p.
• Let Xk be the number of k-term APs in [Z/NZ]p. We show that a precise estimate
on the large deviation rate log Pr[Xk ≥ (1 + δ)EXk] due to Bhattacharya, Ganguly,
Shao and Zhao is valid if
On the existence of 0/1 polytopes with high semidefinite extension complexity
In Rothvoß (Math Program 142(1–2):255–268, 2013) it was shown that
there exists a 0/1 polytope (a polytope whose vertices are in {0, 1}n) such that any
higher-dimensional polytope projecting to it must have 2Ω(n) facets, i.e., its linear
extension complexity is exponential. The question whether there exists a 0/1 polytope
with high positive semidefinite extension complexity was left open. We answer this
question in the affirmative by showing that there is a 0/1 polytope such that any spectrahedron
projecting to it must be the intersection of a semidefinite cone of dimension
2Ω(n) and an affine space. Our proof relies on a new technique to rescale semidefinite
factorizations
Quantum query algorithms are completely bounded forms
We prove a characterization of quantum query algorithms in terms of polynomials satisfying a certain (completely bounded) norm constraint. Based on this, we obtain a refined notion of approximate polynomial degree that equals the quantum query complexity, answering a question of Aaronson et al. (CCC’16). Using this characterization, we show that many polynomials of degree at least 4 are far from those coming from quantum query algorithms. Our proof is based on a fundamental result of Christensen and Sinclair (J. Funct. Anal., 1987) that generalizes the well-known Stinespring representation for quantum channels to multilinear forms. We also give a simple and short proof of one of the results of Aaronson et al. showing an equivalence between one-query quantum algorithms and bounded quadratic polynomials
Tight hardness of the non-commutative Grothendieck problem
We prove that for any ε > 0 it is NP-hard to approximate the non-commutative Grothendieck problem to within a factor 1=2+ε, which matches the approximation ratio of the algorithm of Naor, Regev, and Vidick (STOC’13). Our proof uses an embedding of ℓ2 into the space of matrices endowed with the trace norm with the property that the image of standard basis vectors is longer than that of unit vectors with no large coordinates. We also observe that one can obtain a tight NP-hardness result for the commutative Little Grothendieck problem; previously, this was only known based on the Unique Games Conjecture (Khot and Naor, Mathematika 2009)
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Outlaw distributions and locally decodable codes
Locally decodable codes (LDCs) are error correcting codes that allow for decoding of a single message bit using a small number of queries to a corrupted encoding. Despite decades of study, the optimal trade-off between query complexity and codeword length is far from understood. In this work, we give a new characterization of LDCs using distributions over Boolean functions whose expectation is hard to approximate (in L∞ norm) with a small number of samples. We coin the term “outlaw distributions” for such distributions since they “defy” the Law of Large Numbers. We show that the existence of outlaw distributions over sufficiently “smooth” functions implies the existence of constant query LDCs and vice versa. We give several candidates for outlaw distributions over smooth functions coming from finite field incidence geometry, additive combinatorics and hypergraph (non)expanders. We also prove a useful lemma showing that (smooth) LDCs which are only required to work on average over a random message and a random message index can be turned into true LDCs at the cost of only constant factors in the parameters
High-entropy dual functions over finite fields and locally decodable codes
We show that for infinitely many primes p, there exist dual functions of order k over Fnp that cannot be approximated in L∞-distance by polynomial phase functions of degree k−1. This answers in the negative a natural finite-field analog of a problem of Frantzikinakis on L∞-approximations of dual functions over N (a.k.a. multiple correlation sequences) by nilsequences
Tight hardness of the non-commutative Grothendieck problem
We prove that for any it is NP-hard to approximate the
non-commutative Grothendieck problem to within a factor ,
which matches the approximation ratio of the algorithm of Naor, Regev, and
Vidick (STOC'13). Our proof uses an embedding of into the space of
matrices endowed with the trace norm with the property that the image of
standard basis vectors is longer than that of unit vectors with no large
coordinates