theoretical-computer-science / Computational complexity

Ghasemi-Kopparty Problem on Sparse $S$-Decoding Polynomials

Can $S$-decoding polynomials modulo a product of $k$ primes be built with only $k+1$ nonzero coefficients, the minimum their own lower bound allows? Yes, via a general framework for special prime products. The consequence is that for any constant $s$ there is an $s$-server private information retrieval protocol with communication $\exp(O((\log n)^{1/s}(\log\log n)^{1-1/s}))$ on an $n$-bit database, where previous constructions at that communication needed $2^{O(s)}$ servers.

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theoretical-computer-scienceJul 24, 2026Significance 12/100Registry: unreviewed

Ghasemi-Kopparty Problem on Sparse $S$-Decoding Polynomials

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the PIR consequence is conditional on a number-theoretic conjecture implied by either the generalized repunit conjecture or Schinzel's hypothesis H, and is unconditional for s <= 15

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Can $S$-decoding polynomials modulo a product of $k$ primes be built with only $k+1$ nonzero coefficients, the minimum their own lower bound allows? Yes, via a general framework for special prime products. The consequence is that for any constant $s$ there is an $s$-server private information retrieval protocol with communication $\exp(O((\log n)^{1/s}(\log\log n)^{1-1/s}))$ on an $n$-bit database, where previous constructions at that communication needed $2^{O(s)}$ servers.

the PIR consequence is conditional on a number-theoretic conjecture implied by either the generalized repunit conjecture or Schinzel's hypothesis H, and is unconditional for s <= 15

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