,
Davidson Zhu
Creative Commons Attribution 4.0 International license
The sum-of-squares (SoS) complexity of a d-multiquadratic polynomial f (quadratic in each of d blocks of n variables) is the minimum s such that f = ∑_{i = 1}^s g_i² with each g_i d-multilinear. In the case d = 2, Hrubeš, Wigderson and Yehudayoff [Hrubeš et al., 2011] showed that an n^{1+Ω(1)} lower bound on the SoS complexity of explicit biquadratic polynomials implies an exponential lower bound for non-commutative arithmetic circuits. In this paper, we establish an analogous connection between general multiquadratic sum-of-squares and commutative arithmetic formulas. Specifically, we show that an n^{d-o(log d)} lower bound on the SoS complexity of explicit d-multiquadratic polynomials, for any d = d(n) with ω(1) ≤ d(n) ≤ O((log n)/(log log n)), would separate the algebraic complexity classes VNC¹ and VNP.
@InProceedings{rossman_et_al:LIPIcs.ITCS.2026.113,
author = {Rossman, Benjamin and Zhu, Davidson},
title = {{Multi-Quadratic Sum-Of-Squares Lower Bounds Imply VNC ¹ ≠ VNP}},
booktitle = {17th Innovations in Theoretical Computer Science Conference (ITCS 2026)},
pages = {113:1--113:22},
series = {Leibniz International Proceedings in Informatics (LIPIcs)},
ISBN = {978-3-95977-410-9},
ISSN = {1868-8969},
year = {2026},
volume = {362},
editor = {Saraf, Shubhangi},
publisher = {Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
address = {Dagstuhl, Germany},
URL = {https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ITCS.2026.113},
URN = {urn:nbn:de:0030-drops-254006},
doi = {10.4230/LIPIcs.ITCS.2026.113},
annote = {Keywords: sum-of-squares, arithmetic formulas}
}