The negative bias conjecture for Gaussian-prime representations by sums of squares

Let

D1(x)={p<x:p=a2+4b2, a>2b}{p<x:p=a2+4b2, a<2b}.D_1(x)=\lvert\{p<x:p=a^2+4b^2,\ \lvert a\rvert>\lvert2b\rvert\}\rvert-\lvert\{p<x:p=a^2+4b^2,\ \lvert a\rvert<\lvert2b\rvert\}\rvert.

Here pp ranges over primes, and logarithmic scale means the measure induced by dx/x\mathrm{d}x/x; equivalently, the logarithmic density of a set P[1,)\mathcal P\subset[1,\infty) is defined using

δ(P)=lim supY1Y0Y1P(ey)dy,δ(P)=lim infY1Y0Y1P(ey)dy.\overline{\delta}(\mathcal P)=\limsup_{Y\to\infty}\frac1Y\int_0^Y\mathbf 1_{\mathcal P}(e^y)\,\mathrm{d}y, \qquad \underline{\delta}(\mathcal P)=\liminf_{Y\to\infty}\frac1Y\int_0^Y\mathbf 1_{\mathcal P}(e^y)\,\mathrm{d}y.

Negative bias conjecture. There is a bias towards negative values in the distribution of D1D_1: for more than half of the x[2,)x\in[2,\infty) in logarithmic scale, more than half of the primes below xx can be written as a sum of two squares with the even square larger than the odd square. Moreover,

D1(x)=Ω±(xlogx),D_1(x)=\Omega_{\pm}\left(\frac{\sqrt{x}}{\log x}\right),

so D1D_1 changes signs infinitely often. This conjecture describes a discrepancy in the expected equidistribution of the two possible size orderings in representations p=a2+4b2p=a^2+4b^2. Under the Generalized Riemann Hypothesis, Hecke's results give the bound D1(x)=Oϵ(x1/2+ϵ)D_1(x)=O_{\epsilon}(x^{1/2+\epsilon}), while the asserted logarithmic bias and the stated oscillation are part of the conjectural picture.

Sources & referencesView supporting material

Primary source

Lucile Devin, “Discrepancies in the distribution of Gaussian primes”, arXiv:2105.02492 (2025).

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