Mock theta functions' parity-type conjecture

Let g(q)g(q) be a mock theta function with integer coefficients, and let c(g;n)c(g;n) denote the coefficient of qnq^n in its series expansion. Say that gg is of parity type (12,12)(\frac{1}{2},\frac{1}{2}) if the proportions of indices n0n\geq 0 for which c(g;n)c(g;n) is even and odd are respectively 12\frac{1}{2} and 12\frac{1}{2}, and of parity type (34,14)(\frac{3}{4},\frac{1}{4}) if those proportions are respectively 34\frac{3}{4} and 14\frac{1}{4}. Mock theta functions' parity-type conjecture. The 1919 functions μ(2)(q)\mu^{(2)}(q), f(3)(q)f^{(3)}(q), ϕ(3)(q)\phi^{(3)}(q), χ(3)(q)\chi^{(3)}(q), ϕ0(5)(q)\phi_0^{(5)}(q), ϕ1(5)(q)\phi_1^{(5)}(q), χ0(5)(q)\chi_0^{(5)}(q), χ1(5)(q)\chi_1^{(5)}(q), ϕ(6)(q)\phi^{(6)}(q), ψ(6)(q)\psi^{(6)}(q), γ(6)(q)\gamma^{(6)}(q), F0(7)(q)\mathcal{F}_0^{(7)}(q), F1(7)(q)\mathcal{F}_1^{(7)}(q), F2(7)(q)\mathcal{F}_2^{(7)}(q), S0(8)(q)S_0^{(8)}(q), S1(8)(q)S_1^{(8)}(q), U0(8)(q)U_0^{(8)}(q), X(10)(q)X^{(10)}(q), and χ(10)(q)\chi^{(10)}(q) are all of parity type (12,12)(\frac{1}{2},\frac{1}{2}). The four functions f0(5)(q)f_0^{(5)}(q), f1(5)(q)f_1^{(5)}(q), 2μ(6)(q)2\mu^{(6)}(q), and λ(6)(q)\lambda^{(6)}(q) are all of parity type (34,14)(\frac{3}{4},\frac{1}{4}). The conjecture is based on computations and known properties; for the latter four functions, one parity subsequence is almost always even and the complementary subsequence is odd half of the time. The paper also notes that the assertion for ψ(6)(q)\psi^{(6)}(q) is equivalent to the assertion for λ(6)(q)\lambda^{(6)}(q).

Sources & referencesView supporting material

Primary source

Liuquan Wang, “Parity of coefficients of mock theta functions”, arXiv:2007.03664 (2021).

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