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Let $q$ be an odd power of a prime $pin mathbb{N}$, and $mathrm{PPSP}(sqrt{q})$ be the finite set of isomorphism classes of principally polarized superspecial abelian surfaces in the simple isogeny class over $mathbb{F}_q$ corresponding to the real Weil $q$-numbers $pm sqrt{q}$. We produce explicit formulas for $mathrm{PPSP}(sqrt{q})$ of the following three kinds: (i) the class number formula, i.e. the cardinality of $mathrm{PPSP}(sqrt{q})$; (ii) the type number formula, i.e. the number of endomorphism rings up to isomorphism of members of $mathrm{PPSP}(sqrt{q})$; (iii) the refined class number formula with respect to each finite group $mathbf{G}$, i.e. the number of elements of $mathrm{PPSP}(sqrt{q})$ whose automorphism group coincides with $mathbf{G}$. Similar formulas are obtained for other polarized superspecial members of this isogeny class using polarization modules. We observe several surprising identities involving the arithmetic genus of certain Hilbert modular surface on one side and the class number or type number of $(P, P_+)$-polarized superspecial abelian surfaces in this isogeny class on the other side.
In this paper we determine the number of endomorphism rings of superspecial abelian surfaces over a field $mathbb{F}_q$ of odd degree over $mathbb{F}_p$ in the isogeny class corresponding to the Weil $q$-number $pmsqrt{q}$. This extends earlier works
In the paper [On superspecial abelian surfaces over finite fields II. J. Math. Soc. Japan, 72(1):303--331, 2020], Tse-Chung Yang and the first two current authors computed explicitly the number $lvert mathrm{SSp}_2(mathbb{F}_q)rvert$ of isomorphism c
For an algebraic number $alpha$ and $gammain mathbb{R}$, $h(alpha)$ be the (logarithmic) Weil height, and $h_gamma(alpha)=(mathrm{deg}alpha)^gamma h(alpha)$ be the $gamma$-weighted (logarithmic) Weil height of $alpha$. Let $f:overline{mathbb{Q}}to [0
It was discovered some years ago that there exist non-integer real numbers $q>1$ for which only one sequence $(c_i)$ of integers $c_i in [0,q)$ satisfies the equality $sum_{i=1}^infty c_iq^{-i}=1$. The set of such univoque numbers has a rich topologi
We consider an abelian variety defined over a number field. We give conditional bounds for the order of its Tate-Shafarevich group, as well as conditional bounds for the Neron-Tate height of generators of its Mordell-Weil group. The bounds are implie