Conjecture F_const for constant Brauer classes

Let kk be a number field and let π+=(M,(Lm)mM,(bm)mM,(Km)mM)P+\pi_+=(M,(L_m)_{m\in M},(b_m)_{m\in M},(K_m)_{m\in M})\in{\mathscr P}_+. Let BconstBB_{\mathrm{const}}\subseteq B be the subgroup generated by the corestricted classes associated with characters in Cm,const=CmIm(H1(k(m),Q/Z)H1(Lm,Q/Z))C_{m,\mathrm{const}}=C_m\cap\operatorname{Im}(H^1(k(m),{\mathbf Q}/{\mathbf Z})\to H^1(L_m,{\mathbf Q}/{\mathbf Z})). For cU(k)c\in U(k), let Wc(Ak)BconstW_c({\mathbf A}_k)^{B_{\mathrm{const}}} denote the adelic points orthogonal to the image of BconstB_{\mathrm{const}} on the fibre.

Conjecture F_const. The subset

cU(k)Wc(Ak)Bconst\bigcup_{c\in U(k)}W_c({\mathbf A}_k)^{B_{\mathrm{const}}}

is dense in W(Ak)W({\mathbf A}_k).

Conjecture F_const is an intermediate formulation used to compare Conjectures F and F+. The source notes that, under suitable abelianness assumptions, it is implied by Schinzel's hypothesis (HH1)(\mathrm{HH}_1); its general status is not specified.

Sources & referencesView supporting material

Primary source

Yonatan Harpaz, Dasheng Wei and Olivier Wittenberg, “Rational points on fibrations with few non-split fibres”, arXiv:2109.03547 (2022).

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