Where we got to yesterday

Reduction gives

$$\rho(X_{\mathbf{Q}^{\mathrm{al}}}) \leq \rho(\overline{X}_p) \quad \text{for every good } p.$$

Only the second defeats the unaugmented two-prime argument.

Theorem (Charles)

$$\rho(X_p^{\mathrm{al}})\geq\begin{cases}\rho(X^{\mathrm{al}})&\text{if }E\text{ is CM or }m\text{ is even,}\\\rho(X^{\mathrm{al}})+d&\text{if }E\text{ is totally real and }m\text{ is odd,}\end{cases}$$

Equality occurs infinitely often (density $1$ after some finite extension).

If $E$ is totally real and $m$ is odd, infinitely many good ordinary prime pairs $(p,q)$ satisfy $\rho(X_p^{\mathrm{al}})=\rho(X_q^{\mathrm{al}})=\rho(X^{\mathrm{al}})+d$ and

$$\operatorname{disc}\operatorname{Pic}(X_p^{\mathrm{al}})\not\equiv\operatorname{disc}\operatorname{Pic}(X_q^{\mathrm{al}})\bmod(\Bbb{Q}^{\times})^2$$

It is very hard to prove RM!

We are now not only asking to find algebraic cycles in $X$ but also in $X \times X$.