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Feb 7, 2022 at 14:32 comment added Ariel Weiss When $p=2$, $K = \mathbb Q$, and $j(E_1)$ and $j(E_2)$ are not simultaneously $0$ or $1728$, then a positive answer follows form Theorem 4 of this paper.
Jan 19, 2022 at 8:19 history edited Ariyan Javanpeykar CC BY-SA 4.0
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Jan 19, 2022 at 8:13 history edited Ariyan Javanpeykar CC BY-SA 4.0
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Jan 15, 2022 at 20:06 comment added Ariyan Javanpeykar In the linked paper, for $p\geq 5$, the author (Dave Mendes Da Costa) proves the required statement for an elliptic curve $E$ by showing that there is a higher genus curve $C$, a finite morphism $C\to E$ of degree $<p$ and a morphism $C\to \mathbb{P}^1_K$ of degree $p$. The answer to the question would be positive if we could find a higher genus curve $C$ such that there is a finite morphism $C\to E_1$ of degree $<p$, a finite morphism $C\to E_2$ of degree $<p$, and a finite morphism $C\to \mathbb{P}^1_K$ of degree $p$.
Jan 15, 2022 at 0:54 history edited Ariyan Javanpeykar CC BY-SA 4.0
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Jan 15, 2022 at 0:54 comment added Ariyan Javanpeykar Yes, good point. The ranks are then equal of course.
Jan 15, 2022 at 0:31 comment added Jason Starr The answer is also positive if the two elliptic curves are isogenous over $K$.
Jan 15, 2022 at 0:22 history asked Ariyan Javanpeykar CC BY-SA 4.0