3 improved / fixed some of the LaTeX

$\DeclareMathOperator{\char}{char}\DeclareMathOperator{\gal}{Gal}$ Let $P$ be a smooth projective variety over a field $K$ (one may certainly assume that $K$ is perfect; the case $K=\mathbb{Q}$ already seems to be interesting enough). For some $l\neq \ell\neq \char K$, $n>0$, should the $n$-th ${\mathbb{Q}l}$-adic \mathbb Q_\ell$-adic Galois cohomology of$X_{K^{sep}}$be semi-simple as a$Gal(K)$-representation? \gal(K)$-representation? Certainly; no proof of this fact is known, so I would rather like to know whether it is related with some 'motivic' conjectures.

Some remarks:

1. For a finite $K$ one can consider the 'motivic' Frobenius; thus the conjecture follows from standard (motivic) ones. Yet this argument does not seem to work already for $K=\mathbb{Q}$.K=\mathbb Q$. 2. It is certainly tempting to apply some polarizability argument. Yet my impression is that polarizability can only be applied to Hodge structures (in general); is this true? Upd. It seems (see the comment of Ulrich) that 'my conjecture' is wrong for$K= {\mathbb{Q}_l}$; \mathbb Q_\ell$; this settles my question. Yet I wonder where I can find the details for this example (when is the representation corresponding to an elliptic curve with multiplicative reduction indecomposable).

Let $P$ be a smooth projective variety over a field $K$ (one may certainly assume that $K$ is perfect; the case $K=\mathbb{Q}$ already seems to be interesting enough). For some $l\neq char K$, $n>0$, should the $n$-th ${\mathbb{Q}l}$-adic Galois cohomology of $X_{K^{sep}}$ be semi-simple as a $Gal(K)$-representation? Certainly; no proof of this fact is known, so I would rather like to know whether it is related with some 'motivic' conjectures.

Some remarks:

1. For a finite $K$ one can consider the 'motivic' Frobenius; thus the conjecture follows from standard (motivic) ones. Yet this argument does not seem to work already for $K=\mathbb{Q}$.

2. It is certainly tempting to apply some polarizability argument. Yet my impression is that polarizability can only be applied to Hodge structures (in general); is this true?

Upd. It seems (see the comment of Ulrich) that 'my conjecture' is wrong for $K= {\mathbb{Q}_l}$; this settles my question. Yet I wonder where I can find the details for this example (when is the representation corresponding to an elliptic curve with multiplicative reduction indecomposable).

1

# Should the etale cohomology of a smooth projective variety (over rationals) be semi-simple; why?

Let $P$ be a smooth projective variety over a field $K$ (one may certainly assume that $K$ is perfect; the case $K=\mathbb{Q}$ already seems to be interesting enough). For some $l\neq char K$, $n>0$, should the $n$-th ${\mathbb{Q}l}$-adic Galois cohomology of $X_{K^{sep}}$ be semi-simple as a $Gal(K)$-representation? Certainly; no proof of this fact is known, so I would rather like to know whether it is related with some 'motivic' conjectures.

Some remarks:

1. For a finite $K$ one can consider the 'motivic' Frobenius; thus the conjecture follows from standard (motivic) ones. Yet this argument does not seem to work already for $K=\mathbb{Q}$.

2. It is certainly tempting to apply some polarizability argument. Yet my impression is that polarizability can only be applied to Hodge structures (in general); is this true?