Braid groups of the Projective plane
Daciberg Lima Gon\c calves and John Guaschi
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We study the pure braid group short exact sequence described by Fadell and Neuwirth, namely
$$0 \to P_{m-n}(RP^2-\{x_1,...,x_n\}) \to P_m(RP^2) \to P_n(RP^2) \to
0$$ and the torsion of the pure Braid groups $P_n(RP^2)$ and of the
braid groups $B_n(RP^2)$. The short exact sequence for $n=2$ and $m=3$
splits. This was was shown by Burskirk in the 60's. It is an open
question the cases where $m>3$. We show that the sequence does not
splits if $m>3$. For the torsion we show that there is a torsion
element of $P_n(RP^2)$ of order k if and only if k is either 2 or
4. Similar there is a torsion element of $B_n(RP^2)$ of order k if and
only if k divides either 4n or 4(n-1). Also the only element of order
2 in $B_n(RP^2)$ is the full twist. As a consequence of our result we
can show that a k-th root of the full twist exists if and only if k
divides either 2n or 2(n-1). For the non-splitting result we use some
approach of coincidence theory. For the study of the torsion we use
techniques of fibrations more standard in the study of the braids.
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