Let ℳ0 [resp. ℳ1]
be a coarse moduli space
of rank 2
semistable vector bundles of even [resp. odd] degree
with fixed determinant on
a
smooth projective curve X. The Picard group is
infinite cyclic .
Let L be the
ample
generator. The dimension of a vector space
H0(ℳi,
Lℳ)
(i = 0, 1) is given by the
Verlinde formula. For small m > 0, the meaning of
this dimension can be
explained
in the framework of algebraic geometry. For example, we
have
¶
dimH0(ℳ0, L) =
2g,
¶
where g is the genus of X. On the other hand,
we have
¶
dimH0(Jac(X),O(2ϴ)) =
2g.
¶
In fact we have a natural isomorphism between these two
vector spaces (See [1]).
In
[2], the meaning of the two equations
¶
dimH0(ℳ0, L2)
=
2g-1(2g + 1) ¶
dimH0(ℳ1, L) =
2g-1(2g - 1)
¶
are clarified. The above dimensions are the number of even or odd theta
characterictics
on X. Beauville associated to an even [resp. odd] theta characterictic
κ a
divisor
Dκ on ℳ0 [resp. ℳ1]
that can be described from a moduli-theoretic
viewpoint,
and proved that they form a basis of H0(ℳ0,
L2)
[resp. H0(ℳ1, L)].
In [13],
two
vector spaces H0(ℳ0, L4) and
H0(ℳ1, L2) are considered.
In [15], Pauly deals with
a parabolic case. ¶
The purpose of this paper is to carry out a similar study for a moduli space
ℳ
Par(ℙ1; I) of rank 2 semistable parabolic
vector bundles with half weights of
degree
zero on ℙ1.