
JHEP10(2016)033
Note that this last step is part of t he usual procedure of obtaining a “minimal”
Weierstrass model from a “n on-mi n i mal ” one, and involves a blowdown in the total
space ( se e sections II.3 and III.3 in [
18], eq. (15) in [19], as well as eq. (2.6) and
footnote 10 in [
20]). The blowdown restores the Calabi-Yau property, since the
holomorphic n-form vanishes on the divi sor which is being blown down.
While the possibility of constructing more general classes of M W rank-one CY manifolds
in this manner was hint e d in [
6], the KT m odels are, to our knowledge, the first ex ampl e s
where this scenario is realized. It would be interesting to understand how to systematically
implement these steps to find new CY fibrations with MW rank-one.
Arguably the most interesting aspect of models obtained this way is that their sec-
tions are “taller, ” whose meaning we define in section
2, than those that are birationally
equivalent to (
1.2) by a minimal map. A generating section being tall has a direct phy s-
ical consequence when the ellipti c fibration is a CY threefold — the tall e r the generating
section of the Mordell-Weil group, the bigger the maximum charge of the matter under
the corresponding u(1). As mentioned, the Klevers-Taylor models have matter with u(1)
charge 3, while the matter in models constructed in [6] all have charge ≤ 2.
This pap e r is organized as follows. In section
2, we review some background material.
We first review basic bounds on the height of the rational section of a Weie r st r ass model of
the form (
1.2). We the n show how such bounds get looser by allowing the model (1.2) to be
non-CY, and discuss the property of CY models obtained by a non-minimal map. We also
define a convenient metric to compar e heights of rational sections, and discuss its physical
relevance. We present our main resul t in sec ti on
3 by ex pl icitly identifying b, c
i
and a by
which the Weierstrass coefficients of the KT mode l s can be constructed via equation (
1.4).
We conclude with some remarks in section
4. There are several unwieldy ex pr e ss i ons that
are collected in the appendix.
2 Background
Let us review some salient points about elliptic fibrations with two sections. It was shown
in [6] that any ellipt i cal l y fibration over a base B with MW rank-one , is birationally equiv-
alent to the Weierstrass model X
′
(
1.2)
y
′
2
= x
′
3
+
c
1
c
3
− b
2
c
0
−
c
2
2
3
x
′
+
c
0
c
2
3
−
1
3
c
1
c
2
c
3
+
2
27
c
3
2
−
2
3
b
2
c
0
c
2
+
b
2
c
2
1
4
whose generating sec t i on is given by
[X
′
, Y
′
, Z
′
] =
c
3
3
−
2
3
b
2
c
2
, −c
3
3
+ b
2
c
2
c
3
−
1
2
b
4
c
1
, b
(2.1)
for some b and c
i
. We have introduced the projective coordinate s X
′
, Y
′
and Z
′
for which
x
′
= X
′
/Z
′
2
, y
′
= Y
′
/Z
′
3
, (2.2)
– 3 –