Advances in High Energy Physics 3
already studied in [5] and the corresponding black string
solutions were investigated [5]. e lagrangian proposed in
(3) is the quite one generalization of lagrangian [5]toinclude
the dilaton scalar eld.
For latter convenience we write the lagrangian as
(
,Φ
)
=4
2
2𝛼Φ
L
(
)
,
(5)
where we have dened
L
(
)
=exp
(
−
)
−1,
=
−4𝛼Φ
2
4
2
.
(6)
In this paper, we consider action (2)withaLiouvilletype
potential,
(
Φ
)
=2Λ
2𝛼Φ
,
(7)
where Λis a constant which may be referred to as the
cosmological constant, since in the absence of the dilaton
eld (Φ=0) the action (2)reducestotheactionof
EN electrodynamics in Einstein gravity in the presence of
cosmological constant [5]. e equations of motion can
be obtained by varying the action (2)withrespecttothe
gravitational eld
𝜇]
,thedilatoneldΦ,andthegaugeeld
𝜇
which yields the following eld equations:
R
𝜇]
=2
𝜇
Φ
]
Φ+
1
2
𝜇]
(
Φ
)
−2
−2𝛼Φ
×
𝑌
L
(
)
𝜇𝜂
𝜂
]
+2
2
2𝛼Φ
×2
𝑌
L
(
)
−L
(
)
𝜇]
,
(8)
∇
2
Φ=
1
4
Φ
+2
2
2𝛼Φ
2
𝑌
L
(
)
−L
(
)
,
(9)
∇
𝜇
−2𝛼Φ
𝑌
L
(
)
𝜇]
=0. (10)
In case of linear electrodynamics we have L()=−,and
the system of (8)–(10) reduce to the well-known equations of
Einstein-Maxwell-dilaton (EMd) gravity [36].
Our aim here is to construct charged rotating black string
solutions of the eld equations (8)–(10) and investigate their
properties. e metric of four-dimensional rotating solution
with cylindrical or toroidal horizons can be written as [60, 61]
2
=−
(
)
Ξ−
2
+
2
2
(
)
2
−Ξ
2
+
2
(
)
+
2
2
2
(
)
2
,
(11)
where Ξ=
1+
2
/
2
and is the rotation parameter as
we will see later. e functions ()and ()should be
determined and has the dimension of length which is related
to the constant Λby the relation
2
=−3/Λ.etwo
dimensional space, =constantand=constant,canbe(i)
the at torus model
2
with topology
1
×
1
and 0≤<2,
0≤<2, (ii) the standard cylindrical model with topology
×
1
and 0≤<2, −∞<<∞, and (iii) the innite
plane
2
with −∞<<∞and −∞<<∞.Wewillfocus
upon (i) and (ii).
e modied Maxwell equation (10)canbeintegrated
immediately to give
𝑡𝑟
=
Ξ
2𝛼Φ
2
2
(
)
exp −
1
2
𝑊
2
2
4
4
(
)
,
(12)
𝜙𝑟
=−
Ξ
𝑡𝑟
,
(13)
where is an integration constant which is related to the elec-
tric charge of the black string, and
𝑊
()=Lambert()is
the Lambert function which satises [62, 63]
𝑊
(
)
𝐿
𝑊
(𝑥)
=,
(14)
and it has the following series expansion:
𝑊
(
)
=−
2
+
3
2
3
−
8
3
4
+⋅⋅⋅.
(15)
Clearly, series (15)convergesfor|| < 1. e expansion of
(12)forlarge(or large )isgivenby
𝑡𝑟
=
Ξ
2𝛼Φ
(
)
2
−
Ξ
2
2
3
2𝛼Φ
(
)
6
+
5Ξ
8
4
5
2𝛼Φ
(
)
10
+
1
6
.
(16)
In the absence of the dilaton eld ( = 0,() = 1),(12)
reduces to
𝑡𝑟
=
Ξ
2
exp −
1
2
𝑊
2
2
4
,
(17)
while its expansion (16)reducesto
𝑡𝑟
=
Ξ
2
−
3
Ξ
2
2
6
+
5
5
Ξ
8
4
10
+
1
6
,
(18)
Now, we want to solve the system of (8)and(9)forthree
unknown functions (), (),andΦ().Tothisend,we
make the suitable ansatz [41]
(
)
=
𝛼Φ
.
(19)
Using (19), the electromagnetic elds (12)and(13) and metric
(11), aer some mathematic calculations, we can show that (8)
and (9)havesolutionoftheform
(
)
=
Λ+2
2
2
+1
2
𝛾
2
−3
2−𝛾
−
1−𝛾
−
2
1−𝛾
2
+1
𝛾
×
−𝛾
𝑊
−
1
𝑊
,
Φ
(
)
=
2
+1
ln
,
(20)