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Physics Letters B 780 (2018) 144–148
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Physics Letters B
www.elsevier.com/locate/physletb
Scalar field configurations supported by charged compact reflecting
stars in a curved spacetime
Yan Peng
School of Mathematical Sciences, Qufu Normal University, Qufu, Shandong 273165, China
a r t i c l e i n f o a b s t r a c t
Article history:
Received
22 January 2018
Received
in revised form 18 February 2018
Accepted
27 February 2018
Available
online 5 March 2018
Editor:
M. Cveti
ˇ
c
We study the system of static scalar fields coupled to charged compact reflecting stars through both
analytical and numerical methods. We enclose the star in a box and our solutions are related to cases
without box boundaries when putting the box far away from the star. We provide bottom and upper
bounds for the radius of the scalar hairy compact reflecting star. We obtain numerical scalar hairy star
solutions satisfying boundary conditions and find that the radius of the hairy star in a box is continuous
in a range, which is very different from cases without box boundaries where the radius is discrete in the
range. We also examine effects of the star charge and mass on the largest radius.
© 2018 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
1. Introduction
The no-scalar-hair theorem is a famous physical characteristic
of black holes [1–3]. It was found that the static massive scalar
fields cannot exist in asymptotically flat black holes, for refer-
ences
see [4–15] and a review see [16]. This property is usually
attributed to the fact that the horizon of a classical black hole ir-
reversibly
absorbs matter and radiation fields. Along this line, one
naturally want to know whether this no scalar hair behavior is a
unique property of black holes. So it is interesting to explore pos-
sible
similar no scalar hair theorem in other horizonless curved
spacetimes.
Lately,
hod found a no-scalar-hair theorem for asymptotically
flat horizonless neutral compact reflecting stars with a single mas-
sive
scalar field and specific types of the potential [17]. Bhattachar-
jee
and Sudipta further extended the discussion to spacetimes with
a positive cosmological constant [18]. In fact, the no scalar hair
behavior also exists for massless scalar field nonminimally cou-
pled
to gravity on the neutral compact reflecting star background
[19]. Recently, scalar field configurations were constructed in the
charged compact reflecting shell where the star charge and mass
can be neglected compared to the star radius [20,21]. With ana-
lytical
methods, the physical properties of the asymptotically flat
composed star-field configurations were also analyzed in [22]. In
particular, this work derived a remarkably compact analytical for-
mula
for the discrete spectrum of star radii. Along this line, it is
E-mail address: yanpengphy @163 .com.
interesting to extend the discussion by relaxing the condition that
star radii are much larger than the star charge and mass.
On
the other side, a simple way to invade the black hole no-
scalar-hair
theorem is adding a reflecting box boundary. It should
be emphasized that the boundary conditions imposed by a box
are different from the familiar boundary conditions of asymptoti-
cally
flat spacetimes. In fact, it was found that the low frequency
scalar field perturbation can trigger superradiant instability of the
charged black hole in a box and the nonlinear dynamical evolution
can form a quasi-local hairy black hole [23–26]. From thermody-
namical
aspects, Pallab and other authors showed that there are
stable asymptotically flat hairy black holes in a box invading no-
hair-theorem
of black holes [27]. It was believed that the box
boundary could play a role of the infinity potential to make the
fields bounce back and condense around the black hole. Along this
line, it is interesting to extend the discussion of scalar field config-
urations
supported by a compact reflecting star through including
an additional box boundary and also compare mathematical struc-
tures
between gravities without box boundaries and models in a
box.
The
next sections are planed as follows. In section 2, we intro-
duce
the model of a charged compact reflecting star coupled to
a scalar field. In section 3.1, we provide bounds for the radius of
the scalar hairy star. In section 3.2, we obtain radius of the hairy
star and explore effects of parameters on the largest radius. And
in section 3.3, we also carry out an analytical study of the system
in the limit that star charge and mass can be neglected. We will
summarize our main results in the last section.
https://doi.org/10.1016/j.physletb.2018.02.068
0370-2693/
© 2018 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.