TY - JOUR

T1 - Spontaneous scalarization of charged stars

AU - Minamitsuji, Masato

AU - Tsujikawa, Shinji

N1 - Funding Information:
MM was supported by the Portuguese national fund through the Fundação para a Ciência e a Tecnologia in the scope of the framework of the Decree-Law 57/2016 of August 29 (changed by Law 57/2017 of July 19), and by the CENTRA through the Project No. UIDB/00099/2020 . ST is supported by the Grant-in-Aid for Scientific Research Fund of the JSPS No. 19K03854 .
Funding Information:
MM was supported by the Portuguese national fund through the Funda??o para a Ci?ncia e a Tecnologia in the scope of the framework of the Decree-Law 57/2016 of August 29 (changed by Law 57/2017 of July 19), and by the CENTRA through the Project No. UIDB/00099/2020. ST is supported by the Grant-in-Aid for Scientific Research Fund of the JSPS No. 19K03854.
Publisher Copyright:
© 2021 The Author(s)

PY - 2021/9/10

Y1 - 2021/9/10

N2 - We study static and spherically symmetric charged stars with a nontrivial profile of the scalar field ϕ in Einstein-Maxwell-scalar theories. The scalar field is coupled to a U(1) gauge field Aμ with the form −α(ϕ)FμνFμν/4, where Fμν=∂μAν−∂νAμ is the field strength tensor. Analogous to the case of charged black holes, we show that this type of interaction can induce spontaneous scalarization of charged stars under the conditions (dα/dϕ)(0)=0 and (d2α/dϕ2)(0)>0. For the coupling α(ϕ)=exp(−βϕ2/Mpl2), where β(<0) is a coupling constant and Mpl is a reduced Planck mass, there is a branch of charged star solutions with a nontrivial profile of ϕ approaching 0 toward spatial infinity, besides a branch of general relativistic solutions with a vanishing scalar field, i.e., solutions in the Einstein-Maxwell model. As the ratio ρc/ρm between charge density ρc and matter density ρm increases toward its maximum value, the mass M of charged stars in general relativity tends to be enhanced due to the increase of repulsive Coulomb force against gravity. In this regime, the appearance of nontrivial branches induced by negative β of order −1 effectively reduces the Coulomb force for a wide range of central matter densities, leading to charged stars with smaller masses and radii in comparison to those in the general relativistic branch. Our analysis indicates that spontaneous scalarization of stars can be induced not only by the coupling to curvature invariants but also by the scalar-gauge coupling in Einstein gravity.

AB - We study static and spherically symmetric charged stars with a nontrivial profile of the scalar field ϕ in Einstein-Maxwell-scalar theories. The scalar field is coupled to a U(1) gauge field Aμ with the form −α(ϕ)FμνFμν/4, where Fμν=∂μAν−∂νAμ is the field strength tensor. Analogous to the case of charged black holes, we show that this type of interaction can induce spontaneous scalarization of charged stars under the conditions (dα/dϕ)(0)=0 and (d2α/dϕ2)(0)>0. For the coupling α(ϕ)=exp(−βϕ2/Mpl2), where β(<0) is a coupling constant and Mpl is a reduced Planck mass, there is a branch of charged star solutions with a nontrivial profile of ϕ approaching 0 toward spatial infinity, besides a branch of general relativistic solutions with a vanishing scalar field, i.e., solutions in the Einstein-Maxwell model. As the ratio ρc/ρm between charge density ρc and matter density ρm increases toward its maximum value, the mass M of charged stars in general relativity tends to be enhanced due to the increase of repulsive Coulomb force against gravity. In this regime, the appearance of nontrivial branches induced by negative β of order −1 effectively reduces the Coulomb force for a wide range of central matter densities, leading to charged stars with smaller masses and radii in comparison to those in the general relativistic branch. Our analysis indicates that spontaneous scalarization of stars can be induced not only by the coupling to curvature invariants but also by the scalar-gauge coupling in Einstein gravity.

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U2 - 10.1016/j.physletb.2021.136509

DO - 10.1016/j.physletb.2021.136509

M3 - Article

AN - SCOPUS:85110425277

VL - 820

JO - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

JF - Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics

SN - 0370-2693

M1 - 136509

ER -