Quadrupole moments of rapidly rotating compact objects in dilatonic Einstein-Gauss-Bonnet theory

We study black hole solutions at first order in the Hartle-Thorne slow-rotation approximation in Horndeski gravity theories. We derive the equations of motion including also cases where the scalar depends linearly on time. In the Hartle-Thorne formalism, all first-order rotational corrections are described by a single frame-dragging function. We show that the frame-dragging function is exactly the same as in general relativity for all known black hole solutions in shift symmetric Horndeski theories, with the exception of theories with a linear coupling to the Gauss-Bonnet invariant. Our results extend previous no-hair theorems for a broad class of Horndeski gravity theories.

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“…Replacing this solution into Eq. (37) we find that ω(r) satisfies the same equation (25) as in GR. The standard solution of this equation is…”

Section: Nonminimal Derivative Coupling To the Einstein Tensorsupporting

confidence: 58%

“…[33][34][35] and to rapid rotation in Refs. [36,37]. Other possibilities to violate the nohair theorems include adding a time dependence to the scalar (but not to the metric), as in the solution proposed by Babichev and Charmousis [38], or considering biscalar extensions of Horndeski gravity [11].…”

Section: Introductionmentioning

confidence: 99%

Slowly rotating black hole solutions in Horndeski gravity

et al. 2015

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“…This is for example the case with the Dynamical Chern-Simons gravity where the I-Love-Q relations are still pretty much EOS independent but they are significantly different from the GR case [6,7]. On the other hand the corresponding relations in Eddington-inspired Born-Infeld gravity, scalar-tensor theories of gravity and Einstein-Gauss-Bonnet-dilaton theory [21] are almost indistinguishable from Einstein's theory [22][23][24]. Therefore the I-Love-Q relations can not serve as a test for these theories.…”

Section: Introductionmentioning

confidence: 99%

“…Except the case of Einstein-Gauss-Bonnet-dilaton gravity [24], all of the studies of I-Love-Q relations in alternative theories of gravity up to now are limited to the slow rotation regime. One of the reasons is that constructing rapidly rotating neutron star solutions in alternative theories of gravity is very involved.…”

Section: Introductionmentioning

confidence: 99%

Universal I-Q relations for rapidly rotating neutron and strange stars in scalar-tensor theories

et al. 2014

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We study how rapid rotation influences the relation between the normalized moment of inertiaĪ and quadrupole momentQ for scalarized neutron stars. The questions one has to answer are whether the EOS universality is preserved in this regime and what are the deviations from general relativity. Our results show that theĪ −Q relation is nearly EOS independent for scalarized rapidly rotating stars, but the differences with pure Einstein's theory increase compared to the slowly rotating case. In general, smaller negative values of the scalar field coupling parameters β lead to larger deviations, but these deviations are below the expected accuracy of the future astrophysical observations if one considers values of β in agreement with the current observational constraint. An important remark is that although the normalizedĪ −Q relation is quite similar for scalar-tensor theories and general relativity, the unnormalized moment of inertia and quadrupole moment can be very different in the two theories. This demonstrates that although theĪ −Q relations are potentially very useful for some purposes, they might not serve us well when trying to distinguish between different theories of gravity.

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“…The reason why this problem was not examined up to now is because of its complexity. For example, rapidly rotating neutron stars were constructed only in a few alternative theories of gravity [36][37][38][39][40] because deriving analytically the reduced field equations and solving them numerically in very involved. Studying oscillation modes of rapidly rotating stars, especially the nonaxisymmetric ones, on the other hand is also a very complicated problem even in pure GR that was addressed only recently [3,4,27,29].…”

Section: Introductionmentioning

confidence: 99%

Oscillation modes of rapidly rotating neutron stars in scalar-tensor theories of gravity

2017

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We perform the first study of the oscillation frequencies of rapidly rotating neutron stars in alternative theories of gravity, focusing mainly on the fundamental f -modes. We concentrated on a particular class of alternative theories -the (massive) scalar-tensor theories. The generalization to rapid rotation is important because on one hand the rapid rotation can magnify the deviations from general relativity compared to the static case and on the other hand some of the most efficient emitters of gravitational radiation, such as the binary neutron star merger remnants, are supposed to be rotating close to their Kepler (mass-shedding) limits shortly after their formation. We have constructed several sequences of models starting from the nonrotating case and reaching up to the Kepler limit, with different values of the scalar-tensor theory coupling constant and the scalar field mass. The results show that the deviations from pure Einstein's theory can be significant especially in the case of nonzero scalar field mass. An important property of the oscillation modes of rapidly rotating stars is that they can become secularly unstable due to the emission of gravitational radiation, that is so-called Chandrasekhar-Friedman-Schutz instability. Such unstable modes are efficient emitters of gravitational radiation. Our studies show that the inclusion of nonzero scalar field would decrease the threshold value of the normalized angular momentum where this instability stars to operate, but the growth time of the instability seems to be increased compared to pure general relativity.

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Quadrupole moments of rapidly rotating compact objects in dilatonic Einstein-Gauss-Bonnet theory

Cited by 102 publications

References 40 publications

Slowly rotating black hole solutions in Horndeski gravity

Slowly rotating black hole solutions in Horndeski gravity

Universal I-Q relations for rapidly rotating neutron and strange stars in scalar-tensor theories

Oscillation modes of rapidly rotating neutron stars in scalar-tensor theories of gravity

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