Stable wormholes in scalar-tensor theories

Franciolini, Gabriele; Hui, Lam; Penco, Riccardo; Santoni, Luca; Trincherini, Enrico

doi:10.1007/jhep01(2019)221

Cited by 37 publications

(79 citation statements)

References 42 publications

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“…Therefore, this condition does not guarantee the stability of the theory under perturbations. This behavior is not a surprise since stable wormholes can only be supported in higher-derivative theories of the beyond-Horndeski type [38][39][40], a class in which our theory (3.10) clearly does not belong to. We assume throughout that ǫǫ λ = 1.…”

Section: )mentioning

confidence: 67%

Wormhole solutions in modified Brans-Dicke theory

Papantonopoulos

Vlachos

2020

Phys. Rev. D

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We consider a modified Brans-Dicke theory in which except the usual Brans-Dicke parameter a new dimensionful parameter appears which modifies the kinetic term of the scalar field coupled to gravity. Solving the coupled Einstein-Klein-Gordon equations we find new spherically symmetric solutions. Depending on the choices of the parameters these solutions reduce to the Schwarzschild solution of General Relativity and they give new wormhole solutions which depend on the new parameter.PACS numbers: I. INTRODUCTIONScalar fields play an important role in the General Relativity (GR) on short and large distances. On short distances they are dressing the local black hole solutions with scalar hair and they provide wormhole solutions while on large distances they describe the early inflationary universe and also its late-times cosmic evolution. In a attempt to provide a viable theory of gravity and to cure certain inconsistencies of GR, scalar-tensor theories were introduced. As it is well known, Brans-Dicke theory (BD) [1] is one of the first scalar-tensor gravity theories that modifies GR in a viable way and respects Mach's principle and weak equivalence principle (WEP). In this theory there is an effective Newtonian gravitational constant G which is the inverse of the scalar field, G ∼ 1 φ . It is characterized by a new dimensionless coupling constant ω large values of which mean a significant contribution from the tensor part, while scalar field contribution is important for small values. GR is recovered in the limit ω → ∞.It is interesting to note that BD theory appears in supergravity models such as in string theory at low-energies or in the Kaluza-Klein theories after a dimensional reduction process [2]. These theories yield the correct Newtonian weak-field limit, but care should be taken when one studies these theories and compare their predictions with GR. In general scalar fields, depending on their coupling to gravity, mediate fifth forces. In the case of BD solar system measurements of post-Newtonian corrections require that ω is larger than a few thousands [3]. Therefore in these theories scalar fields should accommodate a mechanism to suppress the scalar interaction on small scales. There are various screening mechanisms to suppress scalar interactions on small scales. One of the basic screening mechanism is the Vainshtein mechanism [4] which was developed for the massive gravity (for an extensive review on the Vainshtein mechanism in massive gravity see [5]).On large scales, ω gets substantially lower values in a model dependent way [6], from cosmological observations. On the other side, the gravitational coupling may depends on the scale [7], having different value at local and at cosmological scale. In this case ω can be smaller at cosmological scales giving deviations from GR, while agreement with local tests is preserved. Special solutions on BD cosmology have been given in [8] which are generalizations of the dust solution first given by Brans-Dicke. In [9] special radiation solutions for spatially curve...

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Section: )mentioning

confidence: 67%

Wormhole solutions in modified Brans-Dicke theory

Papantonopoulos

Vlachos

2020

Phys. Rev. D

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“…Equation (35) enables one to express H 2 and H 1 , using eqs. (34) and (36), in terms of ψ and χ. Hence, upon substituting eqs.…”

Section: Parity Even Sector: Circumventing the No-go Theoremmentioning

confidence: 99%

“…As we pointed out in section 1, our stability analysis (like the ones in Refs. [34,36]) is incomplete, as we do not study angular gradient instabilities as well as "slow" tachyonic instabilities in the parity even sector. In other words, the stability conditions associated with matrices M ij and Q ij in the action (32) are yet to be addressed.…”

Section: Parity Even Sector: Circumventing the No-go Theoremmentioning

confidence: 99%

“…In this paper, we obtain part of the stability conditions for a static, spherically symmetric solution in beyond Horndeski theory in a covariant form (as opposed to ADM EFT form of Ref. [34]). Namely, we derive the conditions ensuring the absence of ghosts and absence of gradient instabilities for non-spherical parity even modes propagating in radial direction.…”

Section: Introductionmentioning

confidence: 99%

“…[35,36] to the beyond Horndeski case; note that neither we nor Refs. [34][35][36] study the full set of stability issues which includes the absence of gradient instability in angular directions in parity even sector as well as the absence of "slow" tachyonic modes. Yet our analysis is sufficient to show explicitly that beyond Horndeski terms modify the stability conditions in such a way that the no-go argument of Ref.…”

Section: Introductionmentioning

confidence: 99%

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More about stable wormholes in beyond Horndeski theory

Mironov

Рубаков

Volkova

2019

Class. Quantum Grav.

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It is known that Horndeski theories, like many other scalar-tensor gravities, do not support static, spherically symmetric wormholes: they always have either ghosts or gradient instabilities among parity-even linearized perturbations. Here we address the issue of whether or not this no-go theorem is valid in "beyond Horndeski" theories. We derive, in the latter class of theories, the conditions for the absence of ghost and gradient instabilities for non-spherical parity even perturbations propagating in radial direction. We find, in agreement with existing arguments, that the proof of the above no-go theorem does not go through beyond Horndeski. We also obtain conditions ensuring the absence of ghosts and gradient instabilities for all parity odd modes. We give an example of beyond Horndeski Lagrangian which admits a wormhole solution obeying our (incomplete set of) stability conditions. Even though our stability analysis is incomplete, as we do not consider spherically symmetric parity even modes and parity even perturbations propagating in angular directions, as well as "slow" tachyonic instabilities, our findings indicate that beyond Horndeski theories may be viable candidates to support traversable wormholes. 1 sa.mironov 1@physics.msu.ru 2 rubakov@inr.ac.ru 3 volkova.viktoriya@physics.msu.ru 1 arXiv:1812.07022v2 [hep-th] 5 Jun 2019 Bπ XK Xwith

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Effective field theory of black hole quasinormal modes in scalar-tensor theories

Franciolini¹,

Hui

Penco

et al. 2019

J. High Energ. Phys.

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149

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The final ringdown phase in a coalescence process is a valuable laboratory to test General Relativity and potentially constrain additional degrees of freedom in the gravitational sector. We introduce here an effective description for perturbations around spherically symmetric spacetimes in the context of scalar-tensor theories, which we apply to study quasinormal modes for black holes with scalar hair. We derive the equations of motion governing the dynamics of both the polar and the axial modes in terms of the coefficients of the effective theory. Assuming the deviation of the background from Schwarzschild is small, we use the WKB method to introduce the notion of "light ring expansion". This approximation is analogous to the slow-roll expansion used for inflation, and it allows us to express the quasinormal mode spectrum in terms of a small number of parameters. This work is a first step in describing, in a model independent way, how the scalar hair can affect the ringdown stage and leave signatures on the emitted gravitational wave signal. Potential signatures include the shifting of the quasi-normal spectrum, the breaking of isospectrality between polar and axial modes, and the existence of scalar radiation. arXiv:1810.07706v3 [hep-th] 1 Feb 2019 F The Regge-Wheeler equations 44 G Isolating the gravitational waves -the large radius limit 44 H Bianchi identities 46 -1 -out. The non-invariance under shifts of the Hamiltonian constraints, responsible for this fact, is at the core of the construction of shift-symmetric adiabatic modes on FLRW spacetimes [33, 34]. 6In other words, the relevant potential for the odd modes depends exclusively on the background metric components, with exactly the same functional dependence as in GR. This still leaves open the possibility of a modification to the odd QNM spectrum if the metric is different from Schwarzschild.

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Stable wormholes in scalar-tensor theories

Cited by 37 publications

References 42 publications

Wormhole solutions in modified Brans-Dicke theory

Wormhole solutions in modified Brans-Dicke theory

More about stable wormholes in beyond Horndeski theory

Effective field theory of black hole quasinormal modes in scalar-tensor theories

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