Asymptotically Flat, Spherical, Self-Interacting Scalar, Dirac and Proca Stars

Herdeiro, Carlos; Radu, Eugen

doi:10.3390/sym12122032

Cited by 38 publications

(48 citation statements)

References 64 publications

(89 reference statements)

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“…It therefore seems natural to add, as a toy model for such interactions, terms in the Lagrangian that are composed of higher-order products of the field. Self-interacting vector fields have also been studied in the context of exotic compact objects, in particular "Proca stars" [10][11][12][13][14][15][16][17], which may be partly stabilized by a quartic potential [18,19].…”

Section: Introductionmentioning

confidence: 99%

The problem with Proca: ghost instabilities in self-interacting vector fields

Clough¹,

Helfer²,

Witek³

et al. 2022

Preprint

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Massive vector fields feature in several areas of particle physics, e.g., as carriers of weak interactions, dark matter candidates, or as an effective description of photons in a plasma. Here we investigate vector fields with self-interactions by replacing the mass term in the Proca equation with a general potential. We show that this seemingly benign modification inevitably introduces ghost instabilities of the same kind as those recently identified for vector-tensor theories of modified gravity (but in this simpler, minimally coupled theory). It has been suggested that nonperturbative dynamics may drive systems away from such instabilities. We demonstrate that this is not the case by evolving a self-interacting Proca field on a black hole background, where it grows due to the superradiant instability. The system initially evolves as in the massive case, but instabilities are triggered in a finite time once the self-interaction becomes significant. These instabilities have implications for the formation of condensates of massive, self-interacting vector bosons, the possibility of spin-one bosenovae, vector dark matter models, and effective models for interacting photons in a plasma.

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Section: Introductionmentioning

confidence: 99%

The problem with Proca: ghost instabilities in self-interacting vector fields

Clough¹,

Helfer²,

Witek³

et al. 2022

Preprint

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show abstract

“…We should mention that solitons in models of self-interacting massive gauge bosons without any scalars have been discussed in refs [16][17][18][19]. but have no relation to our study.…”

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confidence: 84%

Proca Q-balls and Q-shells

Heeck

Rajaraman

Riley

et al. 2021

J. High Energ. Phys.

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Non-topological solitons such as Q-balls and Q-shells have been studied for scalar fields invariant under global and gauged U(1) symmetries. We generalize this frame-work to include a Proca mass for the gauge boson, which can arise either from spontaneous symmetry breaking or via the Stückelberg mechanism. A heavy (light) gauge boson leads to solitons reminiscent of the global (gauged) case, but for intermediate values these Proca solitons exhibit completely novel features such as disconnected regions of viable parameter space and Q-shells with unbounded radius. We provide numerical solutions and excellent analytic approximations for both Proca Q-balls and Q-shells. These allow us to not only demonstrate the novel features numerically, but also understand and predict their origin analytically.

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“…self-gravitating solitons) of yet undetected ultralight scalar [1,2] or vector [3] bosonic fields -see also, e.g. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] for some generalizations and reviews. Such hypothetical ultralight bosons could be part (or the whole) of the dark matter budget in the Universe [20,21].…”

Section: Introductionmentioning

confidence: 99%

The imitation game: Proca stars that can mimic the Schwarzschild shadow

Herdeiro,

Pombo,

Radu

et al. 2021

Preprint

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Can a dynamically robust bosonic star (BS) produce an (effective) shadow that mimics that of a black hole (BH)? We focus on models of spherical BSs with free scalar or vector fields, as well as with polynomial or axionic self-interacting fields. The BH shadow is linked to the existence of light rings (LRs). For free bosonic fields, yielding mini-BSs, it is known that these stars can become ultra-compact -i.e., possess LRs -but only for perturbatively unstable solutions. We show this remains the case even when different self-interactions are considered. However, an effective shadow can arise in a different way: if BSs reproduce the existence of an innermost stable circular orbit (ISCO) for timelike geodesics (located at rISCO = 6M for a Schwarzschild BH of mass M ), the accretion flow morphology around BHs is mimicked and an effective shadow arises in an astrophysical environment. Even though spherical BSs may accommodate stable timelike circular orbits all the way down to their centre, we show the angular velocity Ω along such orbits may have a maximum away from the origin, at RΩ; this scale was recently observed to mimic the BH's ISCO in some scenarios of accretion flow. Then: (i) for free scalar fields or with quartic self-interactions, RΩ = 0 only for perturbatively unstable BSs; (ii) for higher scalar self-interactions, e.g. axionic, RΩ = 0 is possible for perturbatively stable BSs, but no solution with RΩ = 6M was found in the parameter space explored; (iii) but for free vector fields, yielding Proca stars, perturbatively stable solutions with RΩ = 0 exist, and indeed RΩ = 6M for a particular solution. Thus, dynamically robust spherical Proca stars succeed in the imitation game: they can mimic the shadow of a (near-)equilibrium Schwarzschild BH with the same M , in an astrophysical environment, despite the absence of a LR, at least under some observation conditions, as we confirm by explicitly comparing the lensing of such Proca stars and Schwarzschild BHs.

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Asymptotically Flat, Spherical, Self-Interacting Scalar, Dirac and Proca Stars

Cited by 38 publications

References 64 publications

The problem with Proca: ghost instabilities in self-interacting vector fields

The problem with Proca: ghost instabilities in self-interacting vector fields

Proca Q-balls and Q-shells

The imitation game: Proca stars that can mimic the Schwarzschild shadow

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