Research Project: Exiting new degress of freedom in strong gravity
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Contributors
Funders
ID
TB.00492
Authors
Coates, Andrew
Researcher
Publications
Intrinsic pathology of self-interacting vector fields
(American Physical Society (APS), 2022) Coates, Andrew; Ramazanoğlu, Fethi Mübin; Department of Physics; Yes; College of Sciences
We show that self-interacting vector field theories exhibit unphysical behavior even when they are not coupled to any external field. This means any theory featuring such vectors is in danger of being unphysical, an alarming prospect for many proposals in cosmology, gravity, high energy physics, and beyond. The problem arises when vector fields with healthy configurations naturally reach a point where time evolution is mathematically ill defined. We develop tools to easily identify this issue, and provide a simple and unifying framework to investigate it.
Ghost of vector fields in compact stars
(American Physical Society (APS), 2022) Coates, Andrew; Ramazanoğlu, Fethi Mübin; Silva, Hector O.; Sotiriou, Thomas P.; Department of Physics; Yes; College of Sciences
Spontaneous scalarization is a mechanism that allows a scalar field to go undetected in weak gravity environments and yet develop a nontrivial configuration in strongly gravitating systems. At the perturbative level it manifests as a tachyonic instability around spacetimes that solve Einstein's equations. The endpoint of this instability is a nontrivial scalar field configuration that can significantly modify a compact object's structure and can produce observational signatures of the scalar field's presence. Does such a mechanism exists for vector fields? Here we revisit the model that constitutes the most straightforward generalization of the original scalarization model to a vector field and perform a perturbative analysis. We show that a ghost appears as soon as the square of the naive effective mass squared becomes negative anywhere. This result poses a serious obstacle in generalizing spontaneous scalarization to vector fields.
On black hole area quantization and echoes
(Institute of Physics (IOP) Publishing, 2022) Coates, Andrew; Volkel, Sebastian H.; Kokkotas, Kostas D.; Department of Physics; No; College of Sciences
In this work we argue that black hole (BH) area quantization of Bekenstein and Mukhanov should not give rise to measurable effects in terms of so-called gravitational wave echoes during BH mergers. We outline that the quantum spectrum of a BH should be washed out during and after BH mergers, and hence one should not expect echoes in this scenario. The extreme broadening of the spectrum is due to the large particle emission rate during ringdown. Our results question key assumptions being made in recent literature on this topic.
Instability of vectorized stars
(American Physical Society (APS), 2022) Coates, Andrew; Ramazanoğlu, Fethi Mübin; Demirboğa, Ekrem; Department of Physics; Graduate School of Sciences and Engineering; Yes; College of Sciences; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING
In recent papers it has been shown that a large class of vectorization mechanisms in gravity, which involve the vector fields becoming apparently tachyonic in some regime, are actually dominated by ghosts and nonperturbative behavior. Despite this, vectorized compact object solutions have previously been found, which raises the question of how, and if, the newly discovered ghosts are quenched in these cases. Here we develop the tools to study the perturbations of vectorized compact objects, and demonstrate that they suffer from ghosts and gradient instabilities as well. Thus, these vectorized objects do not represent the stable end point of a quenched instability unlike their scalarized counterparts in the spontaneous scalarization literature.
