Electromagnetism and hidden vector fields in modified gravity theories: spontaneous and induced vectorization

Einstein-Maxwell-Vector模型中的自发矢量化

Spontaneous Vectorization in the Einstein-Maxwell-Vector Model

本文在Einstein-Maxwell-Vector模型中研究自发矢量化，通过广义坐标变换解决视界附近矢量场发散问题，并提出组合电荷概念，揭示了矢量化Reissner-Nordström黑洞在热力学和光球性质上的独特优势及其与双电荷黑洞解的联系。

Spontaneous vectorization in the presence of vector field coupling to matter

We examine the possibility of spontaneous vectorization in the vector-tensor theories with the vector conformal and disformal couplings to matter. We study the static and spherically symmetric solutions of the relativistic stars with the nontrivial profile of the vector field satisfying the boundary conditions $A_μ\to 0$ at the spatial infinity, where $A_μ$ represents the vector field. First, we study the linear perturbations about the general relativistic (GR) stellar solutions with the vanishing vector field $A_μ=0$. We show that the pure vector disformal coupling causes the ghost or gradien…

Spontaneous growth of vector fields in gravity

We show that the spontaneous scalarization scenario in scalar-tensor theories is a specific case of a more general phenomenon. The key fact is that the instability causing the spontaneous growth in scalars is due to the nonminimal coupling in the theory, and not related to the nature of the scalar. Another field with the same form of coupling undergoes spontaneous growth as well. We explicitly demonstrate this idea for vectors, naming it "spontaneous vectorization", and study spherically symmetric neutron stars in such a theory. We also comment on other tensor fields the idea can be applied, n…

Emergent Gravity from Noncommutative Spacetime

We showed before that self-dual electromagnetism in noncommutative (NC) spacetime is equivalent to self-dual Einstein gravity. This result implies a striking picture about gravity: Gravity can emerge from electromagnetism in NC spacetime. Gravity is then a collective phenomenon emerging from gauge fields living in fuzzy spacetime. We elucidate in some detail why electromagnetism in NC spacetime should be a theory of gravity. In particular, we show that NC electromagnetism is realized through the Darboux theorem as a diffeomorphism symmetry G which is spontaneously broken to symplectomorphism H…

Generalized disformal coupling leads to spontaneous tensorization

We show that gravity theories involving disformally transformed metrics in their matter coupling lead to spontaneous growth of various fields in a similar fashion to the spontaneous scalarization scenario in scalar-tensor theories. Scalar-dependent disformal transformations have been investigated in this context, and our focus is understanding the transformations that depend on more general fields. We show that vector-dependent disformal couplings can be obtained in various different ways, each leading to spontaneous vectorization as indicated by the instabilities in linearized equations of mo…

Analogues of gravity-induced instabilities in anisotropic metamaterials

In the context of field theory in curved spacetimes, it is known that suitable background spacetime geometries can trigger instabilities of fields, leading to exponential growth of their (quantum and classical) fluctuations --- a phenomenon called $\textit{vacuum awakening}$ in the quantum context, which in some classical scenarios seeds $\textit{spontaneous scalarization/vectorization}$. Despite its conceptual interest, an actual observation in nature of this effect is uncertain since it depends on the existence of fields with appropriate masses and couplings in strong-gravity regimes. Here, …

Embedding Gauss-Bonnet scalarization models in higher dimensional topological theories

In the presence of appropriate non-minimal couplings between a scalar field and the curvature squared Gauss-Bonnet (GB) term, compact objects such as neutron stars and black holes (BHs) can spontaneously scalarize, becoming a preferred vacuum. Such strong gravity phase transitions have attracted considerable attention recently. The non-minimal coupling functions that allow this mechanism are, however, always postulated ad hoc. Here we point out that families of such functions naturally emerge in the context of Higgs--Chern-Simons gravity models, which are found as dimensionally descents of hig…

Scalaroca 星：耦合的标量-Proca 孤子

Scalaroca stars: coupled scalar-Proca solitons

本文构造并研究由复标量场和复Proca场组成的球对称孤子星，分析无相互作用及通过α|Φ|^2 A^μA_μ耦合两种情形，发现强相互作用可产生更大质量解，并讨论同步态、实标量场解及自发标量化与矢量化。