arXiv subjects

Yanjiao Ma

Publications and source records attributed to Yanjiao Ma.

3 recordsLinked to original sources

arXiv2026

On Cosmological Correlators with Boundary Contributions

Cosmological correlators receive contributions from both field interactions in the bulk of quasi-de Sitter (dS) spacetime and boundary terms at the end of inflation. While most of the research efforts focus on the former, boundary contributions are normally believed to be negligible or related to field redefinitions that are associated with redundancies of the bulk Lagrangian. In this paper, we revisit this topic in the light of the cosmological bootstrap. We first establish the correspondence between boundary terms and field redefinitions for cosmological correlators. This result provides a set of criteria for determining when boundary terms lead to non-vanishing contributions to cosmological observables. Next, we apply this general understanding to concrete examples of correlators from massive-exchange diagrams, in both dS-invariant and boost-breaking scenarios. For theories with dS isometries, both IBP and field redefinitions are used to relate derivative and non-derivative exchange diagrams, from which the leading boundary contributions and IR-divergent pieces are extracted; we also derive recursion relations among higher-derivative exchange correlators. For theories with broken dS boosts, we use IBP and EoM to reduce exchange diagrams to a basis of independent templates, and then present a classification of the boundary contributions in the general effective field theory framework. These results pave the way for a more systematic investigation on the boundary physics of the inflationary spacetime.

gr-qc↗

arXiv2024

Survival of the Fittest: Testing Superradiance Termination with Simulated Binary Black Hole Statistics

The superradiance instability of rotating black holes leads to the formation of an ultralight boson cloud with distinctive observational signatures, making black holes an effective probe of ultralight bosons. However, around black holes in a binary system, the superradiance effect of such clouds can be terminated by tidal perturbations from the companion, leading to cloud depletion. In this study, we focus on the superradiance of a scalar boson, and perform the first analysis of the impact of this termination effect on superradiant black hole binaries which are realistically modeled after their statistics in our Galaxy. Working with a dataset of approximately $10^7$ black hole binaries simulated using the Stellar EVolution for N-body (SEVN) population synthesis code, we identify the superradiant candidates and those that manage to survive the termination effect. We then calculate the cloud survival rate for various boson masses and black hole spin models. Our findings reveal that the $l=m=1$ cloud modes are generally stable against termination, whereas the $l=m=2$ modes can be significantly affected, with survival rates dropping below $10\%$ for boson masses below approximately $0.5\times 10^{-12}$ eV. In addition, our analysis indicates that clouds that overcome termination typically exhibit a higher superradiant growth rate and therefore a higher detectability.

gr-qc↗

arXiv2024

Elko as an inflaton candidate

Elko is a spin-half fermion with a two-fold Wigner degeneracy and Klein-Gordon dynamics. In this paper, we show that in a spatially flat FLRW space-time, slow-roll inflation can be initiated by the homogeneous Elko fields. The inflaton is a composite scalar field obtained by contracting the spinor field with its dual. This is possible because the background evolution as described by the Friedmann equation is completely determined by the scalar field. This approach has the advantage that we do not need to specify the initial conditions for every component of the spinor fields. We derive the equation of motion for the inflaton and also show that this solution is an attractor. Finally, we examine the slow-roll parameters and the power-spectrum, showing that obtaining a behavior in agreement with observational requirements is hard to be obtained, unless one uses more complicated potentials, which may act a limitation of Elko inflation.

hep-th↗