arXiv subjects

Ifigeneia Giannakoudi

Publications and source records attributed to Ifigeneia Giannakoudi.

4 recordsLinked to original sources

arXiv2026

Probing ultralight bosons with LISA observations of spinning black hole mergers and follow-up searches of merger remnants

Ultralight bosons can trigger superradiant instabilities around rotating black holes, extracting angular momentum and leading in some cases to observable gravitational signatures. When the associated spin-down timescale is shorter than the black hole lifetimes and the spin-up timescales due to, e.g. accretion, this process imposes an upper limit on black hole spins. In addition, the formation and subsequent dissipation of boson clouds generates quasi-continuous gravitational wave emission. In this work, we explore the prospects for constraining and detecting ultralight bosons with observations of massive black hole binary mergers with the space-based LISA observatory. We consider two complementary approaches: measurements of black hole spins from merging binaries and follow-up gravitational wave searches targeting massive black hole binary merger remnants. We consider three population models for massive black holes, based on either heavy or light seeds, and forecast the exclusion and detection probabilities for both scalar and vector bosons. We find that black hole spin measurements can constrain scalar masses in the range $[5\times10^{-18},10^{-14}]$ eV and vector masses in the range $[6\times10^{-19},2\times10^{-14}]$ eV, with the exact range depending on the model. In contrast, restricting to vector bosons, follow-up gravitational wave searches are sensitive to a narrower vector boson mass range of $\sim[3\times10^{-17},3\times10^{-15}]$ eV, with the specific values again depending on the model. If a vector boson with a mass in the range $[10^{-16},2\times10^{-15}]$ eV existed, the probability of having an event that the follow-up searches would be sensitive to ranges from very small to near unity depending on the astrophysical model.

gr-qc↗

arXiv2022

A Panorama of Viable $F(R)$ Gravity Dark Energy Models

In this work we shall study the late-time dynamics of several $F(R)$ gravity models. By appropriately expressing the field equations in terms of the redshift and of a statefinder function, we shall solve numerically the field equations using appropriate physical motivated initial conditions. We consider models which, by construction, are described by a nearly $R^2$-model at early epochs and we fine tune the parameters to achieve viability and compatibility with the latest Planck constraints at late times. Such models provide a unified description of inflation and dark energy era and notably a common feature of all the models is the presence of dark energy oscillations. Furthermore, we show that, in contrast to general relativistic fluids and scalar field descriptions, a large spectrum of different dark energy physics is generated by simple $F(R)$ gravity models, varying from phantom, to nearly de Sitter and to quintessential dark energy eras.

gr-qc↗

arXiv2022

$\mathcal{R}^2$ Quantum Corrected Scalar Field Inflation

String theory enjoys an elevated role among quantum gravity theories, since it seems to be the most consistent UV completion of general relativity and the Standard Model. However, it is hard to verify the existence of this underlying theory on terrestrial accelerators. One way to probe string theory is to study its imprints on the low-energy effective inflationary Lagrangian, which are quantified in terms of high energy correction terms. It is highly likely, thus, to find higher order curvature terms combined with string moduli, that is scalar fields, since both these types of interactions and matter fields appear in string theory. In this work we aim to stress the probability that the inflationary dynamics are controlled by the synergy of scalar fields and higher order curvature terms. Specifically, we shall consider a well motivated quantum corrected canonical scalar field theory, with the quantum corrections being of the $\mathcal{R}^2$ type. The reason for choosing minimally coupled scalar theory is basically because if scalar fields are evaluated in their vacuum configuration, they will either be minimally coupled or conformally coupled. Here we choose the former case, and the whole study shall be performed in the string frame (Jordan frame), in contrast to similar studies in the literature where the Einstein frame two scalar theory is considered. We derive the field equations of the quantum-corrected theory at leading order and we present the form the slow-roll indices obtain for the quantum corrected theory. We exemplify our theoretical framework by using the quadratic inflation model, and as we show, the $\mathcal{R}^2$ quantum corrected quadratic inflation model produces a viable inflationary phenomenology, in contrast with the simple quadratic inflation model.

gr-qc↗

arXiv2021

Rescaled Einstein-Hilbert Gravity: Inflation and the Swampland Criteria

In this work we shall study a class of $f(R,ϕ)$ gravity models which during the inflationary era, which is the large curvature regime, result to an effective inflationary Lagrangian that contains a rescaled Einstein-Hilbert term $αR$ in the presence of a canonical minimally coupled scalar field. The dimensionless parameter $α$ is chosen to take values in the range $0<α<1$ and the main motivation for studying these rescaled Einstein-Hilbert $f(R,ϕ)$ gravities, is the fact that the rescaled action may render an otherwise incompatible canonical scalar field theory with the Swampland criteria, to be compatible with the Swampland criteria. As we will show, by studying a large number of inflationary potentials appearing in the 2018 Planck collaboration article for the constraints on inflation, the simultaneous compatibility with both the Planck constraints and the Swampland criteria, is achieved for some models, and the main characteristic of the models for which this is possible, is the small values that the parameter $α$ must take.

gr-qc↗