arXiv subjects

Biancamaria Sersante

Publications and source records attributed to Biancamaria Sersante.

4 recordsLinked to original sources

arXiv2026

Extreme mass ratio inspirals from the Hills mechanism, The eccentricity distribution of Hills EMRIs in LISA

Extreme mass ratio inspirals (EMRIs) are promising sources for future space-based gravitational-wave detectors. We investigate EMRIs produced through the Hills mechanism, in which a stellar-mass black-hole binary (BBH) is tidally separated by a massive black hole (MBH), leaving one component bound to it. We present the first self-consistent modelling of this channel, combining an orbit-averaged Fokker-Planck treatment of the nuclear star cluster (NSC), three-body modelling of the binary-MBH encounter, Monte Carlo evolution of captured black holes (BHs), and fully relativistic EMRI trajectories to follow the evolution from binary supply down to final plunge. We find that Hills EMRIs are substantially more circular than classical EMRIs formed through two-body relaxation. For an MBH of $4 \times 10^6 M_\odot$ and circular, equal-mass BBHs of $20 M_\odot$ with initial separation of $0.1$ AU, EMRI mean eccentricities are approximately $0.097$ at our adopted LISA-band entry threshold and $0.034$ at plunge, compared with $0.478$ and $0.228$, respectively, for classical EMRIs. Of the initial BBHs, approximately $0.4$ per cent become EMRIs, whereas approximately $60$ per cent of captured BHs do. For comparable NSC initial compact-object mass, we find approximately $1.6 \times 10^{-8}$ Hills EMRIs per year per galaxy, approximately $12$ per cent of the classical EMRI yield. The Hills channel contribution to the overall eccentricity distribution depends strongly on the binary mass fraction in NSCs. We discuss implications for identifying EMRI formation channels with LISA and for quasi-periodic eruptions.

astro-ph.HE↗

arXiv2026

Fisher Forecasting for the DESC with $\texttt{Augur}$

The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) has begun its ten-year survey of the entire visible southern hemisphere. To ensure robust cosmological measurements, computationally inexpensive investigations of modeling choices must be made to gauge the performance of proposed cosmological analyses. In this paper, we introduce the $\texttt{Augur}$ tool of the Dark Energy Science Collaboration (DESC), which provides Fisher forecasts for cosmological inference for the LSST using software frameworks designed for DESC science. We test the pipeline by comparing it to forecasts produced by external code and direct sampling of the posterior via nested sampling methods, finding good agreement between all methods. We additionally investigate a range of modeling and hyperparameter choices for a 3$\times$2pt investigation in harmonic space, providing users with diagnostics to obtain reliable forecasts. $\texttt{Augur}$ will be continually updated to be compatible with the other tools in the DESC software ecosystem as additional probes and functionality become available.

astro-ph.CO↗

arXiv2026

Inverting Fisher biases for fast systematics exploration

Upcoming cosmological surveys will achieve increasingly precise constraints in cosmological parameter estimation. To guarantee the robustness of cosmological analyses, it is essential to account for and model systematic effects that can bias cosmological constraints, shifting the best fit parameters away from their fiducial values. It is possible to approximately infer the biases that un-modelled systematic effects might introduce in cosmological parameter estimation by means of the Fisher matrix formalism. In this paper, we introduce a new application of this formalism, where by inverting the process, we investigate whether a specific missing or mis-modelled systematic effect can explain away a given tension between two different probes or experiments. We showcase the proposed methodology by examining two representative systematics: galaxy intrinsic alignments and baryonic feedback. As the method is agnostic to the systematic effect and can be applied to a wider range of scenarios, we discuss more possible future applications. While the proposed approach is accurate in the limit of small offsets in the cosmological parameters, where the likelihood can be considered linear in both the cosmological parameters and the systematics, in practice, the region of validity depends on the systematic effect. In general, even beyond this region, the approach still provides a useful test that helps indicate the magnitude and direction of potential biases from systematic effects in data.

astro-ph.CO↗

arXiv2025

Dynamics of recaptures, ejections and mergers of stellar mass binaries over multiple encounters with SgrA*

A common origin for a host of stellar phenomena in galactic centres is the tidal encounter between stellar binaries and a massive black hole (MBH), known as the ``Hills mechanism''. Following the encounter, binaries may disrupt into an ejected star and a captured one, they may merge, or survive to either fly away or come back for one or more subsequent encounters, until they are either disrupted or fly away. In this paper, we analyse how a binary's fate depends on its orbital parameters, by following its evolution through up to three subsequent pericentre passages. We choose an initial population of circular binaries on parabolic orbits. We present results from our restricted three-body formalism, whose strength lies in the ability to easily explore a multidimensional parameter space and make predictions independent of the binary physical properties. We find that fates depend strongly on orbital inclination, how deep the encounter is into the MBH tidal sphere and on the binary eccentricity, developed during encounters. Generally, non retrograde trajectories, high eccentricities or deep encounters produce disruptions preferentially. Disruption is the most common fate. A significant fraction of the surviving binaries fly away at velocities typically two orders of magnitude smaller than those of ejected stars. Multiple encounters boost disruptions by 20\% or more. Finally, using an example system, we investigate the effect of finite stellar sizes and lifetimes, showing that mergers occur 31\% of the time, and that disruptions are still boosted by 10\% through subsequent passages.

astro-ph.GA↗