arXiv subjects

Donald Liveoak

Publications and source records attributed to Donald Liveoak.

7 recordsLinked to original sources

arXiv2026

Shaving the Outskirts of Planetary Systems Probed by Roman via Stellar Flybys

The recently launched Nancy Grace Roman Space Telescope (\textit{Roman}) will soon begin observations that promise to revolutionize our understanding of exoplanet demographics. \textit{Roman}'s Galactic Bulge Time-Domain Survey (GBTDS) will observe the Galactic Bulge via transit and microlensing techniques, providing a unique opportunity to study hot Jupiters as well as long-period/free-floating exoplanets in a dense and kinematically hot stellar environment. In this Letter, we quantify how repeated, impulsive stellar flybys truncate the outskirts of planetary systems in the Bulge. We find that flybys result in ejections on $\sim$Gyr timescales for wide orbits (${\gtrsim} 250\ \text{au}$) around low-mass hosts. Provided these wide orbits are populated, these ejections likely contribute to the population of free-floating planets probed by \textit{Roman}. Surviving planets outside of ${\sim} 10$ au are placed on eccentric and misaligned orbits. We show that, though systems suffer many close encounters, the evolution is dominated by the single strongest perturbation; planetary orbits (even those that evade ejection) undergo superdiffusion (i.e. a L\'evy flight). We comment on the implications of our results for the origin of hot Jupiters amenable to $\textit{Roman}$'s transit search. Our work serves as a quantitative baseline from which future dynamical studies can build to better understand the evolution of planetary systems in the Galactic Bulge.

astro-ph.EP↗

arXiv2026

Intra-system Uniformity through Planetary Embryo Accumulation

Intra-system uniformity is a key trend in observed exoplanet systems. Understanding the physical mechanisms which sculpt planetary systems into uniform or non-uniform configurations will help constrain theories of planet formation. Motivated by previous work showing that intra-system uniformity is a natural consequence of proto-planetary systems dissipating energy and settling into lower energy configurations, this paper explores the energy minimization hypothesis using $N$-body simulations. We find that the accumulation of planetary embryos through inelastic mergers generally dissipates a substantial fraction of the system energy, but the systems do not always reach the global energy minimum. Analytic predictions indicate that planetary pairs have nearly equal masses in their lowest energy state when the total mass falls below a mass threshold. With larger total mass, one member of the pair tends to accrete most of the mass. Our numerical simulations show that pairs with masses above the threshold tend towards non-uniformity, but that the full realization of the effect occurs at a larger mass scale, a factor of $\sim4$ above the threshold. In any case, however, the low-mass planet pairs are generally more uniform than pairs with high mass, in agreement with previous work. Finally, we compare our results to the observed sample of exoplanets and find overall agreement.

astro-ph.EP↗

arXiv2026

Dark Monopoles, Bounds on Hidden Sectors, and Cosmological Implications

Hidden sectors are a generic prediction of string theory compactifications and result in a promising landscape for dark matter model building. We consider the case of hidden sector magnetic monopoles produced via a thermal phase transition in the early Universe and subsequently diluted by pair annihilation. We show that for symmetry-breaking scales $\gtrsim 100\, \text{PeV}$, the monopole abundance is unacceptably high, overclosing the Universe. Our bounds are robust against variations in the initial fraction of energy density deposited in the hidden sector, exhibiting only a weak power-law dependence on this quantity. The bound is substantially tightened in the case of multiple hidden sectors. The standard cosmology may only be recovered if one of the following is true: the hidden sector(s) are non-existent, the hidden sectors have no monopoles with symmetry-breaking scale above 100 PeV, the maximum temperature of each monopole-producing hidden sector after reheating is below its symmetry-breaking scale, or the monopole abundance is diluted during a period of early matter domination.

hep-ph↗

arXiv2026

Case Study of a Super-eccentric Warm Jupiter Migrating via Equilibrium and Dynamical Tides

A leading theory for hot Jupiter formation is high-eccentricity migration, in which planets are born at large separations and excited to near-unity eccentricities, creating extreme tidal dissipation that shrinks and circularizes their orbits. The most direct evidence for this scenario is the detection of highly eccentric planets caught in the act of migrating. Although such planets are rare, the recent discovery of TIC 241249530 b - a super-eccentric ($e = 0.94$) and retrograde hot Jupiter progenitor - presents an ideal case study to explore high-eccentricity migration and the accompanying tidal physics. In this paper, we examine the migration history of TIC 241249530 b and test two different models of tidal dissipation: equilibrium tides and chaotic dynamical tides. We show that TIC 241249530 b's properties can be explained by high-eccentricity migration triggered by von Zeipel-Lidov-Kozai oscillations induced by the observed distant binary star in the system, but only if the dominant tidal dissipation takes the form of equilibrium tides. Chaotic dynamical tides fail to explain the system because they require the planet to have migrated substantially closer to its star.

astro-ph.EP↗

arXiv2026

Uncovering the Rapidly Evolving Orbits of the Dynamic TOI-201 System

Studying planetary interactions in exoplanet systems informs theories of planet formation and evolution, providing essential context for understanding our own solar system. We combine spectroscopy, transit photometry, transit timing variations, and astrometry to characterize the TOI-201 system. The co-transiting system consists of a super-Earth, warm Jupiter, and massive companion at 5.8, 53, and 2900 day orbital periods, respectively. We perform dynamical simulations to study the past and future of the system. von-Zeipel-Kozai-Lidov oscillations emerge as the most plausible scenario to explain the outer companion's high orbital eccentricity, with planet-planet scattering a possible but less likely contender. Due to non-zero mutual inclinations between the planets, the system is visibly evolving on very short timescales, with the current co-transiting configuration ending in 200 years.

astro-ph.EP↗

arXiv2026

Stability of Multiplanet Systems Through Hot Jupiter Destruction

Recent observational and theoretical work suggests that the sub-Jovian desert (periods ${\lesssim}3$ days, masses ${\sim}10{-}100 \ M_{\oplus}$) hosts the remains of destroyed hot Jupiters (``desert dwellers"). In this work, we explore how differing hot Jupiter destruction mechanisms -- Roche lobe overflow (RLO) vs. tidal disruption during high eccentricity migration (HEM) -- may be discerned observationally based on the presence of companion planets to desert dwellers. We show that gas giant destruction via RLO clears out the desert of any companions inside orbital periods ${\lesssim}$4 days; desert dwellers should sit alone in the desert if they form through this mechanism. Numerically mapping the instability threshold in planet mass and orbital distance, we find that the majority of observed companions to desert dwellers are safely in the stability region. RLO therefore does not preclude the existence of nearby companions beyond the desert, in contrast to gas giant tidal disruption during HEM. Further characterization of desert dweller systems may therefore elucidate the fates of hot Jupiters.

astro-ph.EP↗

arXiv2024

Formation of Close-in Neptunes Around Low-Mass Stars Through Breaking Resonant Chains

Conventional planet formation theories predict a paucity of massive planets around small stars, especially very low-mass ($0.1 - 0.3 \ M_{\odot}$) mid-to-late M dwarfs. Such tiny stars are expected to form planets of terrestrial sizes, but not much bigger. However, this expectation is challenged by the recent discovery of LHS 3154 b, a planet with period of 3.7 days and minimum mass of $13.2 \ M_{\oplus}$ orbiting a $0.11 \ M_{\odot}$ star. Here, we propose that close-in Neptune-mass planets like LHS 3154 b formed through an anomalous series of mergers from a primordial compact system of super-Earths. We perform simulations within the context of the "breaking the chains" scenario, in which super-Earths initially form in tightly-spaced chains of mean-motion resonances before experiencing dynamical instabilities and collisions. Planets as massive and close-in as LHS 3154 b ($M_p \sim 12 - 20 \ M_{\oplus}$, $P < 7$ days) are produced in $\sim$1% of simulated systems, in broad agreement with their low observed occurrence. These results suggest that such planets do not require particularly unusual formation conditions but rather are an occasional byproduct of a process that is already theorized to explain compact multi-planet systems. Interestingly, our simulated systems with LHS 3154 b-like planets also contain smaller planets at around $\sim 30$ days, offering a possible test of this hypothesis.

astro-ph.EP↗