arXiv subjects

Shawn Ray

Publications and source records attributed to Shawn Ray.

6 recordsLinked to original sources

arXiv2026

What Can Be Enforced? A Theory of Certified Runtime Safety for Tool-Using Agents

Runtime guardrails act before irreversible tool calls, but their guarantees depend on what policy state is representable, what a judge observes, and whether intervention changes future behavior. We separate three questions. First, relative to fixed oracle predicates, a deterministic gate enforces exactly the nonempty safety policies whose good prefixes its register model recognizes; policy nontriviality is undecidable with two decrementable counters but in PSPACE for a separable monotone fragment. Second, under a fixed exogenous law, Neyman-Pearson gives the exact false-block/miss frontier and conformal calibration gives a finite-sample marginal certificate, possibly via block-all. Third, once blocking changes future proposals, static scores and ungated trajectories need not identify the closed-loop frontier; a specified finite controlled model instead yields an occupancy program. Bounded representation attacks add a robustness margin, so benign calibration alone does not transfer. Experiments target these distinctions through static diagnostics, controlled-model enumeration, representation rewrites, and paired closed-loop reruns.

cs.AI↗

arXiv2026

Graph-SND: Sparse Aggregation for Behavioral Diversity in Multi-Agent Reinforcement Learning

System Neural Diversity (SND) measures behavioral heterogeneity in multi-agent reinforcement learning by averaging pairwise distances over all $\binom{n}{2}$ agent pairs, making each call quadratic in team size. We introduce Graph-SND, which replaces this complete-graph average with a weighted average over the edges of an arbitrary graph $G$. Three regimes follow: $G=K_n$ recovers SND exactly; a fixed sparse $G$ defines a localized diversity measure at $O(|E|)$ cost; and random edge samples yield an unbiased Horvitz-Thompson estimator and a normalized sample mean with $O(1/\sqrt{m})$ concentration in the sampled edge count $m$. For fixed sparse graphs we prove forwarding-index distortion bounds for expanders and a spectral refinement under low-rank distance structure; for random $d$-regular graphs we prove an unconditional probabilistic $\widetilde{\mathcal{O}}(D_{\max}/\sqrt{n})$ bound. On VMAS we verify recovery, unbiasedness, concentration, and wall-clock scaling, with a PettingZoo TVD panel checking non-Gaussian transfer. In a 500-iteration $n=100$ PPO run, Bernoulli-$0.1$ Graph-SND tracks full SND while reducing per-call metric time by about $10\times$, and frozen-policy GPU timing up to $n=500$ follows the predicted $\binom{n}{2}/|E|$ speedup. Random $d$-regular expanders empirically achieve $\mathrm{SND}_{G}^{\mathrm{u}}/\mathrm{SND} \in [0.9987, 1.0013]$ at $\Theta(n \log n)$ edges. In DiCo diversity control at $n=50$, Bernoulli-$0.1$ Graph-SND preserves set-point tracking with paired reward differences indistinguishable from zero across nine matched cells while cutting per-call metric cost by ${\sim}9.5\times$. Together, these results show that the SND aggregation bottleneck can be removed without changing the metric's semantics, yielding a drop-in sparse alternative that scales beyond complete-graph SND and supports both passive measurement and closed-loop diversity control.

cs.LG↗

arXiv2026

McFACTS. IV. Electromagnetic Counterparts to AGN-disk-embedded Binary Black Hole Mergers

The accretion disks of active galactic nuclei (AGNs) are promising environments for producing binary black hole (BBH) mergers, which have been detected via gravitational waves (GWs) with the LIGO-Virgo-KAGRA (LVK) GW detector network. BBH mergers embedded in AGN disks are unique among GW formation channels in their generic ability to produce electromagnetic (EM) counterparts, via interactions between the merger remnant and the surrounding disk gas (though these are not always observable). While such mergers represent valuable multimessenger sources, the lack of predictive statistical models in existing literature currently limits our ability to select possible EM counterparts with GW detections in archival data and in real time using time-domain surveys such as the Zwicky Transient Facility or LSST. Here we employ the Monte Carlo For AGN Channel Testing and Simulation code (McFACTS, https://www.github.com/mcfacts/mcfacts) to predict the bolometric luminosities of jets and shocks associated with LVK-detectable BBH merger remnants in AGN disks. McFACTS predicts the distribution of GW observables for an underlying black hole population and disk model. In this work we present a new capability that simultaneously generates the distribution of bolometric EM luminosities corresponding to these predicted GW detections. Our results are consistent with current observational surveys and indicate that (i) migration in dense, Sirko-Goodman-like disks preferentially produces EM counterparts from high-mass ($\mathscr{M} > 40M_{\odot}$), high-spin remnants across multiple merger generations and (ii) lower chirp mass mergers are more likely to contribute observable counterparts and with shorter emission breakout times in less dense, Thompson-Quataert-Murray-like disks.

astro-ph.HE↗

arXiv2024

McFACTS II: Mass Ratio--Effective Spin Relationship of Black Hole Mergers in the AGN Channel

We use the Monte Carlo For AGN (active galactic nucleus) Channel Testing and Simulation (McFACTS, https://www.github.com/mcfacts/mcfacts) code to study the effect of AGN disk and nuclear star cluster parameters on predicted mass distributions for LIGO-Virgo-KAGRA (LVK) compact binaries forming in AGN disks. The assumptions we vary include the black hole (BH) initial mass function, disk model, disk size, disk lifetime, and the prograde-to-retrograde fraction of newly formed black hole binaries. Broadly we find that dense, moderately short-lived AGN disks are preferred for producing a $(q,\chi_{\rm eff})$ anti-correlation like those identified from existing gravitational wave (GW) observations. Additionally, a BH initial mass function (MF $\propto M^{-2}$) is preferred over a more top-heavy MF ($M^{-1}$). The preferred fraction of prograde-to-retrograde is $>90\%$, to produce results consistent with observations.

astro-ph.HE↗

arXiv2024

McFacts III: Compact binary mergers from AGN disks over an entire synthetic universe

The Active Galactic Nuclei (AGN) channel for the formation of binary black hole (BBH) mergers has been previously studied as a potential formation channel for the merging compact binaries observed by the LIGO/Virgo/KAGRA (LVK) scientific collaboration. The first two papers in this series explored the McFACTS code for the evolution of black hole orbits in AGN accretion disks for individual galaxy models and described the characteristics of predicted BBH populations in realizations of those models (such as the correlation between mass ratio and aligned spin). In this work, we explore the impact of the properties of AGN host galaxies and assume an AGN lifetime and cosmological model for the density of AGN in a universe like our own. By sampling from an inferred population of AGN, we marginalize over galaxy mass to predict a population of BBH mergers observable by modern ground-based gravitational wave observatories. We find that for reasonable assumptions, AGN disk environments may account for massive BBH mergers such as GW190521 and GW190929_012149. We find that the majority of observable BBH mergers from our simulation are expected to originate in galaxies with a super-massive black hole between $10^{7}M_{\odot}$ and $10^{9.4}M_{\odot}$. We also find that if hierarchical mergers from AGN disks account for a substantial part of the LVK population, our current models require an AGN lifetime of 0.5 to 2.5 Myr.

astro-ph.HE↗

arXiv2024

McFACTS I: Testing the LVK AGN channel with Monte Carlo For AGN Channel Testing & Simulation (McFACTS)

Active galactic nuclei (AGN) are a promising source of the binary black hole (BBH) mergers observed in gravitational waves with LIGO-Virgo-Kagra (LVK). Constraining the AGN channel allows us to limit AGN parameter space (disk density, size, average lifetime) and nuclear star cluster (NSC) parameter space. Constraints on AGN and NSCs have implications for $\Lambda$CDM models of AGN feedback and models of AGN-driven SMBH merger and growth. Here we present several qualitative studies of the AGN channel using new public, open-source, fast, reproducible code \texttt{McFACTS}\footnote{https://github.com/mcfacts/mcfacts}:Monte Carlo for AGN channel Testing \& Simulation. We demonstrate several important features for testing the AGN channel, including: i) growth to large mass IMBH is helped by the presence of migration traps or swamps, ii) flat BH initial mass functions highlight hierarchical merger features in the mass spectrum, iii) the ($q,\chi_{\rm eff}$) anti-correlation is a strong test of the bias to prograde mergers in the AGN channel, iv) spheroid encounters can drive a fraction of mergers with high in-plane spin components ($\chi_{\rm p}$), v) a high rate of extreme mass ratio inspirals (EMRIs) are driven by an initial population of embedded retrograde BH, vi) Both LVK and LISA are powerful probes of models of AGN disks and their embedded populations.

astro-ph.HE↗