arXiv subjects

Zachary J. Hoelscher

Publications and source records attributed to Zachary J. Hoelscher.

4 recordsLinked to original sources

arXiv2026

DESI-Like Hubble Expansion From Staged Symmetry Breaking: Constraints on Renormalizable Models

The Dark Energy Spectroscopic Instrument (DESI) second data release shows a moderate preference for dark energy with a time-varying equation of state parameter, suggesting that the standard $Λ$CDM model may need to be revised. In particular, DESI favors dark energy whose equation of state parameter can drop below $-1$, violating the null energy condition. Chen and Loeb have recently suggested that this violation may be avoided if a subcomponent of the dark matter possesses a time-dependent equation of state. In this work, we explore the space of possible models, in an effort to find a natural, renormalizable realization. We find that once one requires the model to be renormalizable, a construction that generates the desired expansion history is fairly broadly obstructed. While we are unable to produce a fully natural, renormalizable realization of their ideas, this work is valuable for constraining directions one might pursue for viable theoretical explanations of the DESI results. Our framework is also interesting for incorporating features that may be of interest for model building elsewhere, as our decay cascades enable decays that switch on at particular redshifts while also naturally incorporating a self-interacting dark matter candidate with a velocity-dependent cross section as a consequence of gauge invariance. The second feature is relevant for addressing tensions between $Λ$CDM and observations of small-scale structure, particularly the diversity of galactic rotation curves.

astro-ph.CO↗

arXiv2026

Partial Relief of the Hubble Tension and a Natural Self-Interacting Dark Matter Candidate From Staged Symmetry Breaking

The values of the Hubble constant ($\rm{H_0}$) inferred from the cosmic microwave background (CMB) and local measurements via the distance ladder exhibit a $\sim5σ$ tension. In this work we propose that the tension might be partially alleviated if a subcomponent of the dark matter undergoes decays triggered by spontaneous symmetry breaking in the dark sector, where dark energy couples to the daughter species, but not the parent. This then allows interactions between dark matter and dark energy to turn on at a particular redshift, which can reduce fifth-force constraints, since early time interactions are absent. We provide an example of such an effective field theory whose structure is partially motivated by the desire for a plausible UV completion. We find that such a construction can naturally incorporate a possible self-interacting dark matter candidate with a velocity-dependent scattering cross section as a by-product of gauge invariance, though this is not necessary for alleviating the Hubble tension. This is relevant for addressing tensions between $Λ$CDM and small-scale structure, such as the core-cusp problem.

astro-ph.CO↗

arXiv2026

Probing the Nature of Dark Matter Self-Interactions Through Observations of Massive Black Hole Mergers

Though the nature of dark matter remains elusive, two models have come to prominence with testable predictions: cold dark matter (CDM) and self-interacting dark matter (SIDM). While CDM remains the widely accepted model, SIDM was introduced to potentially help resolve the discrepancies between the predictions of the CDM model and observational data, in particular the predicted central density profiles. Previous work involving simulations of small numbers of Milky Way-mass galaxies shows that SIDM with a constant cross section of 1 $\rm{cm^2/g}$ delays massive black hole (MBH) mergers as compared to CDM when the host halo has a flattened central density profile. In this work, we use mock gravitational wave observations of MBH mergers to test LISA's capability to indirectly probe dark matter physics. As a proof of concept, we use zoom-in simulations of two galaxy evolutionary histories to show that LISA may be able to distinguish (with a p--value $\leq$ 0.05) between CDM and SIDM with a short-range interaction and a constant cross section of 1 $\rm{cm^2/g}$, provided at least $\sim70$ MBH mergers are observed with signal-to-noise ratios greater than 10. Given our small sample size, this should be regarded as illustrative, rather than definitive. We emphasize that our work does not consider more realistic models with a velocity-dependent cross section, though our exploratory work shows that LISA may provide a pathway to probe dark matter self-interactions, motivating future work with more realistic, currently-favored models and larger simulation suites.

astro-ph.CO↗

arXiv2025

Cosmological Impacts of Black Hole Mergers: No Relief in Sight for the Hubble Tension

The values of the Hubble constant inferred from local measurements and the cosmic microwave background (CMB) exhibit an approximately 5 sigma tension. Some have suggested this tension is alleviated if matter is converted to dark radiation via dark matter decay. As it is not clear that dark matter decays, we instead examine the effects of converting matter to gravitational radiation via black hole mergers. We consider mergers of supermassive black holes (SMBHs), mergers of stellar-mass black holes, and the formation of SMBHs from mergers of smaller black holes. We find that these processes cannot alleviate the tension, as an unrealistically large merger rate, or an overproduction of SMBHs is required. We also consider whether one can use the Integrated Sachs-Wolfe effect to constrain mechanisms that form SMBHs from mergers of smaller black holes. We find that this is also too small to be viable.

astro-ph.CO↗