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Stefano Profumo

Publications and source records attributed to Stefano Profumo.

At least 19 recordsLinked to original sources
arXiv2026

Same Events, Weaker Bound: Model Dependence in Magellanic Microlensing Limits on Primordial Black Holes

OGLE microlensing of the Magellanic Clouds sets the leading bounds on primordial black holes (PBHs) as dark matter from $10^{-8}$ to $10^{3}\,M_\odot$. Holding the detected events and survey efficiencies fixed, we show that changes to the Milky Way halo, the stellar lens populations and the Large Magellanic Cloud halo, each motivated by recent data, weaken the published strict 20-year bound by up to $\simeq6$, and by over an order of magnitude in an extreme stress test. With primordial clustering, the planetary-mass bound weakens by a factor $3.4$--$6$. We strongly recommend that compact-object dark matter limits be quoted together with their modeling assumptions and, generally, be derived under conservative assumptions.

astro-ph.CO↗
arXiv2026

From Axion Detection to Dark Matter Astronomy

A global haloscope network could turn an axion discovery into astronomy of dark matter substructure and transients. We combine interferometric phase, spatial coherence, and spectroscopy to study the formation and evolution of axion substructure through measurements of flow directions and velocity distributions. For tidal streams, a four-site forecast shows how longitudinal and transverse velocity dispersions can be measured jointly. Interpreted with dynamical and population models, these measurements could test axion production scenarios. Extensions to miniclusters, axion stars, and emitted bursts would broaden the astrophysical reach of laboratory detection.

hep-ph↗
arXiv2026

High-frequency gravitational wave transients from superradiance

Ultralight bosons can form macroscopic gravitational-atom clouds around rotating black holes via superradiance, sourcing quasi-monochromatic gravitational waves through level transitions and annihilation. Primordial black holes provide a natural setting for such systems in a frequency range relevant for resonant-cavity experiments. We present a unified treatment of gravitational-wave emission from both isolated and binary-perturbed gravitational atoms in this regime. For isolated systems, we derive analytic expressions for the time- and frequency-domain strain from transition and annihilation channels, emphasizing their narrow-band structure. For binaries, we model resonantly driven level transitions using the Landau--Zener formalism and compute the resulting transient signals. We find that, while binary-driven transitions generically yield signals with durations compatible with detector response times, their characteristic strain lies well below the sensitivity of current experiments at astrophysically plausible distances, and event rates further suppress detectability by requiring sources at unrealistically small separations. We quantify the improvements in sensitivity, bandwidth, and response needed to render these signals observable, and identify gravitational-atom systems around primordial black holes as a theoretically well-motivated target for future high-frequency gravitational-wave searches.

gr-qc↗
arXiv2026

The Clustering of Little Red Dots from Ultra-Strongly Self-Interacting Dark Matter

We predict the effective clustering bias parameter, $b_{\rm{eff}}$, at $z\sim5$ for Little Red Dots (LRDs) seeded by Ultra-Strongly Self-Interacting Dark Matter (uSIDM). From our model, we find that $b_{\rm{eff}}\sim3.6$, thus we infer that LRDs seeded by uSIDM would populate halos of typical masses $\sim 6.3\times10^{10}~M_{\odot}$; this bias factor is consistent with LRDs being a distinct population from high redshift quasars. To the extent that we are aware, this is the first formation-based theoretical prediction of LRD clustering from a model consistent with the LRD mass function. We find that this bias and clustering is insensitive to a wide range of the underlying uSIDM microphysics parameters, including the uSIDM cross-section $σ/m$ and uSIDM fraction $f$. This is therefore a robust prediction from the uSIDM model, and will allow for direct probes of the uSIDM paradigm as the origin of LRDs in the next few years. Upcoming \texttt{JWST} observations will constrain the population of LRDs, including directly measuring their clustering.

astro-ph.CO↗
arXiv2026

Black Holes as Frequency-Dependent Filters of Stochastic Gravitational Waves

Black holes ring when perturbed, whereas their response to a stationary gravitational-wave background is a real-frequency scattering problem, not a source of additional quasi-normal-mode lines. We make this standard distinction quantitative by treating a black hole as a frequency-, angle-, and polarization-dependent filter. For an isotropic stationary background around Schwarzschild holes, elastic scattering produces no net monopole signal, so horizon absorption is the only population-level spectral distortion. We calculate this transfer function for Schwarzschild holes in detail, identify its absorptive and phase-delay signatures, and connect the stationary response to the causal ringdown excited by a finite wave packet. We then promote the single-hole result to an angular and polarization transport kernel for a cosmological population. The resulting optical depth is negligible for realistic black-hole populations, including asteroid-mass primordial black holes comprising all dark matter. We then extend the analysis to Kerr holes, for which superradiance allows genuine amplification in selected co-rotating modes, but isotropic incidence and random spin orientations strongly dilute the diffuse signal. Observable effects are therefore more likely in rare, nearby, aligned, rapidly spinning, or transiently illuminated systems than through cumulative cosmological propagation.

gr-qc↗
arXiv2026

The Galactic Dynamics of Free-Floating Planets: From Ejection Kicks to Microlensing

Free-floating planets (FFPs) may retain dynamical signatures of the mechanisms that eject them from their host systems. We integrate $10^6$ collisionless FFP test particles for $10^8$~yr in a static, phenomenological Galactic potential, comparing a mass-independent kick model with a mass-coupled prescription ($σ_{\rm CB}\propto M^{-0.15}$, $v_{\rm PL}\propto M^{-0.5}$) against a matched no-kick control. The imposed mass dependence is recovered at injection, with the combined-channel median coupled kick decreasing from $10.716$ to $0.708~{\rm km\,s^{-1}}$ across five mass bins---a factor of $\sim15.1$. A mass-dependent trend remains visible after $100$~Myr of Galactic propagation in the matched kicked-versus-control displacement, whose median decreases from $0.7001$ to $0.0539$~kpc across the same bins. The remaining numerical distinction is concentrated in this mass-resolved differential displacement rather than in the bulk phase-space moments: the final velocity dispersions of the null and coupled kicked populations are nearly identical, only a few percent of particles leave the adopted disk region, and the fraction of particles satisfying the formal Galactic-unbound criterion ($E_i>0$) remains negligible in every diagnostic we report. Comparing each kicked population against its matched no-kick control shows that much of the overall kinematic heating arises from the evolution of the initially warm, nonequilibrium disk rather than from the ejection kick itself, isolating the kick's smaller contribution.

astro-ph.EP↗
arXiv2026

Self-Similar Mass Spectra of Hierarchical Black Hole Mergers

Black holes that merge repeatedly carry a record of that history in their mass distribution. We treat hierarchical merging as a coagulation problem, in which a single kernel encodes how the merger rate depends on the masses involved and on cosmic time, and we derive the late-time spectra that such populations approach. The framework yields closed scaling laws, an exactly solvable benchmark, and a classification of merger environments by a single exponent measuring how strongly mergers favor or suppress massive participants. Applying it to primordial black holes requires care in translating published merger rates into kernel form; done correctly, three of the four standard binary-formation channels map onto superlinear kernels and are therefore candidates for runaway growth, in which the heaviest objects would dominate and no steady mass-conserving spectrum exists; establishing physical gelation, however, requires the full population-dependent kernel and its finite coagulation history, neither of which we settle here. Only the early three-body channel maps into the nongelling regime and admits slow self-similar growth. Numerical solutions across thirteen suppressive, nongelling kernels show that the shape of the spectrum is not fixed by the scaling exponent alone, and that accounting for the energy radiated at each merger measurably changes the high-mass cutoff and drains the population's total black-hole mass.

astro-ph.HE↗
arXiv2026

Right Energy, Wrong Profile: Why the 43 GeV Cluster Line Is Unlikely to Be Dark Matter

A narrow gamma-ray line would be a distinctive signature of dark matter, but its interpretation depends as much on its spatial distribution as on its energy. We reanalyze the reported 43 GeV feature in Fermi-LAT observations of Virgo, Fornax, and Ophiuchus. The excess is reproduced in the same public data and survives event-type partitions, a test using data withheld from the original selection, and detector-coordinate permutation tests. Realistic hadronic and inverse-Compton emission is too broad to explain it. A spatial--spectral likelihood analysis restricted to Good Time Intervals and including diffuse backgrounds and catalogued sources finds a broad line-like component. Uniform surface brightness and substructure-enhanced annihilation are preferred, whereas smooth NFW annihilation and a central point source are unlikely explanations. An independent annular analysis agrees: the events associated with the excess extend through much of the virial region. Calibration over 20--70 GeV and five morphologies gives a conditional global significance of approximately $2.7σ$, peaking at 44.5 GeV for uniform brightness. This result is conditional on the preselected three-cluster sample. The broad morphology is the main obstacle to a dark-matter interpretation. Such an interpretation would require photons to be a leading annihilation channel, annihilation to remain efficient in cold subhalos, and subhalos to supply nearly all the cluster luminosity. Yet a boost consistent with $Λ$CDM drives the required two-photon cross section into the range most tightly constrained by Galactic-halo line limits. The most likely explanation is a chance fluctuation amplified by analysis and target-selection effects, possibly compounded by residual Galactic diffuse or unresolved-source mismodeling; if celestial, its morphology makes a simple dark-matter interpretation unlikely.

astro-ph.HE↗
arXiv2026

Low-energy antinuclei measurements for background-free indirect dark matter searches and PBH signatures

Light low-energy cosmic ray antinuclei constitute powerful probes for detecting dark matter or other sources of new physics in our Galaxy. This ASTRA Initiative Mission Concept reviews the theoretical motivation, highlighting the transformative potential and current experimental status. Motivated by exciting tentative results, it makes a clear case for the need for the next flagship mission to confirm or refute claims of cosmic antinuclei as signs of new physics.

astro-ph.HE↗
arXiv2026

Ultra-Strongly Self-Interacting Dark Matter: From Phenomenology to Astrophysical Observables

We develop a minimal, testable framework for two-component self-interacting dark matter (SIDM) in which a dominant, moderately self-interacting species coexists with an ultra-strongly self-interacting subcomponent (uSIDM). A light vector mediator induces velocity-dependent self-scattering, while early-universe dynamics - standard $2 \to 2$ annihilation supplemented by interconversion $χ_1χ_1 \to χ_2χ_2$ - determine the relic abundance analytically. From observations of dwarf and low surface brightness galaxy rotation curves, as well as strong cluster lensing, we place constraints on the microphysics parameters. From these constrained regions, we map the microphysics to effective \texttt{ETHOS} parameters and evolve the linear power spectrum in \texttt{CLASS}. We identify a region where: (1) the SIDM dominant component attains $σ_{\rm{eff}}/m = 20 - 40~\text{cm}^{2}\text{g}^{-1}$ at dwarf velocities while satisfying cluster upper bounds $σ_{\rm{eff}}/m < 0.13~\rm{cm}^{2}\rm{g}^{-1}$; (2) a subpercent uSIDM fraction drives accelerated gravothermal collapse in early halos, providing seeds relevant to high-redshift quasar formation and ``little red dots''; and (3) the small-scale cutoff in the matter power spectrum remains consistent with Lyman-$α$ and satellite counts, but exhibits non-standard features, potentially discernible with future observations. The allowed space can be organized by the mediator-to-DM mass ratio and the late-time uSIDM fraction, with a narrow window singled out by the combined cosmological and astrophysical requirements.

hep-ph↗
arXiv2026

Dark Baryon Black Holes

We explore a novel mechanism for dark matter production through the formation of light black holes from the collapse of dark baryons in confining SU(N) gauge theories in the large $N$ limit. While glueballs and mesons cannot form black holes under physically reasonable conditions, we prove that for appropriate ranges of the confinement scale, quark masses, number of colors $N$, and dark sector temperature, dark baryons can produce Planck-scale black hole relics in the early universe. Assuming the relics are stable, the abundance of both the dark baryon black hole population directly arising at confinement and that frozen in from dark glueball and meson pair annihilation are exponentially suppressed in $N$, leading to an upper limit $N\lesssim 100$ and of a few hundreds Planck units in mass for models where the black hole relics are the entirety of the dark matter. We present a detailed numerical study of the parameter space where this scenario is realized.

hep-ph↗
arXiv2026

Kick Velocities and Mass Function of Free-Floating Planets from Dynamical Ejection in Hierarchical Three-Body Systems

Free-floating planets (FFPs), also known as rogue planets, are sub-stellar objects that travel through the Galaxy unbound to any host star. Their velocity distribution carries information about the dynamical channel that released them from their birth systems, while their mass distribution encodes the underlying abundance of planets available for ejection. We present a suite of direct $N$-body simulations of hierarchical three-body systems consisting of a Solar-mass host star, a massive giant perturber, and a lighter planet treated in the restricted three-body regime. We vary the mass of the ejected planet, the mass of the giant perturber, the light planet's semi-major axis, and the eccentricities of both planets, measuring the asymptotic ejection velocity $v_\infty$ and the finite-radius ejection speed $v_{\rm kick}$ at the first accepted ejection output. The ejected body's mass has little effect on the outcome over four orders of magnitude, confirming the test-particle limit. By contrast, the giant-planet mass sets the ejection scale and time, following the secular scaling $t_{\rm ejec}\propto M_J^{-1}$. The eccentricities mainly affect the high-velocity tail rather than the median: a higher light-planet eccentricity extends the kick ceiling to $\sim23$ km/s, while a highly eccentric giant can yield rare kicks near $80$ km/s via pericentre-enhanced slingshot encounters. We interpret these trends with a semi-analytic framework based on Hill-scale scattering, the Tisserand parameter, and an eccentricity-dependent upper envelope for slingshot energy exchange, and discuss how the ejection velocities map onto the Galactic FFP velocity dispersion and how the mass function sets the microlensing timescale distribution relevant for Roman and Euclid.

astro-ph.EP↗
arXiv2026

What Naturalness Measures: Fine-Tuning and Informational Invariants in Cosmology and Dark Matter

Naturalness is commonly presented as an objective constraint on physical theories: a model requiring fine-tuning is judged implausible. This presentation conflates a representation-dependent quantity with an invariant one. A fine-tuning verdict depends on the choice of fundamental parameters, the prior, and the measure convention, so it does not by itself fix a feature of the world. Here, I argue that what is objective is structural: the universality class of the map from parameters to observables, invariant under admissible changes of parametrization and measure convention, and independent of any prior over parameter space; it constitutes an informational invariant. On this account naturalness is neither an aesthetic preference nor an objective probability, but a statement about the distinguishability geometry of the representations through which physics encodes observation. I trace the certainty of naturalness verdicts to a tradition, from Ockham through Dirac and Weinberg, in which parsimony and beauty are taken as guides to truth; modern naturalness inherits that tradition's authority without its successive justifications. The argument is developed in the gravitational and cosmological sector, where naturalness reasoning is sharpest and its effective-field-theory grounding is weakest. A uniform analysis across gravitational and particle dark matter candidates shows that fine-tuning tracks the analytic structure of the abundance map, not the nature of the candidate; that the resulting classification is invariant across measure conventions while the tuning number is not; and that this decomposition instantiates informational structural realism. I situate the position against the autonomy-of-scales account, which the argument largely accepts, and against the deflationary reading, which identifies the borrowed authority but discards the structural residue.

physics.hist-ph↗
arXiv2026

Charting Dark Matter down to the neutrino floor/fog in the 2HD+a scenario

Next-generation direct detection experiments will probe dark matter (DM) scattering cross-sections deep into the neutrino fog, the regime where coherent neutrino scattering becomes an irreducible background. We investigate whether thermally produced weakly interacting massive particles (WIMPs) can naturally populate this regime while satisfying relic density and indirect detection constraints. Adopting as a case study the 2HD+a model, we have performed comprehensive parameter scans over the Type-I and Type-II Yukawa configurations. We have included the limit of strongly suppressed singlet--doublet {\it A-a} mixing sin$θ\! \to \! 0$ and we show that annihilation into {\it ha} and ${\it Ha}$ final states sustains the correct relic density while loop-induced direct detection cross-sections naturally land inside the neutrino fog; in the same limit the light pseudoscalar boson becomes long-lived, featuring displaced-vertex signatures when produced at colliders. Finally, in the case of zero mixing, we have considered a new possibility for DM phenomenology as the $a$ state becomes cosmologically stable and, consequently, an additional DM component. We map all the viable parameter space against current LZ and FERMI-LAT bounds and projected XLZD and CTA sensitivities. We find that the single component setup lies naturally below the neutrino floor for DM masses above 100 GeV while, on the contrary, most of the parameter space of the two component DM scenario is strongly disfavored already considering present limit. The parameter space of both single and two component DM scenario can be nevertheless broadened by considering specific relations among the model parameters to suppress the coupling between the 125 GeV bosons and two $a$ states. Our results represent in any case a motivation to fully exploit future tonne-scale detectors.

hep-ph↗
arXiv2026

Cosmology as Representation: Informational Invariance and the Limits of Scientific Realism

Modern cosmology is often taken to provide an increasingly accurate description of the universe's underlying ontology through progressively refined mathematical models. I challenge this interpretation by arguing that the empirical success of cosmology underdetermines not only ontology but also the mathematical and conceptual frameworks used to represent observational data. I propose instead that the objective content of cosmology is best identified with cross-representational informational invariants-features of observational structure that persist across empirically adequate descriptions. These invariants can be characterized in information-theoretic terms, including correlation structure, statistical distinguishability, and limits on accessible information, and formalized using tools such as the Fisher-Rao metric on model space. On this view, cosmological models are best understood as efficient encodings of observational structure rather than uniquely privileged descriptions of fundamental reality. Scientific progress, accordingly, consists not in convergence toward a fixed ontology, but in the progressive refinement of the informational structure accessible to observation.

physics.hist-ph↗
arXiv2026

Are Primordial Black Holes a Natural Dark Matter Candidate?

Primordial black holes (PBHs) in the asteroid-mass window ($10^{17}$-$10^{22}$ g) can account for all of the dark matter without violating any observational constraint, yet are routinely dismissed as fine-tuned. I put that dismissal to the test by applying three complementary fine-tuning measures uniformly across a broad landscape: three non-inflationary PBH production mechanisms, six classes of inflationary PBH models, and seven particle dark matter benchmarks, all evaluated against the same observable target. Three distinct naturalness universality classes emerge, determined entirely by the analytic structure of the abundance map rather than by the nature of the dark matter candidate. Biased-domain-wall PBHs are as natural as off-resonance weakly interacting massive particles and freeze-in particles; early-matter-domination and first-order phase transition PBH mechanisms occupy an intermediate tier alongside coannihilating WIMPs, unified by a structural identity in which the fine-tuning measure equals the logarithm of the ratio of the formation scale to the matter-radiation equality scale; and single-field ultra-slow-roll inflationary collapse is severely tuned for a distinct reason: a double exponential in which the power spectrum amplitude is itself exponentially sensitive to the inflaton potential coefficients, on top of the exponential collapse sensitivity of the abundance map. My main conclusion is that {\em the claim that PBH dark matter is generically fine-tuned conflates the worst case with a landscape spanning every naturalness tier}. The three-measure protocol also resolves a tension in the recent literature: the Barbieri-Giudice and Iovino-Riotto fine-tuning measures answer complementary questions and are reconciled within the two-layer decomposition developed here.

hep-ph↗
arXiv2026

Polarized and unpolarized synchrotron emission from dark matter in extragalactic targets

We compute 95% confidence-level upper limits on the dark matter annihilation cross section and decay rate from both total-intensity and polarized synchrotron emission in five extragalactic targets: M31, the Large Magellanic Cloud (LMC), the Draco and Sculptor dwarf spheroidal galaxies, and the Coma cluster. Using Planck maps at 30, 44, and 70 GHz, we solve the diffusion-loss equation for dark-matter-produced electrons and positrons numerically with DRAGON and integrate the resulting synchrotron emission along the line of sight with HERMES, computing both total-intensity and polarized-intensity maps for each target with target-specific magnetic-field, gas, and radiation-field environments. The 30 GHz channel yields the most stringent constraints in all cases, and limits on annihilation or decay into $e^+e^-$ are stronger than those for $b\bar{b}$ due to the harder injected spectrum. For most targets the total-intensity and polarized limits are broadly comparable; the LMC is an exception, where Faraday depolarization in the turbulent disk suppresses the polarized signal relative to total intensity, making total intensity the primary estimator. Our results are robust against the choice of flux estimator and coordinate uncertainty. This work demonstrates that microwave polarimetry provides a complementary and largely independent probe of dark matter synchrotron emission in extragalactic targets.

astro-ph.GA↗
arXiv2026

Primordial black holes versus their impersonators at gravitational wave observatories

The detection of primordial black holes (PBHs) would mark a major breakthrough, with far-reaching implications for early universe cosmology, fundamental physics, and the nature of dark matter. Gravitational wave observations have recently emerged as a powerful tool to test the existence and properties of PBHs, as these objects leave distinctive imprints on the gravitational waveform. Notably, there are no known astrophysical processes that can form sub-solar mass black holes, making their discovery a compelling signal of new physics. In addition to PBHs, we consider other exotic compact object (ECO) candidates-such as strange quark stars and boson stars-which can produce similar gravitational signatures and potentially mimic PBHs. In this work, we employ the Fisher matrix formalism to explore a broad parameter space, including binary masses, spins, and a variety of nuclear and quark matter equations of state. Our goal is to assess the ability of next-generation gravitational wave detectors-specifically Cosmic Explorer and the Einstein Telescope-to distinguish PBHs from ECOs, stellar BHs and neutron stars. We compute the maximum luminosity distances at which confident ($\geq 3σ$) detections of sub-solar masses or tidal effects are possible, providing quantitative benchmarks for PBH identification or exclusion under various observational scenarios. Our results indicate that next-generation detectors will be capable of probing sub-solar mass PBHs out to cosmological distances of $z \sim 3$. For heavier objects with masses up to $M \lesssim 2 M_\odot$, we show that PBHs can be distinguished from neutron stars via their lack of tidal effects up to redshifts of $z \sim 0.2$.

astro-ph.CO↗