arXiv subjects

Stefano Profumo

Publications and source records attributed to Stefano Profumo.

At least 37 records · Page 2Linked to original sources

arXiv2026

What Are Pulsar Companions Made of? Using Gravitational Tides to Probe Their Compositions

Low eccentricity, short orbital period pulsar companions may provide a probe to study novel dense and stable exoplanet internal compositions due to the potentially significant orbital evolution they experience caused by strong gravitational tides. We model the tidal characteristics such as apsidal motion constants, orbital precession, and tidal deformability for a variety of equations of state to be compared with values recovered via pulsar timing for a sample of four systems: PSR J1719-1438b, PSR J0636+5128b, PSR J2322+2650b, and PSR J1807-2459A b. With this method, we hope to place stringent limits on the chemical and structural composition of these objects. Through limiting the internal composition of pulsar companions, we aim to elucidate their unique history and formation.

astro-ph.HE↗

arXiv2026

The Cosmic Horizon of Neutrinos

The persistent discrepancy between the experimental measurement and the Standard Model (SM) prediction of the muon's anomalous magnetic moment $(g-2)_μ$ remains one of the most intriguing hints of physics beyond the SM. A well-motivated explanation involves a light $Z'$ gauge boson associated with a broken $U(1)_{L_μ- L_τ}$ symmetry. Such a boson not only resolves the $(g-2)_μ$ anomaly, but also induces resonant interactions between high-energy cosmic neutrinos and the cosmic neutrino background (C$ν$B), potentially shaping the observable neutrino flux at Earth. In this work, we explore the implications of such interactions for the cosmic propagation of high-energy neutrinos. We compute the optical depth for neutrino attenuation via $Z'$-mediated scattering, accounting for neutrino masses, hierarchies, and thermal distributions. We delineate the regions in $(m_{Z'}, m_ν)$ space where the optical depth exceeds unity, defining a ``neutrino cosmic horizon'' beyond which high-energy neutrinos are significantly attenuated. We confront these results with the parameter space required to simultaneously explain the muon $g-2$ anomaly and ease the Hubble tension via an additional contribution to the effective number of relativistic degrees of freedom, $ΔN_{\mathrm{eff}} \simeq 0.2-0.5$. Our analysis reveals a consistent region in parameter space where all three phenomena-$(g-2)_μ$, $N_{\mathrm{eff}}$, and high-energy neutrino attenuation-can be explained by the same light mediator. These findings motivate future searches for spectral features in IceCube and its next-generation successors as indirect probes of new physics in the neutrino sector.

hep-ph↗

arXiv2026

The Scoured Spike: Suppression of Indirect Dark Matter Signals by a Hidden Companion

A massive ``dark companion'' -- such as an intermediate-mass black hole or other compact dark object -- orbiting the supermassive black hole at the Galactic Center can dynamically reshape the surrounding dark-matter spike. Through gravitational heating and angular-momentum exchange, the companion excavates a ``scoured'' region that lowers the inner density and suppresses the expected annihilation signal. We quantify this effect by computing the suppression of the dark-matter annihilation $J$-factor induced by such a companion, combining an analytic scouring-radius model with full numerical integrations of the modified density profile. We scan the parameter space of companion mass, orbital separation, system age, and spike slope, explicitly including the interplay with the annihilation plateau. \textcolor{black}{For canonical Gondolo--Silk spikes with $γ_{\rm sp} \gtrsim 2$, the scouring radius grows only weakly with injected energy because the binding energy is concentrated at small radii; however, once scouring occurs, the $J$-factor suppression can be substantial, for sufficiently massive or long-lived companions. In the shallower-spike regime with $γ_{\rm sp} \lesssim 2$, the same companion drives $r_{\rm scour}$ to much larger multiples of $R_{\rm core}$, and even a modest ${\sim}10^{4}\,M_\odot$ companion on a $\mathcal{O}(100)\,{\rm AU}$ orbit and $\mathcal{O}({\rm Gyr})$ age can suppress the annihilation flux by one to two orders of magnitude. Whether a steep spike is significantly suppressed therefore depends on the companion's mass and lifetime, not merely on the sign of $(2-γ_{\rm sp})$.} The numerical results are accurately captured (typically at the $\lesssim 10\%$ level) by a simple fitting formula in terms of a dimensionless scouring parameter that measures the ratio between the scoured region and the annihilation core. [...]

astro-ph.HE↗

arXiv2026

Quantum Tunneling of Primordial Black Holes to White Holes: Rates, Constraints, and Implications for Fast Radio Bursts

We calculate the present-day and cosmological volumetric rate of primordial black hole (PBH) quantum tunneling events to white holes, incorporating the competition between Hawking evaporation and tunneling, cosmological depletion, realistic mass-dependent abundance constraints, extended mass functions, and the alternative memory-burden scenario. The burst rate is maximized along a narrow ridge in the mass--tunneling-parameter plane where the effective PBH lifetime is comparable to the age of the Universe. Within the canonical Planck-star range of tunneling timescales, FRB-level rates arise only in two highly restricted regions: a low-mass window near the evaporation boundary, and a narrow sequential window where evaporation precedes tunneling; broadening the PBH mass function does not qualitatively alter this conclusion. We further assess observational constraints from FRB repetition statistics, radio spectral properties, prompt and diffuse gamma-ray limits, host-galaxy demographics, and gravitational-wave signatures. All current observations are consistent with a subdominant white-hole contribution to the FRB population but strongly disfavor a dominant origin. The rate calculation does not generically support FRB-level event densities, and any viable FRB interpretation requires narrow, fine-tuned, and strongly assumption-dependent corners of parameter space.

gr-qc↗

arXiv2026

Structure Formation with Dark Magnetohydrodynamics

Long-range interactions in the dark sector can give rise to collective plasma phenomena that are capable of modifying the evolution of dark matter halos. We present the first study of gravitational collapse in a secluded dark $U(1)_D$ model using a magnetohydrodynamic description of the dark matter. We show that dark magnetic fields generate an anisotropic pressure that alters the Jeans scale and suppresses small-scale power in a direction-dependent manner. For a range of primordial magnetic spectral indices, this effect produces distinctive modifications to the linear matter power spectrum. We find that current observations cannot yet constrain viable dark magnetic fields, as CMB tensor modes mostly provide more stringent constraints. Nevertheless, forthcoming high-resolution probes of the matter power spectrum (CMB-HD lensing, HERA, and EDGES) will be able to test these predictions and are sensitive to dark charge-to-mass ratios in the range $10^{-20}\,\text{GeV}^{-1}\lesssim q_χ/m_χ\lesssim 10^{-14}\,\text{GeV}^{-1}$.

hep-ph↗

arXiv2026

Little Red Dots from Ultra-Strongly Self-Interacting Dark Matter

We investigate the possibility that the recently identified population of high-redshift, obscured quasars - known as "Little Red Dots" (LRDs) - originates from early black hole seed formation driven by ultra-strongly self-interacting dark matter (uSIDM). In this framework, dark matter halos undergo gravothermal core collapse due to large self-interaction cross sections, resulting in the rapid formation of massive black hole (BH) seeds with masses $\gtrsim 10^{5} M_\odot$ at redshifts $z \gtrsim 5$. We develop a semi-analytic model that tracks the evolution of the dark matter halo population, the redshift of collapse $z_{\rm coll}$, and the corresponding BH mass function. Black hole growth is modeled stochastically via a log-normal Eddington ratio distribution and a finite duty cycle. We find that the uSIDM scenario naturally reproduces key observed properties of LRDs, including their abundance, compactness, and characteristic BH masses, while offering a mechanism for early, obscured black hole formation that is difficult to achieve in standard CDM-based models. The predicted SMBH mass function at $z \sim 5$ shows excellent agreement with LRD observational data and SIDM merger-tree simulations, particularly at the high-mass end $(m_{\rm BH} \gtrsim 10^{7} M_\odot)$. These results suggest that LRDs may serve as powerful observational tracers of exotic dark sector physics and that SMBH formation in the early universe could be significantly shaped by non-gravitational dark matter interactions.

astro-ph.GA↗

arXiv2026

Probing Planck-Scale Physics with High-Frequency Gravitational Waves

We develop a framework for testing quantum gravity through the stochastic gravitational-wave background produced by evaporating near-Planck-mass primordial black holes. Because gravitons free-stream from the emission region without rescattering, they preserve a direct spectral record of the black-hole temperature--mass relation $T(M)$, a relation that is erased for all other Hawking-radiated species by rapid thermalization. We translate six representative phenomenological beyond-semiclassical frameworks (the generalized uncertainty principle, loop quantum gravity, noncommutative geometry, asymptotic safety, string/Hagedorn physics, and tunneling backreaction) into distinct $T(M)$ parametrizations and compute the resulting gravitational wave spectra numerically. Modifications that suppress $T(M)$ shift the spectral peak by up to ten decades in frequency, in some cases into the sensitivity bands of next-generation interferometers or resonant-cavity detectors, while models imposing a hard evaporation cutoff produce distinctive peak morphologies that discriminate between quantum-gravity scenarios. We further discuss the impact of different choices for post-inflationary conditions in the very early universe. We find that the relative spectral displacement between the standard Hawking prediction and any modified model is cosmology-independent, hence spectral shape rather than absolute peak frequency provides the cleanest probe of Planck-scale physics.

hep-ph↗

arXiv2026

Constraints on Primordial Black Holes from $N$-body simulations of the Eridanus II Stellar Cluster

The evolution of old, compact stellar structures provides strong constraints on macroscopic dark matter candidates such as primordial black holes. In view of recent observational data for the Eridanus II dwarf galaxy, we perform the first $N$-body simulations of its central stellar cluster to model dynamical heating by PBHs. We find evidence that such candidates must be lighter than about one solar mass if they constitute the totality of the dark matter. We additionally derive constraints on the fraction of the dark matter in macroscopic objects as a function of mass, by modeling the remainder of the dark matter as standard, fluid-like cold dark matter.

astro-ph.CO↗

arXiv2025

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 $b_{\rm{eff}}\sim4.5$, thus we infer that LRDs seeded by uSIDM would populate halos of typical masses $\sim 8\times10^{10}~M_{\odot}$; 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↗

arXiv2025

Precision gravity constraints on large dark sectors

General relativity, treated as a low energy effective field theory, predicts quantum corrections to Newtons law of gravitation arising from loops of matter and graviton fields. While these corrections are negligible for the Standard Model particle content, the situation changes dramatically in the presence of a hidden or dark sector containing a very large number of light degrees of freedom. In such cases, loop induced modifications to the Newtonian potential can accumulate to levels testable in laboratory and astrophysical probes of gravity at short distances. In this work we systematically derive and constrain the impact of large dark sectors on precision tests of Newtons law, translating effective field theory predictions into the experimental language of Yukawa type deviations and inverse square law deformations. By mapping precision fifth force constraints onto bounds on species multiplicities and masses, we show that current and forthcoming experiments already impose nontrivial constraints on the size and structure of hidden sectors coupled only gravitationally. For truly massless hidden states, present data still permit multiplicities as large as 1e61, with modest spin dependence; for finite masses the constraints reduce to the familiar short range Yukawa parameterization. Our results provide a model independent framework for confronting dark sector scenarios with precision gravity data and clarify how non minimal scalar couplings, potential higher derivative poles at large species number, and Kaluza Klein towers fit within this picture. The approach is complementary to cosmological probes: Big Bang Nucleosynthesis and the Cosmic Microwave Background constrain relic abundances under specified production histories, whereas laboratory tests constrain the spectrum of light states irrespective of their cosmological population.

hep-ph↗

arXiv2025

Through the Heliospheric Lens: Directional Deflection of High-Energy Cosmic-Ray Electrons and Positrons

We investigate how the large-scale heliosphere alters the arrival directions of high-energy cosmic-ray electrons and positrons and ask if and when this "heliospheric lens" can be ignored for anisotropy and source-association studies - an especially timely topic given, for instance, the persistent cosmic-ray positron fraction and its unknown origin. Using a modular back-tracing framework, we explore a set of widely used magnetic-field descriptions-from a Parker spiral baseline to more structured configurations that include latitudinal wind contrasts, Smith-Bieber-type azimuthal strengthening, and tilted or wavy heliospheric current sheets. We model the deterministic deflections of high-energy cosmic-ray electrons and positrons (CREs) induced by large-scale heliospheric magnetic-field structures using a back-tracing approach. Our results apply to CREs above tens of GeV, where diffusion, convection, and adiabatic energy losses play a subdominant role; these processes are neglected in the present study and will be addressed in future work. Across these models the picture is consistent: most bending is accumulated within the inner tens of astronomical units and decreases rapidly with energy. Field choices and solar-cycle geometry set the overall normalization, with stronger spiral winding or a more highly tilted current sheet producing larger deflections at the same energy. Differences between electrons and positrons are most apparent at lower energies, where drift histories and current-sheet encounters diverge, and become increasingly small at multi-TeV energies. [...]

astro-ph.HE↗

arXiv2025

Backwards Gamma-Ray Bursts: Searching for Exploding Primordial Black Holes in Short-Duration GRB Catalogs

We present a systematic search for signatures of terminal black-hole evaporation in short gamma-ray burst (sGRB) catalogs. An exploding primordial black hole (PBH) undergoing final-stage Hawking radiation is predicted to produce a distinctive "backwards burst"-a very short, spectrally hard transient with monotonically increasing flux and little or no longer-wavelength afterglow. We develop a forward-modeling framework that directly compares theoretical PBH evaporation light curves, computed with full Standard Model particle content and detector response folding, against empirical GRB pulse templates. Analyzing 39 well-characterized Swift sGRBs with non-detected or extremely faint afterglows, we find that all events exhibit fast-rise, slow-decay temporal profiles inconsistent with the PBH prediction. Model comparison via Akaike and Bayesian information criteria decisively favors conventional FRED or ERCA fits over the PBH template for every burst. No candidates for terminal PBH evaporation are identified. The null result yields an upper bound on the local PBH explosion rate density $R_{\mathrm{PBH}} \lesssim 10^5~\mathrm{pc}^{-3}~\mathrm{yr}^{-1}$, comparable to constraints from dedicated TeV $γ$-ray searches. Our methodology establishes a robust template-matching approach that can be scaled to larger multi-instrument catalogs, providing a foundation for future searches targeting this unique signature of quantum gravity and early-Universe physics.

astro-ph.HE↗

arXiv2025

Constraints on a dark matter sub-halo near the Sun from pulsar timing

Using pulsar accelerations, we identify and constrain the properties of a dark matter sub-halo in the Galaxy for the first time from analyzing the acceleration field of binary and solitary pulsars. Our MCMC calculations show that this sub-halo has a mass of $2.45^{+1.07}_{-0.96} \times 10^{7}~M_{\odot}$ and is located at Galactocentric coordinates $X = 7.43^{+0.2}_{-0.12}~\rm$ kpc, $Y = 0.38^{+0.11}_{-0.16} ~\rm kpc$, $Z = 0.21^{+0.06}_{-0.11} ~\rm kpc$, using flat, uninformative priors, where we have modeled the sub-halo as a compact object. The Bayes factors for the models are in the range of $\sim$ 20-40, which indicates tentative evidence (though not yet decisive) for the sub-halo. Modeling the sub-halo with a NFW profile gives a sub-halo mass within the scale radius (0.1 kpc) of $0.48^{0.15}_{-0.16} \times 10^{7} M_{\odot}$, located at $X = 7.47^{+0.21}_{-0.14}$, $Y=0.38^{+0.11}_{-0.16}$, $Z=0.21^{+0.06}_{-0.11}$. We examine \textit{Gaia} data and the atomic and molecular hydrogen data of our Galaxy and show that the measured deviation from a smooth potential cannot arise from the gas or the stars in our Galaxy. By analyzing the full sample of binary pulsars with available acceleration measurements, we find that massive (with mass $>10^{8}~M_{\odot}~$) sub-halos are disfavored for the Milky Way within several kiloparsec of the Sun. Smaller sub-halos are beyond the reach of current direct acceleration measurements. The presence of a $\sim 10^{7}~M_{\odot}$ sub-halo within a few kpc of the Sun is potentially consistent with the expected number counts of sub-halos in the prevailing $Λ$CDM paradigm, for a substantial sub-halo mass fraction. This work now provides a proof of principle for probing nearby, low-mass sub-halos, and has implications across many fields of astrophysics - from understanding the nature of dark matter to galaxy formation.

astro-ph.GA↗

arXiv2025

Dark-sector modifications to Kerr and Reissner-Nordstrom black hole evaporation

We present a comprehensive comparative analysis of the evaporation dynamics of Schwarzschild, Kerr, and Reissner- Nordstrom black holes, focusing on the evolution of their mass, charge, and angular momentum, using detailed calculations of the corresponding Page factors. We investigate the evolution of black holes during the evaporation process, emphasizing how these quantities evolve relative to one another. Our study incorporates the effects of greybody factors, near-extremal conditions, and the introduction of additional particle species beyond the Standard Model. We demonstrate that the addition of particle degrees of freedom may significantly alter the evaporation hierarchy, potentially leading to scenarios in which the effective black hole charge increases during evaporation. Additionally, we examine the impact of Schwinger pair production and of super-radiance on charged, spinning black hole evaporation. These findings offer new insights into the complex interplay between different black hole parameters during evaporation and highlight the importance of considering additional particle species in the process.

gr-qc↗

arXiv2025

On the (Im)possibility of Electrically Charged Planck Relics

I revisit whether black-hole remnants, from sub-Planckian compact objects to Planck relics and up to (super)massive black holes, can preserve Standard-Model (SM) electric charge. Two exterior-field mechanisms -- Coulomb-focused capture from ambient media and QED Schwinger pair production -- robustly neutralize such objects across cosmic history. I first derive the general capture rate including both Coulomb and gravitational focusing, and sum the stepwise discharge time in closed form via the trigamma function, exhibiting transparent Coulomb- and gravity-dominated limits. I then integrate the Schwinger rate over the near-horizon region to obtain an explicit $\dot Q(Q)$ law: discharge proceeds until the horizon field falls below $E_{\rm crit}$, leaving a residual charge $Q_{\rm stop}^{(e)}\!\propto\! r_h^2$ that is $\ll e$ for Planck radii. Mapping the mass dependence from sub-Planckian to astrophysical scales, I also analyze dark-sector charges with heavy carriers (including kinetic mixing and massive mediators). In a conservative ``no-Schwinger'' limit where vacuum pair creation is absent, cumulative ambient exposures alone force discharge of any integer SM charge. Three possible loopholes remain. (i) A fine-tuned SM corner in which the relic sits arbitrarily close to Reissner-Nordström extremality so greybody factors suppress charged absorption, while Schwinger pair creation is absent due to Planck-scale physics. (ii) Charge relocated to a hidden $U(1)_D$ with no light opposite carriers, e.g. if the lightest state is very heavy and/or kinetic mixing with $U(1)_{\rm EM}$ is vanishingly small. (iii) Discrete or topological charges rather than ordinary SM electric charge. Outside these cases, the conclusion is robust: within SM electromagnetism, charged black-hole relics neutralize efficiently and cannot retain charge over cosmological times.

hep-ph↗

arXiv2025

Chemical and Kinetic Equilibrium in Cosmology: Facts and Myths

We clarify that chemical and kinetic equilibration in the early Universe are distinct: neither implies the other, and the ordering of their decouplings need not be universal. We illustrate this with Standard-Model neutrino decoupling, strong-washout leptogenesis, dark-matter scenarios where kinetic decoupling precedes chemical freeze-out (resonant/forbidden, conversion/coannihilation, coscattering), and dark sectors at with temperatures distinct from the visible-sector temperature, with semi-annihilation or 3 $\to$ 2 cannibal dynamics. The moral of the story is simple: Chemical equilibrium governs numbers, kinetic equilibrium governs shapes. In an expanding Universe the operators that control them rarely fade at the same time, and when they do not, the order of decoupling is model dependent. Turning to phase-space evolution whenever momentum selectivity matters is the surest way to obtain robust cosmological predictions.

hep-ph↗

arXiv2025

A New Census of the Universe's Entropy

The question of what is the total entropy of the universe, how it compares to the maximal entropy of de Sitter space, and how it is distributed across the universe's components, bears considerable importance for a number of reasons. Here, we first update the computation of the entropy associated with various sectors of the observed universe, including in the diffuse cosmic and late-time gamma-ray and neutrino backgrounds, in baryonic matter both in diffuse components, in stars and stellar remnants, and in cosmic rays; we then update, crucially, the estimate of entropy in stellar-mass and super-massive black holes, whose abundance and mass function has come into increasingly sharp definition with recent observations and with the rapidly growing statistics of black-hole-black-hole mergers observed with gravity wave detectors. We also provide a new, corrected estimate of the potential entropy associated with a stochastic gravitational wave background, with dark sector radiations, and with several dark matter models. Finally, we utilize the similarly recently updated constraints on the abundance of hypothetical primordial black holes - black holes, that is, of non-stellar origin - to assess the maximal amount entropy they could store. We find that if supermassive primordial black holes exist, they can dominate the entropy budget of the universe consistently with current constraints on their abundance and mass function, to a level potentially not distant from the posited entropy associated with the cosmic event horizon of de Sitter spacetime. The same conclusion holds for certain dark sector models featuring a large number of dark degrees of freedom.

astro-ph.CO↗

arXiv2025

A Multi-Wavelength Survey of Transient Lensing Opportunities for Primordial Black Hole Searches

Gravitational lensing of short astrophysical transients provides a uniquely direct avenue for searching for primordial black holes (PBHs) across a vast range of masses. While past search efforts have focused on particular source classes-such as fast radio bursts (FRBs) and gamma-ray burst spikes-no systematic, multi-wavelength assessment has compared their relative potential for PBH discovery. We present here a broad assessment of transient lensing search opportunities, spanning more than twenty decades in photon frequency and over twelve orders of magnitude in PBH mass. For each class, we determine the accessible PBH mass window by accounting for wave-optics suppression and time-delay resolution limits, and we estimate potential sensitivities to the PBH abundance using representative event rates, distances, and optical depths. Our survey includes low-frequency radio events (FRBs, pulsar giant pulses, planetary cyclotron bursts), optical/infrared signals, and high-energy phenomena (gamma-ray burst spikes, fast X-ray transients, TeV blazar flares). We synthesize these results in a unified mass-abundance diagram and comprehensive tables summarizing both physical reach and observational requirements. This work serves as a roadmap for optimizing future multi-wavelength lensing searches, guiding the design of instruments and strategies to explore the PBH dark matter hypothesis across its remaining viable parameter space.

astro-ph.HE↗