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Glenn Starkman

Publications and source records attributed to Glenn Starkman.

At least 19 recordsLinked to original sources
arXiv2026

No persuasive evidence yet of gravitational-wave tails from perturbers along the line of sight in LVK observations

Observations of compact binary coalescences (CBCs) by the LIGO-Virgo-KAGRA collaboration resulted in 90 events in the first three observing runs. We search the data near the loudest of these detections for so-called "gravitational glints," by performing Bayesian model comparison. Gravitational glints are gravitational-wave tails caused by interactions between a signal and a spacetime perturber and are theorized to present as echoes of the primary signal. We do not find convincing evidence of gravitational glints in binary black hole or intermediate-mass black hole binary events with a signal-to-noise ratio (SNR) of at least 12. We also found that standard matched-filter CBC searches with template banks that do not contain gravitational glints would likely not have missed signals containing a gravitational glint. We therefore estimate upper limits on the probability of a glint as a function of its relative amplitude and use these estimates to constrain the properties of perturbers in the Universe. With increased sensitivity in the fourth observing run, which will increase the number and SNR of detectable events, we remain optimistic that glints will soon be detectable.

gr-qc↗
arXiv2023

Angular Correlations of Cosmic Microwave Background Spectrum Distortions from Photon Diffusion

During cosmic recombination, charged particles bind into neutral atoms and the mean free path of photons rapidly increases, resulting in the familiar diffusion damping of primordial radiation temperature variations. An additional effect is a small photon spectrum distortion, because photons arriving from a particular sky direction were originally in thermal equilibrium at various spatial locations with different temperatures; the combination of these different blackbody temperature distributions results in a spectrum with a Compton $y$-distortion. Using the approximation that photons had zero mean free path prior to their second-to-last scattering, we derive an expression for the resulting $y$-distortion, and compute the angular correlation function of the diffusion $y$-distortion and its cross-correlation with the square of the photon temperature fluctuation. Detection of the cross-correlation is within reach of existing arcminute-resolution microwave background experiments such as the Atacama Cosmology Telescope and the South Pole Telescope.

astro-ph.CO↗
arXiv2022

How the Universe postpones the evaporation and curtails the quantum spreading of black holes

Black holes are expected to evaporate through the process of Hawking radiation. This process is expected to cause the uncertainty in a black hole's position to grow to $\sim M^2/M_{Pl}^3$ over the course of it's lifetime, even as its momentum spreads only by $\sim M_{Pl}$. For the black holes that have been observed, which have $M\geq M_\odot$, this greatly exceeds the Hubble volume. However, the decay of black holes and their quantum spreading, are delayed in the Universe while the influx of energy into the black holes exceeds their Hawking luminosity. We show that for these $M\geq M_\odot$ black holes, their decay outside galaxies and clusters is prevented far longer than it takes the black holes to be dragged well beyond the Hubble horizon, where their eventual decay occurs away from the prying eyes of any observer who has not hitched a ride with them. Meanwhile, black holes in an observer's galaxy or cluster are themselves prevented from decaying long past the extinction of the last stars, and at least until their galaxy/cluster is swept clean of dark matter, in $\gg 10^{25}$y. Even then, if the black holes become unbound they are dragged beyond the Hubble radius before undergoing significant decay; if not, they remain in bound orbits, spreading at most over a subvolume of the galaxy/cluster, and long localized by scatterings to much smaller volumes.

gr-qc↗
arXiv2022

Milky Way and M31 rotation curves: $Λ$CDM vs. MOND

We analyze the existing rotation-curve data of the Milky Way and M31 galaxies that extends to very large distances and low accelerations. We find a systematic downward trend in the weak acceleration (large distances) segment of the radial acceleration. A similar downward trend has been noticed in the $Λ$CDM EAGLE simulation, while the deviation from the generic MOND prediction would need to be ascribed to an external field effect, or possibly a post facto selected acceleration function $μ(x)$.

astro-ph.GA↗
arXiv2021

Accurate relativistic observables from post-processing light cone catalogues

We introduce and study a new scheme to construct relativistic observables from post-processing light cone data. This construction is based on a novel approach, LC-Metric, which takes general light cone or snapshot output generated by arbitrary N-body simulations or emulations and solves the linearized Einstein equations to determine the spacetime metric on the light cone. We find that this scheme is able to determine the metric to high precision, and subsequently generate accurate mock cosmological observations sensitive to effects such as post-Born lensing and nonlinear ISW contributions. By comparing to conventional methods in quantifying those general relativistic effects, we show that this scheme is able to accurately construct the lensing convergence signal. We also find the accuracy of this method in quantifying the ISW effects in the highly nonlinear regime outperforms conventional methods by an order of magnitude. This scheme opens a new path for exploring and modeling higher-order and nonlinear general relativistic contributions to cosmological observables, including mock observations of gravitational lensing and the moving lens and Rees-Sciama effects.

astro-ph.CO↗
arXiv2021

On the question of measuring spatial curvature in an inhomogeneous universe

The curvature of a spacetime, either in a topological sense, or averaged over super-horizon-sized patches, is often equated with the global curvature term that appears in Friedmann's equation. In general, however, the Universe is inhomogeneous, and gravity is a nonlinear theory, thus any curvature perturbations violate the assumptions of the FLRW model; it is not necessarily true that local curvature, averaged over patches of constant-time surfaces, will reproduce the observational effects of global symmetry. Further, the curvature of a constant-time hypersurface is not an observable quantity, and can only be inferred indirectly. Here, we examine the behavior of curvature modes on hypersurfaces of an inhomogeneous spacetime non-perturbatively in a numerical relativistic setting, and how this curvature corresponds with that inferred by observers. We also note the point at which observations become sensitive to the impact of curvature sourced by inhomogeneities on inferred average properties, finding general agreement with past literature.

astro-ph.CO↗
arXiv2021

Straight Lightning as a Signature of Macroscopic Dark Matter

Macroscopic dark matter (macros) is a broad class of alternative candidates to particle dark matter. These candidates would transfer energy to matter primarily through elastic scattering. A sufficiently large macro passing through the atmosphere would produce a straight channel of ionized plasma. If the cross-section of the macro is $σ_x \gtrapprox 6 \times 10^{-9} cm^2$, then under atmospheric conditions conducive to lightning (eg. a thunderstorm) the plasma channel would be sufficient to seed a lightning strike with a single leader. This is entirely unlike ordinary bolt lightning in which a long sequence of hundreds or thousands of few-meter-long leaders are strung together. This macro-induced lightning would be extremely straight, and thus highly distinctive. Neither wind shear nor magnetohydrodynamic instabilities would markedly spoil its straightness. The only photographically documented case of a straight lightning bolt is probably not straight enough to have been macro-induced. We estimate the region of macro parameter space that could be probed by a search for straight lightning from the number of thunderstorms happening on Earth at any time. We also estimate the parameter space that can be probed by carefully monitoring Jupiter, e.g. using the Hubble Space Telescope. All code and data is available at https://github.com/cwru-pat/macro_lightning.

astro-ph.CO↗
arXiv2020

Macro detection using fluorescence detectors

Macroscopic dark matter (aka macros) constitutes a broad class of alternatives to particulate dark matter. We calculate the luminosity produced by the passage of a single macro as a function of its physical cross section. A general detection scheme is developed for measuring the fluorescence caused by a passing macro in the atmosphere that is applicable to any ground based or space based Fluorescence Detecting (FD) telescopes. In particular, we employ this scheme to constrain the parameter space ($σ_{x} \mbox{ vs} \mbox{ M}_{x}$) of macros than can be probed by the Pierre Auger Observatory and by the Extreme Universe Space Observatory onboard the Japanese Experiment Module (JEM-EUSO). It is of particular significance that both detectors are sensitive to macros of nuclear density, since most candidates that have been explored (excepting primordial black holes) are expected to be of approximately nuclear density.

astro-ph.HE↗
arXiv2020

Antimatter as Macroscopic Dark Matter

Antimatter macroscopic dark matter (macros) refers to a generic class of antimatter dark matter candidates that interact with ordinary matter primarily through annihilation with large cross-sections. A combination of terrestrial, astrophysical, and cosmological observations constrain a portion of the anti-macro parameter space. However, a large region of the parameter space remains unconstrained, most notably for nuclear-dense objects.

astro-ph.CO↗
arXiv2020

Death and Serious Injury by Dark Matter

Macroscopic dark matter refers to a variety of dark matter candidates that would be expected to (elastically) scatter off of ordinary matter with a large geometric cross-section. A wide range of macro masses $M_X$ and cross-sections $σ_X$ remain unprobed. We show that over a wide region within the unexplored parameter space, collisions of a macro with a human body would result in serious injury or death. We use the absence of such unexplained impacts with a well-monitored subset of the human population to exclude a region bounded by $σ_X \geq 10^{-8} - 10^{-7}$ cm$^2$ and $M_X < 50$ kg. Our results open a new window on dark matter: the human body as a dark matter detector.

astro-ph.CO↗
arXiv2019

Macroscopic Dark Matter Constraints from Bolide Camera Networks

Macroscopic dark matter (macros) are a broad class of alternative candidates to particle dark matter. These candidates would transfer energy primarily through elastic scattering, and this linear energy deposition would produce observable signals if a macro were to pass through the atmosphere. We produce constraints for low mass macros from the null observation of bolides formed by a passing macro, across two extensive networks of cameras built originally to observe meteorites. The parameter space that could be probed with planned upgrades to the existing array of cameras in one of these networks still currently in use, the Desert Fireball Network in Australia, is estimated.

astro-ph.CO↗
arXiv2019

A counter-top search for macroscopic dark matter

A number of dark matter candidates have been discussed that are macroscopic, of approximately nuclear density, and scatter ordinary matter essentially elastically with approximately their geometric cross-section. A wide range of mass and geometric cross-section is still unprobed for these "macros." Macros passing through rock would melt the material in cylinders surrounding their long nearly straight trajectories. Once cooled, the resolidified rock would be easily distinguishable from its surroundings. We discuss how, by visually examining ordinary slabs of rock such as are widely available commercially for kitchen countertops, one could probe an interesting segment of the open macro parameter space.

astro-ph.HE↗
arXiv2015

Point particle motion in topologically nontrivial space-times

It is well known that compactifying a space can break symmetries that are present in the covering space. In this paper we study the effects of such topological symmetry breaking on point-particle motion when the particle is coupled to a massless field on the space. For a torus topology where Lorentz invariance is broken but translation invariance is maintained, particles can move at a constant velocity through the space; however, non-local, velocity-dependent forces arise whenever the particle is accelerated. For a topology where translation invariance is broken, such as the Klein bottle, interactions with the massless field generate an effective potential as a function of position. The potential creates special stable points in the space, and prevents constant velocity motion. This latter would appear to be the generic case. This class of effects may be applicable whenever a localized object moves through a compactified bulk, such as in brane-world cosmology, or some condensed matter systems.

hep-th↗
arXiv2013

Novel Probes of Gravity and Dark Energy

The discovery of cosmic acceleration has stimulated theorists to consider dark energy or modifications to Einstein's General Relativity as possible explanations. The last decade has seen advances in theories that go beyond smooth dark energy -- modified gravity and interactions of dark energy. While the theoretical terrain is being actively explored, the generic presence of fifth forces and dark sector couplings suggests a set of distinct observational signatures. This report focuses on observations that differ from the conventional probes that map the expansion history or large-scale structure. Examples of such novel probes are: detection of scalar fields via lab experiments, tests of modified gravity using stars and galaxies in the nearby universe, comparison of lensing and dynamical masses of galaxies and clusters, and the measurements of fundamental constants at high redshift. The observational expertise involved is very broad as it spans laboratory experiments, high resolution astronomical imaging and spectroscopy and radio observations. In the coming decade, searches for these effects have the potential for discovering fundamental new physics. We discuss how the searches can be carried out using experiments that are already under way or with modest adaptations of existing telescopes or planned experiments. The accompanying paper on the Growth of Cosmic Structure describes complementary tests of gravity with observations of large-scale structure.

astro-ph.CO↗
arXiv2012

Quantum kinetics and prethermalization of Hawking radiation

We reinvestigate the emission of Hawking radiation during gravitational collapse to a black hole. Both CGHS collapse of a shock wave in (1+1)-dimensional dilaton gravity and Schwarzschild collapse of a spherically symmetric thin shell in (3+1)-dimensional gravity are considered. Studying the dynamics of in-vacuum polarization, we find that a multi-parametric family of out-vacua exists. Initial conditions for the collapse lead dynamically to different vacua from this family as the final state. Therefore, the form of the out-vacuum encodes memory about the initial quantum state of the system. While most out-vacua feature a non-thermal Hawking flux and are expected to decay quickly, there also exists a thermal vacuum state. Collectively, these observations suggest an interesting possible resolution of the information loss paradox.

hep-th↗
arXiv2012

WIMP abundance and lepton (flavour) asymmetry

We investigate how large lepton asymmetries affect the evolution of the early universe at times before big bang nucleosynthesis and in particular how they influence the relic density of WIMP dark matter. In comparison to the standard calculation of the relic WIMP abundance we find a decrease, depending on the lepton flavour asymmetry. We find an effect of up to 20 per cent for lepton flavour asymmetries $l_f= {\cal O}(0.1)$.

astro-ph.CO↗
arXiv2011

Electroweak stars: how nature may capitalize on the standard model's ultimate fuel

We study the possible existence of an electroweak star - a compact stellar-mass object whose central core temperature is higher than the electroweak symmetry restoration temperature. We found a solution to the Tolman-Oppenheimer-Volkoff equations describing such an object. The parameters of such a star are not substantially different from a neutron star - its mass is around 1.3 Solar masses while its radius is around 8 km. What is different is the existence of a small electroweak core. The source of energy in the core that can at least temporarily balance gravity are standard-model non-perturbative baryon number (B) and lepton number (L) violating processes that allow the chemical potential of $B+L$ to relax to zero. The energy released at the core is enormous, but gravitational redshift and the enhanced neutrino interaction cross section at these energies make the energy release rate moderate at the surface of the star. The lifetime of this new quasi-equilibrium can be more than ten million years. This is long enough to represent a new stage in the evolution of a star if stellar evolution can take it there.

hep-ph↗