Searcharxiv⌕ Search

arXiv subjects

Pierre Sikivie

Publications and source records attributed to Pierre Sikivie.

At least 19 recordsLinked to original sources
arXiv2026

The nine rings of the galaxy LEDA 1313424

The galaxy LEDA 1313424 has recently been discovered by I. Pasha et al. to have nine rings. The authors of the discovery paper interpret the rings to be the result of the passing of a smaller galaxy through the center of the LEDA galaxy 56 Myr ago. In that interpretation the outermost observed ring, which has approximately 70 kpc radius, would have traveled at 1,220 km/s, an implausibly large speed. The expected speed of the 70 kpc ring is 55 km/s in the analytic theory of collisional ring galaxies used in the discovery paper to explain the pattern of ring radii. Furthermore, the widths of the observed rings are inconsistent with the predictions of the analytic theory and the assumptions underlying the analytic theory are violated in the specific case of LEDA. As an alternative interpretation we propose that the rings of LEDA are the imprint upon baryonic matter of caustic rings of dark matter. Our proposal requires that the dark matter is axions forming a Bose-Einstein condensate.

astro-ph.GA↗
arXiv2026

Supermassive black hole formation in the initial collapse of axion dark matter

Axion dark matter thermalizes by gravitational self-interactions and forms a Bose-Einstein condensate. We show that the rethermalization of the axion fluid during the initial collapse of large scale overdensities near cosmic dawn transports angular momentum outward sufficientlly fast that black holes form with masses ranging from approximately $10^5$ to a few times $10^{10}~M_\odot$. This conclusion holds for QCD axions and for axion-like particles of mass larger than $10^{-16}$ eV/$c^2$.

hep-ph↗
arXiv2026

Axions explain the formation of supermassive black holes at cosmic dawn

In a recent paper we pointed out that supermassive black holes, with masses ranging from $10^5$ to $10^{10} M_\odot$ form naturally at cosmic dawn if the dark matter is QCD axions or axion-like particles with mass $m > 10^{-16}\, \mathrm{eV}/c^2$. No additional assumptions are required. Here we answer in detail the most commonly raised questions regarding our work.

astro-ph.HE↗
arXiv2025

Effects of a dark matter caustic passing through the Oort cloud

We investigate the effect of a dark matter caustic passing through the Solar System. We find, confirming a previous result, that the Sun tracks the caustic surface for some time. We integrate numerically the equations of motion of the Sun and a comet for a large number of initial conditions and of caustic passage properties. We calculate the probability for the comet to escape the Solar System and the probability for it to fall within 50 A.U. of the Sun, given the initial semimajor axis and eccentricity of its orbit. We find that the average probability for a comet to fall within 50 A.U. of the Sun is of order $3 \times 10^{-4}$ and that comets which are initially at a distance larger than about $10^5$ A.U. have a probability of order one to be ejected from the Solar System.

astro-ph.CO↗
arXiv2022

Resonant excitation of the axion field during the QCD phase transition

We find that the adiabatic fluctuations produced in the primordial plasma by cosmological inflation resonantly excite the axion field during the QCD phase transition by pumping axions from low momentum modes to modes with momentum up to of order $\sqrt{3} m$ where $m$ is the axion mass. We derive the momentum distribution of the excited axions. The fraction of cold axions that get excited is of order one if the axion mass is larger than a few $μ$eV. The effect occurs whether inflation happens before or after the Peccei-Quinn phase transition.

hep-ph↗
arXiv2021

Clean energy from dark matter?

A contribution to Frank Wilczek's 70th birthday's festschrift, this brief note considers how much power can be extracted from dark matter.

hep-ph↗
arXiv2021

Implications of triangular features in the Gaia skymap for the Caustic Ring Model of the Milky Way halo

The Gaia map of the Milky Way reveals a pair of triangular features at nearly symmetric locations on opposite sides of the Galactic Center. In this paper we explore the implications of these features assuming they are manifestations of a caustic ring in the dark matter distribution of the Milky Way halo. The existence of a series of such rings is predicted by the Caustic Ring Model. The model's phase-space distribution is that acquired by a rethermalizing Bose-Einstein condensate of axions or axion-like particles. We show that dust is gravitationally entrained by cold axion flows and propose this as an explanation for the sharpness of the triangular features. The locations of the features imply that we on Earth are much closer to the fifth caustic ring than thought on the basis of pre-Gaia observations. Most likely we are inside its tricusp cross-section. In that case the dark matter density on Earth is dominated by four cold flows, termed Big, Little, Up and Down. If we are outside the tricusp cross-section the dark matter density on Earth is dominated by two cold flows, Big and Little. We use the triangular features in the Gaia map, and a matching feature in the IRAS map, to estimate the velocity vectors and densities of the four locally dominant flows.

astro-ph.GA↗
arXiv2020

Invisible Axion Search Methods

In the late 1970's, the axion was proposed as a solution to the Strong CP Problem, i.e. the puzzle why the strong interactions conserve parity P and the product CP of charge conjugation and parity in spite of the fact that the Standard Model of elementary particles as a whole violates those symmetries. The original axion was soon ruled out by laboratory experiments and astrophysical considerations, but a new version was invented which is much more weakly coupled and which evades the laboratory and astrophysical constraints. It was dubbed the invisible" axion. However, the axion cannot be arbitrarily weakly coupled because it is overproduced in the early universe by vacuum realignment in the limit of vanishing coupling. The axions produced by vacuum realignment are a form of cold dark matter today. The axion provides a solution then not only to the Strong CP Problem but also to the dark matter problem. Various methods have been proposed to search for dark matter axions and for axions emitted by the Sun. Their implementation and improvement has led to significant constraints on the notion of an invisible axion. Even purely laboratory methods may place significant constraints on invisible axions or axion-like particles. This review discusses the various methods that have been proposed and provides theoretical derivations of their signals.

hep-ph↗
arXiv2019

Production and detection of an axion dark matter echo

Electromagnetic radiation with angular frequency equal to half the axion mass stimulates the decay of cold dark matter axions and produces an echo, i.e. faint electromagnetic radiation traveling in the opposite direction. We propose to search for axion dark matter by sending out to space a powerful beam of microwave radiation and listening for its echo. We estimate the sensitivity of this technique in the isothermal and caustic ring models of the Milky Way halo, and find it to be a promising approach to axion, or axion-like, dark matter detection.

hep-ph↗
arXiv2018

Effects of a caustic ring of dark matter on the distribution of stars and interstellar gas

Caustic rings of dark matter with $\textit{tricusp}$ cross-section were predicted to lie in the galactic disk. Their radii increase on cosmological time scales at a rate of order $1$ kpc/Gyr. When a caustic ring passes through the orbit of a star, the orbit is strongly perturbed. We find that a star moving in a nearly circular orbit is first attracted towards the caustic ring, then moves with and oscillates about the caustic for approximately $1$ Gyr before returning to its original orbit. As a result, a stellar overdensity forms around the caustic ring. We predict such overdensities to be of order $120\%$ near the 2nd caustic ring where the Monoceros Ring is observed and of order $45$, $30$ and $15\%$ near the 3rd, 4th and 5th caustic rings, respectively. We show that the associated bulk velocities of the stars near the caustic rings are less than a few km/s. We also determine the density profile of interstellar gas near the 5th caustic ring assuming it is in thermal equilibrium in the gravitational potential of the caustic and of the gas itself.

astro-ph.GA↗
arXiv2018

Axion dark matter and the 21-cm signal

It was shown in ref. [1] that cold dark matter axions reach thermal contact with baryons, and therefore cool them, shortly after the axions thermalize among themselves and form a Bose-Einstein condensate. The recent observation by the EDGES collaboration of a baryon temperature at cosmic dawn lower than expected under "standard" assumptions is interpreted as new evidence that the dark matter is axions, at least in part. Baryon cooling by dark matter axions is found to be consistent with the observation of baryon acoustic oscillations.

astro-ph.CO↗
arXiv2018

Gravitational self-interactions of a degenerate quantum scalar field

We develop a formalism to help calculate in quantum field theory the departures from the description of a system by classical field equations. We apply the formalism to a homogeneous condensate with attractive contact interactions and to a homogeneous self-gravitating condensate in critical expansion. In their classical descriptions, such condensates persist forever. We show that in their quantum description, parametric resonance causes quanta to jump in pairs out of the condensate into all modes with wavector less than some critical value. We calculate in each case the time scale over which the homogeneous condensate is depleted, and after which a classical description is invalid. We argue that the duration of classicality of inhomogeneous condensates is shorter than that of homogeneous condensates.

hep-ph↗
arXiv2017

Duration of Classicality of Homogeneous Condensates with Attractive Interactions

Dark matter axions and other highly degenerate bosonic fluids are commonly described by classical field equations. In a recent paper \cite{BECprop} we calculated the duration of classicality of homogeneous condensates with attractive contact interactions and of self-gravitating homogeneous condensates in critical expansion. According to their classical equations of motion, such condensates persist forever. In their quantum evolution parametric resonance causes quanta to jump in pairs out of the condensate into all modes with wavevector less than some critical value. We estimated in each case the time scale over which the condensate is depleted and after which a classical description is invalid.

hep-ph↗
arXiv2017

Duration of classicality in highly degenerate interacting Bosonic systems

We study sets of oscillators that have high quantum occupancy and that interact by exchanging quanta. It is shown by analytical arguments and numerical simulation that such systems obey classical equations of motion only on time scales of order their relaxation time $τ$ and not longer than that. The results are relevant to the cosmology of axions and axion-like particles.

hep-ph↗
arXiv2017

Cosmic Axion Bose-Einstein Condensation

QCD axions are a well-motivated candidate for cold dark matter. Cold axions are produced in the early universe by vacuum realignment, axion string decay and axion domain wall decay. We show that cold axions thermalize via their gravitational self-interactions, and form a Bose-Einstein condensate. As a result, axion dark matter behaves differently from the other proposed forms of dark matter. The differences are observable.

astro-ph.CO↗
arXiv2017

New astrophysical bounds on ultralight axionlike particles

Motivated by tension between the predictions of ordinary cold dark matter (CDM) and observations at galactic scales, ultralight axionlike particles (ULALPs) with mass of the order $10^{-22}~{\rm eV}$ have been proposed as an alternative CDM candidate. We consider cold and collisionless ULALPs produced in the early Universe by the vacuum realignment mechanism and constituting most of CDM. The ULALP fluid is commonly described by classical field equations. However, we show that, like QCD axions, the ULALPs thermalize by gravitational self-interactions and form a Bose-Einstein condensate, a quantum phenomenon. ULALPs, like QCD axions, explain the observational evidence for caustic rings of dark matter because they thermalize and go to the lowest energy state available to them. This is one of rigid rotation on the turnaround sphere. By studying the heating effect of infalling ULALPs on galactic disk stars and the thickness of the nearby caustic ring as observed from a triangular feature in the IRAS map of our galactic disk, we obtain lower-mass bounds on the ULALP mass of order $10^{-23}$ and $10^{-20}~{\rm eV}$, respectively.

astro-ph.CO↗
arXiv2015

Evolution of velocity dispersion along cold collisionless flows

The infall of cold dark matter onto a galaxy produces cold collisionless flows and caustics in its halo. If a signal is found in the cavity detector of dark matter axions, the flows will be readily apparent as peaks in the energy spectrum of photons from axion conversion, allowing the densities, velocity vectors and velocity dispersions of the flows to be determined. We discuss the evolution of velocity dispersion along cold collisionless flows in one and two dimensions. A technique is presented for obtaining the leading behaviour of the velocity dispersion near caustics. The results are used to derive an upper limit on the energy dispersion of the Big Flow from the sharpness of its nearby caustic, and a prediction for the dispersions in its velocity components.

astro-ph.CO↗