Search

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 $10^{10}~M_\odot$., Comment: 16 pages, 3 figures

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.

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 $\mu$eV. The effect occurs whether inflation happens before or after the Peccei-Quinn phase transition., Comment: 18 pages, 4 figures. A few typographical errors were corrected. Version to appear in Physical Review D

A contribution to Frank Wilczek's 70th birthday's festschrift, this brief note considers how much power can be extracted from dark matter., Comment: 5 pages, no figures

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., Comment: 40 pages, 14 figures. An analysis of the statistical significance of the Gaia features has been added, and other smaller changes made. Version published in Physics of the Dark Universe

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., Comment: 89 pages, 7 figures, version to appear in Reviews of Modern Physics. A few references have been added. Additional small changes

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., Comment: 5 pages, 2 figures, includes changes suggested by PRL referees

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., Comment: 19 pages, 9 figures

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., Comment: 4 pages, no figures; references and comments were added

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., Comment: 5 pages, no figures, contributed to the 13th Patras Workshop on Axions, WIMPs and WISPs, Thessaloniki, May 15 to 19, 2017

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., Comment: 39 pages, 3 figures. A more detailed discussion of the duration of classicality is given, correcting relatively inconsequential errors/misunderstandings in the original version of this paper

This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017., Comment: 102 pages + references

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., Comment: 14 pages, 3 figures, minor typos corrected, matches published version

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 $\tau$ and not longer than that. The results are relevant to the cosmology of axions and axion-like particles., Comment: 5 pages, 3 figures

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., Comment: 19 pages, 2 figures

The axions produced during the QCD phase transition by vacuum realignment, string decay and domain wall decay thermalize as a result of their gravitational self-interactions when the photon temperature is approximately 500 eV. They then form a Bose-Einstein condensate (BEC). Because the axion BEC rethermalizes on time scales shorter than the age of the universe, it has properties that distinguish it from other forms of cold dark matter. The observational evidence for caustic rings of dark matter in galactic halos is explained if the dark matter is axions, at least in part, but not if the dark matter is entirely WIMPs or sterile neutrinos., Comment: 6 pages, no figures, contributed to the 11th Patras Workshop on Axions, WIMPs and WISPs, Zaragoza, June 22 to 26, 2015

We obtain solutions to the coupled Schr\"odinger-Poisson equations. The solutions describe the evolution of cold dark matter density perturbations in an otherwise homogeneous expanding Friedmann universe. We discuss the relationships between descriptions of cold dark matter in terms of a pressureless fluid, in terms of a wavefunction, of a classical scalar field, and a quantum scalar field. We identify the regimes where the various descriptions coincide and where they differ., Comment: 15 pages

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., Comment: 14 pages. This is a chapter for a book entitled "Universal Themes of Bose-Einstein Condensation", to be published by Cambridge University Press, edited by David Snoke, Nikolaos Proukakis and Peter Littlewood. Affiliations and biblio info added, http://www.cambridge.org/9781107085695

Cold dark matter axions thermalize through gravitational self-interactions and form a Bose-Einstein condensate when the photon temperature reaches approximately 500 eV. Axion Bose-Einstein condensation provides an opportunity to distinguish axions from the other dark matter candidates on the basis of observation. The rethermalization of axions that are about to fall in a galactic potential well causes them to acquire net overall rotation, whereas ordinary cold dark matter falls in with an irrotational velocity field. The inner caustics of galactic halos are different in the two cases., Comment: 4 pages, no figures, contribution to the Proceedings of the 7th Patras Workshop on Axions, WIMPs and WISPs, Mykonos, Greece, June 26 - July 1, 2011

In this work we consider searches for dark matter made of axions or axion-like particles (ALPs) using resonant radio frequency cavities inserted into dipole magnets from particle accelerators, wiggler magnets developed for accelerator based advanced light sources, and toroidal magnets similar to those used in particle physics detectors. We investigate the expected sensitivity of such ALP dark matter detectors and discuss the engineering aspects of building and tuning them. Brief mention is also made of even stronger field magnets that are becoming available due to improvements in magnetic technology. It is concluded that new experiments utilizing already existing magnets could greatly enlarge the mass region in searches for axion-like dark matter particles., Comment: 19 pages, 6 figures

Axions differ from ordinary cold dark matter, such as WIMPs or sterile neutrinos, because they form a Bose-Einstein condensate (BEC). As a result, axions accreting onto a galactic halo fall in with net overall rotation. In contrast, ordinary CDM accretes onto galactic halos with an irrotational velocity field. The inner caustics are different in the two cases. It is shown that if the dark matter is axions, the phase space structure of the halos of isolated disk galaxies, such as the Milky Way, is precisely that of the caustic ring model for which observational support exists. The other dark matter candidates predict a far more chaotic phase space structure for galactic halos., Comment: 11 pages, invited talk at the IDM2010 International Conference on the Identification of Dark Matter, Montpellier, France, July 26-30, 2010

Dark matter axions form a rethermalizing Bose-Einstein condensate. This provides an opportunity to distinguish axions from other forms of dark matter on observational grounds. I show that if the dark matter is axions, tidal torque theory predicts a specific structure for the phase space distribution of the halos of isolated disk galaxies, such as the Milky Way. This phase space structure is precisely that of the caustic ring model, for which observational support had been found earlier. The other dark matter candidates predict a different phase space structure for galactic halos., Comment: 4 pages, no figures

A resonantly-enhanced photon-regeneration experiment to search for the axion or axion-like particles is described. This experiment is a shining light through walls study, where photons travelling through a strong magnetic field are (in part) converted to axions; the axions can pass through an opaque wall and convert (in part) back to photons in a second region of strong magnetic field. The photon regeneration is enhanced by employing matched Fabry-Perot optical cavities, with one cavity within the axion generation magnet and the second within the photon regeneration magnet. Compared to simple single-pass photon regeneration, this technique would result in a gain of (F/pi)^2, where F is the finesse of each cavity. This gain could feasibly be as high as 10^(10), corresponding to an improvement in the sensitivity to the axion-photon coupling, g_(agg), of order (F/pi)^(1/2) ~ 300. This improvement would enable, for the first time, a purely laboratory experiment to probe axion-photon couplings at a level competitive with, or superior to, limits from stellar evolution or solar axion searches. This report gives a detailed discussion of the scheme for actively controlling the two Fabry-Perot cavities and the laser frequencies, and describes the heterodyne signal detection system, with limits ultimately imposed by shot noise., Comment: 10 pages, 5 figures

Dark matter caustics are small scale, high density structures believed to exist in galaxies like ours. If the dark matter consists of Weakly Interacting Massive Particles, these caustics may be detected by means of the gamma rays produced by dark matter particle annihilation. We discuss particle annihilation in outer and inner caustics and provide sky maps of the expected gamma ray distribution., Comment: Minor changes, Introduction expanded, references added, accepted for publication in Phys. Rev. D

Caustic rings of dark matter were predicted to exist in the plane of the Galaxy at radii $a_n \simeq 40 {\rm kpc}/n$ for $n = 1,2,3 ..$. The recently discovered Monoceros Ring of stars is located near the $n=2$ caustic, prompting us to consider a possible connection between these two objects. We identify two processes through which the Monoceros Ring of stars may have formed. One process is the migration of gas to an angular velocity minimum at the caustic leading to enhanced star formation there. The other is the adiabatic deformation of star orbits as the caustic slowly grows in mass and radius. The second process predicts an order 100% enhancement of the density of disk stars at the location of the caustic ring., Comment: 21 pages, 3 figures

Outline: 1. Thermal axions 2. Axion field evolution 3. The domain wall problem 4. Cold axions 5. Axion miniclusters 6. Axion isocurvature perturbations, Comment: 31 pages, prepared for the Lecture Notes on Physics (Springer Verlag) volume on Axions, edited by M. Kuster. A couple references added and a few minor changes in wording

Axions solve the Strong CP Problem and are a cold dark matter candidate. The combined constraints from accelerator searches, stellar evolution limits and cosmology suggest that the axion mass is in the range $3 \cdot 10^{-3} > m_a > 10^{-6}$ eV. The lower bound can, however, be relaxed in a number of ways. I discuss the constraint on axion models from the absence of isocurvature perturbations. Dark matter axions can be searched for on Earth by stimulating their conversion to microwave photons in an electromagnetic cavity permeated by a magnetic field. Using this technique, limits on the local halo density have been obtained by the Axion Dark Matter eXperiment., Comment: 10 pages, invited talk at the 41st Rencontre de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Italy, March 11-18, 2006. Three references were added

We prove that a flow of cold collisionless particles from all directions in and out of a region necessarily forms a caustic. A corollary is that, in cold dark matter cosmology, galactic halos have inner caustics in addition to the more obvious outer caustics. The outer caustics are fold catastrophes located on topological spheres surrounding the galaxy. To obtain the catastrophe structure of the inner caustics, we simulate the infall of cold collisionless particles in a fixed gravitational potential. The structure of inner caustics depends on the angular momentum distribution of the infalling particles. We confirm a previous result that the inner caustic is a "tricusp ring" when the initial velocity field is dominated by net overall rotation. A tricusp ring is a closed tube whose cross section is a section of an elliptic umbilic catastrophe. However, tidal torque theory predicts that the initial velocity field is irrotational. For irrotational initial velocity fields, we find the inner caustic to have a tent-like structure which we describe in detail in terms of the known catastrophes. We also show how the tent caustic transforms into a tricusp ring when a rotational component is added to the initial velocity field., Comment: 35 pages, 20 figures

The Strong CP Problem and its resolution through the existence of an axion are briefly reviewed. The combined constraints from accelerator searches, the evolution of red giants and the duration of the SN 1987a neutrino pulse require the axion mass $m_a$ to be less than $3 \cdot 10^{-3}$ eV. On the other hand, the requirement that the axion does not overclose the universe implies a lower bound on $m_a$ of order $10^{-6}$ eV. This lower bound can, however, be relaxed in a number of ways. If $m_a$ is near the lower bound, axions are an important contribution to the energy density of the universe in the form of (very) cold dark matter. Dark matter axions can be searched for on Earth by stimulating their conversion to microwave photons in an electromagnetic cavity permeated by a magnetic field. Using this technique, limits on the local halo density have been placed by the Axion Dark Matter eXperiment. I'll give a status report on ADMX and its upgrade presently under construction. I'll also report on recent results from solar axion searches and laser experiments., Comment: 7 pages, 3 figures, invited talk at the PASCOS 05 conference in Gyeongju, Korea, May 30 to June 4, 2005. A reference and brief comment were added

Although a simple argument implies that the distribution of dark matter in galactic halos is characterized by discrete flows and caustics, their presence is often ignored in discussions of galactic dynamics and of dark matter detection strategies. Discrete flows and caustics can in fact be irrelevant if the number of flows is very large. We estimate the number of dark matter flows as a function of galactocentric distance and consider the various ways in which that number can be increased, in particular by the presence of structure on small scales (dark matter clumps) and the scattering of the flows by inhomogeneities in the matter distribution. We find that, when all complicating factors are taken into account, discrete flows and caustics in galactic halos remain a robust prediction of cold dark matter cosmology with extensive implications for observation and experiment., Comment: 13 pages, no figures

We calculate the diurnal and annual modulation of the signals in axion and WIMP dark matter detectors on Earth caused by a cold flow of dark matter in the Solar neighborhood. The effects of the Sun's and the Earth's gravity, and of the orbital and rotational motions of the Earth are included. A cold flow on Earth produces a peak in the spectrum of microwave photons in cavity detectors of dark matter axions, and a plateau in the nuclear recoil energy spectrum in WIMP detectors. Formulas are given for the positions and heights of these peaks and plateaux as a function of time in the course of day and year, including all corrections down to the 0.1% level of precision. The results can be applied to an arbitrary dark matter velocity distribution $f(\vec{v})$ by integrating the one-flow results over velocities. We apply them to the set of flows predicted by the caustic ring model of the Galactic halo. The caustic ring model predicts the dark matter flux on Earth to be largest in December $\pm$ one month. Nonetheless, because of the role of energy thresholds, the model is consistent with the annual modulation results published by the DAMA collaboration provided the WIMP mass is larger than approximately 100 GeV., Comment: 36 pages, 10 figures

The recently discovered ring of stars near Galactocentric distance $r = 20$ kpc is interpreted as baryonic matter accreted onto the second caustic ring of dark matter in our galaxy. Caustic rings of dark matter were predicted in the Galactic plane at radii $a_n \simeq 40 kpc/n$ where $n=1,2,3 ..$. They can reveal themselves by their gravitational influence on the distribution of baryonic matter. There is additional evidence for caustic rings of dark matter in the Milky Way from a series of sharp rises in the Galactic rotation curve. The positions of the rises are consistent at the 3% level with the above law for the caustic ring radii. Also, a triangular feature in the IRAS map of the galactic plane is consistent with the imprint of the caustic ring of dark matter nearest to us ($n=5$) upon dust and gas in the Galactic plane. These observations imply that the dark matter in our neighborhood is dominated by a single flow whose density and velocity vector are estimated., Comment: 12 pages, 3 figures, invited talk at the Beyond '03 Conference on Physics beyond the Standard Model, Castle Ringberg, Tegernsee, Germany, June 9 - 14, 2003

We analyze the effect of the Sun's gravitational field on a flow of cold dark matter (CDM) through the solar system in the limit where the velocity dispersion of the flow vanishes. The exact density and velocity distributions are derived in the case where the Sun is a point mass. The results are extended to the more realistic case where the Sun has a finite size spherically symmetric mass distribution. We find that regions of infinite density, called caustics, appear. One such region is a line caustic on the axis of symmetry, downstream from the Sun, where the flow trajectories cross. Another is a cone-shaped caustic surface near the trajectories of maximum scattering angle. The trajectories forming the conical caustic pass through the Sun's interior and probe the solar mass distribution, raising the possibility that the solar mass distribution may some day be measured by a dark matter detector on Earth. We generalize our results to the case of flows with continuous velocity distributions, such as that predicted by the isothermal model of the Milky Way halo., Comment: 30 pages, 8 figures

The late infall of cold dark matter onto our galaxy produces discrete flows and caustics in its halo. The recently discovered ring of stars near galactocentric distance 20 kpc and a series of sharp rises in the Milky Way rotation curve are interpreted as due to the presence of caustic rings of dark matter in the galactic plane. Their locations are consistent at the 3% level with the predictions of the self-similar infall model for the caustic ring radii. Also, a triangular feature in the IRAS map of the galactic plane is consistent with the imprint of a caustic ring of dark matter upon the baryonic matter. These observations imply that the dark matter in our neighborhood is dominated by a single flow whose density and velocity vector are estimated., Comment: 12 pages, 2 figures. Version to be published in Phys. Lett. B. The paper has been revised in response to comments by referees and to include fresh evidence

The late infall of dark matter onto a galaxy produces structure (such as caustics) in the distribution of dark matter in the halo. We argue that such structure is likely to occur generically on length scales proportional to $l \sim t_0 v_{rot}$, where $t_0$ is the age of the universe and $v_{rot}$ is the rotation velocity of the galaxy. A set of 32 extended galactic rotation curves is analyzed. For each curve, the radial coordinate is rescaled according to $r\to \tilde r \equiv r (v_0 / v_{rot})$, where we choose $v_0 = 220 km/s$. A linear fit to each rescaled rotation curve is subtracted, and the residuals are binned and averaged. The sample shows significant features near $\tilde r = 40 kpc$ and $\tilde r = 20 kpc$. This is consistent with the predictions of the self-similar caustic ring model of galactic halos., Comment: 4 pages, LaTeX, 1 epsf figure

Contents: 1. The strong CP problem 2. Dark matter axions 3. The cavity detector of galactic halo axions 4. Caustic rings in the density distribution of cold dark matter halos, Comment: 12 pages, Latex, one eps figure, talk at the Workshop "Beyond the Desert '97" at Castle Ringberg, Tegernsee, Germany, June 8-14, 1997

It is shown that the infall of collisionless dark matter onto isolated galaxies produces a series of caustic rings in the halo dark matter distribution. The properties of these caustics are investigated. The density profile of the caustic is derived for a specific case. Bumps in the rotation curve of NGC 3198 are interpreted as due to caustic rings of dark matter., Comment: 12 pages, 1 figure, Latex, minor changes, version to to be published by Phys. Lett. B

Contents: 1. The strong CP problem 2. Dark matter axions 3. The cavity detector of galactic halo axions 4. The phase space structure of cold dark matter halos, Comment: 12 pages, 2 figures, Latex, invited talk at the APCTP Inauguration Conference in Seoul, Korea, June 4-10, 1996 and at the Workshop on Aspects of Dark Matter in Astro- and Particle Physics in Heidelberg, Germany, Sept. 16-20, 1996

It is argued that the spectrum of cold dark matter particles on Earth has peaks in velocity space associated with particles falling onto the Galaxy for the first time and with particles which have fallen in and out of the Galaxy only a small number of times in the past. Estimates are given for the sizes and velocity magnitudes of the first few peaks. The estimates are based upon the secondary infall model of halo formation which has been generalized to include the effect of angular momentum., Comment: 7 pages, Latex, 4 figures, uuencoded, talk at the DM96 Workshop on Sources and Detection of Dark Matter in the Universe, Santa Monica, CA, Feb. 14-16, 1996

An imaginary character named TSP finds himself in a playroom whose floor is tilted to one side. However, the pooltable in the playroom is horizontal. TSP wonders how this can be. In doing so, he embarks upon an intellectual journey which parallels that which has been travelled during the past two decades by physicists interested in the Strong $CP$ Problem and axion physics., Comment: 8 pages, plain TEX, 4 figures in a separate uuencoded postcript file; based upon a talk at the XXXth Rencontres de Moriond 'Dark Matter in Cosmology' and 'Clocks and Tests of Fundamental Laws', Villars-sur-Ollon, Switzerland, Sept. 21-28, 1995

In the first section, I will try to convey a sense of the variety of observational inputs that tell us about the existence and the spatial distribution of dark matter in the universe. In the second section, I will briefly review the four main dark matter candidates, taking note of each candidate's status in the world of particle physics, its production in the early universe, its effect upon large scale structure formation and the means by which it may be detected. Section 3 concerns the energy spectrum of (cold) dark matter particles on earth as may be observed some day in a direct detection experiment. It is a brief account of work done in collaboration with J. Ipser and, more recently, with I. Tkachev and Y. Wang., Comment: 12 pages, plain TEX, talk at the Conference ``Trends in Particle Astrophysics'', Stockholm, Sweden, Sept. 22-25, 1994; a small glitch was fixed.

We develop a general formalism to calculate the force between beads attached to a flat $d$-dimensional membrane due to the quantum fluctuations of the membrane. The interaction potential is derived as a function of $d$ and the membrane energy density, tension, stiffness and temperature. We find that the induced interactions turn off when $d$ exceeds a certain critical dimension. The potential is attractive in all cases where it is non-zero and at finite temperature falls off exponentially for large distances., Comment: Plain Tex, Tables.tex macro required, 9 pages

How does the amplitude of a wiggle on a string change when the string is stretched? We answer this question for both longitudinal and transverse wiggles and for arbitrary equation of state, {\it i.e.}, for arbitrary relation between the tension $\tau$ and the energy per unit length $\epsilon$ of the string. This completes our derivation of the renormalization of string parameters which results from averaging out small scale wiggles on a string. The program is presented here in its entirety., Comment: Written with ReVTeX 3.0 package. Two figures are not included. Complete paper with postscript figures can be retrieved through anonymous ftp @quark.phys.ufl.edu. Get /preprints/ifthep94_4.tar.gz, gunzip and tar it. UFIFT-HEP-94-4

We propose an experimental scheme to search for galactic halo axions with mass $m_a \sim 10^{-3}$eV, which is above the range accessible with cavity techniques. The detector consists of a large number of parallel superconducting wires embedded in a material transparent to microwave radiation. The wires carry a current configuration which produces a static, inhomogeneous magnetic field $\vec{B}_0(\vec{x})$ within the detector volume. Axions which enter this volume may convert to photons. We discuss the feasibility of the detector and its sensitivity., Comment: LaTex, 9 pages, 4 figures (sent upon request), UFIFT-HEP-93--2

We consider a string with uniform energy density and tension and with a number of pointlike masses attached at fixed interdistances. We evaluate the effective interaction forces between these masses induced by the quantum fluctuations of the string. For interdistances large compared to the thickness of the string and small compared to the total length, these forces are universal and attractive and fall off, for large distances as $1/r^3$ and for small distances as $1/r$. The attractive nature of these forces creates an instability under which masses added to the string tend to aggregate., Comment: 9 pages, TEX, UCLA/92/TEP/31 and UFIFT-HEP-92-33

The exchange of two massless neutrinos gives rise to a long range force which couples to weakly charged matter. As has been noted previously in the literature, the potential for this force is $\VN \propto G_{F}^2 / r^5$ with monopole-monople, spin-spin and more complicated interactions. Unfortunately, this is far too small to be observed in present day experiments. We calculate $\VN$ explicitly in the electroweak theory, and show that under very general assumptions forces arising from the exchange of two massless fermions can at best yield $1 / r^5$ potentials., Comment: 5 pages + 1 figure (not included), UFIFT-HEP-92-28/HUTP-92-A041