The Dilaton as a Candidate for Dark Matter (original) (raw)
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Dark matter axions in models of string cosmology
Physics Letters B, 1998
Axions are produced during a period of dilaton-driven inflation by amplification of quantum fluctuations. We show that for some range of string cosmology parameters and some range of axion masses, primordial axions may constitute a large fraction of the present energy density in the universe in the form of cold dark matter. Due to the periodic nature of the axion potential energy density fluctuations are strongly suppressed. The spectrum of primordial axions is not thermal, allowing a small fraction of the axions to remain relativistic until quite late.
Physical Review D, 2009
We study for what specific values of the theoretical parameters the axion can form the totality of cold dark matter. We examine the allowed axion parameter region in the light of recent data collected by the WMAP5 mission plus baryon acoustic oscillations and supernovae, and assume an inflationary scenario and standard cosmology. If the Peccei-Quinn symmetry is restored after inflation, we recover the usual relation between axion mass and density, so that an axion mass ma=67±2μeV makes the axion 100% of the cold dark matter. If the Peccei-Quinn symmetry is broken during inflation, the axion can instead be 100% of the cold dark matter for ma<15meV provided a specific value of the initial misalignment angle θi is chosen in correspondence to a given value of its mass ma. Large values of the Peccei-Quinn symmetry breaking scale correspond to small, perhaps uncomfortably small, values of the initial misalignment angle θi.
Axions as a model of Dark Matter
Journal of Student Research
The true nature of dark matter is an extremely important and fundamental problem in the study of astrophysics, particle physics, cosmology and many other areas within the study of physics. This paper presents experimental evidence for the existence of dark matter through discussing the experimental results of mass profiling a galaxy and gravitational lensing. The fundamental properties of dark matter are then discussed, and evidence for these properties is presented. This allows further discussion of one of the most promising models of dark matter - the axion. The purpose of this paper is to present the evidence for the axion model, describe the nature of the theoretical axion particle, and to highlight the effects this model would have on other theories in physics such as solving the Strong CP Problem in the theory of quantum chromodynamics.
Axion cold dark matter revisited
Journal of Physics: Conference Series, 2010
We study for what specific values of the theoretical parameters the axion can form the totality of cold dark matter. We examine the allowed axion parameter region in the light of recent data collected by the WMAP5 mission plus baryon acoustic oscillations and supernovae [1], and assume an inflationary scenario and standard cosmology. We also upgrade the treatment of anharmonicities in the axion potential, which we find important in certain cases. If the Peccei-Quinn symmetry is restored after inflation, we recover the usual relation between axion mass and density, so that an axion mass ma = (85 ± 3) µeV makes the axion 100% of the cold dark matter. If the Peccei-Quinn symmetry is broken during inflation, the axion can instead be 100% of the cold dark matter for ma < 15 meV provided a specific value of the initial misalignment angle θi is chosen in correspondence to a given value of its mass ma. Large values of the Peccei-Quinn symmetry breaking scale correspond to small, perhaps uncomfortably small, values of the initial misalignment angle θi.
Cosmological Implications of a Light Dilaton
1998
Supersymmetric Peccei-Quinn symmetry and string theory predict a complex scalar field comprising a dilaton and an axion. These fields are massless at high energies, but it is known since long that the axion is stabilized in an instanton dominated vacuum. Instantons and axions together also provide a mechanism to stabilize a dilaton, thus accounting for a dilaton as a possible
Generalized dilaton couplings to dark matter
Physics Letters B, 1992
Inspired by recent models of inflation within the Jordan-Brans-Dlcke theory, namely the "generahzed extended inflation" models (see Wang [Phys Lett B 250 (1990) 24, Phys Rev D 43 ( 1991 ) 995] ), we propose generallzed couphngs of a dark matter component to the Jordan-Brans-Dlcke, or ddaton, field Assummg the dark matter component to be dominant today we use observational data on the rate of change of Newton's constant, as well as on its value dunng pnmordml nucleosynthes~s, on the age of the Umverse and on the present value of the Hubble constant to put hmlts on these couphngs Our results extended prewous ones by Damour, Gibbons and Gundlach [Phys Rev Lett 64 (1990) 123] Unhke all prewously considered models, the Newton constant would change with time even ff the universe were dominated by an mwslble radmtlonhke component (~ e, whose energy-momentum tensor has vamshmg trace) Using a lagrangmn approach we propose a natural couphng of the dflaton field to a perfect fired dark matter component
Axions as Dark Matter Particles, Duffy & van Bibber
We review the current status of axions as dark matter. Motivation, models, constraints and experimental searches are outlined. The axion remains an excellent candidate for the dark matter and future experiments, particularly the Axion Dark Matter eXperiment (ADMX), will cover a large fraction of the axion parameter space.
Observational Cosmology, 1987
The observational evidence for the presence of dark matter is now generally accepted, with no lack of possible candidates (see e.g. Dekel, Einasto, and Rees 1986). The proposed candidates are devided into two groups, baryonic and non-baryonic. The latter is further devided to hot and cold dark matter. For the cold dark matter, among the first to be proposed is the axion. In this paper we shall not dwell on numerous cold dark matter candidates offered by particle physicists, for there are review articles on the subject (see e.g. Turner 1986, Primack 1986). The main purpose of the present report is to suggest that neutron star cooling theory and future space satellite programs (e.g. AXAF, XAO, LXAO) have a potential for offering the best astrophysical constraint on the axion mass and hence, giving valuable insight to some cosmological problems. Even though other candidates for cold dark matter are perfectly plausible, axions may have the following advantages. Their presence was predicted, independently of cosmology, as a natural solution to the strong CP problem (Peccei and Quinn 1977). Also, once we accept their presence, we can carry out specific calculations, to predict various properties (e.g. their emissivities).