38 research outputs found
Diffuse inverse Compton and synchrotron emission from dark matter annihilations in galactic satellites
Annihilating dark matter particles produce roughly as much power in electrons
and positrons as in gamma ray photons. The charged particles lose essentially
all of their energy to inverse Compton and synchrotron processes in the
galactic environment. We discuss the diffuse signature of dark matter
annihilations in satellites of the Milky Way (which may be optically dark with
few or no stars), providing a tail of emission trailing the satellite in its
orbit. Inverse Compton processes provide X-rays and gamma rays, and synchrotron
emission at radio wavelengths might be seen. We discuss the possibility of
detecting these signals with current and future observations, in particular
EGRET and GLAST for the gamma rays.Comment: 13 pages, 5 figure
The cosmic ray positron excess and neutralino dark matter
Using a new instrument, the HEAT collaboration has confirmed the excess of
cosmic ray positrons that they first detected in 1994. We explore the
possibility that this excess is due to the annihilation of neutralino dark
matter in the galactic halo. We confirm that neutralino annihilation can
produce enough positrons to make up the measured excess only if there is an
additional enhancement to the signal. We quantify the `boost factor' that is
required in the signal for various models in the Minimal Supersymmetric
Standard Model parameter space, and study the dependence on various parameters.
We find models with a boost factor greater than 30. Such an enhancement in the
signal could arise if we live in a clumpy halo. We discuss what part of
supersymmetric parameter space is favored (in that it gives the largest
positron signal), and the consequences for other direct and indirect searches
of supersymmetric dark matter.Comment: 11 pages, 6 figures, matches published version (PRD
Neutralino Gamma-ray Signals from Accreting Halo Dark Matter
There is mounting evidence that a self-consistent model for particle cold
dark matter has to take into consideration spatial inhomogeneities on
sub-galactic scales seen, for instance, in high-resolution N-body simulations
of structure formation. Also in more idealized, analytic models, there appear
density enhancements in certain regions of the halo. We use the results from a
recent N-body simulation of the Milky Way halo and investigate the gamma-ray
flux which would be produced when a specific dark matter candidate, the
neutralino, annihilates in regions of enhanced density. The clumpiness found on
all scales in the simulation results in very strong gamma-ray signals which
seem to already rule out some regions of the supersymmetric parameter space,
and would be further probed by upcoming experiments, such as the GLAST
gamma-ray satellite. As an orthogonal model of structure formation, we also
consider Sikivie's simple infall model of dark matter which predicts that there
should exist continuous regions of enhanced density, caustic rings, in the dark
matter halo of the Milky Way. We find, however, that the gamma-ray signal from
caustic rings is generally too small to be detectable.Comment: 15 pages, 11 figure
Constraints on the Variation of the Fine Structure Constant from Big Bang Nucleosynthesis
We put bounds on the variation of the value of the fine structure constant
, at the time of Big Bang nucleosynthesis. We study carefully all light
elements up to Li. We correct a previous upper limit on estimated from He primordial abundance and we find interesting new
potential limits (depending on the value of the baryon-to-photon ratio) from
Li, whose production is governed to a large extent by Coulomb barriers. The
presently unclear observational situation concerning the primordial abundances
preclude a better limit than |\Delta \alpha/\alpha| \lsim 2\cdot 10^{-2}, two
orders of magnitude less restrictive than previous bounds. In fact, each of the
(mutually exclusive) scenarios of standard Big Bang nucleosynthesis proposed,
one based on a high value of the measured deuterium primordial abundance and
one based on a low value, may describe some aspects of data better if a change
in of this magnitude is assumed.Comment: 21 pages, eps figures embedded using epsfig macr
Long Distance Contribution to and Implications for and
We estimate the long distance (LD) contribution to the magnetic part of the
transition using the Vector Meson Dominance approximation
. We find that this contribution may be significantly
larger than the short distance (SD) contribution to and could
possibly saturate the present experimental upper bound on the decay rate, eV. For the decay , which is driven by as well, we obtain an upper bound on the branching ratio from . Barring the possibility that the Quantum Chromodynamics
coefficient be much smaller than 1, also implies the approximate relation .
This relation agrees quantitatively with a recent independent estimate of the
l.h.s. by Deshpande et al., confirming that the LD contributions to are small. We find that these amount to an increase of in
the magnitude of the transition amplitude, relative to the SD
contribution alone.Comment: 16 pages, LaTeX fil
Gamma rays from dark matter annihilation in the Draco and observability at ARGO
The CACTUS experiment recently observed a gamma ray excess above 50 GeV from
the direction of the Draco dwarf spheroidal galaxy. Considering that Draco is
dark matter dominated the gamma rays may be generated through dark matter
annihilation in the Draco halo. In the framework of the minimal supersymmetric
extension of the standard model we explore the parameter space to account for
the gamma ray signals at CACTUS. We find that the neutralino mass is
constrained to be approximately in the range between 100 GeV ~ 400 GeV and a
sharp central cuspy of the dark halo profile in Draco is necessary to explain
the CACTUS results. We then discuss further constraints on the supersymmetric
parameter space by observations at the ground based ARGO detector. It is found
that the parameter space can be strongly constrained by ARGO if no excess from
Draco is observed above 100 GeV.Comment: 15 pages, 4 figure
Primordial nucleosynthesis with a varying fine structure constant: An improved estimate
We compute primordial light-element abundances for cases with fine structure
constant alpha different from the present value, including many sources of
alpha dependence neglected in previous calculations. Specifically, we consider
contributions arising from Coulomb barrier penetration, photon coupling to
nuclear currents, and the electromagnetic components of nuclear masses. We find
the primordial abundances to depend more weakly on alpha than previously
estimated, by up to a factor of 2 in the case of ^7Li. We discuss the
constraints on variations in alpha from the individual abundance measurements
and the uncertainties affecting these constraints. While the present best
measurements of primordial D/H, ^4He/H, and ^7Li/H may be reconciled pairwise
by adjusting alpha and the universal baryon density, no value of alpha allows
all three to be accommodated simultaneously without consideration of systematic
error. The combination of measured abundances with observations of acoustic
peaks in the cosmic microwave background favors no change in alpha within the
uncertainties.Comment: Phys. Rev. D accepted version; minor changes in response to refere
Indirect Neutralino Detection Rates in Neutrino Telescopes
Neutralinos annihilating in the center of the Sun or the Earth may give rise
to a detectable signal of neutrinos. We derive the indirect detection rates for
neutrino telescopes in the minimal supersymmetric extension of the standard
model. We show that even after imposing all phenomenological and experimental
constraints that make the theories viable, regions of parameter space exist
which can already be probed by existing neutrino telescopes. We compare with
the discovery potential of supersymmetry at LEP2 as well as direct detections
and point out the complementarity of the methods.Comment: LaTeX, 18 pages with 9 eps-figure