A Critique of Drexler Dark Matter

Drexler dark matter is an alternate approach to dark matter that assumes that highly relativistic protons trapped in the halo of the galaxies could account for the missing mass. We look at various energetics involved in such a scenario such as the energy required to produce such particles and the corresponding lifetimes. Also we look at the energy losses from synchrotron and inverse Compton scattering and their signatures. The Coulomb repulsive instability due to the excess charge around the galaxies is also calculated. The above results lead us to conclude that such a model for DM is unfeasible.Comment: 4 pages, 10 equation

Gravitational Equilibrium in the Presence of a Positive Cosmological Constant

We reconsider the virial theorem in the presence of a positive cosmological constant Lambda. Assuming steady state, we derive an inequality of the form rho >= A (Lambda / 4 pi GN) for the mean density rho of the astrophysical object. With a minimum at Asphere = 2, its value can increase by several orders of magnitude as the shape of the object deviates from a spherically symmetric one. This, among others, indicates that flattened matter distributions like e.g. clusters or superclusters, with low density, cannot be in gravitational equilibrium.Comment: 7 pages, no figure

A New WIMP Population in the Solar System and New Signals for Dark-Matter Detectors

We describe in detail how perturbations due to the planets can cause a sub-population of WIMPs captured by scattering in surface layers of the Sun to evolve to have orbits which no longer intersect the Sun. We argue that such WIMPs, if their orbit has a semi-major axis less than 1/2 of Jupiter's, can persist in the solar system for cosmological timescales. This leads to a new, previously unanticipated WIMP population intersecting the Earth's orbit. The WIMP-nucleon cross sections required for this population to be significant are precisely those in the range predicted for SUSY dark matter, lying near the present limits obtained by direct underground dark matter searches using cyrogenic detectors. Thus, if a WIMP signal is observed in the next generation of detectors, a potentially measurable signal due to this new population must exist. This signal, lying in the keV range for Germanium detectors, would be complementary to that of galactic halo WIMPs. A comparison of event rates, anisotropies, and annual modulations would not only yield additional confirmation that any claimed signal is indeed WIMP-based, but would also allow one to gain information on the nature of the underlying dark matter model.Comment: Revtex, 37 pages including 6 figures, accepted by Phys. Rev D. (version to be published, including changes made in response to referees reports

Extreme gravitational lensing in vicinity of Schwarzschild-de Sitter black holes

We have developed a realistic, fully general relativistic computer code to simulate optical projection in a strong, spherically symmetric gravitational field. The standard theoretical analysis of optical projection for an observer in the vicinity of a Schwarzschild black hole is extended to black hole spacetimes with a repulsive cosmological constant, i.e, Schwarzschild-de Sitter spacetimes. Influence of the cosmological constant is investigated for static observers and observers radially free-falling from the static radius. Simulations include effects of the gravitational lensing, multiple images, Doppler and gravitational frequency shift, as well as the intensity amplification. The code generates images of the sky for the static observer and a movie simulations of the changing sky for the radially free-falling observer. Techniques of parallel programming are applied to get a high performance and a fast run of the BHC simulation code

The Uncertainty in Newton's Constant and Precision Predictions of the Primordial Helium Abundance

The current uncertainty in Newton's constant, G_N, is of the order of 0.15%. For values of the baryon to photon ratio consistent with both cosmic microwave background observations and the primordial deuterium abundance, this uncertainty in G_N corresponds to an uncertainty in the primordial 4He mass fraction, Y_P, of +-1.3 x 10^{-4}. This uncertainty in Y_P is comparable to the effect from the current uncertainty in the neutron lifetime, which is often treated as the dominant uncertainty in calculations of Y_P. Recent measurements of G_N seem to be converging within a smaller range; a reduction in the estimated error on G_N by a factor of 10 would essentially eliminate it as a source of uncertainty in the calculation of the primordial 4He abundance.Comment: 3 pages, no figures, fixed typos, to appear in Phys. Rev.

Constraining the cosmic radiation density due to lepton number with Big Bang Nucleosynthesis

The cosmic energy density in the form of radiation before and during Big Bang Nucleosynthesis (BBN) is typically parameterized in terms of the effective number of neutrinos N_eff. This quantity, in case of no extra degrees of freedom, depends upon the chemical potential and the temperature characterizing the three active neutrino distributions, as well as by their possible non-thermal features. In the present analysis we determine the upper bounds that BBN places on N_eff from primordial neutrino--antineutrino asymmetries, with a careful treatment of the dynamics of neutrino oscillations. We consider quite a wide range for the total lepton number in the neutrino sector, eta_nu= eta_{nu_e}+eta_{nu_mu}+eta_{nu_tau} and the initial electron neutrino asymmetry eta_{nu_e}^in, solving the corresponding kinetic equations which rule the dynamics of neutrino (antineutrino) distributions in phase space due to collisions, pair processes and flavor oscillations. New bounds on both the total lepton number in the neutrino sector and the nu_e -bar{nu}_e asymmetry at the onset of BBN are obtained fully exploiting the time evolution of neutrino distributions, as well as the most recent determinations of primordial 2H/H density ratio and 4He mass fraction. Note that taking the baryon fraction as measured by WMAP, the 2H/H abundance plays a relevant role in constraining the allowed regions in the eta_nu -eta_{nu_e}^in plane. These bounds fix the maximum contribution of neutrinos with primordial asymmetries to N_eff as a function of the mixing parameter theta_13, and point out the upper bound N_eff < 3.4. Comparing these results with the forthcoming measurement of N_eff by the Planck satellite will likely provide insight on the nature of the radiation content of the universe.Comment: 17 pages, 9 figures, version to be published in JCA

Production, Collection and Utilization of Very Long-Lived Heavy Charged Leptons

If a fourth generation of leptons exists, both the neutrino and its charged partner must be heavier than 45 GeV. We suppose that the neutrino is the heavier of the two, and that a global or discrete symmetry prohibits intergenerational mixing. In that case, non-renormalizable Planck scale interactions will induce a very small mixing; dimension five interactions will lead to a lifetime for the heavy charged lepton of $O(1-100)$ years. Production of such particles is discussed, and it is shown that a few thousands can be produced and collected at a linear collider. The possible uses of these heavy leptons is also briefly discussed.Comment: 9 pages Late

Superheavy Dark Matter with Discrete Gauge Symmetries

We show that there are discrete gauge symmetries protect naturally heavy X particles from decaying into the ordinary light particles in the supersymmetric standard model. This makes the proposal very attractive that the superheavy X particles constitute a part of the dark matter in the present universe. It is more interesting that there are a class of discrete gauge symmetries which naturally accommodate a long-lived unstable X particle. We find that in some discrete Z_{10} models, for example, a superheavy X particle has lifetime \tau_X \simeq 10^{11}-10^{26} years for its mass M_X \simeq 10^{13}-10^{14} GeV. This long lifetime is guaranteed by the absence of lower dimensional operators (of light particles) couple to the X. We briefly discuss a possible explanation for the recently observed ultra-high-energy cosmic ray events by the decay of this unstable X particle.Comment: 9 pages, Late

A Geometry of the Generations

We propose a geometric theory of flavor based on the discrete group $(S_3)^3$, in the context of the minimal supersymmetric standard model. The group treats three objects symmetrically, while making fundamental distinctions between the generations. The top quark is the only heavy quark in the symmetry limit, and the first and second generation squarks are degenerate. The hierarchical nature of Yukawa matrices is a consequence of a sequential breaking of $(S_3)^3$.Comment: 10 pages, 1 EPS figure as uuencoded tar-compressed file, uses psfig.st

The Tensor to Scalar Ratio of Phantom Dark Energy Models

We investigate the anisotropies in the cosmic microwave background in a class of models which possess a positive cosmic energy density but negative pressure, with a constant equation of state w = p/rho < -1. We calculate the temperature and polarization anisotropy spectra for both scalar and tensor perturbations by modifying the publicly available code CMBfast. For a constant initial curvature perturbation or tensor normalization, we have calculated the final anisotropy spectra as a function of the dark energy density and equation of state w and of the scalar and tensor spectral indices. This allows us to calculate the dependence of the tensor-to-scalar ratio on w in a model with phantom dark energy, which may be important for interpreting any future detection of long-wavelength gravitational waves.Comment: 5 pages, 4 figure