1,181 research outputs found
Annotated Checklist of the Aradidae (Hemiptera: Heteroptera) or Flat Bugs of Iowa
A review of the species of Aradidae or flat bugs found in Iowa is presented. New state records for Aradus aequalis Say, A. crenatus Say, A. implanus, and Mezira lobata (Say) are included
Annotated checklist of the Notonectidae (Hemiptera: Heteroptera) or Backswimmers of Iowa
A review of the Notonectidae or backswimmers of Iowa is presented. New state records for Buenoa macrotibialis Hungerford, Buenoa scimitra Bare, Notonecta insulata Kirby, Notonecta irrorata Uhler, and Notonecta lunata Hungerford are included
Exploring the Expansion History of the Universe
Exploring the recent expansion history of the universe promises insights into
the cosmological model, the nature of dark energy, and potentially clues to
high energy physics theories and gravitation. We examine the extent to which
precision distance-redshift observations can map out the history, including the
acceleration-deceleration transition, and the components and equations of state
of the energy density. We consider the ability to distinguish between various
dynamical scalar field models for the dark energy, as well as higher dimension
and alternate gravity theories. Finally, we present a new, advantageous
parametrization for the study of dark energy.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Letter
A revision of the Generalized Uncertainty Principle
The Generalized Uncertainty Principle arises from the Heisenberg Uncertainty
Principle when gravity is taken into account, so the leading order correction
to the standard formula is expected to be proportional to the gravitational
constant . On the other hand, the emerging picture suggests a
set of departures from the standard theory which demand a revision of all the
arguments used to deduce heuristically the new rule. In particular, one can now
argue that the leading order correction to the Heisenberg Uncertainty Principle
is proportional to the first power of the Planck length . If so, the
departures from ordinary quantum mechanics would be much less suppressed than
what is commonly thought.Comment: 6 pages, 1 figur
Positrons in Cosmic Rays from Dark Matter Annihilations for Uplifted Higgs Regions in MSSM
We point out that there are regions in the MSSM parameter space which
successfully provide a dark matter (DM) annihilation explanation for observed
positron excess (e.g. PAMELA), while still remaining in agreement with all
other data sets. Such regions (e.g. the uplifted Higgs region) can realize an
enhanced neutralino DM annihilation dominantly into leptons via a Breit-Wigner
resonance through the CP-odd Higgs channel. Such regions can give the proper
thermal relic DM abundance, and the DM annihilation products are compatible
with current antiproton and gamma ray observations. This scenario can succeed
without introducing any additional degrees of freedom beyond those already in
the MSSM.Comment: 11 pages, 9 figure
Accretion process onto super-spinning objects
The accretion process onto spinning objects in Kerr spacetimes is studied
with numerical simulations. Our results show that accretion onto compact
objects with Kerr parameter (characterizing the spin)
is very different. In the super-spinning case, for moderately larger than
, the accretion onto the central object is extremely suppressed due to a
repulsive force at short distance. The accreting matter cannot reach the
central object, but instead is accumulated around it, forming a high density
cloud that continues to grow. The radiation emitted in the accretion process
will be harder and more intense than the one coming from standard black holes;
e.g. -rays could be produced as seen in some observations.
Gravitational collapse of this cloud might even give rise to violent bursts. As
increases, a larger amount of accreting matter reaches the central object
and the growth of the cloud becomes less efficient. Our simulations find that a
quasi-steady state of the accretion process exists for ,
independently of the mass accretion rate at large radii. For such high values
of the Kerr parameter, the accreting matter forms a thin disk at very small
radii. We provide some analytical arguments to strengthen the numerical
results; in particular, we estimate the radius where the gravitational force
changes from attractive to repulsive and the critical value
separating the two qualitatively different regimes of accretion. We briefly
discuss the observational signatures which could be used to look for such
exotic objects in the Galaxy and/or in the Universe.Comment: 11 pages, 5 figures. v2: with explanation of the origin of the
critical value |a|/M = 1.
Model-Independent Comparison of Direct vs. Indirect Detection of Supersymmetric Dark Matter
We compare the rate for elastic scattering of neutralinos from various nuclei
with the flux of upward muons induced by energetic neutrinos from neutralino
annihilation in the Sun and Earth. We consider both scalar and axial-vector
interactions of neutralinos with nuclei. We find that the event rate in a kg of
germanium is roughly equivalent to that in a - to -m muon
detector for a neutralino with primarily scalar coupling to nuclei. For an
axially coupled neutralino, the event rate in a 50-gram hydrogen detector is
roughly the same as that in a 10- to 500-m muon detector. Expected
experimental backgrounds favor forthcoming elastic-scattering detectors for
scalar couplings while the neutrino detectors have the advantage for
axial-vector couplings.Comment: 10 pages, self-unpacking uuencoded PostScript fil
Cornering (quasi) degenerate neutrinos with cosmology
In light of the improved sensitivities of cosmological observations, we
examine the status of quasi-degenerate neutrino mass scenarios. Within the
simplest extension of the standard cosmological model with massive neutrinos,
we find that quasi-degenerate neutrinos are severely constrained by present
cosmological data and neutrino oscillation experiments. % % We find that Planck
2018 observations of cosmic microwave background (CMB) anisotropies disfavour
quasi-degenerate neutrino masses at Gaussian 's, while adding
Baryon acoustic oscillations (BAO) data brings the rejection to 5.9's.
% The highest statistical significance with which one would be able to rule out
quasi-degeneracy would arise if the sum of neutrino masses is \meV (the minimum allowed by neutrino oscillation experiments); % indeed a
sensitivity of 15 meV, as expected from a combination of future cosmological
probes, would further improve the rejection level up to 17. % We
discuss the robustness of these projections with respect to assumptions on the
underlying cosmological model, and also compare them with bounds from
decay endpoint and neutrinoless double beta decay studies.Comment: 19 pages, 6 figures, 1 tabl
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